Embedded Scala REPL Interpreter example for 2.10

问题

Please give a code example of how to create an embedded Scala REPL interpreter programmatically, that works in Scala 2.10. (I added this Q&A after spending hours combing various code scraps to get a working interpreter)

回答1:

Example Repl.scala:

import scala.tools.nsc.interpreter._
import scala.tools.nsc.Settings


object Repl extends App {
  def repl = new ILoop {
    override def loop(): Unit = {
      intp.bind("e", "Double", 2.71828)
      super.loop()
    }
  }

  val settings = new Settings
  settings.Yreplsync.value = true


  //use when launching normally outside SBT
  settings.usejavacp.value = true      

  //an alternative to 'usejavacp' setting, when launching from within SBT
  //settings.embeddedDefaults[Repl.type]

  repl.process(settings)
}

Some notes

I choose to show the JLineReader (default) rather than SimpleReader because it works much better, correctly handling arrow keys, delete etc. JLine does add an jar dependency.
The example shows how to bind values into the repl (variable e above).
When I omit settings.Yreplsync.value = true, the REPL hangs and is useless.
From my testing, if both usejavacp and embeddedDefaults settings are combined together, an error results

I find this easiest to test via SBT; a sample build.sbt:

name := "Repl"

organization := "ExamplesRUs"

scalaVersion := "2.10.2"

libraryDependencies ++= Seq(
 "org.scala-lang" % "scala-compiler" % "2.10.2",
 "org.scala-lang" % "jline" % "2.10.2"
)

Sample SBT session:

> run-main Repl
[info] Running Repl
Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_37).
Type in expressions to have them evaluated.
Type :help for more information.
e: Double = 2.71828

scala> 2 * e
res1: Double = 5.43656

scala>

回答2:

Based on Ben's excellent answer, below is a helper class to ease starting the interpreter. Usage:

Repl.run(("e", "Double", 2.71828), ("pi", "Double", 3.1415))

It automatically detects when you're running from SBT and accommodates.

Repl.scala:

import scala.tools.nsc.interpreter.ILoop
import scala.tools.nsc.Settings
import java.io.CharArrayWriter
import java.io.PrintWriter

object Repl {

  def run(params: (String, String, Any)*) {

    def repl = new ILoop {
      override def loop(): Unit = {
        params.foreach(p => intp.bind(p._1, p._2, p._3))
        super.loop()
      }
    }

    val settings = new Settings
    settings.Yreplsync.value = true

    // Different settings needed when running from SBT or normally
    if (isRunFromSBT) {
      settings.embeddedDefaults[Repl.type]
    } else {
      settings.usejavacp.value = true
    }

    repl.process(settings)
  }

  def isRunFromSBT = {
    val c = new CharArrayWriter()
    new Exception().printStackTrace(new PrintWriter(c))
    c.toString().contains("at sbt.")
  }

}

来源：https://stackoverflow.com/questions/18628516/embedded-scala-repl-interpreter-example-for-2-10

标签

scala

read-eval-print-loop