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The repl command starts a Scala REPL, which lets you interactively run your code and inspect its results:

scala-cli repl
scala> println("Hello Scala")
Hello Scala

scala> :exit

Scala CLI by default uses the normal Scala REPL.

If you prefer to use the Ammonite REPL, specify --amm to launch it rather than the default REPL:

scala-cli repl --amm
Welcome to the Ammonite Repl 2.4.0-23-76673f7f (Scala 3.0.2 Java 11.0.11)
@ println("Hello ammonite")
Hello ammonite
@ exit

The repl command accepts the same arguments as the compile command. It first compiles any provided sources, and then exposes those results and any provided dependencies to the REPL session:

package mylibrary

object Messages {
def message = "Hello"
def print(): Unit = println(message)
scala-cli repl mylibrary/Messages.scala
Compiling project (Scala 3.0.2, JVM)
Compiled project (Scala 3.0.2, JVM)
scala> import mylibrary._

scala> Messages.print()

scala> :quit