使用Scala解析器组合器解析方案

发布时间：2020-12-16 10:01:32 所属栏目：安全来源：网络整理

导读：我正在 Scala中编写一个小型的解释器,我在解析Scheme中的列表时遇到了问题.我的代码解析包含多个数字,标识符和布尔值的列表,但如果我尝试解析包含多个字符串或列表的列表,它会发生窒息.我错过了什么？这是我的解析器： class SchemeParsers extends RegexPa

我正在 Scala中编写一个小型的解释器,我在解析Scheme中的列表时遇到了问题.我的代码解析包含多个数字,标识符和布尔值的列表,但如果我尝试解析包含多个字符串或列表的列表,它会发生窒息.我错过了什么？

这是我的解析器：

class SchemeParsers extends RegexParsers {

// Scheme boolean #t and #f translate to Scala's true and false
def bool : Parser[Boolean] = 
    ("#t" | "#f") ^^ {case "#t" => true; case "#f" => false}

// A Scheme identifier allows alphanumeric chars,some symbols,and 
// can't start with a digit
def id : Parser[String] = 
    """[a-zA-Z=*+/<>!?][a-zA-Z0-9=*+/<>!?]*""".r ^^ {case s => s}

// This interpreter only accepts numbers as integers
def num : Parser[Int] = """-?d+""".r ^^ {case s => s toInt}

// A string can have any character except ",and is wrapped in "
def str : Parser[String] = '"' ~> """[^""]*""".r <~ '"' ^^ {case s => s}

// A Scheme list is a series of expressions wrapped in ()
def list : Parser[List[Any]] = 
    '(' ~> rep(expr) <~ ')' ^^ {s: List[Any] => s}

// A Scheme expression contains any of the other constructions
def expr : Parser[Any] = id | str | num | bool | list ^^ {case s => s}
}

解决方法

正如@Gabe正确指出的那样,你留下了一些未处理的白色空间：

scala> object SchemeParsers extends RegexParsers {
     |
     | private def space  = regex("[ n]*".r)
     |
     | // Scheme boolean #t and #f translate to Scala's true and false
     | private def bool : Parser[Boolean] =
     |     ("#t" | "#f") ^^ {case "#t" => true; case "#f" => false}
     |
     | // A Scheme identifier allows alphanumeric chars,and
     | // can't start with a digit
     | private def id : Parser[String] =
     |     """[a-zA-Z=*+/<>!?][a-zA-Z0-9=*+/<>!?]*""".r
     |
     | // This interpreter only accepts numbers as integers
     | private def num : Parser[Int] = """-?d+""".r ^^ {case s => s toInt}
     |
     | // A string can have any character except ",and is wrapped in "
     | private def str : Parser[String] = '"' ~> """[^""]*""".r <~ '"' <~ space ^^ {case s => s}
     |
     | // A Scheme list is a series of expressions wrapped in ()
     | private def list : Parser[List[Any]] =
     |     '(' ~> space  ~> rep(expr) <~ ')' <~ space ^^ {s: List[Any] => s}
     |
     | // A Scheme expression contains any of the other constructions
     | private def expr : Parser[Any] = id | str | num | bool | list ^^ {case s => s}
     |
     | def parseExpr(str: String) = parse(expr,str)
     | }
defined module SchemeParsers   

scala> SchemeParsers.parseExpr("""(("a" "b") ("a" "b"))""")
res12: SchemeParsers.ParseResult[Any] = [1.22] parsed: List(List(a,b),List(a,b))

scala> SchemeParsers.parseExpr("""("a" "b" "c")""")
res13: SchemeParsers.ParseResult[Any] = [1.14] parsed: List(a,b,c)

scala> SchemeParsers.parseExpr("""((1) (1 2) (1 2 3))""")
res14: SchemeParsers.ParseResult[Any] = [1.20] parsed: List(List(1),List(1,2),2,3))

（编辑：李大同）

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