-tc_defaults [DefaultDecl [] locn]
- = returnTc [] -- no defaults
-
-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 ->
+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 ->