Ruby lambda factorial

ruby-lambda-factorial.rb

IS_ZERO = -> (x) { x == 0 }
ONE = -> { 1 }
ONE_LESS = -> (x) { x - 1 }
ITSELF = -> (x) { x }
COND = -> (cond) { -> (doit) { -> (doelse) { cond ? doit.(nil) : doelse.(nil) } } }
MULT = -> (x) { -> (y) { x * y } }

puts(
  -> myself {
    -> (n) {
      COND.(
        IS_ZERO.(n)
      ).(
        -> _ { ONE.() }
      ).(
        -> _ { MULT.(ITSELF.(n)).(myself.(myself).(ONE_LESS.(n))) }
      )
    }
  }.(
    -> myself {
      -> (n) {
        COND.(
          IS_ZERO.(n)
        ).(
          -> _ { ONE.() }
        ).(
          -> _ { MULT.(ITSELF.(n)).(myself.(myself).(ONE_LESS.(n))) }
        )
      }
    }
  ).(6)
)