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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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"http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv=Content-Type content="text/html; charset=utf8">
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<title>Acme: A User Interface for Programmers</title>
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</meta>
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</head>
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<body>
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<p style="margin-top: 0; margin-bottom: 0.50in"></p>
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<p style="margin-top: 0; margin-bottom: 0.21in"></p>
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<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;">
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<span style="font-size: 12pt"><b>Acme: A User Interface for Programmers</b></span></p>
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<p style="margin-top: 0; margin-bottom: 0.21in"></p>
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;">
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<span style="font-size: 10pt"><i></i></span><span style="font-size: 10pt"><i>Rob Pike</i></span><span style="font-size: 10pt"><i></i></span></p>
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<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;">
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<span style="font-size: 10pt"><i></i></span><span style="font-size: 10pt"><i>rob@plan9.bell-labs.com</i></span><span style="font-size: 10pt"><i></i></span></p>
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="margin-top: 0; margin-bottom: 0.08in"></p>
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<p style="margin-top: 0; margin-bottom: 0.33in"></p>
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<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;">
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<span style="font-size: 10pt"><i>ABSTRACT</i></span></p>
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<p style="margin-top: 0; margin-bottom: 0.19in"></p>
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.00in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;">
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<span style="font-size: 10pt">A hybrid of window system, shell, and editor, Acme gives text-oriented
38 
applications a clean, expressive, and consistent style of interaction.
39 
Traditional window systems support interactive client programs and offer libraries of
40 
pre-defined operations such as pop-up menus
41 
and buttons to promote a consistent
42 
user interface among the clients.
43 
Acme instead provides its clients with a fixed user interface and
44 
simple conventions to encourage its uniform use.
45 
Clients access the facilities of Acme through a file system interface;
46 
Acme is in part a file server that exports device-like files that may be
47 
manipulated to access and control the contents of its windows.
48 
Written in a concurrent programming language,
49 
Acme is structured as a set of communicating processes that neatly subdivide
50 
the various aspects of its tasks: display management, input, file server, and so on.
51 
</span><span style="font-size: 10pt"></span><span style="font-size: 10pt"></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
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<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.35in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;">
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<span style="font-size: 10pt">Acme attaches distinct functions to the three mouse buttons:
54 
the left selects text;
55 
the middle executes textual commands;
56 
and the right combines context search and file opening
57 
functions to integrate the various applications and files in
58 
the system.
59 
</span><span style="font-size: 10pt"></span><span style="font-size: 10pt"></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
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<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.35in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;">
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<span style="font-size: 10pt">Acme works well enough to have developed
62 
a community that uses it exclusively.
63 
Although Acme discourages the traditional style of interaction
64 
based on typescript windows&mdash;teletypes&mdash;its
65 
users find Acme&rsquo;s other services render
66 
typescripts obsolete.
67 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
68 
 
