Silly error message suggesting LiberalTypeSynonyms
The following code (rightly) does not compile:
{-# LANGUAGE RankNTypes, TypeFamilies, LiberalTypeSynonyms #-}
type PolyId = (forall a. a -> a)
type family F a
foo :: F PolyId
foo = undefined
The error message is
Illegal polymorphic or qualified type: PolyId
Perhaps you intended to use -XLiberalTypeSynonyms
In the type signature for `foo': foo :: F PolyId
The code doesn't compile because we can't apply a type family to a polytype. The first line of the error message says this well enough, though more information might be helpful here. However, the second line of the error message is silly: I've turned on LiberalTypeSynonyms
!
Trac metadata
Trac field | Value |
---|---|
Version | 7.7 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
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Blocking | |
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