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From: rpd@f.gp.cs.cmu.edu (Richard Draves)
Newsgroups: net.lang.mod2
Subject: Re: ETH Modula2 Single Pass
Message-ID: <5@f.gp.cs.cmu.edu>
Date: Mon, 22-Sep-86 12:27:22 EDT
Article-I.D.: f.5
Posted: Mon Sep 22 12:27:22 1986
Date-Received: Mon, 22-Sep-86 21:26:52 EDT
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Organization: Carnegie-Mellon University, CS/RI
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I don't believe a true one-pass Modula-2 compiler is possible.
I have some experience with the language, having implemented
the front-end (first-pass) for a compiler.  I have also discussed
this issue with Mike Powell, implementor of the famed Powell compiler,
and he concurs.

The problem is that identifiers may be used in statements before they
are declared (although identifiers used in declarations must be declared
before use).  Page 145 of the 3rd edition of Wirth's book is very clear.
You may think a back-patching scheme can overcome this, but I have some
sample programs that I think can convince anyone that the problems with
such an approach are intractable.

Does this purported one-pass compiler compile the whole language or a subset?
If it does compile the whole language, does anyone know how it accomplishes
this in a single pass?  Let me mention that reading a program into memory,
perhaps in the form of a syntax tree, and then generating code is *not*
one pass.

Rich