Opened 10 years ago

Closed 9 years ago

#2767 closed bug (fixed)

Type family bug ?

Reported by: test Owned by: chak
Priority: normal Milestone: 6.12 branch
Component: Compiler (Type checker) Version: 6.10.1
Keywords: Cc: tom.schrijvers@…
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: None/Unknown Test Case: T2767
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:


I get this error when compiling a program with associated type families:

$ ghc --make Queens_v2.hs 
[1 of 5] Compiling Domain           ( Domain.hs, Domain.o )
[2 of 5] Compiling Solver           ( Solver.hs, Solver.o )
[3 of 5] Compiling FD               ( FD.hs, FD.o )
[4 of 5] Compiling SearchTree       ( SearchTree.hs, SearchTree.o )
[5 of 5] Compiling Main             ( Queens_v2.hs, Queens_v2.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.1 for i386-apple-darwin):
	idInfo co{v a629} [tv]

Tom Schrijvers

Change History (6)

comment:1 Changed 10 years ago 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 ()

comment:2 Changed 10 years ago by test

Cc: tom.schrijvers@… added

comment:3 Changed 10 years ago by chak

Operating System: MacOS XUnknown/Multiple
Owner: set to chak

comment:4 Changed 10 years ago by igloo

difficulty: Unknown
Milestone: 6.10.2

comment:5 Changed 9 years ago by igloo

Milestone: branch

comment:6 Changed 9 years ago by chak

Resolution: fixed
Status: newclosed
Test Case: T2767
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