function composition in C

[Anurag Acharya]

In article <6873 at munnari.oz.au> aet at felix.ee.mu.OZ.AU (bert) writes:
> Does anyone know how to write a compose function in C,
> without writing a Scheme interpreter to do it in.
> A call should look something like this:
> (compose(sqr,cube)) (2) which would evaluate to 64.
> "compose" is a one-liner in any functional language,
> but I suspect that it is, given the above constraint, impossible in C.

Nope. it is possible.

Example:

#include <stdio.h>

int compose (foo,bar,baz)
int (*foo) ();
int (*bar) ();
int baz;
{
   return ((*foo) ((*bar)(baz)));
 }

int sqr(x)
int x;
{
 return x * x;
}

int cube(x)
int x;
{
 return x * x * x;
}

main()
{
  printf("The value is %d\n",compose(sqr,cube,2) );
}

try it out. it works. this version of compose will work for any pair of 
int->int functions. liberal use of casts will allow you to write a general
compose as well.

anurag