[Haskell-cafe] Strange type error with associated type synonyms
lemming at henning-thielemann.de
Wed May 27 18:06:36 EDT 2009
On Thu, 28 May 2009, Bulat Ziganshin wrote:
> read x
> Error: type of x is Integer
> while type of read argument should be String
I also have my problems with "inferred/expected" and find your suggested
message easier to understand in this case. But can it be generalized? I
think that "inferred" and "expected" are quite arbitrary terms for the
user, since he does not know, what GHC first believed to know for sure.
Prelude> let a = 'a'; b = "b" in a==b
Couldn't match expected type `Char' against inferred type `[Char]'
Is the type of 'a' wrong or that of 'b'? The compiler cannot know. It can
only state that the types mismatch. The order in which it infers is not
obvious for the user.
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