1 files changed, 131 insertions, 0 deletions
diff --git a/test/peano.go b/test/peano.go
new file mode 100644
index 0000000..1102a97
--- /dev/null
+++ b/test/peano.go
@@ -0,0 +1,131 @@
+// run
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test that heavy recursion works. Simple torture test for
+// segmented stacks: do math in unary by recursion.
+
+package main
+
+import "runtime"
+
+type Number *Number
+
+// -------------------------------------
+// Peano primitives
+
+func zero() *Number {
+	return nil
+}
+
+func is_zero(x *Number) bool {
+	return x == nil
+}
+
+func add1(x *Number) *Number {
+	e := new(Number)
+	*e = x
+	return e
+}
+
+func sub1(x *Number) *Number {
+	return *x
+}
+
+func add(x, y *Number) *Number {
+	if is_zero(y) {
+		return x
+	}
+
+	return add(add1(x), sub1(y))
+}
+
+func mul(x, y *Number) *Number {
+	if is_zero(x) || is_zero(y) {
+		return zero()
+	}
+
+	return add(mul(x, sub1(y)), x)
+}
+
+func fact(n *Number) *Number {
+	if is_zero(n) {
+		return add1(zero())
+	}
+
+	return mul(fact(sub1(n)), n)
+}
+
+// -------------------------------------
+// Helpers to generate/count Peano integers
+
+func gen(n int) *Number {
+	if n > 0 {
+		return add1(gen(n - 1))
+	}
+
+	return zero()
+}
+
+func count(x *Number) int {
+	if is_zero(x) {
+		return 0
+	}
+
+	return count(sub1(x)) + 1
+}
+
+func check(x *Number, expected int) {
+	var c = count(x)
+	if c != expected {
+		print("error: found ", c, "; expected ", expected, "\n")
+		panic("fail")
+	}
+}
+
+// -------------------------------------
+// Test basic functionality
+
+func init() {
+	check(zero(), 0)
+	check(add1(zero()), 1)
+	check(gen(10), 10)
+
+	check(add(gen(3), zero()), 3)
+	check(add(zero(), gen(4)), 4)
+	check(add(gen(3), gen(4)), 7)
+
+	check(mul(zero(), zero()), 0)
+	check(mul(gen(3), zero()), 0)
+	check(mul(zero(), gen(4)), 0)
+	check(mul(gen(3), add1(zero())), 3)
+	check(mul(add1(zero()), gen(4)), 4)
+	check(mul(gen(3), gen(4)), 12)
+
+	check(fact(zero()), 1)
+	check(fact(add1(zero())), 1)
+	check(fact(gen(5)), 120)
+}
+
+// -------------------------------------
+// Factorial
+
+var results = [...]int{
+	1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800,
+	39916800, 479001600,
+}
+
+func main() {
+	max := 9
+	if runtime.GOARCH == "wasm" {
+		max = 7 // stack size is limited
+	}
+	for i := 0; i <= max; i++ {
+		if f := count(fact(gen(i))); f != results[i] {
+			println("FAIL:", i, "!:", f, "!=", results[i])
+			panic(0)
+		}
+	}
+}