如何处理树顶解析树？

Question

我已经使用treetop 编写了一个解析器，它成功生成了一个解析树，下面转载了其中的一部分。

SyntaxNode offset=4043, "   ":
  SyntaxNode offset=4043, " "
  SyntaxNode offset=4044, " "
  SyntaxNode offset=4045, " "
StringLiteral+StringLiteral1 offset=4046, "\"MS Sans Serif\"":
  SyntaxNode offset=4046, "\""
  SyntaxNode offset=4047, "MS Sans Serif":
    SyntaxNode+StringLiteral0 offset=4047, "M":
      SyntaxNode offset=4047, ""
      SyntaxNode offset=4047, "M"
    SyntaxNode+StringLiteral0 offset=4048, "S":
      SyntaxNode offset=4048, ""
      SyntaxNode offset=4048, "S"
    SyntaxNode+StringLiteral0 offset=4049, " ":
      SyntaxNode offset=4049, ""
      SyntaxNode offset=4049, " "
    SyntaxNode+StringLiteral0 offset=4050, "S":
      SyntaxNode offset=4050, ""
      SyntaxNode offset=4050, "S"
    SyntaxNode+StringLiteral0 offset=4051, "a":
      SyntaxNode offset=4051, ""
      SyntaxNode offset=4051, "a"
    SyntaxNode+StringLiteral0 offset=4052, "n":
      SyntaxNode offset=4052, ""
      SyntaxNode offset=4052, "n"
    SyntaxNode+StringLiteral0 offset=4053, "s":
      SyntaxNode offset=4053, ""
      SyntaxNode offset=4053, "s"
    SyntaxNode+StringLiteral0 offset=4054, " ":
      SyntaxNode offset=4054, ""
      SyntaxNode offset=4054, " "
    SyntaxNode+StringLiteral0 offset=4055, "S":
      SyntaxNode offset=4055, ""
      SyntaxNode offset=4055, "S"
    SyntaxNode+StringLiteral0 offset=4056, "e":
      SyntaxNode offset=4056, ""
      SyntaxNode offset=4056, "e"
    SyntaxNode+StringLiteral0 offset=4057, "r":
      SyntaxNode offset=4057, ""
      SyntaxNode offset=4057, "r"
    SyntaxNode+StringLiteral0 offset=4058, "i":
      SyntaxNode offset=4058, ""
      SyntaxNode offset=4058, "i"
    SyntaxNode+StringLiteral0 offset=4059, "f":
      SyntaxNode offset=4059, ""
      SyntaxNode offset=4059, "f"
  SyntaxNode offset=4060, "\""

现在我有了这棵树，我不知道如何过滤它，以便只处理匹配特定规则的特定节点。

我想用一个标识符替换字符串文字，该标识符引用字符串文件中的字符串。

---

cool_parser.treetop

rule string_literal
  '"' (!'"' . / '""')* '"'
end

---

require 'treetop'

# Load the grammar
Treetop.load 'cool'

class Parser

  # Create the parser
  @@parser = CoolParser.new

  def self.parse(data)

    # Pass the data over to the parser instance
    tree = @@parser.parse(data)

    if(tree.nil?)
      raise Exception, "Parse error at offset: #{@@parser.index}"
    end

    return tree
  end

end

tree = Parser.parse(File.open("myfile.txt").read)

puts tree.inspect

Answer 1

我不确定您所说的“替换为标识符”是什么意思？但是，这是一个将字符串节点的值作为数组返回的示例。

---

cool_parser.treetop

   rule start
      (not_string_literal / string_literal)*
      {
         def value
            elements.map {|e| e.value }.compact
         end
      }
   end

   rule string_literal
      '"' (!'"' . / '""')* '"'
      {
         def value
            text_value
         end
      }
   end

   rule not_string_literal
      !string_literal .
      {
         def value
         end
      }
   end

---

然后访问解析对象新添加的value方法：

tree = Parser.parse(File.open("myfile.txt").read)

puts tree.value.inspect

# => ["\"strings\"", "\"sentences\""]