| 2 |
7u83 |
1 |
<!-- Crown Copyright (c) 1998 -->
|
|
|
2 |
<HTML>
|
|
|
3 |
<HEAD>
|
|
|
4 |
<TITLE>PL_TDF Definition</TITLE>
|
|
|
5 |
</HEAD>
|
|
|
6 |
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000FF" VLINK="#400080" ALINK="#FF0000">
|
|
|
7 |
<A NAME=S2>
|
|
|
8 |
<H1>PL_TDF Definition</H1>
|
|
|
9 |
<H3>January 1998</H3>
|
|
|
10 |
<A HREF="pl4.html"><IMG SRC="../images/next.gif" ALT="next section">
|
|
|
11 |
</A> <A HREF="pl1.html">
|
|
|
12 |
<IMG SRC="../images/prev.gif" ALT="previous section"></A>
|
|
|
13 |
<A HREF="pl1.html"><IMG SRC="../images/top.gif" ALT="current document"></A>
|
|
|
14 |
<A HREF="../index.html"><IMG SRC="../images/home.gif" ALT="TenDRA home page">
|
|
|
15 |
</A>
|
|
|
16 |
<IMG SRC="../images/no_index.gif" ALT="document index"><P>
|
|
|
17 |
<HR>
|
|
|
18 |
<DL>
|
|
|
19 |
<DT><A HREF="#S3"><B>2.1 </B> - Syntax description</A><DD>
|
|
|
20 |
<DT><A HREF="#S4"><B>2.2 </B> - Lexical Units</A><DD>
|
|
|
21 |
<DT><A HREF="#S5"><B>2.3 </B> - Pre-processing</A><DD>
|
|
|
22 |
</DL>
|
|
|
23 |
<HR>
|
|
|
24 |
<H1>2 Notation</H1>
|
|
|
25 |
<A NAME=S3>
|
|
|
26 |
<HR><H2>2.1. Syntax description</H2>
|
|
|
27 |
Words enclosed in angle brackets, < >, form non-terminal symbols.
|
|
|
28 |
Other symbols and words stand for themselves as terminal symbols.
|
|
|
29 |
An expansion of a non-terminal is indicated using ::= with its expansion
|
|
|
30 |
given as a sequence (possibly empty) of terminals and non-terminals.
|
|
|
31 |
For example:<P>
|
|
|
32 |
<PRE>
|
|
|
33 |
<Exp> ::= * <ident>
|
|
|
34 |
</PRE>
|
|
|
35 |
is a possible expansion of an EXP SORT. If the word for the non-terminal
|
|
|
36 |
starts with a capital letter then it will be totally described by
|
|
|
37 |
a set of such expansions; otherwise the expansion of the non-terminal
|
|
|
38 |
will be given by other methods in the text. <P>
|
|
|
39 |
The post-fix -Opt on a non terminal is an abreviation allowing an
|
|
|
40 |
empty expansion. For example:<P>
|
|
|
41 |
<PRE>
|
|
|
42 |
<Access>-Opt
|
|
|
43 |
</PRE>
|
|
|
44 |
is equivalent to the use of another non-terminal <AccessOption>
|
|
|
45 |
whose expansions are:<P>
|
|
|
46 |
<PRE>
|
|
|
47 |
<AccessOption> ::=
|
|
|
48 |
<AccessOption> ::= <Access>
|
|
|
49 |
</PRE>
|
|
|
50 |
The post-fix -List on a non terminal is an abreviation for lists of
|
|
|
51 |
objects seperated by the ,-symbol. For example:<P>
|
|
|
52 |
<PRE>
|
|
|
53 |
<Exp>-List
|
|
|
54 |
</PRE>
|
|
|
55 |
is equivalent to the use of another non-terminal <ExpList> whose
|
|
|
56 |
expansions are:<P>
|
|
|
57 |
<PRE>
|
|
|
58 |
<ExpList> ::= <Exp>
|
|
|
59 |
<ExpList> ::= <ExpList> , <Exp>
|
|
|
60 |
</PRE>
|
|
|
61 |
Both of these post-fix notations are also used with sequences of terminals
|
|
|
62 |
and non-terminals within the angle brackets with the same kind of
|
|
|
63 |
expansion. In these cases, the expansion within the angle brackets
|
|
|
64 |
form an anonymous non-terminal.<P>
|
|
|
65 |
<A NAME=S4>
|
|
|
66 |
<HR><H2>2.2. Lexical Units</H2>
|
|
|
67 |
The terminal symbols ( ), [ ], and { } always occur as parenthetic
|
|
|
68 |
pairs and never form part of other terminal symbols.<P>
|
|
|
69 |
The terminal symbols , ; and : are similarly terminators for other
|
|
|
70 |
terminal symbols.<P>
|
|
|
71 |
White space is a terminator for other terminal symbols but is otherwise
|
|
|
72 |
ignored except in strings.<P>
|
|
|
73 |
All other terminal symbols are sequences of ACSII symbols not including
|
|
|
74 |
the above. These are divided into seven classes: keywords, TDF constructors,
|
|
|
75 |
operators, <integer_denotation>s, <floating_denotation>s,
|
|
|
76 |
<string>s and <ident>s.<P>
|
|
|
77 |
The keywords and operators are expressed directly in the syntax description.
|
|
|
78 |
The TDF constructors are those given in the TDF specification which
|
|
|
79 |
have first-class SORTs as parameters and results.<P>
|
|
|
80 |
An <integer_denotatation> allows one to express an integer in
|
|
|
81 |
any base less than 16, with the default being 10. <P>
|
|
|
82 |
<PRE>
|
|
|
83 |
<integer_denotation> ::= <digit>
|
|
|
84 |
<integer_denotation> ::= <integer_denotation> <digit>
|
|
|
85 |
<integer_denotation> ::= <base> <integer_denotation>
|
|
|
86 |
|
|
|
87 |
<base> ::= <integer_denotation> r
|
|
|
88 |
</PRE>
|
|
|
89 |
Examples are 31, 16r1f, 8r37, 2r11111 - all giving the same value.<P>
|
|
|
90 |
A <floating_denotation> is an <integer_denotation> followed
|
|
|
91 |
by the . symbol and a sequence of digits. The radix of the <floating_denotation>
|
|
|
92 |
is given by the base of its component <integer_denotation><P>
|
|
|
93 |
A <string> is the same as a C string - any sequence of characters
|
|
|
94 |
within " ". The same C conventions hold for \ within strings
|
|
|
95 |
for single characters.<P>
|
|
|
96 |
A <character> is an string character within ` `. The same \
|
|
|
97 |
conventions hold.<P>
|
|
|
98 |
An <ident> is any other sequence of characters. They will be
|
|
|
99 |
used to form names for TAGs, TOKENs, AL_TAGs and LABELs.<P>
|
|
|
100 |
<A NAME=S5>
|
|
|
101 |
<HR><H2>2.3. Pre-processing</H2>
|
|
|
102 |
At the moment there is only one pre-processing directive. A line starting
|
|
|
103 |
with #include will textually include the following file (named within
|
|
|
104 |
string quotes), using the same path conventions as C.<P>
|
|
|
105 |
Comments may be included in the text using the /* ... */ notation;
|
|
|
106 |
this differs slightly from the C convention in that comments may be
|
|
|
107 |
nested.<P>
|
|
|
108 |
<HR>
|
|
|
109 |
<P><I>Part of the <A HREF="../index.html">TenDRA Web</A>.<BR>Crown
|
|
|
110 |
Copyright © 1998.</I></P>
|
|
|
111 |
</BODY>
|
|
|
112 |
</HTML>
|