[Haskell-cafe] Re: Wondering about c type in haskell.
Magicloud Magiclouds
magicloud.magiclouds at gmail.com
Tue Jun 30 00:46:05 EDT 2009
I think Integer is prefered in Haskell. I mean normally, I should use
it in my code. So following my example, why cannot CPid be treated as
Integer. Only when it needs to be transfered to C or whatsoever, we
convert it to Long or whatsoever. So we have a unified type system,
not a bunch of types I need to convert, convert, convert.
And, let say using Integer for pid is insane. Then if I do not convert
it into Integer, when serialised, I have to point out with
Word32/Word64, which is definitely bad.
On Tue, Jun 30, 2009 at 11:01 AM, Ahn, Ki Yung<kyagrd at gmail.com> wrote:
> 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.
>
> --
> Ahn, Ki Yung
>
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