#3057: Standalone deriving of Functor does not work for HsDoc
-----------------------------+----------------------------------------------
Reporter: waern | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.11 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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I tried to use the new `DerivingFunctor` extension to derive `Functor` for
the `HsDoc` type from the ghc package:
{{{
{-# StandaloneDeriving, DerivingFunctor #-}
import HsDoc
deriving instance Functor HsDoc
}}}
But I got this error message:
{{{
da...@david-laptop:~/dev/test$ /home/david/ghc-head/bin/ghc --make Test.hs
-package ghc
[1 of 1] Compiling Test ( Test.hs, Test.o )
Test.hs:9:0:
Couldn't match expected type `b' against inferred type `a'
`b' is a rigid type variable bound by
the type signature for `fmap' at <no location info>
`a' is a rigid type variable bound by
the type signature for `fmap' at <no location info>
Expected type: HsDoc b
Inferred type: HsDoc a
In the first argument of `DocAppend', namely `a1'
In the expression: DocAppend a1 a2
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3057>
GHC <http://www.haskell.org/ghc/>
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