Jactl-Repl

The Jactl-Repl project is a command line shell for the Jactl scripting language. It provides a Read-Evaluate-Print-Loop execution shell for testing simple Jactl scripts, using the excellent JLine for command line editing and history.

Download

You can download the Jactl REPL jar file from Maven Central using this link: https://repo1.maven.org/maven2/io/jactl/jactl-repl/2.2.0/jactl-repl-2.2.0.jar

Since it is built as a "fat" jar it can be run standalone (see Running section below).

Building

Requirements

• Java 8+
• JLine 3.21.0
• Jactl 2.2.0
• Gradle 8.0.2

Build

Download a zip file of the source from GitHub or use git to clone the repository:

git clone https://github.com/jaccomoc/jactl-repl.git
cd jactl-repl
./gradlew build

That will build jactl-repl-${VERSION}.jar under the build/libs directory where ${VERSION} is the current version or the version of the tag/branch you are using.

Running

To run the REPL:

java -jar jactl-repl-${VERSION}.jar

This will present a single > prompt where you can enter Jactl code that will be compiled, executed, and the result printed out. If the code looks like it continues on a subsequent line, the REPL will output two spaces and wait for the additional code to be entered.

For example:

$ java -jar jactl-repl-${VERSION}.jar
> def isPrime(n) { n > 1 && !n.sqrt().filter{ it > 0 && n % (it+1) == 0 } }
Function@1864869682
> def primes = 100.map{ it + 1 }.filter(isPrime)
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]
> primes.map{
    def fib(n) { n <= 2 ? 1 : fib(n - 1) + fib(n - 2) }
    fib(it)
  }.limit(10)
[1, 2, 5, 13, 89, 233, 1597, 4181, 28657, 514229]
>

You can use the up and down arrows on the keyboard to cycle through previous commands and the left and right arrows to navigate within a recent command if you want to change anything.

Other keybindings map to common keybindings used by shells such as bash or zsh when in emacs mode.

The main ones to remember:

Key Binding	Description
<up-arrow> <ctrl-P>	Previous input line
<down-arrow> <ctrl-N>	Next input line
<left-arrow> <ctrl-B>	Previous character
<right-arrrow> <ctrl-F>	Next character
<ctrl-A>	Beginning of line
<ctrl-E>	End of line
<ctrl-R>	Search backwards for previous matching input line (incremental search based on characters entered after the <ctrl-R>). Once searching has started <ctrl-R> will continue searching for the previous matching entry to the one being displayed.
<ctrl-L>	Clear the screen
<ctrl-U>	Discard characters currently typed on the line

Commands

As well as entering Jactl code at the prompt, the REPL understands a limit set of commands that all start with :. For example, :h or :? will print out the help text listing the commands available:

$ java -jar build/libs/jactl-repl-${VERSION}.jar
> :h

Available commands:
  :h       Help - print this text
  :?       Alias for :h
  :x       Exit
  :q       Quit - alias for :x
  :c       Clear current buffer
  :r file  Read and execute contents of file
  :l       Load - alias for :r
  :s       Show variables and their values (concise form)
  :S       Show variables and their values in pretty printed form
  :p       Purge variables
  :e arg   Enable/disable stack traces for errors (true - enable, false - disable)
  :d level Enable/disable debug output for errors (0 - off, 1 - on, 2 - more detail)
  :H [n]   Show recent history (last n entries - defaults to 50)
  :! n     Recall history entry with given number

>

These are the commands:

Command	Description
:h :?	Print help text.
:x :q	Exit.
:c	In the middle of a multi-line statement this will clear the buffer and allow you to start again.
:r file :l file	Read/load a Jactl script file and compile and run it. Tab completion is availabe for the file name.
:s	Show all top level variables and their values.
:S	Show all top level variables and pretty print their values
:p	Purge (delete) all variables.
:e arg	Enable/disable stack traces for errors (true - enable, false - disable)
:d level	Enable/disable debug output (0 - disable, 1 - enable, 2 - more detail)
:H n	Show recent history (default 50 entries). If a value for n is given then that many entries will be shown.
:! n	Recall history entry n and evaluate it.

History File

The command line history is persisted in a file called .jactl_history in your home directory. A maximum of 10000 lines is kept.

.jactlrc File

At start up time the contents of ~/.jactlrc are read. This file, if it exists, is itself a Jactl script and allows you to customise the behaviour of the Jactl REPL by setting the values of some global variables. This file is also used when running Jactl scripts from the command line and is documented in the Jactl project documentation here: .jactl File.