Am Mittwoch, 20. Februar 2008 00:39 schrieben Sie:
Why are the value-level reflecting functionsimplemented as type-class methods? It makes the code more verbose and I don't see any advantage compared to simply defining a function per class. Let me show you an example:
This is your implementation of Not:
class (Boolean boolean, Boolean boolean') => Not boolean boolean' | boolean -> boolean', boolean' -> boolean where not :: boolean -> boolean'
instance Not False True where not _ = true
instance Not True False where not _ = false
This is how I would do it:
class (Boolean boolean, Boolean boolean') => Not boolean boolean' | boolean -> boolean', boolean' -> boolean where
instance Not False True instance Not True False
not :: Not a b => a -> b not = undefined
Your definition of the not function uses the implementation detail that false and true are actually undefined. My implementation of the not function also works if false and true are defined to be something different. Of course, false and true are in the same library, so we know this implementation detail and could make use of it.
Furthermore, why did you choose to use Boolean instead of simply Bool?
To avoid a name clash. Feel free to change this. Note that False and True don’t cause a name clash since they live in a namespace different from the one Prelude’s False and True live in.
Cheers,
Fons
Best wishes, Wolfgang