Twan van Laarhoven wrote:
Isaac Dupree wrote:
Unfortunately, I get puzzling type errors if I annotate either one of
them with their type (e.g.
(Applicative f) => f (a -> b) -> f a -> f (Int, b)
) in an expression. The very answer doesn't seem to typecheck.
> :t \f x -> fmap ((,) (0::Int)) (f <*> x) :: (Applicative f) => f
(a1 -> a) -> f a1 -> f (Int, a)
Here the type annotation applies to the *body* of the lambda
abstraction, adding parentheses around the whole thing solve your problem.
> :t (\f x -> fmap ((,) (0::Int)) (f <*> x)) :: (Applicative f) => f
(a1 -> a) -> f a1 -> f (Int, a)
Aside from the fact that ghci has some trouble formating the output.
thank you, oops, how annoying. I wonder if GHCi should output
parentheses to make its :type result be a valid expression...
Isaac
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