Better error message for missing Rank2Types (or RankNTypes) flag
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.)
Trac metadata
Trac field | Value |
---|---|
Version | 6.8.2 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | Unknown |
Architecture | Unknown |