- case tau_tys of
- [] -> returnTc [] -- no defaults
-
- _ ->
- -- Check that all the types are instances of Num
- -- We only care about whether it worked or not
-
- tcLookupClassByKey numClassKey `thenNF_Tc` \ num ->
- tcSimplifyCheckThetas
- [ (num, ty) | ty <- tau_tys ] `thenTc_`
-
- returnTc tau_tys
-
-tc_defaults decls
- = failTc (dupDefaultDeclErr decls)
-
-
-dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things) sty
- = ppAboves (item1 : map dup_item dup_things)
+tcDefaults []
+ = getDefaultTys -- No default declaration, so get the
+ -- default types from the envt;
+ -- i.e. use the curent ones
+ -- (the caller will put them back there)
+ -- It's important not to return defaultDefaultTys here (which
+ -- we used to do) because in a TH program, tcDefaults [] is called
+ -- repeatedly, once for each group of declarations between top-level
+ -- splices. We don't want to carefully set the default types in
+ -- one group, only for the next group to ignore them and install
+ -- defaultDefaultTys
+
+tcDefaults [L locn (DefaultDecl [])]
+ = returnM (Just []) -- Default declaration specifying no types
+
+tcDefaults [L locn (DefaultDecl mono_tys)]
+ = setSrcSpan locn $
+ addErrCtxt defaultDeclCtxt $
+ tcLookupClass numClassName `thenM` \ num_class ->
+ mappM tc_default_ty mono_tys `thenM` \ 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] `thenM_`
+
+ returnM (Just tau_tys)
+
+tcDefaults decls@(L locn (DefaultDecl _) : _) =
+ setSrcSpan locn $
+ failWithTc (dupDefaultDeclErr decls)
+
+
+tc_default_ty hs_ty
+ = tcHsSigType DefaultDeclCtxt hs_ty `thenM` \ ty ->
+ checkTc (isTauTy ty) (polyDefErr hs_ty) `thenM_`
+ returnM ty
+
+defaultDeclCtxt = ptext SLIT("when checking that each type in a default declaration")
+ $$ ptext SLIT("is an instance of class Num")
+
+
+dupDefaultDeclErr (L _ (DefaultDecl _) : dup_things)
+ = hang (ptext SLIT("Multiple default declarations"))
+ 4 (vcat (map pp dup_things))