Fri, 12 May 2000 14:52:55 -0600 (MDT), Thomas Harke <[EMAIL PROTECTED]> pisze:
> > You don't ask for instances for type synonyms; you ask for partial
> > application of type synonyms.
>
> This I don't follow.
You want to write:
type M a = ...
instance Monad M where ...
You cannot do this. But not because you cannot use type synonyms in
instance definitions. In GHC you can.
It is because you cannot use a type synonym like M without applying
it to its full number of arguments (i.e. one).
You cannot use M without the argument anywhere, not only in instances.
OTOH in GHC you can write:
type Foo = Either String
instance Monad Foo where ...
-- Equivalent to: instance Monad (Either String) where
You cannot write the above instance if Foo was defined as
type Foo a = Either String a
--
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