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From: ka@felix.UUCP (Kenneth Almquist)
Newsgroups: comp.lang.icon
Subject: Re: Algol->Icon & Pascal
Message-ID: <163508@felix.UUCP>
Date: 23 May 91 00:31:56 GMT
References: <1991May14.222651.16502@midway.uchicago.edu>
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goer@ellis.uchicago.edu (Richard L. Goerwitz) writes:
> I've always wondered why Icon uses the brace notation (rather than
> begin ... end;) for most groupings, but yet for procedures, a kind
> of mixed procedure name(vars)...end notation is used.

My guess is that this produces better diagnostics when braces are
omitted.  If you omit an open brace in C, the compiler will eventually
encounter a closing brace in the middle of the procedure which appears
to match the start of the procedure.  None of the C compilers that I
have seen are capable of recognizing this situation and determining
that the procedure hasn't actually ended.  Instead, they treat the
procedure as ended and squawk about every line from the closing brace
until the actual end of the procedure.  Using something other than a
closing brace to mark the end of a procedure avoids this problem.

> I'm also a bit curious why the notion of functions and procedures
> was collapsed into procedures, and yet with retention of the notion
> that a procedure is a value (i.e. like what we normally associate
> with functions).

I'm not sure what you mean by a procedure being a value.  Calling ICON
procedures "functions" would be a mistake because the term "function"
is defined by mathematicians to be something that returns exactly one
value.  In contrast, "procedure" is defined by usage within the compu-
ter science community.  In Algol and Pascal, a procedure can return
values by setting parameters, but not by returning a value using the
syntax for returning a value from a function.  In PL/1 (which is more
widely used than either Algol or Pascal) this restriction was lifted
and a procedure can return a value using a "return" statement.  So
ICON's use of the term "procedure" to refer to something that can
return zero or more values is a natural extension of prior practice.
				Kenneth Almquist