+ = tcLookupGlobal_maybe numClassName `thenM` \ maybe_num ->
+ case maybe_num of
+ Just (AClass num_class) -> common_case num_class
+ other -> returnM []
+ -- 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
+ = addSrcLoc locn $
+ addErrCtxt defaultDeclCtxt $
+ 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 tau_tys
+
+tcDefaults decls@(DefaultDecl _ loc : _) =
+ addSrcLoc loc $
+ failWithTc (dupDefaultDeclErr decls)