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="margin-top: 0; margin-bottom: 0.17in"></p>
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<p style="margin-top: 0; margin-bottom: 0.50in"></p>
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<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
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<span style="font-size: 10pt"><b>History and motivation
74 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
75 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
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<span style="font-size: 10pt">The usual typescript style of interaction with
77 
Unix and its relatives is an old one.
78 
The typescript&mdash;an intermingling of textual commands and their
79 
output&mdash;originates with the scrolls of paper on teletypes.
80 
The advent of windowed terminals has given each user what
81 
amounts to an array of teletypes, a limited and unimaginative
82 
use of the powers of bitmap displays and mice.
83 
Systems like the Macintosh
84 
that do involve the mouse as an integral part of the interaction
85 
are geared towards general users, not experts, and certainly
86 
not programmers.
87 
Software developers, at least on time-sharing systems, have been left behind.
88 
</span></p><center><table width=60% cellspacing=0 cellpadding=0 border=0><tr height=1>	<td width=1 bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td width=1 bgcolor=#000000 /></tr><tr height=10>	<td width=1 bgcolor=#000000 />	<td width=10 />	<td />	<td width=10 />	<td width=1 bgcolor=#000000 /></tr>
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<tr>
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<td width=1 bgcolor=#000000 /><td width=10 /><td>
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<center><a href="acme.fig1.gif"><img src="acme.fig1.gif" /></a></center>
92 
<p style="line-height: 1.2em; text-indent: 0.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
93 
<span style="font-size: 10pt">Figure 1.  A small Acme screen&mdash;normally it runs on a larger display&mdash;demonstrating
94 
some of the details discussed in the text.
95 
The right column contains some guide files,
96 
a mailbox presented by Acme&rsquo;s mail program,
97 
the columnated display of files in Acme&rsquo;s own source directory,
98 
a couple of windows from the OED browser,
99 
a debugger window,
100 
and an error window showing diagnostics from a compilation.
101 
The left column holds a couple of source files
102 
(</span><span style="font-size: 10pt"><tt>dat.h</tt></span><span style="font-size: 10pt">
103 
and
104 
</span><span style="font-size: 10pt"><tt>acme.l</tt></span><span style="font-size: 10pt">),
105 
another debugger window displaying a stack trace,
106 
and a third source file
107 
(</span><span style="font-size: 10pt"><tt>time.l</tt></span><span style="font-size: 10pt">).
108 
</span><span style="font-size: 10pt"><tt>Time.l</tt></span><span style="font-size: 10pt">
109 
was opened from the debugger by clicking the right mouse button
110 
on a line in the stack window;
111 
the mouse cursor landed on the offending line of
112 
</span><span style="font-size: 10pt"><tt>acme.l</tt></span><span style="font-size: 10pt">
113 
after a click on the compiler message.
114 
</span></p></td>
115 
<td width=10 /><td width=1 bgcolor=#000000 />
116 
</tr>
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<tr height=10><td width=1 bgcolor=#000000 />	<td width=10 /><td /><td width=10 />	<td width=1 bgcolor=#000000 /></tr><tr height=1>	<td width=1 bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td width=1 bgcolor=#000000 /></tr>
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</table></center>
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<p style="margin-top: 0; margin-bottom: 0.05in"></p>
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<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
121 
<span style="font-size: 10pt">Some programs have mouse-based editing of
122 
text files and typescripts;
123 
ones I have built include
124 
the window systems
125 
</span><span style="font-size: 10pt"><tt>mux</tt></span><span style="font-size: 10pt">
126 
[Pike88]
127 
and
128 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">
129 
[Pike91]
130 
and the text editor
131 
Sam [Pike87].
132 
These have put the programmer&rsquo;s mouse to some productive work,
133 
but not wholeheartedly.  Even experienced users of these programs
134 
often retype text that could be grabbed with the mouse,
135 
partly because the menu-driven interface is imperfect
136 
and partly because the various pieces are not well enough integrated.
137 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
138 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
139 
<span style="font-size: 10pt">Other programs&mdash;EMACS [Stal93] is the prime example&mdash;offer a high
140 
degree of integration but with a user interface built around the
141 
ideas of cursor-addressed terminals that date from the 1970&rsquo;s.
142 
They are still keyboard-intensive and
143 
dauntingly complex.
144 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
145 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
146 
<span style="font-size: 10pt">The most ambitious attempt to face these issues was the Cedar
147 
system, developed at Xerox [Swei86].
148 
It combined a new programming language, compilers,
149 
window system, even microcode&mdash;a complete system&mdash;to
150 
construct a productive, highly
151 
integrated and interactive environment
152 
for experienced users of compiled languages.
153 
Although successful internally, the system was so large
154 
and so tied to specific hardware that it never fledged.
155 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
156 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
157 
<span style="font-size: 10pt">Cedar was, however, the major inspiration for Oberon [Wirt89],
158 
a system of similar scope but much smaller scale.
159 
Through careful selection of Cedar&rsquo;s ideas, Oberon shows
160 
that its lessons can be applied to a small, coherent system
161 
that can run efficiently on modest hardware.
162 
In fact, Oberon probably
163 
errs too far towards simplicity: a single-process system
164 
with weak networking, it seems an architectural throwback.
165 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
166 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
167 
<span style="font-size: 10pt">Acme is a new program,
168 
a combined window system, editor, and shell,
169 
that applies
170 
some of the ideas distilled by Oberon.
171 
Where Oberon uses objects and modules within a programming language (also called Oberon),
172 
Acme uses files and commands within an existing operating system (Plan 9).
173 
Unlike Oberon, Acme does not yet have support for graphical output, just text.
174 
At least for now, the work on Acme has concentrated on
175 
producing the smoothest user interface possible for a programmer
176 
at work.
177 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
178 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
179 
<span style="font-size: 10pt">The rest of this paper describes Acme&rsquo;s interface,
180 
explains how programs can access it,
181 
compares it to existing systems,
182 
and finally presents some unusual aspects of its implementation.
183 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
184 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
185 
<span style="font-size: 10pt"><b>User interface
186 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
187 
<center><table width=60% cellspacing=0 cellpadding=0 border=0><tr height=1>	<td width=1 bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td width=1 bgcolor=#000000 /></tr><tr height=10>	<td width=1 bgcolor=#000000 />	<td width=10 />	<td />	<td width=10 />	<td width=1 bgcolor=#000000 /></tr>
188 
<tr>
189 
<td width=1 bgcolor=#000000 /><td width=10 /><td>
190 
<center><a href="acme.fig2.gif"><img src="acme.fig2.gif" /></a></center>
191 
<p style="line-height: 1.2em; text-indent: 0.35in; margin-top: 0; margin-bottom: 0; text-align: justify;">
192 
<span style="font-size: 10pt">Figure 2.  An Acme window showing a section of code.
193 
The upper line of text is the tag containing the file name,
194 
relevant commands, and a scratch area (right of the vertical bar);
195 
the lower portion of the window is the
196 
body, or contents, of the file.
197 
Here the scratch area contains a command for the middle button
198 
(</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt">)
199 
and a word to search for with the right button
200 
(</span><span style="font-size: 10pt"><tt>cxfidalloc</tt></span><span style="font-size: 10pt">).
201 
The user has just
202 
clicked the right button on
203 
</span><span style="font-size: 10pt"><tt>cxfidalloc</tt></span><span style="font-size: 10pt">
204 
and Acme has searched for the word, highlighted it,
205 
and moved the mouse cursor there.  The file has been modified:
206 
the center of the layout box is black and the command
207 
</span><span style="font-size: 10pt"><tt>Put</tt></span><span style="font-size: 10pt">
208 
appears in the tag.
209 
</span></p></td>
210 
<td width=10 /><td width=1 bgcolor=#000000 />
211 
</tr>
212 
<tr height=10><td width=1 bgcolor=#000000 />	<td width=10 /><td /><td width=10 />	<td width=1 bgcolor=#000000 /></tr><tr height=1>	<td width=1 bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td bgcolor=#000000 />	<td width=10 bgcolor=#000000 />	<td width=1 bgcolor=#000000 /></tr>
213 
</table></center>
214 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
215 
<span style="font-size: 10pt">Acme windows are arrayed in columns (Figure 1) and are used more
216 
dynamically than in an environment like X Windows or
217 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">
218 
[Sche86, Pike91].
219 
The system frequently creates them automatically and the user
220 
can order a new one with a single mouse button click.
221 
The initial placement of a new window is determined
222 
automatically, but the user may move an existing window anywhere
223 
by clicking or dragging a
224 
</span><span style="font-size: 10pt"><i>layout box</i></span><span style="font-size: 10pt">
225 
in the upper left corner of
226 
the window.
227 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
228 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
229 
<span style="font-size: 10pt">Acme windows have two parts: a
230 
</span><span style="font-size: 10pt"><i>tag</i></span><span style="font-size: 10pt">
231 
holding a single line of text,
232 
above a
233 
</span><span style="font-size: 10pt"><i>body</i></span><span style="font-size: 10pt">
234 
holding zero or more lines (Figure 2).
235 
The body typically contains an image of a file being edited
236 
or the editable output of a
237 
program, analogous to an
238 
EMACS shell
239 
window.  The tag contains
240 
the name of the window
241 
(usually the name of the associated
242 
file or directory), some built-in commands, and a scratch area to hold arbitrary text.
243 
If a window represents a directory, the name in the tag ends with
244 
a slash and the body contains a list of the names of the files
245 
in the directory.
246 
Finally, each non-empty body holds a scroll bar at the left of the text.
247 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
248 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
249 
<span style="font-size: 10pt">Each column of windows also has a layout box and a tag.
250 
The tag has no special meaning, although Acme pre-loads it with a few
251 
built-in commands.
252 
There is also a tag across the whole display, also loaded with
253 
helpful commands and a list of active processes started
254 
by Acme.
255 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
256 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
257 
<span style="font-size: 10pt">Typing with the keyboard and selecting with the left button are as in
258 
many other systems, including the Macintosh,
259 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">,
260 
and Sam.
261 
The middle and right buttons are used, somewhat like the left button,
262 
to &lsquo;sweep&rsquo; text, but the indicated text is treated in a way
263 
that depends on the text&rsquo;s location&mdash;</span><span style="font-size: 10pt"><i>context</i></span><span style="font-size: 10pt">&mdash;as well as its content.
264 
This context, based on the directory of the file containing the text,
265 
is a central component of Acme&rsquo;s style of interaction.
266 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
267 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
268 
<span style="font-size: 10pt">Acme has no single notion of &lsquo;current directory&rsquo;.
269 
Instead, every command, file name,
270 
action, and so on is interpreted or executed in the directory named by the
271 
tag of the window containing the command.  For example, the string
272 
</span><span style="font-size: 10pt"><tt>mammals</tt></span><span style="font-size: 10pt">
273 
in a window labeled
274 
</span><span style="font-size: 10pt"><tt>/lib/</tt></span><span style="font-size: 10pt">
275 
or
276 
</span><span style="font-size: 10pt"><tt>/lib/insects</tt></span><span style="font-size: 10pt">
277 
will be interpreted as the file name
278 
</span><span style="font-size: 10pt"><tt>/lib/mammals</tt></span><span style="font-size: 10pt">
279 
if such a file exists.
280 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
281 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
282 
<span style="font-size: 10pt">Throughout Acme, the middle mouse button is used to execute commands
283 
and the right mouse button is used to locate and select files and text.
284 
Even when there are no true files on which to operate&mdash;for example
285 
when editing mail messages&mdash;Acme and its applications use
286 
consistent extensions of these basic functions.
287 
This idea is as vital to Acme as icons are to the Macintosh.
288 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
289 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
290 
<span style="font-size: 10pt">The middle button executes commands: text swept with the button
291 
pressed is underlined; when the button is released, the underline is
292 
removed and the indicated text is executed.
293 
A modest number of commands are recognized as built-ins: words like
294 
</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">,
295 
</span><span style="font-size: 10pt"><tt>Paste</tt></span><span style="font-size: 10pt">,
296 
and
297 
</span><span style="font-size: 10pt"><tt>New</tt></span><span style="font-size: 10pt">
298 
name
299 
functions performed directly by Acme.
300 
These words often appear in tags to make them always available,
301 
but the tags are not menus: any text anywhere in Acme may be a command.
302 
For example, in the tag or body of any window one may type
303 
</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">,
304 
select it with the left button, use the middle button to execute it,
305 
and watch it disappear again.
306 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
307 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
308 
<span style="font-size: 10pt">If the middle button indicates a command that is not recognized as a built-in,
309 
it is executed in the directory
310 
named by the tag of the window holding the text.
311 
Also, the file to be executed is searched for first in that directory.
312 
Standard input is connected to
313 
</span><span style="font-size: 10pt"><tt>/dev/null</tt></span><span style="font-size: 10pt">,
314 
but standard and error outputs are connected to an Acme window,
315 
created if needed, called
316 
</span><span style="font-size: 10pt"><i>dir</i></span><span style="font-size: 10pt"><tt>/+Errors</tt></span><span style="font-size: 10pt"> where
317 
</span><span style="font-size: 10pt"><i>dir</i></span><span style="font-size: 10pt">
318 
is the directory of the window.
319 
(Programs that need interactive input use a different interface, described below.)
320 
A typical use of this is to type
321 
</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt">
322 
(Plan 9&rsquo;s
323 
</span><span style="font-size: 10pt"><tt>make</tt></span><span style="font-size: 10pt">)
324 
in the scratch area in the tag of a C source window, say
325 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/regexp.c</tt></span><span style="font-size: 10pt">,
326 
and execute it.
327 
Output, including compiler errors, appears in the window labeled
328 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/+Errors</tt></span><span style="font-size: 10pt">,
329 
so file names in the output are associated with the windows and directory
330 
holding the source.
331 
The
332 
</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt">
333 
command remains in the tag, serving as a sort of menu item for the associated
334 
window.
335 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
336 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
337 
<span style="font-size: 10pt">Like the middle button, the right button is used to indicate text by sweeping it out.
338 
The indicated text is not a command, however, but the argument of a generalized
339 
search operator.
340 
If the text, perhaps after appending it to the directory of the window containing it,
341 
is the name of an existing file, Acme creates a new window to hold the file
342 
and reads it in.  It then moves the mouse cursor to that window.  If the file is
343 
already loaded into Acme, the mouse motion happens but no new window is made.
344 
For example, indicating the string
345 
</span><span style="font-size: 10pt"><tt>sam.h</tt></span><span style="font-size: 10pt">
346 
in
347 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
348 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
349 
<span style="font-size: 9pt"><tt>#include "sam.h"</tt></span></p>
350 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
351 
 
