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From: dwp@willett.UUCP (Doug Philips)
Newsgroups: comp.lang.forth
Subject: New Directions: Forth is not postfix
Message-ID: <284.UUL1.3#5129@willett.UUCP>
Date: 19 Jan 90 14:58:02 GMT
Organization: Latest Link in ForthNet Chain (Pittsburgh, PA)
Lines: 42

Let me say right off that I am *not* proposing any of this for ANSI Forth.

One of the things that is an annoying inconsistency is that
Forth is not fully postfix.  The words ':', 'IF', 'DO', 'ELSE'
etc. are prefix.  Has anyone out there done real postfix forth?

For example:

    {{ I . }} 10 0 ITERATE

where '{{' and '}}' make a nameless word and push its address (say in
whatever form @EXECUTE needs) on the stack.  Of course one could always do
something to the effect of:

    ['] Foo 10 0 ITERATE

but having to name every 'closure' would be a pain, not to mention
confusing and unnecessary.  (Assume that ['] is right for @EXECUTE)

IF ELSE THEN might be:

    else-addr then-addr condition IF-THEN-ELSE

IF THEN might be:

    then-addr condition IF-THEN

One of the benefits to this is that UNLOOP is just a plain exit.
One of the drawbacks to this is that it highlights Forth's lack of paradigm
for doing controlled exits of more than just the immediately enclosing
construct, as in:

... {{ ... EXIT-:-WE-ARE-IN CheckError IF-THEN ... }} 100 0 ITERATE ...

<<I'm not interested in arguing over the spelling of the names, I'm interested
in the semantics.>>

		-Doug

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