我有一个弦
input = "maybe (this is | that was) some ((nice | ugly) (day |night) | (strange (weather | time)))"
Ruby中解析此字符串的最佳方法是什么?我的意思是脚本应该能够像这样构建哨兵:
依此类推,您明白了……
我应该按char读取字符串char并用堆栈堆叠一个状态机来存储括号值以供以后计算,还是有更好的方法?
也许已经为此准备好了一个现成的库?
最佳答案
尝试 Treetop 。它是一种类似于Ruby的DSL,用于描述语法。解析给定的字符串应该很容易,并且通过使用真正的解析器,您以后可以轻松扩展语法。
您要解析的字符串类型的示例语法(另存为sentences.treetop
):
grammar Sentences
rule sentence
# A sentence is a combination of one or more expressions.
expression* <Sentence>
end
rule expression
# An expression is either a literal or a parenthesised expression.
parenthesised / literal
end
rule parenthesised
# A parenthesised expression contains one or more sentences.
"(" (multiple / sentence) ")" <Parenthesised>
end
rule multiple
# Multiple sentences are delimited by a pipe.
sentence "|" (multiple / sentence) <Multiple>
end
rule literal
# A literal string contains of word characters (a-z) and/or spaces.
# Expand the character class to allow other characters too.
[a-zA-Z ]+ <Literal>
end
end
上面的语法需要一个附带的文件,该文件定义了允许我们访问节点值的类(另存为
sentence_nodes.rb
)。class Sentence < Treetop::Runtime::SyntaxNode
def combine(a, b)
return b if a.empty?
a.inject([]) do |values, val_a|
values + b.collect { |val_b| val_a + val_b }
end
end
def values
elements.inject([]) do |values, element|
combine(values, element.values)
end
end
end
class Parenthesised < Treetop::Runtime::SyntaxNode
def values
elements[1].values
end
end
class Multiple < Treetop::Runtime::SyntaxNode
def values
elements[0].values + elements[2].values
end
end
class Literal < Treetop::Runtime::SyntaxNode
def values
[text_value]
end
end
下面的示例程序显示,解析给出的例句非常简单。
require "rubygems"
require "treetop"
require "sentence_nodes"
str = 'maybe (this is|that was) some' +
' ((nice|ugly) (day|night)|(strange (weather|time)))'
Treetop.load "sentences"
if sentence = SentencesParser.new.parse(str)
puts sentence.values
else
puts "Parse error"
end
该程序的输出为:
maybe this is some nice day
maybe this is some nice night
maybe this is some ugly day
maybe this is some ugly night
maybe this is some strange weather
maybe this is some strange time
maybe that was some nice day
maybe that was some nice night
maybe that was some ugly day
maybe that was some ugly night
maybe that was some strange weather
maybe that was some strange time
您还可以访问语法树:
p sentence
The output is here。
在那里,您可以找到:一种可伸缩的解析解决方案,该解决方案应该非常接近您要在50行代码中执行的操作。有帮助吗?