pchannel.sml

    fun pchannel insert = 
    let val (sendch, recvch) = (channel (), channel ())
        val sendEvtp = wrap (recvEvt sendch, fn (p,v,e) => (p, SEND (v,e)))
        val recvEvtp = wrap (recvEvt recvch, fn (p,e) => (p, RECV (e)))
        fun loop pq = case pq of 
             [] => loop [select [sendEvtp, recvEvtp]]
        |   (\_, SEND (v1,e1))::xs => (case select [sendEvtp, recvEvtp] of
                 (p, SEND(v2,e2)) => loop (insert (p, SEND(v2,e2)) pq)
             |   (\_, RECV(e2))    => (sync (e2 v1); sync e1; loop xs))
        |   (\_, RECV (e1))::xs => (case select [sendEvtp, recvEvtp] of
                (p, RECV(e2))    => loop (insert (p, RECV(e2)) pq)
             |   (\_, SEND(v2,e2)) => (sync (e1 v2); sync e2; loop xs))
    in
        spawn (fn () => loop []);
        PCHAN\{sendch=sendch, recvch=recvch\}
    end

    fun sendP (PCHAN\{sendch=sendch, ...\}, v, p) = 
    let val c = channel () 
    in send (sendch, (v, p, sendEvt (c, ()))); recv c
    end

    fun recvP (PCHAN\{recvch=recvch, ...\}, p) = 
    let val c = channel () 
    in send (recvch, (p, fn v => sendEvt (c, v))); recv c
    end