⍝ Define the "double up" function
f←{
        (who message)←{1 ⍵} RECV ⍬ ⍝ Recieve a message with no timeout
        (2×message) SEND who       ⍝ Reply with 2×message
        ∇⍵                         ⍝ Recurse
      }

⍝ Spawn it as a seperate thread
id←f&'double up'⊢⍬

⍝ Check it's status (id, name, mails in mailbox)
id ⎕tasks 0 1 4

⍝ Check our own status
⎕self ⎕tasks 0 1 4

⍝ Send a few messages to our own mailbox
'hello' SEND ⎕self
(⍳2 2) SEND ⎕self

⍝ Send a message to the double up thread
(⍳5) SEND id

⍝ Check our own status again
⎕self ⎕tasks 0 1 4

⍝ We now have a few messages, but we want a specific one..
⍝ That is, the one where the sender = id
{id=⊃⍵:1 ⍵ ⋄ 0} RECV 0

⍝ We might as well get the other messages as well
flush←{
        12::⍵ ⍝ Stop when we get a timeout error
        m←{1 ⍵} RECV 0
        ∇⍵,⊂m
      }

flush ⍬