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Replic

Building a readline application is cool, but readline gives you the basics and you must still build a REPL around it: loop and read commands, catch a C-c, a C-d, ask confirmation to quit, print the general help, the help of a command, setup the completion of commands, the completion of their arguments, load an init file, colorize output,… replic does this for you.

You can use replic as a ready-to-use executable or as a library.

Using the executable, you can define functions and variables in ~/.replic.lisp, give them completion candidates, and use them straight away on the replic command line.

With the library you can automatically build a REPL and turn functions you already have into commands in the readline prompt, with the process described below.

There are a few examples below, in src/examples.lisp and expect more to come.

This is an attempt at generalizing what I did several times with cl-readline.

What this is not:

  • this is not a Lisp REPL. See cl-repl for that (itself not a replacement for Slime ;) )
  • this is not a shell. See shcl.

Example applications built on replic:

Installation

You can download the executable (a 14MB zipped download, a 60Mo GNU/Linux x64 self-contained binary, instant start-up !), make it executable (chmod +x replic) and run it: ./replic,

or build it yourself.

  • the library is on Quicklisp (since the 2019-01-07 dist) and on Ultralisp:
(ql:quickload :replic)

or clone this repo into ~/quicklisp/local-projects/,

then build the executable with make build.

__Note__: you need the cl-readline library from Quicklisp of end of may, 2018 (for the read and write history feature). See make install for a quick clone.

Run it:

replic -h
./replic

and see the available commands:

replic > help
replic > help help

Now add commands in your lisp init file (see next section) or build an application with it (see the Developer section).

User: the executable and the init file

Given the example ~/.replic.lisp below, you can try hello <name> (completion for hello) and goodbye <name>, where <name> can be completed from what was given to hello.

(in-package :replic.user)

(defparameter *names* '()
  "List of names (string) given to `hello`. Will be autocompleted by `goodbye`.")

(defun hello (name)
  "Takes only one argument. Adds the given name to the global
  `*names*` variable, used to complete arguments of `goodbye`.
  "
  (format t "hello ~a~&" name)
  (push name *names*))

(defun goodbye (name)
  "Says goodbye to name, where `name` should be completed from what was given to `hello`."
  (format t "goodbye ~a~&" name))

(replic.completion:add-completion "goodbye" (lambda () *names*))

(export '(hello goodbye))

Note that only the export‘ed functions and parameters will be taken into account.

See more examples in the src/examples.lisp file of this repository.

Define custom completion for arguments

Write a function or a variable and export it.

You can associate a function name with a list of completion candidates (a list of strings) or a function:

(replic.completion:add-completion "goodbye" (lambda () *names*))

When you have many functions that should complete from the same list, you can set a default completion function:

(setf replic.completion:*default-command-completion* #'my-function)

Built-in commands

You get a built-in help command that shows the documentation of functions and variables:

replic > help

Available commands
==================
help       ... Print the help of all available commands.
reload     ... NIL
set        ... Change a variable, see its value, or see all variables.
quit       --- Quit the application.

Available variables
===================
*verbose*  ... If true, print debugging information during the program execution.

Write a preamble and a postamble in *help-preamble* and *help-postamble*.

You can read the help of a specific command or variable (with completion):

help help

The general help shows the first paragraph of the functions/parameters docstring, the help <cmd> function is more complete and shows all of it.

Setting and seeing variables

set can be used with zero, one or two arguments:

set

shows all available variables,

set *variable*

this prints the value of this variable (use auto-completion),

set *variable* new-value

and this sets a new value. “yes”, “true” and “t” denote true.

We kept the “earmuffs” to denote variables.

Configuration file

Replic reads an init-like configuration file. It searches a .replic.conf file under ~/.config/ and at the user’s home directory (~/.replic.conf).

These are the default parameters with their default values:

[default]
confirm-exit = true
verbose = false
prompt = > 
history = true
write-history = true

“true”, “True” and “t” are truthy and “false”, “False” and “nil” are falsy.

It must begin with a section name (default) (we don’t handle different profiles yet).