352 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
353 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
354 
<span style="font-size: 10pt">in a window on the file
355 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/regexp.c</tt></span><span style="font-size: 10pt">
356 
will open the file
357 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/sam.h</tt></span><span style="font-size: 10pt">.
358 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
359 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
360 
<span style="font-size: 10pt">If the file name is followed immediately by a colon and a legal address in
361 
Sam notation (for example a line number or a regular expression delimited in
362 
slashes or a comma-separated compound of such addresses), Acme highlights
363 
the target of that address in the file and places the mouse there.  One may jump to
364 
line 27 of
365 
</span><span style="font-size: 10pt"><tt>dat.h</tt></span><span style="font-size: 10pt">
366 
by indicating with the right button the text
367 
</span><span style="font-size: 10pt"><tt>dat.h:27</tt></span><span style="font-size: 10pt">.
368 
If the file is not already open, Acme loads it.
369 
If the file name is null, for example if the indicated string is
370 
</span><span style="font-size: 10pt"><tt>:/^main/</tt></span><span style="font-size: 10pt">,
371 
the file is assumed to be that of the window containing the string.
372 
Such strings, when typed and evaluated in the tag of a window, amount to
373 
context searches.
374 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
375 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
376 
<span style="font-size: 10pt">If the indicated text is not the name of an existing file, it is taken to be literal
377 
text and is searched for in the body of the window containing the text, highlighting
378 
the result as if it were the result of a context search.
379 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
380 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
381 
<span style="font-size: 10pt">For the rare occasion when a file name
382 
</span><span style="font-size: 10pt"><i>is</i></span><span style="font-size: 10pt">
383 
just text to search for, it can be selected with the left button and used as the
384 
argument to a built-in
385 
</span><span style="font-size: 10pt"><tt>Look</tt></span><span style="font-size: 10pt">
386 
command that always searches for literal text.
387 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
388 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
389 
<span style="font-size: 10pt"><b>Nuances and heuristics
390 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
391 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
392 
<span style="font-size: 10pt">A user interface should not only provide the necessary functions, it should also
393 
</span><span style="font-size: 10pt"><i>feel</i></span><span style="font-size: 10pt">
394 
right.
395 
In fact, it should almost not be felt at all; when one notices a
396 
user interface, one is distracted from the job at hand [Pike88].
397 
To approach this invisibility, some of Acme&rsquo;s properties and features
398 
are there just to make the others easy to use.
399 
Many are based on a fundamental principle of good design:
400 
let the machine do the work.
401 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
402 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
403 
<span style="font-size: 10pt">Acme tries to avoid needless clicking and typing.
404 
There is no &lsquo;click-to-type&rsquo;, eliminating a button click.
405 
There are no pop-up or pull-down menus, eliminating the mouse action needed to
406 
make a menu appear.
407 
The overall design is intended to make text on the screen useful without
408 
copying or retyping; the ways in which this happens involve
409 
the combination of many aspects of the interface.
410 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
411 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
412 
<span style="font-size: 10pt">Acme tiles its windows and places them automatically
413 
to avoid asking the user to place and arrange them.
414 
For this policy to succeed, the automatic placement must behave well enough
415 
that the user is usually content with the location of a new window.
416 
The system will never get it right all the time, but in practice most
417 
windows are used at least for a while where Acme first places them.
418 
There have been several complete rewrites of the
419 
heuristics for placing a new window,
420 
and with each rewrite the system became
421 
noticeably more comfortable.  The rules are as follows, although
422 
they are still subject to improvement.
423 
The window appears in the &lsquo;active&rsquo; column, that most recently used for typing or
424 
selecting.
425 
Executing and searching do not affect the choice of active column,
426 
so windows of commands and such do not draw new windows towards them,
427 
but rather let them form near the targets of their actions.
428 
Output (error) windows always appear towards the right, away from
429 
edited text, which is typically kept towards the left.
430 
Within the column, several competing desires are balanced to decide where
431 
and how large the window should be:
432 
large blank spaces should be consumed;
433 
existing text should remain visible;
434 
existing large windows should be divided before small ones;
435 
and the window should appear near the one containing the action that caused
436 
its creation.
437 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
438 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
439 
<span style="font-size: 10pt">Acme binds some actions to chords of mouse buttons.
440 
These include
441 
</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">
442 
and
443 
</span><span style="font-size: 10pt"><tt>Paste</tt></span><span style="font-size: 10pt">
444 
so these common operations can be done without
445 
moving the mouse.
446 
Another is a way to apply a command in one window to text (often a file name)
447 
in another, avoiding the actions needed to assemble the command textually.
448 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
449 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
450 
<span style="font-size: 10pt">Another way Acme avoids the need to move the mouse is instead to move the cursor
451 
to where it is likely to be used next.  When a new window is made, Acme
452 
moves the cursor to the new window; in fact, to the selected text in that window.
453 
When the user deletes a newly made window, the cursor is
454 
returned to the point it was before the window was made,
455 
reducing the irritation of windows that pop up to report annoying errors.
456 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
457 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
458 
<span style="font-size: 10pt">When a window is moved, Acme moves the cursor to the layout box in
459 
its new place, to permit further adjustment without moving the mouse.
460 
For example, when a click of the left mouse button on the layout box grows
461 
the window, the cursor moves to the new location of the box so repeated clicks,
462 
without moving the mouse, continue to grow it.
463 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
464 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
465 
<span style="font-size: 10pt">Another form of assistance the system can offer is to supply precision in
466 
pointing the mouse.  The best-known form of this is &lsquo;double-clicking&rsquo; to
467 
select a word rather than carefully sweeping out the entire word.
468 
Acme provides this feature, using context to decide whether to select
469 
a word, line, quoted string, parenthesized expression, and so on.
470 
But Acme takes the idea much further by applying it to execution
471 
and searching.
472 
A
473 
</span><span style="font-size: 10pt"><i>single</i></span><span style="font-size: 10pt">
474 
click, that is, a null selection, with either the middle or right buttons,
475 
is expanded automatically to indicate the appropriate text containing
476 
the click.  What is appropriate depends on the context.
477 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
478 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
479 
<span style="font-size: 10pt">For example, to execute a single-word command
480 
such as
481 
</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">,
482 
it is not necessary to sweep the entire word; just clicking the button once with
483 
the mouse pointing at the word is sufficient.  &lsquo;Word&rsquo;
484 
means the largest string of likely file name characters surrounding the location
485 
of the click: click on a file name, run that program.
486 
On the right button, the rules are more complicated because
487 
the target of the click might be a file name, file name with address,
488 
or just plain text.  Acme examines the text near the click to find
489 
a likely file name;
490 
if it finds one, it checks that it names an existing file (in the directory named in the tag, if the name is relative)
491 
and if so, takes that as the result, after extending it with any address
492 
that may be present.  If there is no file with that name, Acme
493 
just takes the largest alphanumeric string under the click.
494 
The effect is a natural overloading of the button to refer to plain text as
495 
well as file names.
496 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
497 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
498 
<span style="font-size: 10pt">First, though, if the click occurs over the left-button-selected text in the window,
499 
that text is taken to be what is selected.
500 
This makes it easy to skip through the occurrences of a string in a file: just click
501 
the right button
502 
on some occurrence of the text in the window (perhaps after typing it in the tag)
503 
and click once for each subsequent occurrence.  It isn&rsquo;t even necessary to move
504 
the mouse between clicks; Acme does that.
505 
To turn a complicated command into a sort of menu item, select it:
506 
thereafter, clicking the middle button on it will execute the full command.
507 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
508 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
509 
<span style="font-size: 10pt">As an extra feature, Acme recognizes file names in angle brackets
510 
</span><span style="font-size: 10pt"><tt>&lt;&gt;</tt></span><span style="font-size: 10pt">
511 
as names of files in standard directories of include files,
512 
making it possible for instance to look at
513 
</span><span style="font-size: 10pt"><tt>&lt;stdio.h&gt;</tt></span><span style="font-size: 10pt">
514 
with a single click.
515 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
516 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
517 
<span style="font-size: 10pt">Here&rsquo;s an example to demonstrate how the actions and defaults work together.
518 
Assume
519 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/regexp.c</tt></span><span style="font-size: 10pt">
520 
is
521 
open and has been edited.  We write it (execute
522 
</span><span style="font-size: 10pt"><tt>Put</tt></span><span style="font-size: 10pt">
523 
in the tag; once the file is written, Acme removes the word from the tag)
524 
and type
525 
</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt">
526 
in the tag.  We execute
527 
</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt">
528 
and get some errors, which appear in a new window labeled
529 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/+Errors</tt></span><span style="font-size: 10pt">.
530 
The cursor moves automatically to that window.
531 
Say the error is
532 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
533 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
534 
<span style="font-size: 9pt"><tt>main.c:112: incompatible types on assignment to &lsquo;pattern&rsquo;</tt></span></p>
535 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
536 
 
537 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
538 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
539 
<span style="font-size: 10pt">We move the mouse slightly and click the right button
540 
at the left of the error message; Acme
541 
makes a new window, reads
542 
</span><span style="font-size: 10pt"><tt>/sys/src/cmd/main.c</tt></span><span style="font-size: 10pt">
543 
into it, selects line 112
544 
and places the mouse there, right on the offending line.
545 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
546 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
547 
<span style="font-size: 10pt"><b>Coupling to existing programs
548 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
549 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
550 
<span style="font-size: 10pt">Acme&rsquo;s syntax for file names and addresses makes it easy for other programs
551 
to connect automatically to Acme&rsquo;s capabilities.  For example, the output of
552 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
553 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
554 
<span style="font-size: 9pt"><tt>grep -n variable *.[ch]</tt></span></p>
555 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
556 
 
