Church numerals

gistfile1.rb

# Church numerals

zero = lambda{|f|
  lambda{|x| x }
}
one = lambda{|f|
  lambda{|x|
    f.call(x)
  }
}
two = lambda{|f|
  lambda{|x|
    f.call(f.call(x))
  }
}
three = lambda{|f|
  lambda{|x|
    f.call(f.call(f.call(x)))
  }
}


p zero.call(lambda{|x| x + 1 }).call(0)
p one.call(lambda{|x| x + 1 }).call(0)
p two.call(lambda{|x| x + 1 }).call(0)
p three.call(lambda{|x| x + 1 }).call(0)

add = lambda{|a, b|
  lambda{|f|
    lambda{|x|
      a.call(f).call(b.call(f).call(x))
    }
  }
}

p add.call(two, three).call(lambda{|x| x + 1 }).call(0)