#3297: Compiler panic on incorrect code (TcTyFuns.flattenType: synonym family
in a
rank-n type)
----------------------+-----------------------------------------------------
Reporter: hesselink | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.11 | Severity: normal
Keywords: | Testcase:
Os: Linux | Architecture: x86
----------------------+-----------------------------------------------------
On the following code sample the compiler panics with:
{{{
ghc: panic! (the 'impossible' happened)
(GHC version 6.11.20090403 for i386-unknown-linux):
TcTyFuns.flattenType: synonym family in a rank-n type
}}}
I found this when working on some code when I made a mistake; the code
should not type check, but should probably not crash the compiler either.
I simplified the code to:
{{{
{-# LANGUAGE TypeFamilies
, KindSignatures
, RankNTypes
#-}
type family PF a :: (* -> *) -> * -> *
class Ix a where
type Es a :: * -> *
from :: a -> PF a (Es a) a
crash :: (forall n. Es a n) -> a
crash = from
}}}
It seems similar to #3101, but that one was about data types. A similar
example also seems to be in #1897, but this bug doesn't seem to fit that
ticket's description.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3297>
GHC <http://www.haskell.org/ghc/>
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