⍝ The following demonstrates message passing between an 'iota sever',
⍝ and a client (the user of the iota function). The client always initiates
⍝ communication, and the server must be running, but the client should not
⍝ be able to notice a difference between monadic ⍳ and the iota function,
⍝ even though one does the computation in a different thread.

iotaServer←{
	msg←1⍨⍇0
	msg≡'stop': ⎕←'Bye bye from indexer'
	(from num)←msg
	_←(⍳num)⍈from
	∇⍵
}

id←0 ⍝ this is an invalid thread id, so it is a sane starting point

start←{
	id=0: iotaServer&⍬
	id
}

stop←{
	'stop'⍈id
}

iota←{
	⍝ Sending messages to a nonexisting thread throws a domain error (11)
	11::'Sorry, the iota server is not running'
	_←(⎕self ⍵)⍈id
	1⍨⍇0
}