gcc/testsuite/go.test/test/turing.go

   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 simulating a Turing machine, sort of.
   8
   9 package main
  10
  11 // brainfuck
  12
  13 var p, pc int
  14 var a [30000]byte
  15
  16 const prog = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.!"
  17
  18 func scan(dir int) {
  19         for nest := dir; dir*nest > 0; pc += dir {
  20                 switch prog[pc+dir] {
  21                 case ']':
  22                         nest--
  23                 case '[':
  24                         nest++
  25                 }
  26         }
  27 }
  28
  29 func main() {
  30         r := ""
  31         for {
  32                 switch prog[pc] {
  33                 case '>':
  34                         p++
  35                 case '<':
  36                         p--
  37                 case '+':
  38                         a[p]++
  39                 case '-':
  40                         a[p]--
  41                 case '.':
  42                         r += string(a[p])
  43                 case '[':
  44                         if a[p] == 0 {
  45                                 scan(1)
  46                         }
  47                 case ']':
  48                         if a[p] != 0 {
  49                                 scan(-1)
  50                         }
  51                 default:
  52                         if r != "Hello World!\n" {
  53                                 panic(r)
  54                         }
  55                         return
  56                 }
  57                 pc++
  58         }
  59 }