[Haskell-beginners] help with error
Tyler Hayes
tgh at pdx.edu
Sat Feb 20 22:07:50 EST 2010
I'm getting an error and I do not know why...
This is what I have:
class Finite a where
elements' :: [a]
instance (Finite a, Show a, Show b) => Show (a -> b) where
show f = concat (map show [ a | a <- elements'::[a] ])
and this is what ghci gives me:
Could not deduce (Finite a1) from the context ()
arising from a use of `elements'' at Hw06.lhs:119:42-50
Possible fix:
add (Finite a1) to the context of an expression type signature
In the expression: elements' :: [a]
In a stmt of a list comprehension: a <- elements' :: [a]
In the second argument of `map', namely
`[a | a <- elements' :: [a]]'
What's going on here?
Thanks for the help!
- Tyler
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