Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!brutus.cs.uiuc.edu!wuarchive!wugate!uunet!philmtl!ray
From: ray@philmtl.philips.ca (Raymond Dunn)
Newsgroups: comp.lang.misc
Subject: Re: Language Tenets
Message-ID: <612@philmtl.philips.ca>
Date: 21 Jul 89 22:37:11 GMT
References: <57125@linus.UUCP> <1989Jun24.230056.27774@utzoo.uucp> <1207@quintus.UUCP> <1406@l.cc.purdue.edu>
Reply-To: ray@philmtl.philips.ca (Raymond Dunn)
Organization: Philips Electronics Ltd. -  St. Laurent  P.Q., Canada
Lines: 61

I missed the start of this discussion,  I hope the following is a relevant
contribution.

In the POP-2 language and its derivatives, multi-result functions are handled
in a very straight forward manner:

Assignment in POP-2 is left to right, e.g.

5 -> x;

Thus to assign the result of a single result function one can do:

foo(x) -> y;

To assign the results of a multi-result function then, one does:

foo(x) -> y -> z;

with no practical limitations on the number of results that can be returned in
this way.

[someone] wrote:
>> There's a big problem with this:  you have an expression that's no good
>> for anything but putting on the right side of an assignment.  What good
>> are expressions if you can't nest them?

In POP-2 this is not the case, if foo is a function of n arguments and bar is
a function of one argument and n results, then:

foo(bar(x));

is meaningful.

Indeed if foo is a function of *one* argument and bar is a function of two
results, then:

foo(bar()->x);

is "equivalent" to:

bar() -> x -> y;  foo(y);

etc.  (I don't hold this up as pretty useage, only as a demonstration of the
feature).

If you think of "f(x,y)" as "push x, push y, call f", and "-> x" as "pop x",
then the underlying [stack] mechanism and its usages should be self evident.

The types of arguments and results of functions are also not restricted in any
way, a value of any type may be passed and returned (integer, real, array,
record [structure], function, list etc).

As a POP-2 programmer of old, I *still* find it a pain in 'C' to be forced into
creating unnecessary structures (or, god forbid, using global variables) just
to be able to return multiple values.

-- 
Ray Dunn.                    | UUCP: ..!uunet!philmtl!ray
Philips Electronics Ltd.     | TEL : (514) 744-8200  Ext: 2347
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