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From: ForthNet@willett.pgh.pa.us (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: ANS TC - Between the cracks
Message-ID: <2315.UUL1.3#5129@willett.pgh.pa.us>
Date: 9 Feb 91 03:15:23 GMT
Organization: (n.) to be organized.  But that's not important right now.
Lines: 31

Category 10,  Topic 28
Message 107       Fri Feb 08, 1991
B.RODRIGUEZ2 [Brad]          at 19:57 EST
 
Here's something else which (to my mind) cannot be implemented _efficiently_
in a portable way using ANS Forth.  Even the inefficient ways are difficult.

: ||   IF R> DROP -1 THEN ;     ( t - t)  ( f - )  ( exit on true)
 : &&   0= IF R> DROP 0 THEN ;   ( t - )  ( f - f)  ( exit on false)

I've named these in honor of the "C" operators they mimic.  Marla Bartel named
them TEXIT and FEXIT, respectively, in The Computer Journal #43.

I have used these words since about 1985 on a variety of systems, and I have
found them _very_ useful to build parsers (sigForth Newsletter, pending),
pattern matchers (FORML '89), and expert systems (Rochester '90).

Their dependence on return-stack manipulation means that they can't be
implemented portably in ANS Forth.  I've implemented similar words using
conditional branches -- requiring a closure word -- but the result is
incredibly clumsy, noticeably slower, and requires roughly twice the memory in
my typical applications.

Perhaps I should submit these words for consideration.  :-)

- Brad
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