Scala source code compatible with both scala/scalac

scala/scalac両対応なScalaソース

This is the defacto standard of executable Scala script, using shebang (little bit verbose for explanation below).
これは 実行可能な Scalaソースの標準です。本来不要なobjectとか付いていますが以下の説明のためです。

#!/usr/bin/env scala
!#
object hello extends App{
    println("Hello World");
}
hello.main(args)

Note: !# does not seem to be required if your Scala is 2.10(?)
2.10では!#は不要なようです(?)。

Actually hello.main(args) is verbose. Because (cited from scala -help:

A file argument will be run as a scala script unless it contains only
self-contained compilation units (classes and objects) and exactly one
runnable main method.  In that case the file will be compiled and the
main method invoked.  This provides a bridge between scripts and standard
scala source.

So let's strip it.
hello.main(args)は不要なので取り除きましょう。

#!/usr/bin/env scala
!#
object hello extends App{
    println("Hello World");
}

Now the scala command is dumb. We need explicit main method. Unfortunately App trait cannot be used.
scalaコマンドは何も出力しなくなってしまいました。mainメソッドを明示しなければなりません。残念ながらApp traitは使えないのです。

#!/usr/bin/env scala
!#
object hello{
    def main(args: Array[String]){
        println("Hello World");
    }
}

Finally, to satisfy scalac, let's use http://qiita.com/ando-masaki/items/323c6b08e07ec4538c3d trick (//usr/bin/env go run $0 $@;exit).
scalacを満足させるため、「Go言語でshebang」のトリックを使います。

//usr/bin/env scala $0 $@;exit
object hello{
    def main(args: Array[String]){
        println("Hello World");
    }
}

Great. Now this source is compatible with both scala/scalac.
素晴らしい！このソースはscala/scalac互換になりました。

Finally, don't forget that there must be only one class/object or this trick won't work anymore.
最後に、このトリックを使うにはclass/objectは複数置けないことに留意してください。

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I have found that similar technique can be applied to F#.
Make the file extention .fsx and make the first line //usr/bin/env fsharpi $0 $@;exit.