import macros, tables # === class defination === type MessageListener = proc (msg: string): void MessageType = enum UserEnter, UserLeave, UserMsg MessageDispather = object of RootObj listeners : Table[MessageType, MessageListener] func initMessageDispatcher(): MessageDispather = MessageDispather( listeners: initTable[MessageType, MessageListener]() ) func setOnMessageListener(self: var MessageDispather, msgType: MessageType, listener: MessageListener) = self.listeners[msgType] = listener func dispatch(self: MessageDispather, msgType: MessageType, msg: string) = if self.listeners.hasKey(msgType): self.listeners[msgType](msg) func run(self: MessageDispather) = self.dispatch(UserEnter, "7sDream") self.dispatch(UserMsg, "hello, everyone") self.dispatch(UserLeave, "7sDream") # === shortcut macro ==== template listenerFunc(funcName, msgType: untyped): untyped = proc funcName(msg: string) = let msg {.inject.} = msg template setListenerStmt(client, funcName, typeName: untyped): untyped = client.setOnMessageListener(MessageType.typeName, funcName) macro OnMessage(dispatcher, ls: untyped): untyped = expectKind(dispatcher, nnkIdent) expectKind(ls, nnkStmtList) result = newStmtList() for i in 0..<ls.len: let listenerDef = ls[i] expectKind(listenerDef, nnkCall) let cls = listenerDef[0] expectKind(cls, nnkIdent) let doWhat = listenerDef[1] expectKind(doWhat, nnkStmtList) let funcName = genSym(nskFunc, "on" & $cls) listenerFuncDef = getAst(listenerFunc(funcName, cls)) listenerFuncStmts = listenerFuncDef[^1] doWhat.copyChildrenTo(listenerFuncStmts) result.add(listenerFuncDef) let addListenerStmtDef = getAst(setListenerStmt(dispatcher, funcName, cls)) result.add(addListenerStmtDef) # uncomment the line below to see what the macro generated # result.repr.echo # === Use example === var dispatcher = initMessageDispatcher() OnMessage(dispatcher): UserEnter: echo "User enter: " & msg UserMsg: echo "Message: " & msg UserLeave: echo "User leave: " & msg dispatcher.run()