+checkValSig lhs@(L l _) _
+ | looks_like_foreign lhs
+ = parseError l "Invalid type signature; perhaps you meant to use -XForeignFunctionInterface?"
+ | otherwise
+ = parseError l "Invalid type signature: should be of form <variable> :: <type>"
+ where
+ -- A common error is to forget the ForeignFunctionInterface flag
+ -- so check for that, and suggest. cf Trac #3805
+ -- Sadly 'foreign import' still barfs 'parse error' because 'import' is a keyword
+ looks_like_foreign (L _ (HsVar v)) = v == foreign_RDR
+ looks_like_foreign (L _ (HsApp lhs _)) = looks_like_foreign lhs
+ looks_like_foreign _ = False
+
+ foreign_RDR = mkUnqual varName (fsLit "foreign")