Question

Here are the errors我在sbt run的此商家信息[3.5]上运行[1]后收到：

import util.parsing.combinator.JavaTokenParsers

trait ArithParser extends JavaTokenParsers {
    type T
    def expr: Parser[T] = chainl1(term,   "+" ^^^ Add |  "-" ^^^ Sub)
    def term            = chainl1(factor, "*" ^^^ Mul |  "/" ^^^ Div)
    def factor          = floatingPointNumber  ^^ Num | "(" ~> expr <~ ")"

    def Add = (T,T)  => T
    def Sub = (T,T)  => T
    def Mul = (T,T)  => T
    def Div = (T,T)  => T
    def Num = String => T
}

trait DirectEvaluation {
    type T = Double
    val Add = (_: Double) + (_:Double)
    val Sub = (_: Double) - (_:Double)
    val Mul = (_: Double) * (_:Double)
    val Div = (_: Double) / (_:Double)
    val Num = (_: String).toDouble
}

trait ASTBuilding {
    type T = Expr
    sealed abstract class Expr

    case class Add(e1: Expr, e2: Expr) extends Expr
    case class Sub(e1: Expr, e2: Expr) extends Expr
    case class Mul(e1: Expr, e2: Expr) extends Expr
    case class Div(e1: Expr, e2: Expr) extends Expr
    case class Num(e: String) extends Expr
}

object Interpreter extends ArithParser with DirectEvaluation
object Compiler extends ArithParser with ASTBuilding

object Main extends ArithParser {
    def main(args: Array[String]) {
        val defArgs = if (args.isEmpty) Array("10.5 - 4*2") else args
        val parser: ArithParser = if(defArgs.head === "eval") {
                println("Interpreter!"); Interpreter
            } else {
                println("Compiler!"); Compiler
            }
        defArgs.tail foreach {arg =>
            println("Input: " + arg)
            println("Output: " + parseAll(parser.expr, arg))
        }
    }
}

[1] E. Labun, “Combinator Parsing in Scala,” Technische Hochschule Mittelhessen, 2012.

如何修复这些错误？

Answer 1

(T,T) => T是一种类型注释，因此您必须将=替换为:。

def Add: (T,T) => T

这也正如你所提到的论文中的那样。

列表中不存在===，它只是==。

你必须在解析器上调用parseAll：

parser.parseAll(...)

在我看来，您缺少scala编程的基础知识，否则您可以自己轻松修复这些错误。我的建议是，在开始使用高级主题之前，先阅读一本好的scala书，以便对该语言有一个基本的了解。

模板类型在Scala中不起作用？

1 个答案: