RPN Calculator

rpn-calculator.rb

# Simple RPN calculator with stack.
# Example usage:
#   >> 400 400 400 *
#   Top of stack: 64000000
#   >> 40 40 *
#   Top of stack: 102400000000
#   >> 40
#   Top of stack: 40
#   >> 30
#   Top of stack: 30
#   >> +
#   Top of stack: 102400000070

require 'readline'
require 'strscan'

stack = []

while line = Readline.readline('>> ', true)
  next if line.empty?

  scanner = StringScanner.new(line)

  until scanner.eos?
    if scanner.scan(/([+-]?[0-9]+\.[0-9]+)/)
      stack << scanner[1].to_f
    elsif scanner.scan(/([+-]?(?:0|[1-9])[0-9]*)/)
      stack << scanner[1].to_i
    elsif scanner.scan(%r(([*/+-])))
      operand = scanner[1]
      stack = [stack.inject{|sum, value| sum.send(operand, value) }]
    elsif scanner.scan(/\s+/)
    end
  end

  puts "Top of stack: %p" % [stack.last]
end