modernc.org/gc@v1.0.1-0.20240304020402-f0dba7c97c2b/testdata/errchk/test/peano.go (about) 1 // run 2 3 // Copyright 2009 The Go Authors. All rights reserved. 4 // Use of this source code is governed by a BSD-style 5 // license that can be found in the LICENSE file. 6 7 // Test that heavy recursion works. Simple torture test for 8 // segmented stacks: do math in unary by recursion. 9 10 package main 11 12 type Number *Number 13 14 // ------------------------------------- 15 // Peano primitives 16 17 func zero() *Number { 18 return nil 19 } 20 21 func is_zero(x *Number) bool { 22 return x == nil 23 } 24 25 func add1(x *Number) *Number { 26 e := new(Number) 27 *e = x 28 return e 29 } 30 31 func sub1(x *Number) *Number { 32 return *x 33 } 34 35 func add(x, y *Number) *Number { 36 if is_zero(y) { 37 return x 38 } 39 40 return add(add1(x), sub1(y)) 41 } 42 43 func mul(x, y *Number) *Number { 44 if is_zero(x) || is_zero(y) { 45 return zero() 46 } 47 48 return add(mul(x, sub1(y)), x) 49 } 50 51 func fact(n *Number) *Number { 52 if is_zero(n) { 53 return add1(zero()) 54 } 55 56 return mul(fact(sub1(n)), n) 57 } 58 59 // ------------------------------------- 60 // Helpers to generate/count Peano integers 61 62 func gen(n int) *Number { 63 if n > 0 { 64 return add1(gen(n - 1)) 65 } 66 67 return zero() 68 } 69 70 func count(x *Number) int { 71 if is_zero(x) { 72 return 0 73 } 74 75 return count(sub1(x)) + 1 76 } 77 78 func check(x *Number, expected int) { 79 var c = count(x) 80 if c != expected { 81 print("error: found ", c, "; expected ", expected, "\n") 82 panic("fail") 83 } 84 } 85 86 // ------------------------------------- 87 // Test basic functionality 88 89 func init() { 90 check(zero(), 0) 91 check(add1(zero()), 1) 92 check(gen(10), 10) 93 94 check(add(gen(3), zero()), 3) 95 check(add(zero(), gen(4)), 4) 96 check(add(gen(3), gen(4)), 7) 97 98 check(mul(zero(), zero()), 0) 99 check(mul(gen(3), zero()), 0) 100 check(mul(zero(), gen(4)), 0) 101 check(mul(gen(3), add1(zero())), 3) 102 check(mul(add1(zero()), gen(4)), 4) 103 check(mul(gen(3), gen(4)), 12) 104 105 check(fact(zero()), 1) 106 check(fact(add1(zero())), 1) 107 check(fact(gen(5)), 120) 108 } 109 110 // ------------------------------------- 111 // Factorial 112 113 var results = [...]int{ 114 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 115 39916800, 479001600, 116 } 117 118 func main() { 119 for i := 0; i <= 9; i++ { 120 if f := count(fact(gen(i))); f != results[i] { 121 println("FAIL:", i, "!:", f, "!=", results[i]) 122 panic(0) 123 } 124 } 125 }