#3038: Associated type use triggers a bogus error message
------------------------------------+---------------------------------------
Reporter: conal | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.11 | Severity: normal
Keywords: associated type synonym | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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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
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3038>
GHC <http://www.haskell.org/ghc/>
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