557 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
558 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
559 
<span style="font-size: 10pt">can be used to help Acme step through the occurrences of a variable in a program;
560 
every line of output is potentially a command to open a file.
561 
The file names need not be absolute, either: the output
562 
appears in a window labeled with the directory in which
563 
</span><span style="font-size: 10pt"><tt>grep</tt></span><span style="font-size: 10pt">
564 
was run, from which Acme can derive the full path names.
565 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
566 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
567 
<span style="font-size: 10pt">When necessary, we have changed the output of some programs,
568 
such as compiler error messages, to match
569 
Acme&rsquo;s syntax.
570 
Some might argue that it shouldn&rsquo;t be necessary to change old programs,
571 
but sometimes programs need to be updated when systems change,
572 
and consistent output benefits people as well as programs.
573 
A historical example is the retrofitting of standard error output to the
574 
early Unix programs when pipes were invented.
575 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
576 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
577 
<span style="font-size: 10pt">Another change was to record full path names in
578 
the symbol table of executables, so line numbers reported by the debugger
579 
are absolute names that may be used directly by Acme; it&rsquo;s not necessary
580 
to run the debugger in the source directory.  (This aids debugging
581 
even without Acme.)
582 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
583 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
584 
<span style="font-size: 10pt">A related change was to add lines of the form
585 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
586 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
587 
<span style="font-size: 9pt"><tt>#pragma src "/sys/src/libregexp"</tt></span></p>
588 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
589 
 
590 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
591 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
592 
<span style="font-size: 10pt">to header files; coupled with Acme&rsquo;s ability to locate a header file,
593 
this provides a fast, keyboardless way to get the source associated with a library.
594 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
595 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
596 
<span style="font-size: 10pt">Finally, Acme directs the standard output of programs it runs to
597 
windows labeled by the directory in which the program is run.
598 
Acme&rsquo;s splitting of the
599 
output into directory-labeled windows is a small feature that has a major effect:
600 
local file names printed by programs can be interpreted directly by Acme.
601 
By indirectly coupling the output of programs to the input,
602 
it also simplifies the management of software that occupies multiple
603 
directories.
604 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
605 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
606 
<span style="font-size: 10pt"><b>Coupling to new programs
607 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
608 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
609 
<span style="font-size: 10pt">Like many Plan 9 programs,
610 
Acme offers a programmable interface to
611 
other programs by acting as a file server.
612 
The best example of such a file server is the window system
613 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">
614 
[Pike91],
615 
which exports files with names such as
616 
</span><span style="font-size: 10pt"><tt>screen</tt></span><span style="font-size: 10pt">,
617 
</span><span style="font-size: 10pt"><tt>cons</tt></span><span style="font-size: 10pt">,
618 
and
619 
</span><span style="font-size: 10pt"><tt>mouse</tt></span><span style="font-size: 10pt">
620 
through which applications may access the I/O capabilities of the windows.
621 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">
622 
provides a
623 
</span><span style="font-size: 10pt"><i>distinct</i></span><span style="font-size: 10pt">
624 
set of files for each window and builds a private file name space
625 
for the clients running &lsquo;in&rsquo; each window;
626 
clients in separate windows see distinct files with the same names
627 
(for example
628 
</span><span style="font-size: 10pt"><tt>/dev/mouse</tt></span><span style="font-size: 10pt">).
629 
Acme, like the process file system [PPTTW93], instead associates each
630 
window with a directory of files; the files of each window are visible
631 
to any application.
632 
This difference reflects a difference in how the systems are used:
633 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">
634 
tells a client what keyboard and mouse activity has happened in its window;
635 
Acme tells a client what changes that activity wrought on any window it asks about.
636 
Putting it another way,
637 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">
638 
enables the construction of interactive applications;
639 
Acme provides the interaction for applications.
640 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
641 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
642 
<span style="font-size: 10pt">The root of
643 
Acme&rsquo;s file system is mounted using Plan 9 operations on the directory
644 
</span><span style="font-size: 10pt"><tt>/mnt/acme</tt></span><span style="font-size: 10pt">.
645 
In
646 
that root directory appears a directory for each window, numbered with the window&rsquo;s identifier,
647 
analogous to a process identifier, for example
648 
</span><span style="font-size: 10pt"><tt>/mnt/acme/27</tt></span><span style="font-size: 10pt">.
649 
The window&rsquo;s directory
650 
contains 6 files:
651 
</span><span style="font-size: 10pt"><tt>/mnt/acme/27/addr</tt></span><span style="font-size: 10pt">,
652 
</span><span style="font-size: 10pt"><tt>body</tt></span><span style="font-size: 10pt">,
653 
</span><span style="font-size: 10pt"><tt>ctl</tt></span><span style="font-size: 10pt">,
654 
</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">,
655 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">,
656 
and
657 
</span><span style="font-size: 10pt"><tt>tag</tt></span><span style="font-size: 10pt">.
658 
The
659 
</span><span style="font-size: 10pt"><tt>body</tt></span><span style="font-size: 10pt">
660 
and
661 
</span><span style="font-size: 10pt"><tt>tag</tt></span><span style="font-size: 10pt">
662 
files contain the text of the respective parts of the window; they may be
663 
read to recover the contents.  Data written to these files is appended to the text;
664 
</span><span style="font-size: 10pt"><tt>seeks</tt></span><span style="font-size: 10pt">
665 
are ignored.
666 
The
667 
</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">
668 
and
669 
</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">
670 
files provide random access to the contents of the body.
671 
The
672 
</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">
673 
file is written to set a character position within the body; the
674 
</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">
675 
file may then be read to recover the contents at that position,
676 
or written to change them.
677 
(The tag is assumed
678 
small and special-purpose enough not to need special treatment.
679 
Also,
680 
</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">
681 
indexes by character position, which is not the same as byte offset
682 
in Plan 9&rsquo;s multi-byte character set [Pike93]).
683 
The format accepted by the
684 
</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">
685 
file is exactly the syntax of addresses within the user interface,
686 
permitting regular expressions, line numbers, and compound addresses
687 
to be specified.  For example, to replace the contents of lines 3 through 7,
688 
write the text
689 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
690 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
691 
<span style="font-size: 9pt"><tt>3,7</tt></span></p>
692 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
693 
 
694 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
695 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
696 
<span style="font-size: 10pt">to the
697 
</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">
698 
file, then write the replacement text to the
699 
</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">
700 
file.  A zero-length write deletes the addressed text; further writes extend the replacement.
701 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
702 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
703 
<span style="font-size: 10pt">The control file,
704 
</span><span style="font-size: 10pt"><tt>ctl</tt></span><span style="font-size: 10pt">,
705 
may be written with commands to effect actions on the window; for example
706 
the command
707 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
708 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
709 
<span style="font-size: 9pt"><tt>name /adm/users</tt></span></p>
710 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
711 
 
712 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
713 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
714 
<span style="font-size: 10pt">sets the name in the tag of the window to
715 
</span><span style="font-size: 10pt"><tt>/adm/users</tt></span><span style="font-size: 10pt">.
716 
Other commands allow deleting the window, writing it to a file, and so on.
717 
Reading the
718 
</span><span style="font-size: 10pt"><tt>ctl</tt></span><span style="font-size: 10pt">
719 
file recovers a fixed-format string containing 5 textual numbers&mdash;the window
720 
identifier, the number of characters in the tag, the number in the body,
721 
and some status information&mdash;followed by the text of the tag, up to a newline.
722 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
723 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
724 
<span style="font-size: 10pt">The last file,
725 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">,
726 
is the most unusual.
727 
A program reading a window&rsquo;s
728 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">
729 
file is notified of all changes to the text of the window, and
730 
is asked to interpret all middle- and right-button actions.
731 
The data passed to the program is fixed-format and reports
732 
the source of the action (keyboard, mouse, external program, etc.),
733 
its location (what was pointed at or modified), and its nature (change,
734 
search, execution, etc.).
735 
This message, for example,
736 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
737 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
738 
<span style="font-size: 9pt"><tt>MI15 19 0 4 time</tt></span></p>
739 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
740 
 
741 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
742 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
743 
<span style="font-size: 10pt">reports that actions of the mouse
744 
(</span><span style="font-size: 10pt"><tt>M</tt></span><span style="font-size: 10pt">)
745 
inserted in the body (capital
746 
</span><span style="font-size: 10pt"><tt>I</tt></span><span style="font-size: 10pt">)
747 
the 4 characters of
748 
</span><span style="font-size: 10pt"><tt>time</tt></span><span style="font-size: 10pt">
749 
at character positions 15 through 19; the zero is a flag word.
750 
Programs may apply their own interpretations of searching and
751 
execution, or may simply reflect the events back to Acme,
752 
by writing them back to the
753 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">
754 
file, to have the default interpretation applied.
755 
Some examples of these ideas in action are presented below.
756 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
757 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
758 
<span style="font-size: 10pt">Notice that changes to the window are reported
759 
after the fact; the program is told about them but is not required to act
760 
on them.  Compare this to a more traditional interface in which a program
761 
is told, for example, that a character has been typed on the keyboard and
762 
must then display and interpret it.
763 
Acme&rsquo;s style stems from the basic model of the system, in which any
764 
number of agents&mdash;the keyboard, mouse, external programs
765 
writing to
766 
</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">
767 
or
768 
</span><span style="font-size: 10pt"><tt>body</tt></span><span style="font-size: 10pt">,
769 
and so on&mdash;may
770 
change the contents of a window.
771 
The style is efficient: many programs are content
772 
to have Acme do most of the work and act only when the editing is completed.
773 
An example is the Acme mail program, which can ignore the changes
774 
made to a message being composed
775 
and just read its body when asked to send it.
776 
A disadvantage is that some traditional ways of working are impossible.
777 
For example, there is no way &lsquo;to turn off echo&rsquo;: characters appear on the
778 
screen and are read from there; no agent or buffer stands between
779 
the keyboard and the display.
780 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
781 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
782 
<span style="font-size: 10pt">There are a couple of other files made available by Acme in its root directory
783 
rather than in the directory of each window.
784 
The text file
785 
</span><span style="font-size: 10pt"><tt>/mnt/acme/index</tt></span><span style="font-size: 10pt">
786 
holds a list of all window names and numerical identifiers,
787 
somewhat analogous to the output of the
788 
</span><span style="font-size: 10pt"><tt>ps</tt></span><span style="font-size: 10pt">
789 
command for processes.
790 
The most important, though, is
791 
</span><span style="font-size: 10pt"><tt>/mnt/acme/new</tt></span><span style="font-size: 10pt">,
792 
a directory that makes new windows, similar to the
793 
</span><span style="font-size: 10pt"><tt>clone</tt></span><span style="font-size: 10pt">
794 
directory in the Plan 9 network devices [Pres93].
795 
The act of opening any file in
796 
</span><span style="font-size: 10pt"><tt>new</tt></span><span style="font-size: 10pt">
797 
creates a new Acme window; thus the shell command
798 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
799 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
800 
<span style="font-size: 9pt"><tt>grep -n var *.c &gt; /mnt/acme/new/body</tt></span></p>
801 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
802 
 
