Roberto Zunino wrote:
When you type some expression such as
\x -> x
you have to choose among an infinite number of valid types for it:
Int -> Int
Char -> Char
forall a . a -> a
forall a b . (a,b) -> (a,b)
...
Yet the type inference is smart enough to choose the "best" one:
forall a. a -> a
because this is the "most general" type.
Alas, for code like yours:
foo = \f -> (f 'J', f True)
there are infinite valid types too:
(forall a. a -> Int) -> (Int, Int)
(forall a. a -> Char)-> (Char, Char)
(forall a. a -> (a,a)) -> ((Char,Char),(Bool,Bool))
...
and it is much less clear if a "best", most general type exists at all.
Requiring a type annotation for these not-so-common code snippets
seems to be a fair compromise, at least to me.
Thank you for coming up with a clear and comprehensible answer.
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