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

[Cristian Baboi]

On Sat, 22 Dec 2007 16:48:51 +0200, Peter Verswyvelen <[EMAIL PROTECTED]>
wrote:

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 know FP have automatic garbage collection.
I know FP compilers use strictness analysis.

In C++ one can isolate memory management in constructors and destructors.
There are C compilers that are also able to do some optimizations.

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.

I am new to Haskell, but not new to declarative programming. I programmed
in Prolog for several years, and I tryed LISP, but I don't liked the LISP
syntax.

I don't take my C example seriously either.
The thing is I think that for a language to have "first-class" functions,
it must be "homoiconic" if I understand the terms correctly.

Have you tryed to write a Haskell program that manipulate Haskell programs
?
Please don't tell me that Haskell compiler is written in Haskell, because
there are C compilers written in C.


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