anchor.diff:  %% Main entry point.
   -export([module/2]).
   
  --import(ordsets, [from_list/1,union/2]).
   -import(lists,   [member/2,foldl/3,foldr/3]).
   
   -type fa() :: {atom(), arity()}.
  
positive.code:     PreExp=PreDef,
      {[gen_beh_info(Callbacks, OptionalCallbacks)],
       St#expand{defined=gb_sets:union(gb_sets:from_list(PreDef), Defined),
  	       exports=union(from_list(PreExp), Exports)}}.
  
  gen_beh_info(Callbacks, OptionalCallbacks) ->
      List = make_list(Callbacks),
  
negative.code:           [{atom,0,St#expand.module},{var,0,'X'}]}]}]}],
       St#expand{defined=gb_sets:union(gb_sets:from_list(PreDef),
  				     St#expand.defined),
                 exports=ordsets:union(ordsets:from_list(PreExp),
  				     St#expand.exports)}}.
  
  %% forms(Forms, State) ->
  %%      {TransformedForms,State'}
  