A Queue Process

Process Queue
output var $i.ack$, $o.sig$ initially 0, $o.val$;
internal var $q$ initially <$q$>;
input var $i.sig$, $i.val$, $o.ack$;
cobegin
   loop <
   if ($i.ack$ notequal $i.sig$) and (|$q$| $N$)
   then $q$ := $q$ o <$i.val$>; $i.ack$ := not $i.ack$
   > endloop
||
   loop <
   if ($o.ack$ notequal $o.sig$) and (|$q$| $>$ 0)
   then $o.val$ := $head(q)$; $q$ := $tail(q)$; $o.sig$ := not $o.sig$
   > endloop
coend