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"))

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