[Haskell-cafe] Re: Wondering about c type in haskell.
Ahn, Ki Yung
kyagrd at gmail.com
Mon Jun 29 23:01:33 EDT 2009
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.
Ahn, Ki Yung
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