#2538: Better error message for missing Rank2Types (or RankNTypes) flag
--------------------------------+-------------------------------------------
Reporter: tim | Owner:
Type: feature request | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.8.2 | Severity: minor
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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For a rank-2 type signature when the {{{Rank2Types}}} language option
isn't enabled, GHC gives:
{{{
Illegal polymorphic or qualified type: (Data a) => a -> RnM a
In the type signature for `rnVarsIn':
rnVarsIn :: ((Data a) => a -> RnM a)
-> [Vdef] -> Exp -> S.Set Var -> RnM ([Vdef], Exp)
}}}
It would be good to suggest using {{{-XRank2Types}}} or
{{{-XRankNTypes}}}. (Sorry if this is already fixed; I don't have a
working HEAD to test it with.)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2538>
GHC <http://www.haskell.org/ghc/>
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