Re: [Haskell-cafe] Pattern synonyms and explicit forall.
The end of your error message:
| 63 | pattern Any a <- Some a | ^
Appears to have program text (a mono-directional pattern binding) that doesn't correspond to the program text you quote. Whereas
pattern Any :: forall a. a -> Some
pattern Any a = Some
Is a implicitly bi-directional pattern binding that will never work. (The free var `a` on LHS does not appear in RHS.) I'm suspecting the explicit forall is not much to do with it.
On Saturday, September 18th, 2021 at 14:12, Anthony Clayden
The end of your error message:
| 63 | pattern Any a <- Some a | ^
Appears to have program text (a mono-directional pattern binding) that doesn't correspond to the program text you quote.
I just tried both ways of writing bidirectional pattern synonmys, neither worked with explicit `forall`.
I'm suspecting the explicit forall is not much to do with it.
With an implicit forall, the code does type check. Regards, Marcin
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