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Diffstat (limited to 'doc/play/peano.go')
-rw-r--r-- | doc/play/peano.go | 88 |
1 files changed, 0 insertions, 88 deletions
diff --git a/doc/play/peano.go b/doc/play/peano.go deleted file mode 100644 index 214fe1b613..0000000000 --- a/doc/play/peano.go +++ /dev/null @@ -1,88 +0,0 @@ -// Peano integers are represented by a linked -// list whose nodes contain no data -// (the nodes are the data). -// http://en.wikipedia.org/wiki/Peano_axioms - -// This program demonstrates that Go's automatic -// stack management can handle heavily recursive -// computations. - -package main - -import "fmt" - -// Number is a pointer to a Number -type Number *Number - -// The arithmetic value of a Number is the -// count of the nodes comprising the list. -// (See the count function below.) - -// ------------------------------------- -// Peano primitives - -func zero() *Number { - return nil -} - -func isZero(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 isZero(y) { - return x - } - return add(add1(x), sub1(y)) -} - -func mul(x, y *Number) *Number { - if isZero(x) || isZero(y) { - return zero() - } - return add(mul(x, sub1(y)), x) -} - -func fact(n *Number) *Number { - if isZero(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 isZero(x) { - return 0 - } - return count(sub1(x)) + 1 -} - -// ------------------------------------- -// Print i! for i in [0,9] - -func main() { - for i := 0; i <= 9; i++ { - f := count(fact(gen(i))) - fmt.Println(i, "! =", f) - } -} |