#7255: Wrong suggestion when deriving Generic on an instantiated type
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Reporter: dreixel | Owner: dreixel
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.6.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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The following code
{{{
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE FlexibleInstances #-}
import GHC.Generics
data A a
data B
deriving instance Generic (A B)
}}}
gives rise to the error
{{{
Can't make a derived instance of `Generic (A B)':
A must not be instantiated; try deriving `A B' instead
In the stand-alone deriving instance for `Generic (A B)'
}}}
It should indeed fail, but the suggestion should be to try deriving `A a`
instead.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7255>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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