I see. The type inference algorithm requires type variables to betype
constructors, not functions. Equality constraints aresimplified assuming that
is the case. I knew that typefunctions had to be fully applied, but I didn't
know that they alsocouldn't be "taken apart" by unification. This explains why
thefollowing doesn't typecheck:type family T a :: *my_id :: f a -> f a; my_id =
idx :: T a -> T a; x = my_idIMHO, this was not clear from the documentation or
from the errormessage (It certainly _looks_ like "T a" should match "f
a"...).Thanks for the explanation.-heatsink
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