tail call optimization

vm/vm.go

@@ -880,9 +880,9 @@ func (v *VM) callFunction(fn *objects.CompiledFunction, freeVars []*objects.Obje
 
 	// check if this is a tail-call (recursive call right before return)
 	curFrame := &(v.frames[v.framesIndex-1])
-	if fn == curFrame.fn {
+	if fn == curFrame.fn { // recursion
 		nextOp := compiler.Opcode(curFrame.fn.Instructions[curFrame.ip+1])
-		if nextOp == compiler.OpReturnValue ||
+		if nextOp == compiler.OpReturnValue || // tail call
 			(nextOp == compiler.OpPop &&
 				compiler.OpReturn == compiler.Opcode(curFrame.fn.Instructions[curFrame.ip+2])) {
 
@@ -904,10 +904,7 @@ func (v *VM) callFunction(fn *objects.CompiledFunction, freeVars []*objects.Obje
 			//  |  ARG1  | <- BP  for current function
 			//  |--------|
 
-			for i := 0; i < numArgs; i++ {
-				v.stack[curFrame.basePointer+i] = v.stack[v.sp-numArgs+i]
-			}
-
+			copy(v.stack[curFrame.basePointer:], v.stack[v.sp-numArgs:v.sp])
 			v.sp -= numArgs
 			curFrame.ip = -1
 

vm/vm_function_test.go

@@ -194,19 +194,34 @@ out = outer() + g
 	out = f2();
 	`, 99)
 
-	// fibonacci
+	// recursion
 	expect(t, `
 	fib := func(x) {
-		if(x == 0) {
-			return 0;
+		if x == 0 {
+			return 0
+		} else if x == 1 {
+			return 1
 		} else {
-			if(x == 1) {
-				return 1;
-			} else {
-				return fib(x-1) + fib(x-2);
-			}
+			return fib(x-1) + fib(x-2)
 		}
-	};
-	out = fib(15);
-	`, 610)
+	}
+	out = fib(15)`, 610)
+
+	// TODO: currently recursion inside the local scope function definition is not supported.
+	// Workaround is to define the identifier first then assign the function like below.
+	// Want to fix this.
+	expect(t, `
+func() {
+	fib := 0
+	fib = func(x) {
+		if x == 0 {
+			return 0
+		} else if x == 1 {
+			return 1
+		} else {
+			return fib(x-1) + fib(x-2)
+		}
+	}
+	out = fib(15)
+}()`, 610)
 }

vm/vm_tail_call_test.go

@@ -4,74 +4,82 @@ import "testing"
 
 func TestTailCall(t *testing.T) {
 	expect(t, `
-fac := func(n, a) {
-	if n == 1 {
-		return a
+	fac := func(n, a) {
+		if n == 1 {
+			return a
+		}
+		return fac(n-1, n*a)
 	}
-	return fac(n-1, n*a)
-}
-out = fac(5, 1)`, 120)
+	out = fac(5, 1)`, 120)
 
 	expect(t, `
-fac := func(n, a) {
-	if n == 1 {
-		return a
+	fac := func(n, a) {
+		if n == 1 {
+			return a
+		}
+		x := {foo: fac} // indirection for test
+		return x.foo(n-1, n*a)
 	}
-	x := {foo: fac} // indirection for test
-	return x.foo(n-1, n*a)
-}
-out = fac(5, 1)`, 120)
+	out = fac(5, 1)`, 120)
 
 	expect(t, `
-fib := func(x, s) {
-	if x == 0 {
-		return 0 + s
-	} else if x == 1 {
-		return 1 + s
+	fib := func(x, s) {
+		if x == 0 {
+			return 0 + s
+		} else if x == 1 {
+			return 1 + s
+		}
+		return fib(x-1, fib(x-2, s))
 	}
-	return fib(x-1, fib(x-2, s))
-}
-out = fib(15, 0)`, 610)
+	out = fib(15, 0)`, 610)
+
+	expect(t, `
+	fib := func(n, a, b) {
+		if n == 0 {
+			return a
+		} else if n == 1 {
+			return b
+		}
+		return fib(n-1, b, a + b)
+	}
+	out = fib(15, 0, 1)`, 610)
 
 	// global variable and no return value
 	expect(t, `
-	out = 0
-	foo := func(a) {
-	   if a == 0 {
-	       return
-	   }
-	   out += a
-	   foo(a-1)
-	}
-	foo(10)`, 55)
+			out = 0
+			foo := func(a) {
+			   if a == 0 {
+			       return
+			   }
+			   out += a
+			   foo(a-1)
+			}
+			foo(10)`, 55)
 
-	// TODO: see comment inside the code
 	expect(t, `
-f1 := func() {
-	f2 := undefined  // TODO: this is really inconvenient 
-	f2 = func(n, s) {
-		if n == 0 { return s }
-		return f2(n-1, n + s)
+	f1 := func() {
+		f2 := 0    // TODO: this might be fixed in the future
+		f2 = func(n, s) {
+			if n == 0 { return s }
+			return f2(n-1, n + s)
+		}
+		return f2(5, 0)
 	}
-
-	return f2(5, 0)
+	out = f1()`, 15)
 }
 
-out = f1()`, 15)
-
-	// tail call with free vars
-	//	expect(t, `
-	//f1 := func() {
-	//	a := 10
-	//	f2 := undefined
-	//	f2 = func(n, s) {
-	//		a += s
-	//		if n == 0 {
-	//			return
-	//		}
-	//		f2(n-1, n + s)
-	//	}
-	//	return f2
-	//}
-	//out = f1()(5, 0)`, 25)
+// tail call with free vars
+func TestTailCallFreeVars(t *testing.T) {
+	expect(t, `
+func() {
+	a := 10
+	f2 := 0
+	f2 = func(n, s) {
+		if n == 0 {
+			return s + a
+		}
+		return f2(n-1, n+s)
+	}
+	out = f2(5, 0)
+}()`, 25)
 }