803 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
804 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
805 
<span style="font-size: 10pt">places its output in the body of a fresh window.
806 
More sophisticated applications may open
807 
</span><span style="font-size: 10pt"><tt>new/ctl</tt></span><span style="font-size: 10pt">,
808 
read it to discover the new window&rsquo;s identifier, and then
809 
open the window&rsquo;s other files in the numbered directory.
810 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
811 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
812 
<span style="font-size: 10pt"><b>Acme-specific programs
813 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
814 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
815 
<span style="font-size: 10pt">Although Acme is in part an attempt to move beyond typescripts,
816 
they will probably always have utility.
817 
The first program written for Acme was therefore one
818 
to run a shell or other traditional interactive application
819 
in a window, the Acme analog of
820 
</span><span style="font-size: 10pt"><tt>xterm</tt></span><span style="font-size: 10pt">.
821 
This program,
822 
</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt">,
823 
has a simple structure:
824 
it acts as a two-way intermediary between Acme and the shell,
825 
cross-connecting the standard input and output of the shell to the
826 
text of the window.
827 
The style of interaction is modeled after
828 
</span><span style="font-size: 10pt"><tt>mux</tt></span><span style="font-size: 10pt">
829 
[Pike88]: standard output is added to the window at the
830 
</span><span style="font-size: 10pt"><i>output point;</i></span><span style="font-size: 10pt">
831 
text typed after the output point
832 
is made available on standard input when a newline is typed.
833 
After either of these actions, the output point is advanced.
834 
This is different from the working of a regular terminal,
835 
permitting cut-and-paste editing of an input line until the newline is typed.
836 
Arbitrary editing may be done to any text in the window.
837 
The implementation of
838 
</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt">,
839 
using the
840 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">,
841 
</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">,
842 
and
843 
</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">
844 
files, is straightforward.
845 
</span><span style="font-size: 10pt"><tt>Win</tt></span><span style="font-size: 10pt">
846 
needs no code for handling the keyboard and mouse; it just monitors the
847 
contents of the window.  Nonetheless, it allows Acme&rsquo;s full editing to be
848 
applied to shell commands.
849 
The division of labor between
850 
</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt">
851 
and
852 
</span><span style="font-size: 10pt"><tt>Acme</tt></span><span style="font-size: 10pt">
853 
contrasted with
854 
</span><span style="font-size: 10pt"><tt>xterm</tt></span><span style="font-size: 10pt">
855 
and the X server demonstrates how much work Acme handles automatically.
856 
</span><span style="font-size: 10pt"><tt>Win</tt></span><span style="font-size: 10pt">
857 
is implemented by a single source file 560 lines long and has no graphics code.
858 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
859 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
860 
<span style="font-size: 10pt"></span><span style="font-size: 10pt"><tt>Win</tt></span><span style="font-size: 10pt">
861 
uses the middle and right buttons to connect itself in a consistent way
862 
with the rest of Acme.
863 
The middle button still executes commands, but in a style more suited
864 
to typescripts.  Text selected with the middle button is treated as if
865 
it had been typed after the output point, much as a similar feature in
866 
</span><span style="font-size: 10pt"><tt>xterm</tt></span><span style="font-size: 10pt">
867 
or
868 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">,
869 
and therefore causes it to be &lsquo;executed&rsquo; by the application running in the window.
870 
Right button actions are reflected back to Acme but refer to the appropriate
871 
files because
872 
</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt">
873 
places the name of the current directory in the tag of the window.
874 
If the shell is running, a simple shell function replacing the
875 
</span><span style="font-size: 10pt"><tt>cd</tt></span><span style="font-size: 10pt">
876 
command can maintain the tag as the shell navigates the file system.
877 
This means, for example, that a right button click on a file mentioned in an
878 
</span><span style="font-size: 10pt"><tt>ls</tt></span><span style="font-size: 10pt">
879 
listing opens the file within Acme.
880 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
881 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
882 
<span style="font-size: 10pt">Another Acme-specific program is a mail reader that begins by presenting,
883 
in a window, a listing of the messages in the user&rsquo;s mailbox, one per line.
884 
Here the middle and right button actions are modified to refer to
885 
mail commands
886 
and messages, but the change feels natural.
887 
Clicking the right button on a line creates a new window and displays the
888 
message there, or, if it&rsquo;s already displayed, moves the mouse to that window.
889 
The metaphor is that the mailbox is a directory whose constituent files are messages.
890 
The mail program also places some relevant commands in the tag lines of
891 
the windows; for example, executing the word
892 
</span><span style="font-size: 10pt"><tt>Reply</tt></span><span style="font-size: 10pt">
893 
in a message&rsquo;s tag creates a new window
894 
in which to compose a message to the sender of the original;
895 
</span><span style="font-size: 10pt"><tt>Post</tt></span><span style="font-size: 10pt">
896 
then dispatches it.
897 
In such windows, the addressee is just a list of names
898 
on the first line of the body, which may be edited to add or change recipients.
899 
The program also monitors the mailbox, updating the &lsquo;directory&rsquo; as new messages
900 
arrive.
901 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
902 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
903 
<span style="font-size: 10pt">The mail program is as simple as it sounds; all the work of interaction,
904 
editing, and management of the display is done by Acme.
905 
The only
906 
difficult sections of the 1200
907 
lines of code concern honoring the external protocols for managing
908 
the mailbox and connecting to
909 
</span><span style="font-size: 10pt"><tt>sendmail</tt></span><span style="font-size: 10pt">.
910 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
911 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
912 
<span style="font-size: 10pt">One of the things Acme does not provide directly is a facility like
913 
Sam&rsquo;s command language to enable actions such as global substitution;
914 
within Acme, all editing is done manually.
915 
It is easy, though, to write external programs for such tasks.
916 
In this, Acme comes closer to the original intent of Oberon:
917 
a directory,
918 
</span><span style="font-size: 10pt"><tt>/acme/edit</tt></span><span style="font-size: 10pt">,
919 
contains a set of tools for repetitive editing and a template
920 
or &lsquo;guide&rsquo; file that gives examples
921 
of its use.
922 
Acme&rsquo;s editing guide,
923 
</span><span style="font-size: 10pt"><tt>/acme/edit/guide</tt></span><span style="font-size: 10pt">,
924 
looks like this:
925 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
926 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
927 
<span style="font-size: 9pt"><tt>e file | x &rsquo;/regexp/&rsquo; | c &rsquo;replacement&rsquo;</tt></span></p>
928 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
929 
<span style="font-size: 9pt"><tt>e file:&rsquo;0,$&rsquo; | x &rsquo;/.*word.*\n/&rsquo; | p -n</tt></span></p>
930 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
931 
<span style="font-size: 9pt"><tt>e file | pipe command args ...</tt></span></p>
932 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
933 
 
934 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
935 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
936 
<span style="font-size: 10pt">The syntax is reminiscent of Sam&rsquo;s command language, but here the individual
937 
one-letter commands are all stand-alone programs connected by pipes.
938 
Passed along the pipes are addresses, analogous to structural expressions
939 
in Sam terminology.
940 
The
941 
</span><span style="font-size: 10pt"><tt>e</tt></span><span style="font-size: 10pt">
942 
command, unlike that of Sam, starts the process by generating the address
943 
(default dot, the highlighted selection) in the named files.
944 
The other commands are as in Sam:
945 
</span><span style="font-size: 10pt"><tt>p</tt></span><span style="font-size: 10pt">
946 
prints the addressed text on standard output (the
947 
</span><span style="font-size: 10pt"><tt>-n</tt></span><span style="font-size: 10pt">
948 
option is analogous to that of
949 
</span><span style="font-size: 10pt"><tt>grep</tt></span><span style="font-size: 10pt">,
950 
useful in combination with the right mouse button);
951 
</span><span style="font-size: 10pt"><tt>x</tt></span><span style="font-size: 10pt">
952 
matches a regular expression to the addressed (incoming) text,
953 
subdividing the text;
954 
</span><span style="font-size: 10pt"><tt>c</tt></span><span style="font-size: 10pt">
955 
replaces the text; and so on.  Thus, global substitution throughout a file,
956 
which would be expressed in Sam as
957 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
958 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
959 
<span style="font-size: 9pt"><tt>0,$ x/regexp/ c/replacement/</tt></span></p>
960 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
961 
 
