+tc_defaults [DefaultDecl mono_tys locn]
+ = tcLookupGlobal_maybe numClassName `thenNF_Tc` \ maybe_num ->
+ case maybe_num of
+ Just (AClass num_class) -> common_case num_class
+ other -> returnTc []
+ -- In the Nothing case, Num has not been sucked in, so the
+ -- defaults will never be used; so simply discard the default decl.
+ -- This slightly benefits modules that don't use any
+ -- numeric stuff at all, by avoid the necessity of
+ -- always sucking in Num
+ where
+ 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