[Haskell-beginners] Questions on data/type

Matthew Wong matwong at rogers.com
Mon Nov 16 00:31:00 EST 2009


I have the following data defined.

data TypeCon a = ValConA a | ValConB [a] | ValConC [[a]]

So I can use functions with type like  (a->a->a) -> TypeCon a -> TypeCon a -> TypeCon a
for all 3 value types, and I think is easier to define one single typeclass for (+), (*) etc.

If I want to express the following idea (the following won't compiler):

data TypeCon a = ValConA a | ValConB [ValConA a] | ValConC [ValConB a]

Is this even a good idea?  If so how could I proceed?  The closest thing I can get to compiler is like this:

data TypeCon a = ValConA a | ValConB [TypeCon a] 

Which is a nightmare when I try to manipulate anything in this structure.  The alternative is use 3 different type constructors,

data TypeConA a = ValConA a
data TypeConB a = ValConB a
data TypeConC a = ValConC a

but then I can't use one signal typeclass for (+) etc.



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