Question

我在这里看到了其他一些相关的SO帖子，这表明使用特质进行继承是解决此问题的唯一方法，但是我看不到如何使用它。

我正在编写一个汇编器，该汇编器的指令使您可以更改处理器的模型，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。（针对不同的处理器型号，将会有更多）。当解析“ cpu”指令时，它将选择适当的指令解析器。这是一个非常简略的插图：

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 https://stackoverflow.com/questions/2650254/scala-how-to-combine-parser-combinators-from-different-objects
        // I can't see how to apply the solution from https://stackoverflow.com/questions/40166258/reuse-parser-within-another-parser-with-scala-parser-combinators
        // Is it possible to convert an 'ip.Parser[Statement]' into a 'KeywordParser.this.Parser[Statement]' ?
    }
}

directOpcode和指令都返回Parser [Statement]，为什么我不能这样组合它们？自我类型注释可以在这里提供帮助吗？在此先感谢您可以提供的任何帮助...（或显示其他引用的SO帖子中发布的解决方案可能有帮助的插图。

Answer 1

从这个问题来看，为什么您“不能使用特征”并不清楚。至少您的具体示例确实适用于特征：

// 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 
        }
    }
}

在运行时组成Scala解析器组合器

1 个答案: