Associated type defaults + MultiParamTypeClasses error
If I try this with GHC HEAD as of yesterday:
{-# LANGUAGE TypeFamilies, MultiParamTypeClasses #-}
class Foo a b where
type X a
type X a = b
type Y b
type Y b = a
I get this error:
test2.hs:7:5:
Type indexes must match class instance head
Found `b' but expected `a'
In the type synonym instance declaration for `Y'
In the class declaration for `Foo'
Notably, it doesn't complain about type X a = b
, only type Y b = a
. Unless I'm doing something dumb, it should probably work both ways.
Trac metadata
Trac field | Value |
---|---|
Version | 7.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |