Question says it all.
(Yet, the details of how to get access to the shift and reset operations has changed over the years. Old blog entries and Stack Overflow answers may have out of date information.)
See also What are Scala continuations and why use them? which talks about what you might want to do with shift and reset once you have them.
Scala 2.12 or 2.11
The easiest way is to use sbt. Here's what to put in your build.sbt:
scalaVersion := "2.12.2"
addCompilerPlugin(
"org.scala-lang.plugins" % "scala-continuations-plugin" % "1.0.3"
cross CrossVersion.patch)
libraryDependencies +=
"org.scala-lang.plugins" %% "scala-continuations-library" % "1.0.3"
scalacOptions += "-P:continuations:enable"
In your code (or the REPL), do import scala.util.continuations._
You can now use shift and reset to your heart's content.
Note that I used a Scala version of 2.12.2 because that's the last version the plugin was published for. If you want to use a newer 2.12.x version, you'd need to build the plugin yourself from source. If you use 2.12.2, you'll probably need to be on Java 8, since according to https://docs.scala-lang.org/overviews/jdk-compatibility/overview.html Java 11 support didn't land until 2.12.4.
historical information for Scala 2.8, 2.9, 2.10
You have to start scala (or scalac) with the -P:continuations:enable flag.
In your code, do import scala.util.continuations._
You can now use shift and reset to your heart's content.
If you're using sbt 0.7, see https://groups.google.com/forum/#!topic/simple-build-tool/Uj-7zl9n3f4
If you're using sbt 0.11+, see https://gist.github.com/1302944
If you're using maven, see http://scala-programming-language.1934581.n4.nabble.com/scala-using-continuations-plugin-with-2-8-0-RC1-and-maven-td2065949.html#a2065949