They are overriden by command line arguments.

Developer: using replic as a library with an existing system

replic is in Quicklisp (2019-01-07):

(ql:quickload :replic)

Change the prompt

You can change the prompt. It defaults to “> “. It can contain ansi colours.

(setf replic:*prompt* (cl-ansi-text:green "replic > "))

You can add a prefix to it, for example one that changes with the state of the application (current directory,…):

(setf replic:*prompt-prefix* (format t "(~a) " "sthg"))

and concatenate the two with (replic:prompt).

Load base commands (help, reload, set)

If you want to have the base commands (help, reload, set, quit), import the base package:

(replic.completion:functions-to-commands :replic.base)

Create commands from a package’s exported functions

Create the commands from all the exported functions and variables:

(replic.completion:functions-to-commands :my-package)

To exclude functions, use the :exclude list:

(replic.completion:functions-to-commands :my-package :exclude '("main"))

Create a command from one function:

(replic.completion:add-command :function :package)
;; add a variable:
(replic.completion:add-variable :*variable* :package)

Load a config file

replic searches by default for a .replic.conf (see above). The function replic.config:apply-config takes as first parameter a package name (as a symbol):

(replic.config:apply-config :replic)

and as an optional second parameter, you can give another file name:

(replic.config:apply-config :torrents ".torrents.conf")

The exported variables from the package can then be overriden in the config file. For example, the :replic package exports

(:export :main
         :confirm
         :repl
         :help
         :set
         :reload
         ;; settings
         :*help-preamble*
         :*help-postamble*
         :*prompt*
         :*prompt-prefix*
         :*confirm-exit*
         :*write-history*
         :*verbose*))

so we can configure:

[default]
write-history = true
verbose = true
prompt = my silly prompt

and so on.

Note: for now, we look only at the “default” section.

Start the repl

Start the repl:

(replic:repl)

That’s it. You didn’t have to write the REPL.

Settings

Variables that are exported from a package on the lisp side will be automacitally available for the config file and read when the application starts up. The rule is that in the config file, we don’t use earmuffs (*foo* -> foo). Lispers shall use a lispy config file anyway.

The available variables are:

  • *verbose* (bool): if true, print debugging information during the program execution.
  • *confirm-exit* (bool): if true (the default), ask for confirmation when a user tries to exit the program with a C-d (EOF).
  • *prompt* (str): the readline prompt. Defaults to simply . Can contain ansi colours (use cl-ansi-text:green for example).
  • *confirm-exit* (t or nil): if t (the default), ask for confirmation when the user tries to exit the command line with a C-d (EOF).
  • *write-history* (t or nil): if t (the default), write the commands to the app’s history. (this needs cl-readline superior to may, 2018)
  • *help-preamble*: text to display at the beginning of the help.
  • *help-postamble*: text to display last.

Other helpers

  • print colored output from markdown or code with pygments: (format-markdown txt :lang "md"). It outputs text for a console display with ansi colours. Needs pygments, or does nothing.

Readline settings

The GNU Readline library provides settings you might take advantage of. We can set the settings in the readline init file (~/.inputrc by default, obeys the INPUTRC environment variable).

For example, you can change the completion behavior. This:

TAB: menu-complete

inserts the first completion candidate, even if there are many, instead of showing the list of choices under the prompt.

If you prefer vi mode:

set editing-mode vi

etc. See readline’s documentation.

Dev

This is a generalization on cl-readline. See also the simple cl-readline example. Once you’ve built two even basic readline apps you’ll want to factorize the common parts.

We want to store a list of commands (functions, “verbs”) and a list of variables (the ones to use with “set”). We want to read them from any Lisp file, hence we need to remember the package they come from. This mechanism is provided through an interface in completion.lisp.

Clone this repo in QL’s local projects (~/quicklisp/local-projects).

Build the executable:

make build

Develop and test interactively into the console

By starting a swank server in the (real) Lisp repl we can compile code in our editor and try instantly in the terminal, without re-building the executable. See this cl-charms crash course for now. Some details need fixing.

Resources

Learning:

Getting started:

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