#2767: Type family bug ?
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Reporter: test | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.10.1
Severity: normal | Resolution:
Keywords: | Testcase:
Architecture: Unknown/Multiple | Os: MacOS X
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Comment (by test):
I've narrowed down the problem to the code below.
The problem is one of type inference.
If either type signature is added, then it compiles fine.
{{{
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -fglasgow-exts #-}
module Main where
main = return ()
-- eval' :: Solver solver => Tree solver a -> [(Label solver,Tree solver
a)] -> solver [a]
eval' (NewVar f) wl = do v <- newvarSM
eval' (f v) wl
eval' Fail wl = continue wl
-- continue :: Solver solver => [(Label solver,Tree solver a)] -> solver
[a]
continue ((past,t):wl) = do gotoSM past
eval' t wl
data Tree s a
= Fail
| NewVar (Term s -> Tree s a)
class Monad solver => Solver solver where
type Term solver :: *
type Label solver :: *
newvarSM :: solver (Term solver)
gotoSM :: Label solver -> solver ()
}}}
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2767#comment:1>
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