Use the callback operator to enable passing callback functions to API calls. In general, the callback operator can only be used on identifiers of functions that are defined with a callback function attribute such as <ASYNC_CALLBACK_FUNCTION>.
dclfunc
function asyncCallback <ASYNC_CALLBACK_FUNCTION>
begin
Print("callback");
end AsyncCallback;
dcltrans
transaction TMain
begin
WebAsyncPreparePush(callback(AsyncCallback));
end TMain;