[Haskell-cafe] What are Kind errors and how do you fix them?
MR K P SCHUPKE
k.schupke at imperial.ac.uk
Wed Mar 24 08:31:19 EST 2004
I dont understand what you are trying to do:
type ReverseType a string = (string ->(string,a))
takes a string an returns a string and another value (looks like the
state monad with state=String.
data Reverse a string = Reverse (ReverseType a string)
this just declares a type wrapper... why have both of the above, you only
data Reverse a s = Reverse (s -> (s,a))
NOw for your class definition:
return x = Reverse (\text -> (text,x))
this is the standard return from a state monad.
(Reverse p) >>= k = Reverse p3
p3 s0 = p2 s1
(Reverse p2) = k a
the second parameter (k) needs the state passed as well
after unwrapping like:
p2 = (\(Reverse x) -> x) (k a) s1
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