\section[TcDefaults]{Typechecking \tr{default} declarations}
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module TcDefaults ( tcDefaults ) where
import HsSyn
-- one group, only for the next group to ignore them and install
-- defaultDefaultTys
-tcDefaults [L locn (DefaultDecl [])]
+tcDefaults [L _ (DefaultDecl [])]
= return (Just []) -- Default declaration specifying no types
tcDefaults [L locn (DefaultDecl mono_tys)]
failWithTc (dupDefaultDeclErr decls)
+tc_default_ty :: [Class] -> LHsType Name -> TcM Type
tc_default_ty deflt_clss hs_ty
= do { ty <- tcHsSigType DefaultDeclCtxt hs_ty
; checkTc (isTauTy ty) (polyDefErr hs_ty)
= do { (_, mb_res) <- tryTc (tcSimplifyDefault [mkClassPred cls [ty]])
; return (isJust mb_res) }
+defaultDeclCtxt :: SDoc
defaultDeclCtxt = ptext (sLit "When checking the types in a default declaration")
+dupDefaultDeclErr :: [Located (DefaultDecl Name)] -> SDoc
dupDefaultDeclErr (L _ (DefaultDecl _) : dup_things)
= hang (ptext (sLit "Multiple default declarations"))
4 (vcat (map pp dup_things))
where
pp (L locn (DefaultDecl _)) = ptext (sLit "here was another default declaration") <+> ppr locn
+dupDefaultDeclErr [] = panic "dupDefaultDeclErr []"
+polyDefErr :: LHsType Name -> SDoc
polyDefErr ty
= hang (ptext (sLit "Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty)
+badDefaultTy :: Type -> [Class] -> SDoc
badDefaultTy ty deflt_clss
= hang (ptext (sLit "The default type") <+> quotes (ppr ty) <+> ptext (sLit "is not an instance of"))
2 (foldr1 (\a b -> a <+> ptext (sLit "or") <+> b) (map (quotes. ppr) deflt_clss))