On 25 Apr 2011, at 08:16, Eric Stansifer wrote:
Let 'c2h' convert CStrings to Haskell Strings, and 'h2c' convert Haskell Strings to CStrings. (If I understand correctly, c2h . h2c === id, but h2c . c2h is not the identity on all inputs;
That is correct. CStrings are 8-bits, and Haskell Strings are 32-bits. Converting from Haskell to C loses information, unless you use a multi-byte encoding on the C side (for instance, UTF8).
or perhaps c2h is not defined for all CStrings.
Rather, h2c is not necessarily well-defined for all Haskell Strings. In particular, the marshalling functions in Foreign.C.String simply truncate any character larger than one byte, to its lowest byte. I suggest you look at the utf8-string package, for instance Codec.Binary.UTF8.String.{encode,decode}, which convert Haskell strings to/from a list of Word8, which can then be transferred via the FFI to wherever you like. Regards, Malcolm