Impossible error when deriving lower-cased type class (nameModule show{tv a9Y})
I had a student who incorrectly typed 'deriving (show)' instead of 'deriving (Show)', and got a very interesting error, as shown below. It happens in both ghc and ghci. The file should of course be rejected, but perhaps with a different error message.
$ cat Bug.hs module Types where data FuelEfficiency = MPG Float | LPHK Float deriving (show) $ ghc Bug.hs [1 of 1] Compiling Types ( Bug.hs, Bug.o ) ghc: panic! (the 'impossible' happened)
(GHC version 7.4.2 for x86_64-unknown-linux):
nameModule show{tv a9Y}
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.4.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
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