MATH_METHODS = {"+" => :+, "-" => :-, "*" => :*, "/" => :/} STACK_METHODS = {"drop", "swap", "dup", "over"} REQUIRE_AMOUNT = {"+" => 2, "-" => 2, "*" => 2, "/" => 2, "swap" => 2, "over" => 2, "dup" => 1, "drop" => 1} class Forth def self.stack_operation(operation, min, result) if result.size < min raise ArgumentError.new end case operation when "dup" result << result[-1] when "drop" result.pop when "swap" result[-2], result[-1] = result[-1], result[-2] when "over" result << result[-2] end result end def self.math_operation(operation, result) if result.size < 2 || (operation == :/ && result[-1] == 0) raise ArgumentError.new end a = result.pop b = result.pop case operation when :+ result << (b + a) when :- result << (b - a) when :/ result << (b / a).to_i when :* result << (b * a) end result end def self.evaluate(inputs, result = [] of Int32, methods = {} of String => String) status = false method = [] of String inputs = inputs.downcase inputs = inputs.gsub(";", "; ") inputs_array = inputs.split(" ") inputs_array.each do |x| if x == ";" methods[method[0]] = method[1..-1].map { |x| methods.keys.includes?(x) ? self.evaluate(x, [] of Int32, methods).join(" ") : x }.join(" ") status = false method = [] of String elsif status method << x elsif methods.keys.includes?(x) result = self.evaluate(methods[x], result, methods) elsif x.match(/[0-9]/) result << x.to_i elsif MATH_METHODS.keys.includes?(x) result = self.math_operation(MATH_METHODS[x], result) elsif STACK_METHODS.includes?(x) result = self.stack_operation(x, REQUIRE_AMOUNT[x], result) elsif x == ":" status = true else raise ArgumentError.new end end result end end