The Scala REPL

Lesson Notes

Introduction: Based on Chapter 8 of Learn Scala 3 The Fast Way! (Book 1: The Adventure Begins)

• REPL acronym (read/evaluate/print/loop)

How to start

It’s currently April, 2023, and this will change at some point:

$ scala-cli repl

• I start the REPL with a classpath

  • clear function
  • help function

Create variables and expressions

• val is the keyword to create an immutable variable
• types: Int, String, Char, Boolean, Double

• res0, res1, etc.

Scala is both an FP and OOP language

• type -1
  • instance of Int type
  • .[tab]
  • has all these methods
• type "foo".tab
  • has 254 methods
  • type .to then tab (tab completion)

Create and use functions

def double(i: Int): Int = i * 2
val a = 1
val res = double(a)

REPL commands

• :reset
• :help

• Quitting

  • :quit
  • ^d

Show Scastie as an online REPL

Ammonite repl

• double function output is different
• -1.tab output is different

$ scala-cli --power repl --amm

Summary

• Showed how to start REPL
• How to create variables
• res0, etc. (creates own variables)
• Tab completion
• :quit, ctrl-d