rubyによるedの部分的実装

ed.rb

#!/usr/bin/env ruby
# coding: utf-8
require 'pp'
require 'readline'

class Ed
  class Command
    def initialize(secondary, primary, type, param)
      @secondary = secondary
      @primary = primary
      @type  = type
      @param = param
    end

    attr_accessor :secondary, :primary, :type, :param
  end

  def initialize
    @buffer = []
    @command = nil
    @current = 0
    @error = nil
    @file = nil
    @prompt = ''
    @shell = nil
    @verbose = false
  end

  @@forward_regexp = /\/((\\\/|[^\/])*)\//
  @@backward_regexp = /\?((\\\?|[^\?])*)\?/
  @@address_regexp = /(\.|\$|\d+|-|\^\d+|\+|\+\d+|,|;|#{@@forward_regexp}|#{@@backward_regexp}|'.*)/
  @@type_regexp = /(wq|.|\z)/
  @@command_regexp = /^\s*((?<one>#{@@address_regexp})?(\s*(,|;)\s*(?<two>#{@@address_regexp}))?)?\s*(?<type>#{@@type_regexp})\s*(?<param>.+)?\s*$/
  def read
    # 行番号は無限に指定できるため,原理上は正規表現だけでパースするのは不可能である
    # 3つ以上の行番号を利用するコマンドは存在しないため,実用上は問題はない
    line = Readline.readline(@prompt, true)
    m = @@command_regexp.match(line)
    if m[:two]
      secondary = m[:one]
      primary = m[:two]
    else
      primary = m[:one] || m[:two]
    end

    case
    when primary == ','
      secondary = 1
      primary = '$'
    when primary == ';'
      secondary = '.'
      primary = '$'
    when re = @@forward_regexp.match(primary)
      r = Regexp.new(re[1])
      if primary = @buffer.drop(@current - 1).index { |b| r.match(b) }
        primary += @current
        secondary = primary
      else
        raise 'No match'
      end
    when re = @@backward_regexp.match(primary)
      r = Regexp.new(re[1])
      if primary = @buffer.take(@current).rindex { |b| r.match(b) }
        secondary = primary
      else
        raise 'No match'
      end
    end
    @command = Command.new(line_to_i(secondary), line_to_i(primary), m[:type], m[:param])
  end

  def eval
    case @command.type
    when 'a'
      @command.primary ||= line_to_i('.')
      ins = self.insert
      @buffer.insert(@command.primary, *ins)
      @current = @command.primary + ins.size
    when 'c'
      @command.secondary ||= line_to_i('.')
      @command.primary ||= line_to_i('.')
      ins = self.insert
      @buffer.fill(@command.secondary - 1 .. @command.primary - 1, ins).flatten!
      @current = @command.primary + ins.size
    when 'd'
      @command.secondary ||= line_to_i('.')
      @command.primary ||= line_to_i('.')
      @buffer.slice!(@command.secondary - 1 .. @command.primary - 1)
      @current = @command.primary - 1
    when 'f'
      @file = @command.param
    when 'g'
      @command.secondary ||= line_to_i('1')
      @command.primary ||= line_to_i('$')
      regexp = Regexp.union(@@forward_regexp, @@backward_regexp)
      m = /(?<re>#{regexp})(?<command_list>.*)/.match(@command.param)
      re = regexp.match(m[:re])
      reg = Regexp.new(re[1] || re[2])
      @buffer[@command.secondary - 1 .. @command.primary - 1].each.with_index { |l, i|
        if reg === l
          @command.secondary = i + 1
          @command.primary = i + 1
          cm = @@command_regexp.match(m[:command_list])
          @command.type = cm[:type]
          @command.param = cm[:param]
          eval
        end
      }
    when 'H'
      @verbose = ! @verbose
    when 'h'
      pp @error
    when 'i'
      @command.primary ||= line_to_i('.')
      ins = self.insert
      @buffer.insert(@command.primary - 1, *ins)
      @current = @command.primary + ins.size - 1
    when 'j'
      @command.secondary ||= line_to_i('.')
      @command.primary ||= line_to_i('.') + 1
      @buffer[@command.secondary - 1 .. @command.primary - 1] =
        @buffer[@command.secondary - 1 .. @command.primary - 1].join
      @current = @command.secondary
    when 'n'
      @command.secondary ||= line_to_i('.')
      @command.primary ||= line_to_i('.')
      puts (@command.secondary .. @command.primary).to_a.
             zip(@buffer[@command.secondary - 1 .. @command.primary - 1]).
             map{ |(n, l)| n.to_s + "\t" + l }
      @current = @command.primary
    when 'p'
      @command.secondary ||= line_to_i('.')
      @command.primary ||= line_to_i('.')
      # -1が末尾になってしまうためオリジナルのedとは少し動作が違うが,
      # 制限がゆるい分にはまあ問題ないだろう…
      puts @buffer[@command.secondary - 1 .. @command.primary - 1]
      @current = @command.primary
    when 'P'
      @prompt = '*'
    when 'q'
      exit
    when 'r'
      @command.primary ||= line_to_i('$')
      if @command.param.start_with?('!')
        @command.param[0] = ''
        o = shell(@command.param)
      else
        @command.param ||= @file
        o = IO.read(@command.param)
      end
      @buffer.insert(@command.primary, o)
    when 'w'
      @command.param ||= @file
      b = @buffer.join("\n")
      unless b.end_with?("\n")
        b << "\n"
      end
      IO.write(@command.param, b)
      @file = @command.param
    when 'wq'
      @command.type = 'w'
      eval
      @command.type = 'q'
      eval
    when '!'
      puts shell(@command.param)
      puts '!'
    when '='
      @command.primary ||= line_to_i('$')
      puts @command.primary
    when ''
      @command.primary ||= line_to_i('.') + 1
      puts @buffer[@command.primary - 1]
      @current = @command.primary
    else
      raise 'Unknown command'
    end
  end

  def loop
    Kernel.loop {
      begin
        read
        eval
        @command = nil
      rescue
        if @verbose
          pp $!
          pp $!.backtrace
          pp self
        else
          puts '?'
        end
        @error = $!
      end
    }
  end

  def line_to_i(l)
    case
    when l == nil
      nil
    when l.is_a?(Integer)
      l
    when l == '.'
      @current
    when l == '$'
      @buffer.size
    when /^\d$/.match(l)
      Integer(l)
    when l == '-'
      @current - 1
    when /^\^(\d)$/.match(l)
      @current - Integer(/^\^(\d)$/.match(l)[1])
    when l == '+'
      @current + 1
    when /^'(\p{Lower})$/
      raise 'k command un impl'
    else
      raise 'Invalid address'
    end
  end

  def shell(c)
    if c.start_with?('!')
      if @shell
        c.sub!('!', @shell)
      else
        raise 'No previous command'
      end
    end
    file_regexp = /(?<!\\)%/
    if file_regexp === c
      if @file
        c.gsub!(file_regexp, @file)
      else
        raise 'No current filename'
      end
    end
    @shell = c
    `#{c}`
  end

  def insert
    buf = []
    while l = Readline.readline('', false)
      if l == '.'
        return buf
      else
        buf << l
      end
    end
  end
end

Ed.new.loop