#1469: GHC suggests -fglasgow-exts, and not {-# LANGUAGE #-} pragmas or
"Extensions:" cabal field
-----------------------+----------------------------------------------------
Reporter: SamB | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.6
Severity: normal | Keywords:
Difficulty: Unknown | Os: Unknown
Testcase: | Architecture: Unknown
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Instead of:
{{{
Pdp1Emu.hs:14:8:
Can't make a derived instance of `Monad Pdp1'
(`Monad' is not a derivable class
Try -fglasgow-exts for GHC's newtype-deriving extension)
When deriving instances for `Pdp1'
}}}
I'd like to see something like:
{{{
Pdp1Emu.hs:14:8:
Can't make a derived instance of `Monad Pdp1'
(`Monad' is not a derivable class
Try -fglasgow-exts or GeneralizedNewtypeDeriving for GHC's newtype-
deriving extension)
When deriving instances for `Pdp1'
}}}
I'm not sure if this message makes it quite clear enough how to use
GeneralizedNewtypeDeriving, though... (seeing as it sheds no light on the
subject whatsoever ;-)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1469>
GHC <http://www.haskell.org/ghc/>
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