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From: bliss@sp64.csrd.uiuc.edu (Brian Bliss)
Newsgroups: comp.lang.misc
Subject: Re: composition of functions
Keywords: composition, function, first-class object
Message-ID: <1991Feb15.230112.2902@csrd.uiuc.edu>
Date: 15 Feb 91 23:01:12 GMT
References: <1991Feb8.191014.6430@spool.cs.wisc.edu> <1991Feb13.212250.27437@csrd.uiuc.edu> <4771@goanna.cs.rmit.oz.au>
Sender: news@csrd.uiuc.edu (news)
Reply-To: bliss@sp64.csrd.uiuc.edu (Brian Bliss)
Organization: Center for Supercomputing Research and Development
Lines: 37

>the question was:  how do I write a function
	typedef int i2ifn(int);
	i2ifn compose(i2ifn f, i2ifn g) { /* fill this in */ }
>so that compose(f,g)(x) == f(g(x)).


you say

int (*f1)(), (*f2)();

int retval (x) { (*f1)((*f2)(x));}

int (*compose (f, g))()
   int (*f)(), (*g)();
   {
      f1 = f;
      f2 = g;
      return (retval);
   }



if you don't like using global variables, then you have to
say

struct CLOSURE {
   int (*func)();
   struct LOCALS *locals;
}
with the understanding that applying a closure is to say
(*func)(locals, args...),
and that any (would-be)local variables that the called function 
uses are found in the struct LOCALS.

this is plain, portable C.

bb