代码之家 › 专栏 › 技术社区 › Andy

Ruby中的解析器:处理粘性注释和引号

recursive-descent parsing ruby

Andy · 技术社区 · 14 年前

我试图用Ruby为一种语法创建一个递归的下降解析器,它由以下规则定义

输入包括 白色空间 分离的卡从A开始 停止字 , 在哪里? 白色空间 是正则表达式 /[ \n\t]+/
卡可以包括 关键词 或/和 价值观 也被空白隔开, 有卡特定的顺序/模式
所有停止词和关键字都不区分大小写,即: /^[a-z]+[a-z0-9]*$/i
值可以是 双引号字符串 ,不能与用空格表示的其他单词,例如:
```
word"quoted string"word
```
值也可以是单词 /^[a-z]+[a-z0-9]*$/ 或整数或浮动 (例如) -1.15 或 1.0e+2 )
单行注释 用 # 不可与其他词,例如:
```
word#single-line comment\n
```
多行注释 用 /* 和 */ 也许不是与其他词分开,例如:
```
word/*multi-line 
comment*/word
```

# Input example. Stop-words are chosen just to highlight them: set, object
set title"Input example"set objects 2#not-separated by white-space. test: "/*
set test "#/*"
object 1 shape box/* shape is a Keyword, 
box is a Value. test: "#*/object 2 shape sphere
set data # message and complete are Values
0 0 0 0 1 18 18 18 1 35 35 35 72 35 35 # all numbers are Values of the Card "set"

因为大多数单词都是用空格分隔的,所以有一段时间我一直在考虑将整个输入拆分并逐字解析。为了处理评论和引用,我打算

words = input_text.gsub( /([\"\#\n]|\/\*|\*\/)/, ' \1 ' ).split( /[ \t]+/ )

但是,以这种方式修改字符串(和注释,如果我想保留它们的话)的内容。你会如何处理这些粘乎乎的评论和引用?

1 回复 | 直到 14 年前

Community miroxlav 7 年前

好的,我自己做的。如果不需要可读性,可以最小化以下代码

class WordParser
  attr_reader :words

  def initialize text
    @text = text
  end

  def parse
    reset_parser
    until eof?
      case curr_char
        when '"' then
          start_word and add_chars_until? '"'
          close_word
        when '#','%' then
          start_word and add_chars_until? "\n"
          close_word
        when '/' then
          if next_is? '*' then
            start_word and 2.times { add_char }
            add_char until curr_is? '*' and next_is? '/' or eof?
            2.times { add_char } unless eof?
            close_word
          else
            # parser_error "unexpected symbol '/'" # if not allowed in the grammar
            start_word unless word_already_started?
            add_char
          end
        when /[^\s]/ then
          start_word unless word_already_started?
          add_char
      else # skip whitespaces etc. between words
        move and close_word
      end
    end
    return @words
  end

private

  def reset_parser
    @position = 0
    @line, @column = 1, 1
    @words = []
    @word_started = false
  end

  def parser_error s
    Kernel.puts 'Parser error on line %d, col %d: ' + s
    raise 'Parser error'
  end

  def word_already_started?
    @word_started
  end

  def close_word
    @word_started = false
  end

  def add_chars_until? ch
    add_char until next_is? ch or eof?
    2.times { add_char } unless eof?
  end

  def add_char
    @words.last[:to] = @position
    # @words.last[:length] += 1
    # @word.last += curr_char # if one just collects words
    move
  end

  def start_word
    @words.push from: @position, to: @position, line: @line, column: @column
    # @words.push '' unless @words.last.empty? # if one just collects words
    @word_started = true
  end

  def move
    increase :@position
    return if eof?
    if prev_is? "\n"
      increase :@line
      reset :@column
    else
      increase :@column
    end
  end

  def reset var; instance_variable_set(var, 1) end
  def increase var; instance_variable_set(var, instance_variable_get(var)+1) end

  def eof?; @position >= @text.length end

  def prev_is? ch; prev_char == ch end
  def curr_is? ch; curr_char == ch end
  def next_is? ch; next_char == ch end

  def prev_char; @text[ @position-1 ] end
  def curr_char; @text[ @position   ] end
  def next_char; @text[ @position+1 ] end
end

使用我问题中的示例进行测试

words = WordParser.new(text).parse
p words.collect { |w| text[ w[:from]..w[:to] ] } .to_a

# >> ["# Input example. Stop-words are chosen just to highlight them: set, object\n", 
# >>  "set", "title", "\"Input example\"", "set", "objects", "2", 
# >>  "#not-separated by white-space. test: \"/*\n", "set", "test", "\"#/*\"", 
# >>  "object", "1", "shape", "box", "/* shape is a Keyword, \nbox is a Value. test: \"#*/", 
# >>  "object", "2", "shape", "sphere", "set", "data", "# message and complete are Values\n", 
# >>  "0", "0", "0", "0", "1", "18", "18", "18", "1", "35", "35", "35", "72", 
# >>  "35", "35", "# all numbers are Values of the Card \"set\"\n"]

所以现在我可以用 something like this 进一步分析单词。