Hello Brian, Saturday, June 10, 2006, 3:05:25 AM, you wrote:
It is possible that this feature was added to the language for the benefit of people who prefer not to use explicit type signatures but afaiu this goes against best practice where everything should always have an explicit signature to make code easy to understand and facilitate debugging of type errors.
when you work with C++ or some other OOP language, you can define that some field in structure should some some specific interface and this allows to use functions of this interface on this field. i required the same feature in Haskell, for example: data UTF8Stream h = (ByteStream h) => UTF8Stream h instance TextStream (UTF8Stream h) ... addUTF8Encoding :: h -> (UTF8Stream h) and so on. currently i should add type constraint to each and every class and function i declared. i don't tried using existential types here, so i'm not sure that they will give the same high speed for inlined functions. moreover, they "lose" information about other type classes that 'h' supports, although functions from these classes may be required for application that use "UTF8Stream h" and even by other definitions in my lib: instance (ByteStringStream h) => ByteStringStream (UTF8Stream h) ... -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com