Impredicative type-class context causes stack overflow or non-termination in type checker
This program makes GHC loop. The first time the stack overflows; the second time GHCi just hangs.
$ cat Bug.hs
{-# OPTIONS -fglasgow-exts #-}
module Bug where
data T t where
T :: (forall a. T (f a)) -> T (forall a. f a)
instance Show (T t) where
show (T t) = show t
$ ghci Bug.hs
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base ... linking ... done.
[1 of 1] Compiling Bug ( Bug.hs, interpreted )
*** Exception: stack overflow
> :reload
[1 of 1] Compiling Bug ( Bug.hs, interpreted )
Interrupted.
>
Trac metadata
Trac field | Value |
---|---|
Version | 6.6 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | Unknown |
Architecture | Unknown |