在运行时组合 Scala 解析器组合器

Question

我在这里看到了其他几个相关的 SO 帖子，建议使用特征继承是解决这个问题的唯一方法，但我在这里看不到如何使用它。

我正在编写一个汇编器，它有一个允许您更改处理器模型的指令，从而影响可解析的操作码集。我有两个解析器类，一个处理所有指令关键字，一个处理指令。（对于不同的处理器型号，会有更多）。当 'cpu' 指令被解析时，它会选择合适的指令解析器。这是一个非常简化的插图：

import scala.util.parsing.combinator.JavaTokenParsers

class ComposingParser {

    sealed abstract class Statement {
    }
    case class Dinst(value: String) extends Statement
    case class Keyword(value: String) extends Statement

    class InstructionParser extends JavaTokenParsers {
        def directOpcode: Parser[Statement] = j | ldlp | pfix

        private def j: Parser[Dinst]     = """(?i)J""".r     ^^ ( x => Dinst(x.toUpperCase) )
        private def ldlp: Parser[Dinst]  = """(?i)LDLP""".r  ^^ ( x => Dinst(x.toUpperCase) )
        private def pfix: Parser[Dinst]  = """(?i)PFIX""".r  ^^ ( x => Dinst(x.toUpperCase) )
    }

    class KeywordParser extends JavaTokenParsers {
        def program: Parser[Statement] = keys | instruction // the main, top-level parser

        def keys: Parser[Keyword] = start | end

        private def start: Parser[Keyword]  = """(?i)START""".r  ^^ ( x => Keyword(x.toUpperCase) )
        private def end: Parser[Keyword]  = """(?i)END""".r  ^^ ( x => Keyword(x.toUpperCase) )

        private def instruction: Parser[Statement] = {
            val ip = new InstructionParser // will be dynamically instantiating different parsers for different instruction sets so can't use traits
            ip.directOpcode
            // Error:(46, 16) type mismatch;
            // found   : ip.Parser[ComposingParser.this.Statement]
            // required: KeywordParser.this.Parser[ComposingParser.this.Statement]
            // ip.directOpcode
        }
        // I can't use traits as in 
        // I can't see how to apply the solution from 
        // Is it possible to convert an 'ip.Parser[Statement]' into a 'KeywordParser.this.Parser[Statement]' ?
    }
}

directOpcode 和 instruction 都是 returnParser[Statement]，为什么我不能这样组合它们？自类型注释可以帮助解决这个问题吗？提前感谢您提供的任何帮助...（或显示引用的其他 SO 帖子中发布的解决方案如何提供帮助的插图）。

Answer 1

从问题来看，您 "cannot use traits" 的原因并不明显。至少您的具体示例确实可以很好地处理特征：

// uses `$ivy`-imports, either run with Ammonite, or remove the import and
// compile using SBT.
import $ivy.`org.scala-lang.modules:scala-parser-combinators_2.12:1.1.1`
import scala.util.parsing.combinator.JavaTokenParsers

class ComposingParser {

    sealed abstract class Statement {
    }
    case class Dinst(value: String) extends Statement
    case class Keyword(value: String) extends Statement

    trait InstructionParser extends JavaTokenParsers {
        def directOpcode: Parser[Statement] = j | ldlp | pfix

        private def j: Parser[Dinst]     = """(?i)J""".r     ^^ ( x => Dinst(x.toUpperCase) )
        private def ldlp: Parser[Dinst]  = """(?i)LDLP""".r  ^^ ( x => Dinst(x.toUpperCase) )
        private def pfix: Parser[Dinst]  = """(?i)PFIX""".r  ^^ ( x => Dinst(x.toUpperCase) )
    }

    trait InstructionParser2 extends JavaTokenParsers {
        def directOpcode2: Parser[Statement] = j | ldlp | pfix

        private def j: Parser[Dinst]     = """(?i)J""".r     ^^ ( x => Dinst(x.toUpperCase) )
        private def ldlp: Parser[Dinst]  = """(?i)LDLP""".r  ^^ ( x => Dinst(x.toUpperCase) )
        private def pfix: Parser[Dinst]  = """(?i)PFIX""".r  ^^ ( x => Dinst(x.toUpperCase) )
    }

    class KeywordParser extends JavaTokenParsers 
    with InstructionParser 
    with InstructionParser2 {
        def program: Parser[Statement] = keys | instruction // the main, top-level parser

        def keys: Parser[Keyword] = start | end

        private def start: Parser[Keyword]  = """(?i)START""".r  ^^ ( x => Keyword(x.toUpperCase) )
        private def end: Parser[Keyword]  = """(?i)END""".r  ^^ ( x => Keyword(x.toUpperCase) )

        private def instruction: Parser[Statement] = {
            if (math.random < 0.5) directOpcode else directOpcode2 
        }
    }
}

在运行时组合 Scala 解析器组合器

Composing scala parser combinators at runtime

scala

types

inner-classes

parser-combinators