more trouble with class method types: as a workaround for :browse!,
i'm using GHC.exprType, even though that is a rather roundabout way
of getting a type for a name. is there really no way of just printing the
TyThing for a class method id correctly?
note that things are going wrong in this area even without my patch.
consider this module
--------------------------
{-# OPTIONS_GHC -fglasgow-exts #-}
module Main where
class C a b where
c1 :: Num b => a -> b
c2 :: (Num b,Show b) => a -> b
c3 :: forall a. a -> b
--------------------------
and this ghci-6.6.1 session for it:
*Main> :b Main
class C a b where
c1 :: (Num b) => a -> b
c2 :: (Num b, Show b) => a -> b
c3 :: a -> b
*Main> :t c3
c3 :: (C a b) => a1 -> b
*Main> :set -fglasgow-exts
*Main> :b Main
class C a b where
c1 :: (Num b) => a -> b
c2 :: (Num b, Show b) => a -> b
c3 :: forall a. a -> b
apparently, the printing of C uses dropForAlls on c3, without
considering scope issues, so the output of that first browse is
simply wrong. also, i wonder how the ghci-session can be in
*Main without having -fglasgow-exts set? these issues are still
with us in today's head.
claus
| class C a where c :: (Num b) => a -> b
| c :: C a -> forall b. (Num b) => a -> b
I think the right thing here is to change Type.dropForAlls,
so that it drops for-alls nested to the right of arrows. Then
you'd get c :: (C a, Num b) => a -> b
yes, that makes sense. but i'm wary of those type-manipulating
functions, as they only operate on the structure of the types,
not seeming to look at scopes. what if the inner forall shadows
a type variable binding from the outer forall? or, if i want to
lift the inner forall outwards, what if the inner forall captures
a type variable in the context? do i really have to do all this
myself, just to print out the type associated with a name?
| class C a where c :: forall b. (Num b) => a -> b
| c :: forall a. (C a) => forall b. (Num b) => a -> b
This *really is* c's type, so it's only honest to say so.
shouldn't the correct type be something that would be
valid source code as well?
c :: forall a, b. (C a, Num b) => a -> b
the type shouldn't distinguish between class methods and
other overloaded functions, should it?
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