diff --git a/test/peano.go b/test/peano.go new file mode 100644 index 00000000000..bc52c0612ce --- /dev/null +++ b/test/peano.go @@ -0,0 +1,131 @@ +// $G $F.go && $L $F.$A && ./$A.out + +// 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. + +package main + +type Number struct { + next *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.next = x; + return e; +} + + +func sub1(x *Number) *Number { + return x.next; +} + + +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 { + panic "error: found ", c, "; expected ", expected, "\n"; + } +} + + +// ------------------------------------- +// Test basic functionality + +func verify() { + 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 + + +func main() { + + verify(); + for i := 0; i <= 10; i++ { + print i, "! = ", count(fact(gen(i))), "\n"; + } +} +