wren ng thornton wrote:
(Though it doesn't necessarily generalize to cover similar messages like:
Prelude> :t (\x -> x) :: a -> b <interactive>:1:7: Couldn't match expected type `b' against inferred type `a' `b' is a rigid type variable bound by the polymorphic type `forall a b. a -> b' at <interactive>:1:0 `a' is a rigid type variable bound by the polymorphic type `forall a b. a -> b' at <interactive>:1:0 In the expression: x )
I find this slightly more complicated case quite confusing with the current wording: Prelude> :t (\x -> x) :: (a -> b) -> (a -> a) <interactive>:1:7: Couldn't match expected type `a' against inferred type `b' `a' is a rigid type variable bound by an expression type signature at <interactive>:1:14 `b' is a rigid type variable bound by an expression type signature at <interactive>:1:19 In the expression: x In the expression: (\ x -> x) :: (a -> b) -> (a -> a) This message suggests that ghc has inferred type b for x. Tillmann