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In GHCi, version 6.11.20090115 built from HEAD

{-# LANGUAGE TypeOperators, TypeFamilies #-}
{-# OPTIONS_GHC -Wall #-}

-- With associate type synonym, the ch' definition leads to
-- 
--       Couldn't match expected type `Basis u1'
--              against inferred type `Basis u'
--         Expected type: u1 :-* v
--         Inferred type: u :-* v
--       In the expression: ch
--       In the definition of `ch'': ch' = ch
-- 
-- With associated data type, no problem.


class HasBasis u where type Basis u :: *

-- class HasBasis u where data Basis u :: *


type u :-* v = Basis u -> v

ch :: (HasBasis u, HasBasis v) =>
      (v :-* w) -> (u :-* v) -> (u :-* w)
ch = undefined

ch' :: (HasBasis u, HasBasis v) =>
       (v :-* w) -> (u :-* v) -> (u :-* w)
ch' = ch

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	conal@conal.net
Operating system
Architecture