unless.io

unless := method(
    (call sender doMessage(call message argAt(0))) ifFalse( 
    call sender doMessage(call message argAt(1))) ifTrue( 
    call sender doMessage(call message argAt(2)))
)

unless(1 == 2, write("One is not two\n"), write("one is two\n"))

Guys, i've came here from tweet of caffo that said the code is beautiful so I decided to show the real beauty. Nothing personal.

Wow, only 1 Class 1 Singleton and 2 methods had to be defined in the Scala version.
And if I see this correctly a totally different activation context is created whereas the Io version is transparent, which makes it slightly longer but cleaner. An easier version which breaks the contexts is:

unless := method(b,
    if(b not, call evalArgAt(1), call evalArgAt(2))))

The smalltalky ifFalse is really the way to go here because it keeps the message structure clear for the Programmer without obscuring semantics with syntax, one thing ruby didn't get quite right imho.

To me the inversion of control that is used here seems unjustified, if I want to evaluate something based on a boo lean the boolean object is the one to handle the task, bool condition(toEvaluate), having a block evaluate based on a boolean seems unOO to me, as with block(toEvaluate) condition(bool) which would also be possible.

As @Ticking already points out, Io already has an unless:

someCondition ifFalse(doSomething)

Enjoy.

@paulmillr - Beauty is in the eye of the beholder because I personally find the Io solution much more lucid & elegant. So in my eyes its more beautiful compared to the Scala version.

BTW... the postfix unless is Perl like because that's where Ruby got the Statement Modifiers from: http://perldoc.perl.org/perlsyn.html#Statement-Modifiers

Except the postfix version has nothing to do with perl. Io's a message passing language, everything is a message and all messages are expressions. The equivalent code in a language that uses a dot instead a space for passing a message to an object (and supports either first class messages like Io or higher order functions):

condition.ifFalse(doSomething)

It's no different than:

model.update_attributes(bleh: 42)

In a Ruby/Rails app. The same mechanisms are at play. Lookup, & perform

@jeremytregunna: I'm referring to the (syntax of the) Scala example provided: println("flag is " + flag) unless flag

In Haskell:

unless p a b = if p then b else a

If if was just a function instead of special syntax (or one had defined a function with the same behavior), it could look like this:

unless = if . not