Impredicativity bug: GHC crash by type signature
Quick and dirty, this is the bug:
Prelude> [1,2,3] :: [Num a => a]
ghc: panic! (the 'impossible' happened)
(GHC version 6.10.1 for i386-unknown-linux):
TcTyFuns.flattenType: unexpected PredTypeI'm running Gentoo Linux. I can reproduce this bug in the interpreter as well as in the compiler. It seems like it happens only with -fglasgow-exts, and only if you use show on that specific list. It doesn't happen, if you only use the head or the tail of the list. There is also no problem with appending something using (++) or consing through (:).
This is an amd64 architecture, but I'm using a 32 bits system, so this should be irrelevant.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.10.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | Linux |
| Architecture | x86_64 (amd64) |
Edited by Simon Peyton Jones