mirror of
https://github.com/golang/go
synced 2024-11-13 17:30:24 -07:00
bc2f5f1dce
1) fix print statements, panic statements (parentheses required) 2) len is now allowed as a var name (bug053) R=gri OCL=14106 CL=14106
132 lines
1.9 KiB
Go
132 lines
1.9 KiB
Go
// $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");
|
|
}
|
|
}
|
|
|