package examples.pilib
import scala.concurrent.pilib._
/** Church encoding of naturals in the Pi-calculus */
object piNat extends Application {
/** Locations of Pi-calculus natural */
class NatChan extends Chan[Triple[Chan[Unit], Chan[NatChan], Chan[NatChan]]]
/** Zero */
def Z(l: NatChan): Unit = choice (
l * { case Triple(z, sd, d) => z.write(()) }
)
/** Successor of Double */
def SD(n: NatChan, l: NatChan): Unit = choice (
l * { case Triple(z, sd, d) => sd.write(n) }
)
/** Double */
def D(n: NatChan, l: NatChan): Unit = choice (
l * { case Triple(z, sd, d) => d.write(n) }
)
/** Make "l" a location representing the natural "n" */
def make(n: Int, l: NatChan): Unit =
if (n == 0) Z(l)
else if (n % 2 == 0) { val l1 = new NatChan; spawn < D(l1, l) >; make(n/2, l1) }
else { val l1 = new NatChan; spawn < SD(l1, l) >; make(n/2, l1) }
/** Consume the natural "m" and put it successor at location "n" */
def Succ(m: NatChan, n: NatChan) {
val z = new Chan[Unit]
val sd = new Chan[NatChan]
val d = new Chan[NatChan]
spawn < m.write(Triple(z, sd, d)) >;
choice (
z * { x => make(1, n) },
sd * { m1 => { val n1 = new NatChan; spawn < D(n1, n) >; Succ(m1, n1) } },
d * { m1 => SD(m1, n) }
)
}
/** Consume the natural "l" and put two copies at locations "m" and "n" */
def Copy(l: NatChan, m: NatChan, n: NatChan) {
val z = new Chan[Unit]
val sd = new Chan[NatChan]
val d = new Chan[NatChan]
spawn < l.write(Triple(z, sd, d)) >;
choice (
z * { x => spawn < Z(m) >; Z(n) },
sd * { l1 => { val m1 = new NatChan; val n1 = new NatChan;
spawn < SD(m1, m) | SD(n1, n) >;
Copy(l1, m1, n1) } },
d * { l1 => { val m1 = new NatChan; val n1 = new NatChan;
spawn < D(m1, m) | D(n1, n) >;
Copy(l1, m1, n1) } }
)
}
/** Consume the natural at location "n" and return its value */
def value(n: NatChan): Int = {
val z = new Chan[Unit]
val sd = new Chan[NatChan]
val d = new Chan[NatChan]
spawn < n.write(Triple(z, sd, d)) >;
choice (
z * { x => 0 },
sd * { n1 => 2 * value(n1) + 1 },
d * { n1 => 2 * value(n1) }
)
}
// Test
val i = 42
val l = new NatChan
val l1 = new NatChan
val l2 = new NatChan
val l3 = new NatChan
spawn <
make(i, l) |
Copy(l, l1, l2) |
Succ(l2, l3) |
println("" + i + " = " + value(l1)) |
println("succ " + i + " = " + value(l3)) >
}
