[Haskell-cafe] wildcards for type variables?
sebf at informatik.uni-kiel.de
Wed Jan 13 08:22:14 EST 2010
On Jan 13, 2010, at 2:16 PM, Antoine Latter wrote:
>> He's looking for the self-documentation aspect of "this argument is
>> completely irrelevant". Neither rolling a random unused type
>> variable nor
>> "forall"ing it (my first idea) really accomplishes that.
> Isn't that what we have here? a function of type (a -> A -> B) cannot
> use the first argument in any meaningful way.
I think, he wants to document that the type variable 'a' is not used
in the *type*.
Just like you can document that the second argument of 'const' is
unused by using a wildcard. You can write
const x _ = x
const x y = x
and it would be nice to write 'const's type as
a -> _ -> a
a -> b -> a
Underestimating the novelty of the future is a time-honored tradition.
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