Scoped type variables
simonpj at microsoft.com
Wed Feb 8 12:48:24 EST 2006
| > b) A pattern type signature may bring into scope a skolem bound
| > in the same pattern:
| > data T where
| > MkT :: a -> (a->Int) -> T
| > f (MkT (x::a) f) = ...
| > The skolem bound by MkT can be bound *only* in the patterns that
| > are the arguments to MkT (i.e. pretty much right away).
| I see -- my scheme was overly simple. But this too feels
| What if we want to give signatures for both arguments? Will the a's
| be the same?
f (MkT (x::a) (f::a->Int)) = ...
You can imagine that either (a) both bind 'a' to the skolem, but must do
consistently; or (b) that (x::a) binds 'a', and (f::a->Int) is a bound
occurrence. It doesn't matter which you choose, I think.
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