- item1
- = addShortErrLocLine locn1 (\ sty ->
- ptext SLIT("multiple default declarations")) sty
-
- dup_item (DefaultDecl _ locn)
- = addShortErrLocLine locn (\ sty ->
- ptext SLIT("here was another default declaration")) sty
+ common_case num_class
+ = tcAddSrcLoc locn $
+ tcAddErrCtxt defaultDeclCtxt $
+ mapTc tc_default_ty mono_tys `thenTc` \ tau_tys ->
+
+ -- Check that all the types are instances of Num
+ -- We only care about whether it worked or not
+ tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys] `thenTc_`
+
+ returnTc tau_tys
+
+tc_defaults decls@(DefaultDecl _ loc : _) =
+ tcAddSrcLoc loc $
+ failWithTc (dupDefaultDeclErr decls)
+
+
+tc_default_ty hs_ty
+ = tcHsType hs_ty `thenTc` \ ty ->
+ checkTc (isTauTy ty) (polyDefErr hs_ty) `thenTc_`
+ returnTc ty
+
+defaultDeclCtxt = ptext SLIT("when checking that each type in a default declaration")
+ $$ ptext SLIT("is an instance of class Num")
+
+
+dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things)
+ = hang (ptext SLIT("Multiple default declarations"))
+ 4 (vcat (map pp dup_things))
+ where
+ pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn