[Haskell-cafe] Re: Wondering about c type in haskell.

[Ahn, Ki Yung]

Ahn, Ki Yung 쓴 글:
> Magicloud Magiclouds 쓴 글:
>> Hi,
>>   There are times, when we need to make some system calls, or call C
>> library. So we have to deal with C data types.
>>   For example, CPid, which is an integer, actually. So we can do
>> "fromIntegral pid". Then why do not we define "type CPid = Integer",
>> and convert Haskell Integer with C Int internally. So the "user" does
>> not have to care about the type convert (everywhere, which is ugly).
>> And, specially, when doing something like serialisation, for Haskell
>> Integer, the user does not have to do things with precision. But for
>> CPid, without the fromIntegral, we have to specify its precision,
>> well, on different machine/OS, the precision may not be the same.
> 
> Integer is not a fixed length chunk of bits.  It can be arbitrarily 
> large as long as there is memory left in the system.  It's theoretically 
> more clean being close to a mathematical definition of integers, but 
> internally a complicated beast.  So defining CPid as Integer is just not 
> sane.
> 
> In addition, we cannot use Int either.  Int is not a 32 bit or 64 bit 
> word.  The Haskell 98 standard does not require that, and in most 
> implementations it is 2^31 singed bits using one bit as a mark to 
> distinguish pointers from values for garbage collection purposes. (OCaml 
> int types are like that too.)
> 
> I hope this gives enough explanation.

I wrote this and thought that you might already know this.  For 
convenience of serialization, wouldn't defining Data.Binary instances 
for C types be enough in the library level?

-- 
   Ahn, Ki Yung