writeChan overwrites or queues up

Question

Following thing is stated in the RWH book:

If a Chan is empty, readChan blocks until there is a value to read. The writeChan function never blocks: it writes a new value into a Chan immediately.

What is not clear to me is whether a call to writeChan will overwrite the already existing message (assuming some message isn't already read) or will it queue up the message in proper order so that the unread message isn't lost ?

Answer 1

It queues up. Chan is a channel, in which messages can be queued. By comparison MVar can instead take just one value, behaving as a variable and not as a queue.