作ろう、ミニ言語 | 初心者向け | DoRuby https://doruby.jp/users/yam/entries/mini_lang

racoon.y

# coding: utf-8
class RacoonParser
rule
  start code
  code    : code s_exp
          | s_exp
  s_exp   : '(' func params ')' { result = @racoon.send(val[1], val[2]) }
  param   : s_exp
          | atom
  params  : params param { result = val[0..1] }
          | param
  func    : TEXT
          | ID
  atom    : DEC
          | TEXT { result = @racoon.vars[val[0]] if @racoon.vars[val[0]] }
          | ID
end

---- header
require 'strscan'

---- inner
attr_accessor :racoon

def parse(str)
  scanner = StringScanner.new(str)
  @q = []
  until scanner.eos?
    scanner.scan(/#[^\n]*\n/) ? nil :
    scanner.scan(/\s+/) ? nil :
    scanner.scan(/\d+/) ? @q << [:DEC, scanner.matched] :
    scanner.scan(/[\(|\)]/) ? @q << [scanner.matched, scanner.matched] :
    scanner.scan(/[a-zA-Z0-9\-\_\/]+/) ? @q << [:TEXT, scanner.matched] :
    scanner.scan(/./) ? @q << [:ID, scanner.matched] :
    nil
  end
  do_parse
end

def next_token
  @q.shift
end

---- footer
class Racoon
  attr_accessor :vars
  def initialize
    @vars = Hash.new
  end
  
  %w(+ - * /).each{|id|
    define_method(id) {|args|
      args.flatten.map(&:to_i).inject(id.to_sym)
    }
  }
  def var(args)
    variable_name, value = args
    @vars[variable_name] = value
  end

  def display(args)
    puts "=> #{args}"
  end
end

parser = RacoonParser.new
parser.racoon = Racoon.new
line_count = 0
loop do
  begin
    line_count += 1
    print "#{line_count.to_s.rjust(3, '0')} #{0x1F363.chr("UTF-8")} > "
    parser.parse(gets)
  rescue Racc::ParseError => e
    $stderr.puts e
  end
end