#3330: Type checker hangs
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Reporter: MartijnVanSteenbergen | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.10.1 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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The following module causes `ghc --make` and `ghci` to hang. `-ddump-tc-
trace` produces output indefinitely.
{{{
{-# LANGUAGE GADTs #-}
{-# LANGUAGE FlexibleContexts #-}
import Generics.MultiRec
import Control.Monad.Writer
data AnyF s f where
AnyF :: s ix -> f ix -> AnyF s f
children :: HFunctor s (PF s) => s ix -> (PF s) r ix -> [AnyF s r]
children p x = execWriter (hmapM p collect x) where
collect :: (HFunctor s (PF s)) => s ix -> r ix -> Writer [AnyF s r] (r
ix)
collect w x = tell [AnyF w x] >> return x
}}}
Module `Generics.MultiRec` is from Hackage package `multirec-0.4`.
The code contains a type error: if arguments `p` and `collect` are swapped
the code compiles fine.
I haven't tried making this example any smaller.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3330>
GHC <http://www.haskell.org/ghc/>
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