+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 $
+ mapTc tcHsType mono_tys `thenTc` \ tau_tys ->
+
+ -- Check that all the types are instances of Num
+ -- We only care about whether it worked or not
+ tcAddErrCtxt defaultDeclCtxt $
+ tcSimplifyCheckThetas
+ [{- Nothing given -}]
+ [ mkClassPred num_class [ty] | ty <- tau_tys ] `thenTc_`
+
+ returnTc tau_tys