[Haskell-cafe] Re: Wondering about c type in haskell.
Ahn, Ki Yung
kyagrd at gmail.com
Mon Jun 29 23:27:17 EDT 2009
Ahn, Ki Yung 쓴 글:
> Magicloud Magiclouds 쓴 글:
>> 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
> 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
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