#3330: Type checker hangs
--------------------------------------+-------------------------------------
Reporter: MartijnVanSteenbergen | Owner: chak
Type: bug | Status: new
Priority: normal | Milestone: 6.12.1
Component: Compiler (Type checker) | Version: 6.12.1 RC1
Resolution: | Keywords:
Difficulty: Unknown | Os: Unknown/Multiple
Testcase: | Architecture: x86_64 (amd64)
Failure: Compile-time crash |
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Changes (by byorgey):
* failure: => Compile-time crash
* version: 6.10.3 => 6.12.1 RC1
* os: MacOS X => Unknown/Multiple
Comment:
I think I've also tickled this bug, which appears to still exist in
6.12.1rc2. Here's a stripped-down version of the code that causes GHC to
diverge for me:
{{{
{-# LANGUAGE EmptyDataDecls, TypeFamilies, TypeOperators, GADTs,
KindSignatures #-}
data (f :+: g) x = Inl (f x) | Inr (g x)
data R :: (* -> *) -> * where
RSum :: R f -> R g -> R (f :+: g)
class Rep f where
rep :: R f
instance (Rep f, Rep g) => Rep (f :+: g) where
rep = RSum rep rep
type family Der (f :: * -> *) :: * -> *
type instance Der (f :+: g) = Der f :+: Der g
plug :: Rep f => Der f x -> x -> f x
plug = plug' rep where
plug' :: R f -> Der f x -> x -> f x
plug' (RSum rf rg) (Inl df) x = Inl (plug rf df x)
}}}
Note that this code has a bug; the call to plug in the last line ought to
be plug' (and it works properly when fixed), but I would expect a type
error instead of a diverging compiler.
I'm classifying this as a "compile-time crash" since one bottom is as good
as another. ;)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3330#comment:7>
GHC <http://www.haskell.org/ghc/>
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