Comments on: Don’t — in Scala

By: Vince

Vince — Wed, 11 Nov 2009 22:53:28 +0000

Great article. This was a really simple explanation of how to write your own control structures in Scala. More please!

By: Aleksander Kmetec

Aleksander Kmetec — Wed, 11 Nov 2009 17:49:20 +0000

@wolverian: Oh, that’s a tough one. I only managed to implement a more polite version, “please don’t”, by jumping through a couple of hoops:

object please { def don(code: => Unit) = new DontCommand(code) }


  implicit def symbolExtender(s: Symbol) = new { def apply(r: Unit) = () }

please don't { println("HEY HEY HEY!") } unless (2 > 1)

By: wolverian

wolverian — Wed, 11 Nov 2009 17:18:44 +0000

Now implement “don’t”, like the original code? :)

By: Aleksander Kmetec

Aleksander Kmetec — Tue, 10 Nov 2009 19:41:36 +0000

That one is left as an exercise to the reader. ;-)

Actually, a simple
dont { dont { println("Hello there!") } }
is perfectly doable by just adding an overloaded definition of dont, like this:

def dont(dontExecCode: DontCommand) = dontExecCode.unless(true)

But this only works if the outer dont block doesn’t contain anything else than another dont block and there also can’t be any unless/until conditions.

By: Matjaž Lipuš

Matjaž Lipuš — Tue, 10 Nov 2009 19:28:47 +0000

I like the resulting syntax.

What about nested dont?
dont {
dont {
println(“Hello? Can anyone hear me?”);
}
}

In math minus and minus gives plus. :)