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<TITLE>PL_TDF Definition</TITLE>
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<H1>PL_TDF Definition</H1>
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<H3>January 1998</H3>
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<P>
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<P>
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<DL>
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<DT><A HREF="#intro"><B>1 </B> - Introduction</A><DD>
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<DT><A HREF="pl3.html#S2"><B>2 </B> - Notation</A><DD>
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<DT><A HREF="pl4.html#S6"><B>3 </B> - The Language</A><DD>
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<DT><A HREF="pl5.html#S41"><B>4 </B> - Example PL_TDF programs</A><DD>
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<DT><A HREF="pl6.html#S47"><B>5 </B> - Use of the PL_TDF compiler</A><DD>
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<H1><A NAME="intro">1 Introduction</A></H1>
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PL_TDF is a language in the lineage of Wirth's PL360 and its later
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derivatives. The basic idea in PL360 was to give one an assembler
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in which one could express all of the order-code of the IBM 360 while
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still preserving the logical structure of the program using familiar
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programming constructs. If one had to produce a program at the code
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level, this approach was much preferable to writing "flat"
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assembly code using a traditional assembler, as anyone who has used
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both can testify.<P>
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In the TDF "machine" the problem is not lack of structure
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at its "assembly" level, but rather too much of it; one
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loses the sense of a TDF program because of its deeply nested structure.
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Also the naming conventions of TDF are designed to make them tractable
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to machine manipulation, rather than human reading and writing. However,
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the approach is basically the same. PL_TDF provides shorthand notations
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for the commonly occuring control structures and operations while
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still allowing one to use the standard TDF constructors which, in
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turn, may have shorthand notations for their parameters. The naming
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is always done by identifiers where the sort of the name is determined
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by its declaration, or by context.<P>
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The TDF derived from PL_TDF is guaranteed to be SORT correct; however,
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there is no SHAPE checking, so one can still make illegal TDF.<P>
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<P><I>Part of the <A HREF="../index.html">TenDRA Web</A>.<BR>Crown
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Copyright © 1998.</I></P>
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