gistfile1.rb

RATIONALE =<<_END
The case for a maybe:
We all know true and false, right? Larry Wall once said that truth should be
considered evident; therefore anything in Perl is either true or false, along with
anything else it may be. Truth is just an aspect.

And we use it easily, with the if/else construct:

if something
  do_something
else
  do_something_else
end

How about the cases where we don't know? Let's say you're a meteorologist, and somone asks
if it will rain tomorrow. Let's say you don't know, it's a 50/50 chance of each. Would you
accept being forced in to answering yes or no?

if it_will_rain?
  bring_an_umbrella
else
  wear_sunglasses
else
  bring_an_umbrella
  wear_sunglasses
end

Makes sense, doesn't it?
Let's give it a try
_END

require 'singleton'
class MaybeClass
  include Singleton
  def to_s
    "maybe"
  end
end
class Object
  def maybe
    MaybeClass.instance
  end
end

puts maybe

OMG_AN_OPERATOR=<<_END
But wait, if/else is a language construct, isn't it? What would a Smalltalker do in this situation?

In Smalltalk, there is no if/else statement. Instead you use methods on true and false, like this:
it_will_rain?.if_true {
  bring_an_umbrella
}
Let's try
_END

class TrueClass
  def if_true
    yield
  end
  def if_false;end
end

class FalseClass
  def if_true;end
  def if_false
    yield
  end
end

false.if_true {
  puts "No way"
}
true.if_true {
  puts "Why, of course"
}

MAKES_SENSE=<<_END
See where I'm going? 
_END

class FalseClass
  def true_nor_false;end
end

class TrueClass
  def true_nor_false;end
end

class MaybeClass
  def if_true;end
  def if_false;end
  def true_nor_false
    yield
  end
end

def will_it_rain?
  maybe
end

will_it_rain?.if_true {
  puts "Bring an umbrella"
}

will_it_rain?.if_false {
  puts "Wear sunglasses"
}

will_it_rain?.true_nor_false {
  puts "Bring an umbrella and wear sunglasses"
}

Marius the Philosopher :)

probably_not = within the p10 percentile

will_it_rain?.probably_not {
   puts "Maybe you should bring along your tiny compact umbrella along with your sunglasses
}

but is more to it than syntactic sugar?

Haha!
On a serious note: if we're measuring percentiles, there's probably something more than a simple boolean at play:

class Forecast
  def rain_probability
    RainProbability.new(20.percent)
  end
  def will_it_rain?
    rain_probability
  end      
end

class RainProbability
  def initialize(percentage)
    @percentage = percentage
  end
  def probably_not
    yield if (10.percent..40.percent).include(@percentage)
  end
  def if_true
    yield if @percentage == 100.percent
  end
  def if_false
    yield if @percentage == 0.percent
  end
end

Why this approach over using a symbol?

def forecast
  :maybe
end

bring_umbrella = case forecast
  when true
    true
  when false
    false
  else
    true
  end

Haha, didn't think of that, you actually introduced a third alternative to true and false. Clever!