#1469: GHC suggests -fglasgow-exts, and not {-# LANGUAGE #-} pragmas or
"Extensions:" cabal field
-------------------------+--------------------------------------------------
Reporter: SamB | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.8
Component: Compiler | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Os: Unknown | Testcase:
Architecture: Unknown |
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Changes (by simonpj):
* milestone: => 6.8
Old description:
> 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 ;-)
New description:
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 ;-)
Comment:
There is no `X=NewtypeDeriving` language-extension flag at the moment.
There should be, because we are slowly trying to get rid of the
portmanteau `-fglasgow-exts` in favour of more specific language-extension
flags.
I take that as the main force of this bug report. With that more specific
reference, a user should be able to find the right section of the manual.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1469>
GHC <http://www.haskell.org/ghc/>
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