mirror of
https://github.com/golang/go
synced 2024-11-13 17:50:23 -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
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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type Number struct {
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next *Number
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}
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// -------------------------------------
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// Peano primitives
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func zero() *Number {
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return nil;
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}
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func is_zero(x *Number) bool {
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return x == nil;
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}
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func add1(x *Number) *Number {
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e := new(Number);
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e.next = x;
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return e;
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}
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func sub1(x *Number) *Number {
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return x.next;
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}
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func add(x, y *Number) *Number{
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if is_zero(y) {
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return x;
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}
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return add(add1(x), sub1(y));
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}
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func mul(x, y *Number) *Number {
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if is_zero(x) || is_zero(y){
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return zero();
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}
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return add(mul(x, sub1(y)), x);
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}
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func fact(n *Number) *Number {
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if is_zero(n) {
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return add1(zero());
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}
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return mul(fact(sub1(n)), n);
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}
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// -------------------------------------
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// Helpers to generate/count Peano integers
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func gen(n int) *Number {
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if n > 0 {
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return add1(gen(n - 1));
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}
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return zero();
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}
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func count(x *Number) int {
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if is_zero(x) {
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return 0;
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}
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return count(sub1(x)) + 1;
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}
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func check(x *Number, expected int) {
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var c = count(x);
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if c != expected {
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panic("error: found ", c, "; expected ", expected, "\n");
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}
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}
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// -------------------------------------
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// Test basic functionality
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func verify() {
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check(zero(), 0);
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check(add1(zero()), 1);
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check(gen(10), 10);
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check(add(gen(3), zero()), 3);
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check(add(zero(), gen(4)), 4);
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check(add(gen(3), gen(4)), 7);
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check(mul(zero(), zero()), 0);
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check(mul(gen(3), zero()), 0);
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check(mul(zero(), gen(4)), 0);
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check(mul(gen(3), add1(zero())), 3);
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check(mul(add1(zero()), gen(4)), 4);
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check(mul(gen(3), gen(4)), 12);
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check(fact(zero()), 1);
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check(fact(add1(zero())), 1);
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check(fact(gen(5)), 120);
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}
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// -------------------------------------
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// Factorial
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func main() {
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verify();
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for i := 0; i <= 10; i++ {
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print(i, "! = ", count(fact(gen(i))), "\n");
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}
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}
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