The following won't compile for me
isnull :: (forall a . [a]) -> Bool
isnull ([] :: forall b . [b]) = True
Couldn't match expected type `forall b. [b]'
against inferred type `[a]'
In the pattern: []
Wrapping it in a constructor doesn't help, though I can define a "null":
data NullList = NullList (forall a . [a])
null = NullList []
isnull2 :: NullList -> Bool
isnull2 (NullList []) = True
Why?
Jim
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