method vterm t =
match t.term_node with
| Tapp (lf,_ , targs) ->
debug "[Calls_collection] app %a" !Ast_printer.d_term t;
collect_apps lf targs ; SkipChildren
| Tblock_length ta ->
debug "[Calls_collection] block_length %a" !Ast_printer.d_term t;
collect_apps_builtin [ta] ; SkipChildren
| _ -> DoChildren