plus/minus/times/divide parser

pmtd-parser-rational.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

# plus/minus/times/divide parser (rational numbers ready)
# by takehikom (http://d.hatena.ne.jp/takehikom/)

# ruby pmtd-parser-rational.rb
# ruby -d pmtd-parser-rational.rb

# see also: http://getnews.jp/archives/114382
#           http://umashika-news.jp/archives/51836921.html

if RUBY_VERSION < "1.9"
  $KCODE = "u"
  require "jcode"
end

require "rational"

class Rational
  def to_s
    num = numerator
    den = denominator
    if den == 1
      num.to_s
    else
      "#{num}/#{den}"
    end
  end
end

# http://raa.ruby-lang.org/project/syntax
# http://raa.ruby-lang.org/cache/syntax/syntax.rb
# http://jp.rubyist.net/magazine/?0008-RLR
require "./syntax.rb"

class PmtdParser
  INF = +1.0/0
  LOOP0 = 0..INF
  LOOP1 = 1..INF

  def initialize
    # 式
    @expr = Syntax::Pass.new()

    # 数
    @num = (("0".."9") * LOOP1).qualify{|x|
      val = Rational(x.join.to_i)
      debug_print("num", x, val)
      val
    }

    # 括弧
    @prim = @num.qualify{|x|
      val = x
      debug_print("prim_num", x, val)
      val
    } | ("(" + @expr + ")").qualify{|x|
      val = x[1]
      debug_print("prim_par", x, val)
      val
    }

    # 連接（かけ算）
    @prim2 = (@prim + ((" " | "・" | "") + @prim) * LOOP0).qualify{|x|
      val = x[0]
      x[1].each{|y|
        val *= y[1]
      }
      debug_print("prim2", x, val)
      val
    }

    # 符号
    @prim3 = @prim2.qualify{|x|
      val = x
      debug_print("prim3_num", x, val)
      val
    } | (("+" | "-") + @prim2).qualify{|x|
      val = x[1]
      val = -val if x[0] == "-"
      debug_print("prim3_sign", x, val)
      val
    }

    # 乗除
    @expr2 = (@prim3 + (("*" | "/" | "×" | "÷") + @prim3) * LOOP0).qualify{|x|
      val = x[0]
      x[1].each{|y|
        case y[0]
        when "*", "×", " ", "・", ""
          val *= y[1]
        when "/", "÷"
          val /= y[1]
        end
      }
      debug_print("expr2", x, val)
      val
    }

    # 式（加減）
    @expr << (@expr2 + (("+" | "-") + @expr2) * LOOP0).qualify{|x|
      val = x[0]
      x[1].each{|y|
        case y[0]
        when "+"
          val += y[1]
        when "-"
          val -= y[1]
        end
      }
      debug_print("expr", x, val)
      val
    }
  end

  def start(str)
    str = str.tr("０-９（）＋－", "0-9()+-")
    print "#{str}="
    puts if $DEBUG
    puts((@expr === RandomAccessStream.new(str)).to_s)
  end

  def debug_print(name, x, val)
    return unless $DEBUG
    puts "#{name}: x=#{x.inspect}:#{x.class}, val=#{val}"
  end
  private :debug_print
end

if __FILE__ == $0
  if ARGV[0]
    PmtdParser.new.start(ARGV.shift)
  else
    expr = "（63÷21）×18－27＋53"
    PmtdParser.new.start(expr)
    expr = expr.split(//u).reverse.join.tr("（）", "）（")
    PmtdParser.new.start(expr)
  end
end