In the current design of Msglang, a send expression transmits a message to the receiver and proceeds without waiting for a response from the recipient. This messagedelivery style is called asynchronous message send or nonblocking send. At a future time, the recipient might not receive the actual message or the message format might not match. An alternative message delivery style is called synchronous message send or blocking send, where the sender waits for the receiver to send a reply message.

Design and implement a variation of Msglang in which sending a message blocks a process until a response is received from the recipient. The value of the receive expression is the response received by the sender, as well as the value of the send expression.