我试图匹配这个语法:
pgm ::= exprs
exprs ::= expr [; exprs]
expr ::= ID | expr . [0-9]+
我的 scala packrat 解析器组合器如下所示:
import scala.util.parsing.combinator.PackratParsers
import scala.util.parsing.combinator.syntactical._
object Dotter extends StandardTokenParsers with PackratParsers {
lexical.delimiters ++= List(".",";")
def pgm = repsep(expr,";")
def expr :Parser[Any]= ident | expr~"."~num
def num = numericLit
def parse(input: String) =
phrase(pgm)(new PackratReader(new lexical.Scanner(input))) match {
case Success(result, _) => println("Success!"); Some(result)
case n @ _ => println(n);println("bla"); None
}
def main(args: Array[String]) {
val prg = "x.1.2.3;" +
"y.4.1.1;" +
"z;" +
"n.1.10.30"
parse(prg);
}
}
但这不起作用。要么它“匹配贪婪”并告诉我:
[1.2] failure: end of input expected
x.1.2.3;y.4.1.1;z;n.1.10.30
或者如果我将其更改|
为 a|||
我会得到一个 stackoverflow:
Exception in thread "main" java.lang.StackOverflowError
at java.lang.Character.isLetter(Unknown Source)
at java.lang.Character.isLetter(Unknown Source)
at scala.util.parsing.combinator.lexical.Lexical$$anonfun$letter$1.apply(Lexical.scala:32)
at scala.util.parsing.combinator.lexical.Lexical$$anonfun$letter$1.apply(Lexical.scala:32)
...
我有点理解为什么会出现错误;我能做些什么来解析像上面这样的语法?对我来说似乎并不深奥
编辑:基于http://scala-programming-language.1934581.n4.nabble.com/Packrat-parser-guidance-td1956908.html中引用的论文, 我发现我的程序实际上并没有使用新的 packrat 解析器。
IE。更改Parser[Any]
为PackratParser[Any]
并使用lazy val
而不是def
我将上面的内容重写为:
import scala.util.parsing.combinator.PackratParsers
import scala.util.parsing.combinator.syntactical._
object Dotter extends StandardTokenParsers with PackratParsers {
lexical.delimiters ++= List(".",";")
lazy val pgm : PackratParser[Any] = repsep(expr,";")
lazy val expr :PackratParser[Any]= expr~"."~num | ident
lazy val num = numericLit
def parse(input: String) =
phrase(pgm)(new PackratReader(new lexical.Scanner(input))) match {
case Success(result, _) => println("Success!"); Some(result)
case n @ _ => println(n);println("bla"); None
}
def main(args: Array[String]) {
val prg = "x.1.2.3 ;" +
"y.4.1.1;" +
"z;" +
"n.1.10.30"
parse(prg);
}
}