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|
//############################################################################
// Tail Calls
//############################################################################
//############################################################################
// Calibration
class Calibrator {
def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
//############################################################################
// Tail calls in different contexts
class Class {
def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class SubClass extends Class {
override def f(n: Int, v: Int): Int = v;
}
sealed class Sealed {
def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class SubSealed extends Sealed {
override def f(n: Int, v: Int): Int = v;
}
final class Final {
def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
object Object {
def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
//############################################################################
// Tail calls in nested objects/classes
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
val c: C = new C;
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
object O {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
class C {
final def f(n: Int, v: Int): Int = if (n == 0) v else f(n - 1, v - 1);
}
val c: C = new C;
}
val c: C = new C;
}
val c: C = new C;
}
//############################################################################
// Tail calls with different signatures
class TailCall[S](s: S) {
def getS: S = s;
final def f1(n: Int, v: Int): Int =
if (n == 0) v else f1(n - 1, v - 1);
final def f2[T](n: Int, v: Int): Int =
if (n == 0) v else f2[T](n - 1, v - 1);
final def f3[T](n: Int, v: Int, ls: List[T]): Int =
if (n == 0) v else f3(n - 1, v - 1, ls);
final def g1(x: Int, y: Int): Int = {
def aux(n: Int, v: Int): Int =
if (n == 0) v else aux(n - 1, v - 1);
aux(x, y);
}
final def g2[T](x: Int, y: Int): Int = {
def aux[U](n: Int, v: Int): Int =
if (n == 0) v else aux[U](n - 1, v - 1);
aux[T](x, y);
}
final def g3[T](x: Int, y: Int, zs: List[T]): Int = {
def aux[U](n: Int, v: Int, ls: List[Tuple2[T,U]]): Int =
if (n == 0) v else aux(n - 1, v - 1, ls);
aux(x, y, Nil);
}
final def b1(x: Int): Boolean =
(x == 1) || b1(x - 1)
final def b2(x: Int): Boolean =
(x > 0) && ((x == 1) || b1(x - 1))
def h1(n: Int, v: Int): Int = hP(n, v);
private def hP(n: Int, v: Int): Int = if (n == 0) v else hP(n - 1, v - 1);
// !!! test return in non-tail-call position
// !!! test non-same-instance calls
// !!! test non-same-type calls
}
object FancyTailCalls {
val f1 = new FancyTailCalls
val f2 = new FancyTailCalls
}
object PolyObject extends App {
def tramp[A](x: Int): Int =
if (x > 0)
tramp[A](x - 1)
else
0
}
class FancyTailCalls {
def tcTryLocal(x: Int, v: Int): Int = {
try {
def loop(n: Int): Int = {
if (n == 0) v else loop(n - 1)
}
loop(x)
} finally {}
}
def tcInBooleanExprFirstOp(x: Int, v: Int): Boolean = {
{
def loop(n: Int): Int = if (n == 0) v else loop(n - 1)
loop(x)
} == v && true
}
def tcInBooleanExprSecondOp(x: Int, v: Int): Boolean = {
true && {
def loop(n: Int): Int = if (n == 0) v else loop(n - 1)
loop(x)
} == v
}
def tcInIfCond(x: Int, v: Int): Boolean = {
if ({
def loop(n: Int): Int = if (n == 0) v else loop(n - 1)
loop(x)
} == v) true else false
}
def tcInPatternGuard(x: Int, v: Int): Boolean =
v match {
case _ if
{
def loop(n: Int): Int = if (n == 0) v else loop(n - 1)
loop(x) == v
} => true
}
import FancyTailCalls._
final def differentInstance(n: Int, v: Int): Int = {
if (n == 0) v
else if ((n % 2) == 0) f1.differentInstance(n - 1, v)
else f2.differentInstance(n - 1, v)
}
}
class NonTailCall {
final def f1(n: Int): Int = try {
if (n == 0) 0
else f1(n - 1)
} finally {
Console.print(" " + n)
}
final def f2(n: Int): Int = synchronized {
if (n == 0) 0
else f2(n - 1)
}
}
//############################################################################
// Test code
object Test {
def check_success(name: String, closure: => Int, expected: Int) {
print("test " + name)
try {
val actual: Int = closure
if (actual == expected) {
print(" was successful")
} else {
print(" failed: expected "+ expected +", found "+ actual)
}
} catch {
case exception: Throwable => {
print(" raised exception " + exception)
}
}
println
}
def check_success_b(name: String, closure: => Boolean, expected: Boolean) {
print("test " + name)
try {
val actual: Boolean = closure
if (actual == expected) {
print(" was successful")
} else {
print(" failed: expected "+ expected +", found "+ actual)
}
} catch {
case exception: Throwable => {
Console.print(" raised exception " + exception);
}
}
println
}
def check_overflow(name: String, closure: => Int) {
print("test " + name)
try {
val actual: Int = closure;
} catch {
case exception: compat.Platform.StackOverflowError =>