962 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
963 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
964 
<span style="font-size: 10pt">in Acme&rsquo;s editor becomes
965 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
966 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
967 
<span style="font-size: 9pt"><tt>e &rsquo;file:0,$&rsquo; | x &rsquo;/regexp/&rsquo; | c &rsquo;replacement&rsquo;</tt></span></p>
968 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
969 
 
970 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
971 
<p style="margin-top: 0; margin-bottom: 0.05in"></p>
972 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
973 
<span style="font-size: 10pt">To use the Acme editing commands, open
974 
</span><span style="font-size: 10pt"><tt>/acme/edit/guide</tt></span><span style="font-size: 10pt">,
975 
use the mouse and keyboard to edit one of the commands to the right form,
976 
and execute it with the middle button.
977 
Acme&rsquo;s context rules find the appropriate binaries in
978 
</span><span style="font-size: 10pt"><tt>/acme/edit</tt></span><span style="font-size: 10pt">
979 
rather than
980 
</span><span style="font-size: 10pt"><tt>/bin</tt></span><span style="font-size: 10pt">;
981 
the effect is to turn
982 
</span><span style="font-size: 10pt"><tt>/acme/edit</tt></span><span style="font-size: 10pt">
983 
into a toolbox containing tools and instructions (the guide file) for their use.
984 
In fact, the source for these tools is also there, in the directory
985 
</span><span style="font-size: 10pt"><tt>/acme/edit/src</tt></span><span style="font-size: 10pt">.
986 
This setup allows some control of the file name space for binary programs;
987 
not only does it group related programs, it permits the use of common
988 
names for uncommon jobs.  For example, the single-letter names would
989 
be unwise in a directory in everyone&rsquo;s search path; here they are only
990 
visible when running editing commands.
991 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
992 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
993 
<span style="font-size: 10pt">In Oberon,
994 
such a collection would be called a
995 
</span><span style="font-size: 10pt"><i>tool</i></span><span style="font-size: 10pt">
996 
and would consist
997 
of a set of entry points in a module and a menu-like piece of text containing
998 
representative commands that may be edited to suit and executed.
999 
There is, in fact, a tool called
1000 
</span><span style="font-size: 10pt"><tt>Edit</tt></span><span style="font-size: 10pt">
1001 
in Oberon.
1002 
To provide related functionality,
1003 
Acme exploits the directory and file structure of the underlying
1004 
system, rather than the module structure of the language;
1005 
this fits well with Plan 9&rsquo;s
1006 
file-oriented philosophy.
1007 
Such tools are central to the working of Oberon but they are
1008 
less used in Acme, at least so far.
1009 
The main reason is probably that Acme&rsquo;s program interface permits
1010 
an external program to remain executing in the background, providing
1011 
its own commands as needed (for example, the
1012 
</span><span style="font-size: 10pt"><tt>Reply</tt></span><span style="font-size: 10pt">
1013 
command in the mail program); Oberon uses tools to
1014 
implement such services because its must invoke
1015 
a fresh program for each command.
1016 
Also,
1017 
Acme&rsquo;s better integration allows more
1018 
basic functions to be handled internally; the right mouse button
1019 
covers a lot of the basic utility of the editing tools in Oberon.
1020 
Nonetheless, as more applications are written for Acme,
1021 
many are sure to take this Oberon tool-like form.
1022 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1023 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1024 
<span style="font-size: 10pt"><b>Comparison with other systems
1025 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1026 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1027 
<span style="font-size: 10pt">Acme&rsquo;s immediate ancestor is Help [Pike92], an experimental system written
1028 
a few years ago as a first try at exploring some of Oberon&rsquo;s ideas
1029 
in an existing operating system.
1030 
Besides much better engineering, Acme&rsquo;s advances over Help
1031 
include the actions of the right button (Help had nothing comparable),
1032 
the ability to connect long-running programs to the user interface
1033 
(Help had no analog of the
1034 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">
1035 
file),
1036 
and the small but important change to split command output into
1037 
windows labeled with the directory in which the commands run.
1038 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1039 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1040 
<span style="font-size: 10pt">Most of Acme&rsquo;s style, however, derives from the user interface and window
1041 
system of Oberon [Wirt89, Reis91].
1042 
Oberon includes a programming language and operating system,
1043 
which Acme instead borrows from an existing system, Plan 9.
1044 
When I first saw Oberon, in 1988, I was struck by the
1045 
simplicity of its user interface, particularly its lack of menus
1046 
and its elegant use of multiple mouse buttons.
1047 
The system seemed restrictive, though&mdash;single process,
1048 
single language, no networking, event-driven programming&mdash;and
1049 
failed to follow through on some of its own ideas.
1050 
For example, the middle mouse button had to be pointed accurately and
1051 
the right button was essentially unused.
1052 
Acme does follow through:
1053 
to the basic idea planted by Oberon, it adds
1054 
the ability to run on different operating systems and hardware,
1055 
connection to existing applications including
1056 
interactive ones such as shells and debuggers,
1057 
support for multiple processes,
1058 
the right mouse button&rsquo;s features,
1059 
the default actions and context-dependent properties
1060 
of execution and searching,
1061 
and a host of little touches such as moving the mouse cursor that make the system
1062 
more pleasant.
1063 
At the moment, though, Oberon does have one distinct advantage: it incorporates
1064 
graphical programs well into its model, an issue Acme has not yet faced.
1065 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1066 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1067 
<span style="font-size: 10pt">Acme shares with the Macintosh a desire to use the mouse well and it is
1068 
worth comparing the results.
1069 
The mouse on the Macintosh has a single button, so menus are essential
1070 
and the mouse must frequently move a long way
1071 
to reach the appropriate function.
1072 
An indication that this style has trouble is that applications provide
1073 
keyboard sequences to invoke menu selections and users often prefer them.
1074 
A deeper comparison is that the Macintosh uses pictures where Acme uses text.
1075 
In contrast to pictures, text can be edited quickly, created on demand,
1076 
and fine-tuned to the job at hand; consider adding an option to a command.
1077 
It is also self-referential; Acme doesn&rsquo;t need menus because any text can be
1078 
in effect a menu item.
1079 
The result is that, although a Macintosh screen is certainly prettier and probably
1080 
more attractive, especially to beginners, an Acme screen is more dynamic
1081 
and expressive, at least for programmers and experienced users.
1082 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1083 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1084 
<span style="font-size: 10pt">For its role in the overall system,
1085 
Acme most resembles EMACS [Stal93].
1086 
It is tricky to compare Acme to EMACS, though, because there are
1087 
many versions of EMACS and, since it is fully programmable, EMACS
1088 
can in principle do anything Acme does.
1089 
Also, Acme is much younger and therefore has not
1090 
had the time to acquire as many features.
1091 
The issue therefore is less what the systems can be programmed to do than
1092 
how they are used.
1093 
The EMACS versions that come closest to Acme&rsquo;s style are those that
1094 
have been extended to provide a programming environment, usually
1095 
for a language such as LISP [Alle92, Lucid92].
1096 
For richness of the existing interface, these EMACS versions are certainly superior to Acme.
1097 
On the other hand, Acme&rsquo;s interface works equally well already for a variety
1098 
of languages; for example, one of its most enthusiastic users works almost
1099 
exclusively in Standard ML, a language nothing like C.
1100 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1101 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1102 
<span style="font-size: 10pt">Where Acme excels is in the smoothness of its interface.
1103 
Until recently, EMACS did not support the mouse especially well,
1104 
and even with the latest version providing features such as &lsquo;extents&rsquo;
1105 
that can be programmed to behave much like Acme commands,
1106 
many users don&rsquo;t bother to upgrade.
1107 
Moreover, in the versions that provide extents,
1108 
most EMACS packages don&rsquo;t take advantage of them.
1109 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1110 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1111 
<span style="font-size: 10pt">The most important distinction is just that
1112 
EMACS is fundamentally keyboard-based, while
1113 
Acme is mouse-based.
1114 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1115 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1116 
<span style="font-size: 10pt">People who try Acme find it hard to go back to their previous environment.
1117 
Acme automates so much that to return to a traditional interface
1118 
is to draw attention to the extra work it requires.
1119 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1120 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1121 
<span style="font-size: 10pt"><b>Concurrency in the implementation
1122 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1123 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1124 
<span style="font-size: 10pt">Acme is about 8,000 lines of code in Alef, a concurrent object-oriented language syntactically similar to C [Alef].
1125 
Acme&rsquo;s structure is a set of communicating
1126 
processes in a single address space.
1127 
One subset of the processes drives the display and user interface,
1128 
maintaining the windows; other processes forward mouse and keyboard
1129 
activity and implement the file server interface for external programs.
1130 
The language and design worked out well;
1131 
as explained elsewhere [Pike89, Gans93, Reppy93],
1132 
user interfaces built with concurrent systems
1133 
can avoid the clumsy
1134 
top-level event loop typical of traditional interactive systems.
1135 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1136 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1137 
<span style="font-size: 10pt">An example of the benefits of the multi-process style
1138 
is the management of the state of open
1139 
files held by clients of the file system interface.
1140 
The problem is that some I/O requests,
1141 
such as reading the
1142 
</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">
1143 
file, may block if no data is available, and the server must
1144 
maintain the state of (possibly many) requests until data appears.
1145 
For example,
1146 
in
1147 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">,
1148 
a single-process window system written in C, pending requests were queued in
1149 
a data structure associated with each window.
1150 
After activity in the window that might complete pending I/O,
1151 
the data structure was scanned for requests that could now finish.
1152 
This structure did not fit well with the rest of the program and, worse,
1153 
required meticulous effort
1154 
to guarantee correct behavior under all conditions
1155 
(consider raw mode, reads of partial lines, deleting a window,
1156 
multibyte characters, etc.).
1157 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1158 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1159 
<span style="font-size: 10pt">Acme instead creates a new dedicated process
1160 
for each I/O request.
1161 
This process coordinates with the rest of the system
1162 
using Alef&rsquo;s synchronous communication;
1163 
its state implicitly encodes the state of
1164 
the I/O request and obviates the need for queuing.
1165 
The passage of the request through Acme proceeds as follows.
1166 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1167 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1168 
<span style="font-size: 10pt">Acme contains a file server process, F, that executes a
1169 
</span><span style="font-size: 10pt"><tt>read</tt></span><span style="font-size: 10pt">
1170 
system call to receive a Plan 9 file protocol (9P) message from the client [AT&amp;T92].
1171 
The client blocks until Acme answers the request.
1172 
F communicates with an allocation process, M,
1173 
to acquire an object of type
1174 
</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">
1175 
(&lsquo;executing fid&rsquo;; fid is a 9P term)
1176 
to hold the request.
1177 
M sits in a loop (reproduced in Figure 2) waiting for either a request for
1178 
a new
1179 
</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">
1180 
or notification that an existing one has finished its task.
1181 
When an
1182 
</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">
1183 
is created, an associated process, X,
1184 
is also made.
1185 
M queues idle
1186 
</span><span style="font-size: 10pt"><tt>Xfids</tt></span><span style="font-size: 10pt">,
1187 
allocating new ones only when the list is empty.
1188 
Thus, there is always a pool of
1189 
</span><span style="font-size: 10pt"><tt>Xfids</tt></span><span style="font-size: 10pt">,
1190 
some executing, some idle.
1191 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1192 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1193 
<span style="font-size: 10pt">The
1194 
</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">
1195 
object contains a channel,
1196 
</span><span style="font-size: 10pt"><tt>Xfid.c</tt></span><span style="font-size: 10pt">,
1197 
for communication with its process;
1198 
the unpacked message; and some associated functions,
1199 
mostly corresponding to 9P messages such as
1200 
</span><span style="font-size: 10pt"><tt>Xfid.write</tt></span><span style="font-size: 10pt">
1201 
to handle a 9P write request.
1202 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1203 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1204 
<span style="font-size: 10pt">The file server process F parses the message to see its nature&mdash;open,
1205 
close, read, write, etc.  Many messages, such as directory
1206 
lookups, can be handled immediately; these are responded to directly
1207 
and efficiently
1208 
by F without invoking the
1209 
</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">,
1210 
which is therefore maintained until the next message.
1211 
When a message, such as a write to the display, requires the attention
1212 
of the main display process and interlocked access to its data structures,
1213 
F enables X
1214 
by sending a function pointer on
1215 
</span><span style="font-size: 10pt"><tt>Xfid.c</tt></span><span style="font-size: 10pt">.
1216 
For example, if the message is a write, F executes
1217 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
1218 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1219 
<span style="font-size: 9pt"><tt>x-&gt;c &lt;-= Xfid.write;</tt></span></p>
1220 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
1221 
 
