Ruby Prefix Notation Parser

prefix.rb

class Prefix
	
	def initialize
		@expression_regex = /\([\w+*\-]+ (\w+ ?)+\)/
		@operators = {}
		@operators["+"] = lambda {|args| return args.map{|x| x.to_i}.inject(:+) }
		@operators["*"] = lambda {|args| return args.map{|x| x.to_i}.inject(:*) }
		@operators["-"] = lambda {|args| return args.map{|x| x.to_i}.inject(:-) }
	end

	def process(expression)
		while fragment = @expression_regex.match(expression) do
			stack = fragment.to_s.gsub('(','').gsub(')','').split(' ')
			expression.sub!(@expression_regex, @operators[stack.shift].call(stack).to_s)
		end
		return expression.to_i
	end

end


prefix = Prefix.new

tests = [
	'(+ 3 3)',
	'(* 2 6)',
	'(* 2 2 2)',
	'(- 5 4)',
	'(+ (* 2 3) 4)',
	'(+ (* 2 3) (- 9 8))',
]

tests.each do |test|
	print test + " => "
	print prefix.process(test).to_s + "\n"
end

# puts tests