println(" was successful")
case exception: Throwable => {
print(" raised exception " + exception)
}
}
println
}
def calibrate: Int = {
val calibrator = new Calibrator();
var stop = false;
var n = 1;
while (!stop) {
try {
calibrator.f(n, n);
if (n >= Int.MaxValue / 2) sys.error("calibration failure");
n = 2 * n;
} catch {
case exception: compat.Platform.StackOverflowError => stop = true
}
}
4 * n
}
def main(args: Array[String]) {
// compute min and max iteration number
val min = 16;
val max = if (scala.tools.partest.utils.Properties.isAvian) 10000 else calibrate
// test tail calls in different contexts
val Final = new Final()
val Class = new Class()
val SubClass = new SubClass()
val Sealed = new Sealed()
val SubSealed = new SubSealed()
check_success("Object .f", Object .f(max, max), 0)
check_success("Final .f", Final .f(max, max), 0)
check_success("Class .f", Class .f(max, max), 0)
check_success("SubClass .f", SubClass .f(max, max), max)
check_success("Sealed .f", Sealed .f(max, max), 0)
check_success("SubSealed.f", SubSealed.f(max, max), max)
println
// test tail calls in nested classes/objects
val c: C = new C
check_success("O .f", O .f(max, max), 0)
check_success("c .f", c .f(max, max), 0)
check_success("O.O .f", O.O .f(max, max), 0)
check_success("O.c .f", O.c .f(max, max), 0)
check_success("c.O .f", c.O .f(max, max), 0)
check_success("c.c .f", c.c .f(max, max), 0)
check_success("O.O.O .f", O.O.O .f(max, max), 0)
check_success("O.O.c .f", O.O.c .f(max, max), 0)
check_success("O.c.O .f", O.c.O .f(max, max), 0)
check_success("O.c.c .f", O.c.c .f(max, max), 0)
check_success("c.O.O .f", c.O.O .f(max, max), 0)
check_success("c.O.c .f", c.O.c .f(max, max), 0)
check_success("c.c.O .f", c.c.O .f(max, max), 0)
check_success("c.c.c .f", c.c.c .f(max, max), 0)
check_success("O.O.O.O.f", O.O.O.O.f(max, max), 0)
check_success("O.O.O.c.f", O.O.O.c.f(max, max), 0)
check_success("O.O.c.O.f", O.O.c.O.f(max, max), 0)
check_success("O.O.c.c.f", O.O.c.c.f(max, max), 0)
check_success("O.c.O.O.f", O.c.O.O.f(max, max), 0)
check_success("O.c.O.c.f", O.c.O.c.f(max, max), 0)
check_success("O.c.c.O.f", O.c.c.O.f(max, max), 0)
check_success("O.c.c.c.f", O.c.c.c.f(max, max), 0)
check_success("c.O.O.O.f", c.O.O.O.f(max, max), 0)
check_success("c.O.O.c.f", c.O.O.c.f(max, max), 0)
check_success("c.O.c.O.f", c.O.c.O.f(max, max), 0)
check_success("c.O.c.c.f", c.O.c.c.f(max, max), 0)
check_success("c.c.O.O.f", c.c.O.O.f(max, max), 0)
check_success("c.c.O.c.f", c.c.O.c.f(max, max), 0)
check_success("c.c.c.O.f", c.c.c.O.f(max, max), 0)
check_success("c.c.c.c.f", c.c.c.c.f(max, max), 0)
println
// test tail calls with different signatures
val TailCall = new TailCall("S")
check_success("TailCall.f1", TailCall.f1(max, max ), 0)
check_success("TailCall.f2", TailCall.f2(max, max ), 0)
check_success("TailCall.f3", TailCall.f3(max, max, Nil), 0)
check_success("TailCall.g1", TailCall.g1(max, max ), 0)
check_success("TailCall.g2", TailCall.g2(max, max ), 0)
check_success("TailCall.g3", TailCall.g3(max, max, Nil), 0)
check_success("TailCall.h1", TailCall.h1(max, max ), 0)
println
val NonTailCall = new NonTailCall
check_success("NonTailCall.f1", NonTailCall.f1(2), 0)
check_overflow("NonTailCall.f2", NonTailCall.f2(max))
check_success_b("TailCall.b1", TailCall.b1(max), true)
check_success_b("TailCall.b2", TailCall.b2(max), true)
val FancyTailCalls = new FancyTailCalls;
check_success("FancyTailCalls.tcTryLocal", FancyTailCalls.tcTryLocal(max, max), max)
check_success_b("FancyTailCalls.tcInBooleanExprFirstOp", FancyTailCalls.tcInBooleanExprFirstOp(max, max), true)
check_success_b("FancyTailCalls.tcInBooleanExprSecondOp", FancyTailCalls.tcInBooleanExprSecondOp(max, max), true)
check_success_b("FancyTailCalls.tcInIfCond", FancyTailCalls.tcInIfCond(max, max), true)
check_success_b("FancyTailCalls.tcInPatternGuard", FancyTailCalls.tcInPatternGuard(max, max), true)
check_success("FancyTailCalls.differentInstance", FancyTailCalls.differentInstance(max, 42), 42)
check_success("PolyObject.tramp", PolyObject.tramp[Int](max), 0)
}
// testing explicit tailcalls.
import scala.util.control.TailCalls._
def isEven(xs: List[Int]): TailRec[Boolean] =
if (xs.isEmpty) done(true) else tailcall(isOdd(xs.tail))
def isOdd(xs: List[Int]): TailRec[Boolean] =
if (xs.isEmpty) done(false) else tailcall(isEven(xs.tail))
def fib(n: Int): TailRec[Int] =
if (n < 2) done(n) else for {
x <- tailcall(fib(n - 1))
y <- tailcall(fib(n - 2))
} yield (x + y)
def rec(n: Int): TailRec[Int] =
if (n == 1) done(n) else for {
x <- tailcall(rec(n - 1))
} yield x
assert(isEven((1 to 100000).toList).result)
//assert(fib(40).result == 102334155) // Commented out, as it takes a long time
assert(rec(100000).result == 1)
}
//############################################################################
|