1222 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
1223 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1224 
<span style="font-size: 10pt">which sends
1225 
the address of
1226 
</span><span style="font-size: 10pt"><tt>Xfid.write</tt></span><span style="font-size: 10pt">
1227 
on
1228 
</span><span style="font-size: 10pt"><tt>Xfid.c</tt></span><span style="font-size: 10pt">,
1229 
waking up X.
1230 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1231 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1232 
<span style="font-size: 10pt">The
1233 
</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">
1234 
process, X, executes a simple loop:
1235 
</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p>
1236 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1237 
<span style="font-size: 9pt"><tt>void</tt></span></p>
1238 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1239 
<span style="font-size: 9pt"><tt>Xfid.ctl(Xfid *x)</tt></span></p>
1240 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1241 
<span style="font-size: 9pt"><tt>{</tt></span></p>
1242 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1243 
<span style="font-size: 9pt"><tt>    for(;;){</tt></span></p>
1244 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1245 
<span style="font-size: 9pt"><tt>        (*&lt;-x-&gt;c)(x);      /* receive and execute message */</tt></span></p>
1246 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1247 
<span style="font-size: 9pt"><tt>        bflush();          /* synchronize bitmap display */</tt></span></p>
1248 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1249 
<span style="font-size: 9pt"><tt>        cxfidfree &lt;-= x;   /* return to free list */</tt></span></p>
1250 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1251 
<span style="font-size: 9pt"><tt>    }</tt></span></p>
1252 
<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1253 
<span style="font-size: 9pt"><tt>}</tt></span></p>
1254 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
1255 
 
