如何以编程方式检查在scala解释器内部发生的错误 [英] how to check errors happening inside scala interpreter programatically

问题描述

我正在使用scala.tools.nsc.Interpreter执行Scala代码段 当代码片段正确时，一切都很好，但是当它有错误时，我的代码无法找出并愉快地继续下去.我想获取一个异常或调用方法，以获取解释器上次评估期间发生的任何错误.

I am executing scala code snippets using scala.tools.nsc.Interpreter When the code snippet is correct, everything is fine, but when it is buggy, my code is unable to find out and happily goes on. I would like to get an exception or method to call to get any error that happened during last evaluation by the interpreter.

我的代码:

import scala.tools.nsc.Interpreter
import scala.tools.nsc.Settings
object RuntimeEval {
  def main(args: Array[String]): Unit = {
    var msg = "fail"
    val eval = new RuntimeEval
    msg = eval.eval(msg,"\"success\"")
    println(msg)
    var anInt = 0
    while(true){
    println("Enter an integer")
      val userInput = Console.readLine
      anInt = eval.eval(anInt,userInput)
      println("-->"+anInt)
      println
    }
  }
}
class ResContainer(var value: Any)
class RuntimeEval {
  val settings = new Settings
  settings.classpath.value = System.getProperty("java.class.path")
  val interp = new Interpreter(settings)

  def eval[A <: Any](obj: A, expression: String): A={
    val res = new ResContainer(obj)
    interp.beQuietDuring {
      interp.bind("res", res.getClass.getCanonicalName, res)
      interp.interpret("res.value = "+expression)
    }
    val info = obj match{
      case x: AnyRef => "expected type: \n"+x.getClass.getCanonicalName+"\n"
      case _ => "expected type is not an AnyRef\n"
    }
    res.value match{
      case x: A => x
      case x: AnyRef => error("unexpected result type, "+info+"result type:\n"+x.getClass.getCanonicalName)
      case _ => error("unexpected result type, "+info+"result type is not an AnyRef")
    }
  }
}

问题的示例:

success
Enter an integer
9/12
-->0

Enter an integer
9/0
java.lang.ArithmeticException: / by zero
    at .<init>(<console>:6)
    at .<clinit>(<console>)
    at RequestResult$.<init>(<console>:5)
    at RequestResult$.<clinit>(<console>)
    at RequestResult$scala_repl_result(<console>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at scala.tools.nsc.Interpreter$Request$$anonfun$loadAndRun$1$$anonfun$apply$17.apply(Interpreter.scala:988)
    at scala.tools.nsc.Interpreter$Request$$anonfun$loadAndRun$1$$anonfun$apply$17.apply(Interpreter.scala:988)
    at scala.util.control.Exception$Catch.apply(Exception.scala:79)
    at scala...-->0

Enter an integer
9/4
-->2

Enter an integer

ArithmeticException发生在解释器内部，然后似乎什么也没返回，因此我的代码得到的结果与上一个操作相同，即0. 如何抓住这个?

The ArithmeticException happened inside the interpreter, then it seems it returned nothing, so my code got the same result as previous operation, 0. How to catch this ?

推荐答案

解释器的interpret方法返回结果值，该结果指示代码是否可以成功解释.因此:

The interpret method of the Interpreter returns a result value which indicates if the code could be successfully interpreted or not. Thus:

interp.beQuietDuring {
  interp.bind("res", res.getClass.getCanonicalName, res)
  interp.interpret("res.value = "+expression)
} match {
   case Results.Error => error( ... )
   case Results.Incomplete => error( ... )
   case Results.Success => res.value
}

还有两件事:您不必为每个eval都绑定"res"，一旦初始化解释器就足够了.另外，请注意，有一个方法mostRecentVar，因此您可以完全取消结果绑定.这是Scala 2.9(与2.8相同，但使用IMain代替Interpreter)的示例:

Two more things: You don't need to bind "res" for every eval, it should be sufficient to do that once you initialize the interpreter. Also, note that there is a method mostRecentVar, so you may do away with the result binding altogether. Here is an example for Scala 2.9 (same as 2.8, but instead of Interpreter you use IMain):

import tools.nsc.interpreter.{IMain, Results}
import sys.error
val interp = new IMain()
def eval( expression: String ) : AnyRef =
   interp.interpret( expression ) match {
      case Results.Error => error( "Failed" )
      case Results.Incomplete => error( "Incomplete" )
      case Results.Success => interp.valueOfTerm( interp.mostRecentVar )
        .getOrElse( error( "No result" ))
   }

测试:

scala> val x = eval( "1 + 2" )
res0: Int = 3
x: AnyRef = 3

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