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

[Cristian Baboi]

On Sat, 22 Dec 2007 16:48:51 +0200, Peter Verswyvelen <bf3 at telenet.be>
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.