1256 
<p style="margin-top: 0; margin-bottom: 0.08in"></p>
1257 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1258 
<span style="font-size: 10pt">Thus X
1259 
will wake up with the address of a function to call (here
1260 
</span><span style="font-size: 10pt"><tt>Xfid.write</tt></span><span style="font-size: 10pt">)
1261 
and execute it; once that completes, it returns itself to the pool of
1262 
free processes by sending its address back to the allocator.
1263 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1264 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1265 
<span style="font-size: 10pt">Although this sequence may seem complicated, it is just a few lines
1266 
of code and is in fact far simpler
1267 
than the management of the I/O queues in
1268 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">.
1269 
The hard work of synchronization is done by the Alef run time system.
1270 
Moreover, the code worked the first time, which cannot be said for the code in
1271 
</span><span style="font-size: 10pt"><tt>8&frac12;</tt></span><span style="font-size: 10pt">.
1272 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1273 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1274 
<span style="font-size: 10pt"><b>Undo
1275 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1276 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1277 
<span style="font-size: 10pt">Acme provides a general undo facility like that of Sam, permitting
1278 
textual changes to be unwound arbitrarily.
1279 
The implementation is superior to Sam&rsquo;s, though,
1280 
with much higher performance and the ability to &lsquo;redo&rsquo; changes.
1281 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1282 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1283 
<span style="font-size: 10pt">Sam uses
1284 
a multi-pass algorithm that builds
1285 
a transcript of changes to be made simultaneously
1286 
and then executes them atomically.
1287 
This was thought necessary because the elements of a repetitive
1288 
command such as a global substitution should all be applied to the same
1289 
initial file and implemented simultaneously; forming the complete
1290 
transcript before executing any of the changes avoids the
1291 
cumbersome management of addresses in a changing file.
1292 
Acme, however, doesn&rsquo;t have this problem; global substitution
1293 
is controlled externally and may be made incrementally by exploiting
1294 
an observation: if the changes are sorted in address order and
1295 
executed in reverse, changes will not invalidate the addresses of
1296 
pending changes.
1297 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1298 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1299 
<span style="font-size: 10pt">Acme therefore avoids the initial transcript.  Instead, changes are applied
1300 
directly to the file, with an undo transcript recorded in a separate list.
1301 
For example, when text is added to a window, it is added directly and a record
1302 
of what to delete to restore the state is appended to the undo list.
1303 
Each undo action and the file are marked with a sequence number;
1304 
actions with the same sequence number are considered a unit
1305 
to be undone together.
1306 
The invariant state of the structure
1307 
is that the last action in the undo list applies to the current state of the file,
1308 
even if that action is one of a related set from, for example, a global substitute.
1309 
(In Sam, a related set of actions needed to be undone simultaneously.)
1310 
To undo an action, pop the last item on the undo list, apply it to the file,
1311 
revert it, and append it to a second, redo list.
1312 
To redo an action, do the identical operation with the lists interchanged.
1313 
The expensive operations occur
1314 
only when actually undoing; in normal editing the overhead is minor.
1315 
For example, Acme reads files about seven times faster than Sam, partly
1316 
because of this improvement and partly because of a cleaner implementation.
1317 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1318 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1319 
<span style="font-size: 10pt">Acme uses a temporary file to hold the text, keeping in memory only the
1320 
visible portion, and therefore can edit large files comfortably
1321 
even on small-memory machines such as laptops.
1322 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1323 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1324 
<span style="font-size: 10pt"><b>Future
1325 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1326 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1327 
<span style="font-size: 10pt">Acme is still under development.
1328 
Some things are simply missing.
1329 
For example, Acme should support non-textual graphics, but this is being
1330 
deferred until it can be done using a new graphics model being developed
1331 
for Plan 9.  Also, it is undecided how Acme&rsquo;s style of interaction should best be
1332 
extended to graphical applications.
1333 
On a smaller scale, although the system feels smooth and comfortable,
1334 
work continues to tune the heuristics and
1335 
try new ideas for the user interface.
1336 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1337 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1338 
<span style="font-size: 10pt">There need to be more programs that use Acme.  Browsers for
1339 
Usenet and AP News articles, the Oxford English Dictionary, and other
1340 
such text sources exist, but more imaginative applications will
1341 
be necessary to prove that Acme&rsquo;s approach is viable.
1342 
One that has recently been started is an interface to the debugger Acid [Wint94],
1343 
although it is still
1344 
unclear what form it will ultimately take.
1345 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1346 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1347 
<span style="font-size: 10pt">Acme shows that it is possible to make a user interface a stand-alone component
1348 
of an interactive environment.  By absorbing more of the interactive
1349 
functionality than a simple window system, Acme off-loads much of the
1350 
computation from its applications, which helps keep them small and
1351 
consistent in their interface.  Acme can afford to dedicate
1352 
considerable effort to making that interface as good as possible; the result
1353 
will benefit the entire system.
1354 
</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1355 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1356 
<span style="font-size: 10pt">Acme is complete and useful enough to attract users.
1357 
Its comfortable user interface,
1358 
the ease with which it handles multiple tasks and
1359 
programs in multiple directories,
1360 
and its high level of integration
1361 
make it addictive.
1362 
Perhaps most telling,
1363 
Acme shows that typescripts may not be the most
1364 
productive interface to a time-sharing system.
1365 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1366 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1367 
<span style="font-size: 10pt"><b>Acknowledgements
1368 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1369 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1370 
<span style="font-size: 10pt">Howard Trickey, Acme&rsquo;s first user, suffered buggy versions gracefully and made
1371 
many helpful suggestions.  Chris Fraser provided the necessary insight for the Acme editing
1372 
commands.
1373 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1374 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1375 
<span style="font-size: 10pt"><b>References
1376 
</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p>
1377 
<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1378 
<span style="font-size: 10pt">[Alef] P. Winterbottom,
1379 
&lsquo;&lsquo;Alef Language Reference Manual&rsquo;&rsquo;,
1380 
</span><span style="font-size: 10pt"><i>Plan 9 Programmer&rsquo;s Manual,
1381 
</i></span><span style="font-size: 10pt">AT&amp;T Bell Laboratories,
1382 
Murray Hill, NJ,
1383 
1992;
1384 
revised in this volume.
1385 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1386 
<span style="font-size: 10pt">[Alle92]
1387 
</span><span style="font-size: 10pt"><i>Allegro Common Lisp user Guide, Vol 2,
1388 
</i></span><span style="font-size: 10pt">Chapter 14, "The Emacs-Lisp Interface".
1389 
March 1992.
1390 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1391 
<span style="font-size: 10pt">[AT&amp;T92] Plan 9 Programmer&rsquo;s manual, Murray Hill, New Jersey, 1992.
1392 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1393 
<span style="font-size: 10pt">[Far89] Far too many people, XTERM(1), Massachusetts Institute of Technology, 1989.
1394 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1395 
<span style="font-size: 10pt">[Gans93] Emden R. Gansner and John H. Reppy,  &lsquo;&lsquo;A Multi-threaded Higher-order User Interface Toolkit&rsquo;&rsquo;, in
1396 
</span><span style="font-size: 10pt"><i>Software Trends, Volume 1,
1397 
User Interface Software,
1398 
</i></span><span style="font-size: 10pt">Bass and Dewan (Eds.),
1399 
John Wiley &amp; Sons 1993,
1400 
pp. 61-80.
1401 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1402 
<span style="font-size: 10pt">[Lucid92] Richard Stallman and Lucid, Inc.,
1403 
</span><span style="font-size: 10pt"><i>Lucid GNU EMACS Manual,
1404 
</i></span><span style="font-size: 10pt">March 1992.
1405 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1406 
<span style="font-size: 10pt">[Pike87] Rob Pike, &lsquo;&lsquo;The Text Editor </span><span style="font-size: 10pt"><tt>sam</tt></span><span style="font-size: 10pt">&rsquo;&rsquo;, Softw. - Pract. and Exp., Nov 1987, Vol 17 #11, pp. 813-845; reprinted in this volume.
1407 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1408 
<span style="font-size: 10pt">[Pike88] Rob Pike, &lsquo;&lsquo;Window Systems Should Be Transparent&rsquo;&rsquo;, Comp. Sys., Summer 1988, Vol 1 #3, pp. 279-296.
1409 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1410 
<span style="font-size: 10pt">[Pike89] Rob Pike, &lsquo;&lsquo;A Concurrent Window System&rsquo;&rsquo;, Comp. Sys., Spring 1989, Vol 2 #2, pp. 133-153.
1411 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1412 
<span style="font-size: 10pt">[PPTTW93] Rob Pike, Dave Presotto, Ken Thompson, Howard Trickey, and Phil Winterbottom, &lsquo;&lsquo;The Use of Name Spaces in Plan 9&rsquo;&rsquo;,
1413 
Op. Sys. Rev.,  Vol. 27, No. 2, April 1993, pp. 72-76,
1414 
reprinted in this volume.
1415 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1416 
<span style="font-size: 10pt">[Pike91] Rob Pike, &lsquo;&lsquo;8&frac12;, the Plan 9 Window System&rsquo;&rsquo;, USENIX Summer Conf. Proc., Nashville, June, 1991, pp. 257-265,
1417 
reprinted in this volume.
1418 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1419 
<span style="font-size: 10pt">[Pike92] Rob Pike, &lsquo;&lsquo;A Minimalist Global User Interface&rsquo;&rsquo;, Graphics Interface &rsquo;92 Proc., Vancouver, 1992, pp. 282-293.  An earlier version appeared under the same title in USENIX Summer Conf. Proc., Nashville, June, 1991, pp. 267-279.
1420 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1421 
<span style="font-size: 10pt">[Pike93] Rob Pike and Ken Thompson, &lsquo;&lsquo;Hello World or &Kappa;&alpha;&lambda;&eta;&mu;&#941;&rho;&alpha; &kappa;&#972;&sigma;&mu;&epsilon; or
1422 
</span><span style="font-size: 10pt">&#12371;&#12435;&#12395;&#12385;&#12399; &#19990;&#30028;</span><span style="font-size: 10pt">&rsquo;&rsquo;, USENIX Winter Conf. Proc., San Diego, 1993, pp. 43-50,
1423 
reprinted in this volume.
1424 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1425 
<span style="font-size: 10pt">[Pres93] Dave Presotto and Phil Winterbottom, &lsquo;&lsquo;The Organization of Networks in Plan 9&rsquo;&rsquo;, Proc. Usenix Winter 1993, pp. 271-287, San Diego, CA,
1426 
reprinted in this volume.
1427 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1428 
<span style="font-size: 10pt">[Reis91] Martin Reiser, </span><span style="font-size: 10pt"><i>The Oberon System,</i></span><span style="font-size: 10pt"> Addison Wesley, New York, 1991.
1429 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1430 
<span style="font-size: 10pt">[Reppy93] John H. Reppy,
1431 
&lsquo;&lsquo;CML: A higher-order concurrent language&rsquo;&rsquo;, Proc. SIGPLAN&rsquo;91 Conf. on Programming, Lang. Design and Impl., June, 1991, pp. 293-305.
1432 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1433 
<span style="font-size: 10pt">[Sche86] Robert W. Scheifler and Jim Gettys,
1434 
&lsquo;&lsquo;The X Window System&rsquo;&rsquo;,
1435 
ACM Trans. on Graph., Vol 5 #2, pp. 79-109.
1436 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1437 
<span style="font-size: 10pt">[Stal93] Richard Stallman,
1438 
</span><span style="font-size: 10pt"><i>Gnu Emacs Manual, 9th edition, Emacs version 19.19,
1439 
</i></span><span style="font-size: 10pt">MIT.
1440 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1441 
<span style="font-size: 10pt">[Swei86] Daniel Sweinhart, Polle Zellweger, Richard Beach, and Robert Hagmann,
1442 
&lsquo;&lsquo;A Structural View of the Cedar Programming Environment&rsquo;&rsquo;,
1443 
ACM Trans. Prog. Lang. and Sys., Vol. 8, No. 4, pp. 419-490, Oct. 1986.
1444 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1445 
<span style="font-size: 10pt">[Wint94], Philip Winterbottom, &lsquo;&lsquo;Acid: A Debugger based on a Language&rsquo;&rsquo;, USENIX Winter Conf. Proc., San Francisco, CA, 1993,
1446 
reprinted in this volume.
1447 
</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1448 
<span style="font-size: 10pt">[Wirt89] N. Wirth and J. Gutknecht, &lsquo;&lsquo;The Oberon System&rsquo;&rsquo;, Softw. - Prac. and Exp., Sep 1989, Vol 19 #9, pp 857-894.
1449 
</span></p><p style="margin-top: 0; margin-bottom: 0.50in"></p>
1450 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
1451 
<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.35in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1452 
<span style="font-size: 10pt"></span><span style="font-size: 10pt"><b>Notes</b></span><span style="font-size: 10pt">
1453 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1454 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
1455 
 
1456 
<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.00in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;">
1457 
<span style="font-size: 10pt">Originally appeared in
1458 
</span><span style="font-size: 10pt"><i>Proc. of the Winter 1994 USENIX Conf.,
1459 
</i></span><span style="font-size: 10pt">pp. 223-234,
1460 
San Francisco, CA
1461 
</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p>
1462 
<p style="margin-top: 0; margin-bottom: 0.17in"></p>
1463 
 
1464 
</body>
1465 
</html>
1466