Deriving Read of an empty datatype crashes
Standalone deriving Read of an empty datatype crashes:
{-# LANGUAGE StandaloneDeriving #-}
data A
deriving instance Read Aghc: panic! (the 'impossible' happened)
(GHC version 7.7.20130515 for x86_64-unknown-linux):
Prelude.foldr1: empty list
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug(Oddly, the "panic" message is given only by ghc, not ghci, but this is minor.)
While the Read instance seems to be of little use, it can be used for reading types such as Either Void Int.
Patch attached.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.6.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
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