hello worldより「コラッツの問題」書くほうがいろいろ学べそう ref: http://qiita.com/inaba178/items/9dc2026780ca7d148b26

collatz.dart

library collatz;

collatz(int n) {
  print(n.toString());

  if (n > 1) {
    if (n % 2 == 1) {
      collatz(3 * n + 1);
    } else {
      collatz((n / 2).round());
    }
  }
}

collatz.go

package main

import (
    "flag"
    "fmt"
    "time"
)

func main() {
    n := flag.Uint64("n", 1, "collatz start num")
    flag.Parse()

    num := *n

    if num < 1 {
        fmt.Println("Invalid value:", num)
        return
    }

    collatz(num)
}

func collatz(num uint64) {
    fmt.Println(num)
    time.Sleep(time.Second / 2)

    if num%2 == 1 && num > 1 {
        collatz(3*num + 1)
    } else if num%2 == 0 {
        collatz(num / 2)
    }
}

collatz.sh

#!/bin/sh
collatz() {
    n=$1
    echo $n
    sleep 0.5s
    if [ `echo "$n % 2" | bc` -eq 1 ] && [ $n != "1" ]; then
        collatz `echo "3 * $n + 1" | bc`
    elif [ `echo $n % 2 | bc` -eq 0 ]; then
        collatz `echo $n / 2 | bc`
    fi
}

collatz $1

collatz2.go

package main

import (
    "flag"
    "fmt"
    "os"
    "time"
)

var isSleep bool

func main() {
    n := flag.Uint64("n", 1, "collatz target num. infinite loop if it was the this flag is 1 and l flag is true.")
    l := flag.Bool("l", false, "loop from 1 to the target. infinite loop if it was the this flag is true and n flag is 1.")
    s := flag.Bool("s", false, "0.5 seconds sleep every calculation.")
    flag.Parse()

    num := *n
    isSleep = *s
    loop := *l

    if num < 1 {
        fmt.Println("invalid value:", num)
        os.Exit(1)
    }

    if loop {
        if num == 1 {
            for i := uint64(1); ; i++ {
                loopCollatz(i)
            }
        } else {
            for i := uint64(1); i <= num; i++ {
                loopCollatz(i)
            }
        }
    } else {
        ret := collatz(num)
        retCheck(ret)
    }
}

func loopCollatz(i uint64) {
    ret := collatz(i)
    fmt.Println("----------")
    retCheck(ret)
}

func collatz(num uint64) (ret uint64) {
    fmt.Println(num)

    if isSleep {
        time.Sleep(time.Second / 2)
    }

    if num > 1 {
        if num%2 == 1 {
            ret = collatz(3*num + 1)
        } else if num%2 == 0 {
            ret = collatz(num / 2)
        }
    } else {
        ret = num
    }

    return
}

func retCheck(ret uint64) {
    if ret != 1 {
        fmt.Println("invalid collatz return:", ret)
        os.Exit(1)
    }
}

file0.txt

def collatz(n)
  show n
  if n.odd? and n > 1
    collatz(3n + 1)
  else if n.even?
    collatz(n / 2)

main.dart

import 'package:collatz/collatz.dart' as collatz;
import 'package:args/args.dart';
import 'dart:io';

main(List<String> arguments) {
  final parser = new ArgParser()..addOption('num', defaultsTo: '1', abbr: 'n');

  ArgResults arg = parser.parse(arguments);

  int num = int.parse(arg['num']);
  if (num < 1) {
    print('invalid value:' + arg['num']);
    exit(1);
  }

  collatz.collatz(num);
}