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From: koopman@a.gp.cs.cmu.edu (Philip Koopman)
Newsgroups: comp.lang.forth
Subject: Infix/Postfix notation
Keywords: infix, postfix, stacks
Message-ID: <2768@pt.cs.cmu.edu>
Date: 22 Aug 88 18:59:03 GMT
Sender: netnews@pt.cs.cmu.edu
Organization: Carnegie-Mellon University, CS/RI
Lines: 27

Several recent postings have debated the merits of infix versus
postfix notation in Forth.  I'd like to present a different
viewpoint for discussion.  Postfix notation is just a side-effect
of a much more important issue: parameter passing for subroutines.

One of the most useful aspects of Forth is implicit parameter
passing.  That eliminates the tedious lists of parameters in
parenthesis found in other languages.  This makes the code much
cleaner and more flexible than other languages.  It also makes
defining words and immediate words handy. 

The arithmetic operators are treated as subroutines just like
any other word.  This allows a blurring of the distinction between
hardware supported primitives and high level routines, improving
transportability and making optimization of inner loops in
assembly language or microcode quite easy.
So, to me, the RPN notation is just an inconvenient side-effect
of the implicit parameter passing mechanism used by the language,
and is not really an important feature itself.

As an aside, real infix notation parsers are relatively simple
to write (for example, the one Chuck Moore wrote for his tiny
BASIC interpretter.)  I think that most people don't bother with
them because most expressions that are evaluated are very simple.

Phil Koopman         koopman@faraday.ece.cmu.edu  Arpanet
Student at CMU, sometime consultant to Harris Semiconductor.