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

[Peter Verswyvelen]

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;
  union
  {
    int Value;
    struct
    {
       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.

Peter