[Haskell-cafe] Functions are first class values in C

Peter Verswyvelen bf3 at telenet.be
Sat Dec 22 09:48:51 EST 2007

Cristian Baboi wrote
> Lazy constant in C:
> int C1 (){ return 7; }

Not really, this is not lazy, since it always recomputes the value "7". 

To have "lazy" values in C you would have to do something like:

struct ValueInt
  int IsComputed;
    int Value;
       int (*ComputeValue)(void *args);
       void* Args; 

int GetLazyInt (ValueInt* v)
  if( !v->IsComputed )
    v->Value = v->ComputeValue(v->Args);
    v->IsComputed = true;
  return v->Value;

But this of course, is totally useless in C and very bulky. It's also impossible to know when to call freemem on the Args (hence garbage collection in FP), when *not* to use lazy values but strict values instead (hence strictness analysis in FP), etc...

I must say I had the same opinion as you had for many many years. I always thought "functions as first class values" where just function pointers, so what is it these Haskell/FP guys are so excited about? But if you dig deeper, you'll see the magic... Notice you will have to give yourself some time; it is very hard to get out of the imperative blob. E.g. I'm still being sucked into the imperative blob after my first year of Haskell hacking :)

PS: As I'm relatively new to Haskell, don't take the above C code too seriously; it certainly will not reflect the way a real Haskell system works.


More information about the Haskell-Cafe mailing list