implement associated type synonyms

When I try to compile:

class Foo a where
    type Bar a :: *
    aBar :: Bar a

I get this "type error":

Test.hs:1:0:
    Type synonym `Bar' should have 1 argument, but has been given 1
    When checking the class method: aBar :: Bar a
    In the class declaration for `Foo'

I've tracked it down to this case in typecheck/TcMType.lhs:

check_tau_type rank ubx_tup ty@(TyConApp tc tys)
  | isSynTyCon tc	

which calls tcView, which in turn calls tcExpandTyCon_maybe, which doesn't handle open type synonyms. (And so Nothing is returned down the line, and you get this nasty error.)

It should be pretty easy to fix if you actually have a clue what you are doing ;-). So, please fix it. Then I can get back to trying to reimplement the MTL with ATs ;-).

Trac metadata

Trac field	Value
Version	6.5
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown