Femto is an extended version of Atto Emacs with a tiny Lisp extension language.

A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. -- Antoine de Saint-Exupery

Femto comes with Markdown and HTML documentation. To rebuild the documentation Pandoc is required. Rebuild both documentation formats from their respective source files by running:

make doc

The documentation is prebuilt in this repository and can be found in

• femto.md (HTML) for Femto
• flisp.md (HTML) for fLisp.

• To be an extendable version of the Atto Emacs editor using a Tiny Lisp extension language
• Provide a number of useful extension packages written in Tiny Lisp (these include an interface to git (similar to GNU Emacs Magit), a small version of dired, a buffer management menu (buffer menu), defmacro allows for a macro to be recorded and invoked using c-x e, and an interface to grep.
• Be easy to understand without extensive study (to encourage further experimentation).

As far as I know Femto is the only Emacs style editor to provide a macro recorder that generates usable Lisp code that can then be used to build a larger, more complex utility. Whilst GNU Emacs has a macro recorder facility it only allows you to dump out the keystrokes used during macro recording. Femto does this by writing the lisp code to a text buffer called macro. Though I have tried dozens of text editors over the years (mostly on PCs, but a few on mini and mainframe computers) I am not aware of any other editor that works this way. This feature was born out of the principle of keeping a small editor code written in C and where possible using Lisp to implement new features. The standard Emacs macro keystrokes [C-x (, C-c ), C-x e] are all written in Lisp in the file examples/defmacro.lsp. This meant that no special C code was needed in Femto to know when it was in macro mode or not.

The small Emacs naming scheme appears to use sub-unit prefixes in decending order with each further reduction of functionality. The Nano and Pico Emacs editors have been around for a while.

• Nano means 10 to the power of minus 9
• Pico means 10 to the power of minus 12
• Femto means 10 to power of minus 15
• Atto means 10 to power of minus 18
• Zepto means 10 to the power of minus 21
• Zep is smaller version of Zepto Emacs

In Defining Atto as the lowest functional Emacs I have had to consider the essential feature set that makes Emacs, 'Emacs'. I have defined this point as a basic Emacs command set and key bindings; the ability to edit multiple files (buffers), and switch between them; edit the buffers in mutliple windows, cut, copy and paste; forward and reverse searching, a replace function and basic syntax hilighting. The proviso being that all this will fit in less than 2000 lines of C.

Femto is an extended version of Atto Emacs with its own extension language.

• In late 2015 Hugh Barney wrote the Atto editor 'A minimum functioning Emacs is less than 2000 lines of C'. Atto was based on Anthony Howe's editor (commonly known as Anthony's Editor or AE, [2]).
• Femto is based on the Atto codebase [0]
• Femto was originally an intermediate project to form a codebase for the FemtoEmacs Editor [8], [9] which was a collaboration between Hugh Barney, Ed Costa and Lucas Guerra. FemtoEmacs uses Jeff Bezanson's Femtolisp LISP [10] implementation as the basis for its extension language. However the Femtolisp codebase is in excess of 12K line of code and fairly difficult to understand how to use it inside an embedded application.
• In late 2016 Hugh Barney decided to look for a smaller lisp implementation for Femto and settled on Tiny-Lisp[7] by Mattias Pirstitz.
• Zepl was an initial project that established the suitability of Tiny-Lisp for use within an Emacs type editor. The results surpassed expectations.
• In late 2017 Hugh Barney decided to return to the Femto editor and extend it using Tiny-Lisp.
• In 2023/24/25 Georg Lehner refactored the Lisp infrastructure and started to add additional Emacs functionality.

For a full version history please refer to the file CHANGE.LOG.md

Femto has almost the same level of functionality as MicroEmacs 3.10 for a codebase about 15% of the size.

Editor         Binary   BinSize     KLOC  Files

atto           atto       33002     1.9k      10
pEmacs         pe         59465     5.7K      16
Esatz-Emacs    ee         59050     5.7K      14
femto          femto     143280  8.2k/5.9k 22/34 **
GNOME          GNOME      55922     9.8k      13
Zile           zile      257360    11.7k      48
Mg             mg        585313    16.5K      50
uEmacs/Pk      em        147546    17.5K      34
Pico           pico      438534    24.0k      29
Nano           nano      192008    24.8K      17
jove           jove      248824    34.7k      94
Qemacs         qe        379968    36.9k      59
ue3.10         uemacs    171664    52.4K      16 ++
GNUEmacs       emacs   14632920   358.0k     186

Since femto 2.12 C code has been moved out to Lisp. The first number in the KLOC column is the line count, the second the sloccount. The first number in the files count are the C-files, the second number includes the required Lisp files.

These instructions should work with most versions of linux

$ cd $HOME
$ mkdir -p ~/src
$ git clone https://github.com/hughbarney/femto.git
$ cd femto
$ sudo make install

When building on Ubuntu you will need to install the libcurses dev package. NOTE: As of Femto 1.2 you will also need the libncursesw (wide) library

$ sudo apt-get install apt-file
$ apt-file update

now search for which package would have curses.h

$ apt-file search curses.h

libncurses5-dev: /usr/include/curses.h

$ sudo apt-get install libncurses5-dev libncursesw5-dev

The following enhancements are envisaged.

• Directory and file manegement (Dired) functionality. A basic start has been made with dired.lsp

• Ability to configure the syntax highlighter for python

• Ability to load a file in read-only-mode

• Ability to setup themes of colors that can be applied to different buffers This will allow users to control their own colour scheme

• Pipe a buffer through a shell command and read the output back into a different buffer

See STYLE.MD

Femto code is released to the public domain. hughbarney@gmail.com November 2017

• [0] Atto Emacs - https://github.com/hughbarney/atto
• [1] Perfect Emacs - https://github.com/hughbarney/pEmacs
• [2] Anthony's Editor - https://github.com/hughbarney/Anthony-s-Editor
• [3] MG - https://github.com/rzalamena/mg
• [4] Jonathan Payne, Buffer-Gap: http://ned.rubyforge.org/doc/buffer-gap.txt
• [5] Anthony Howe, http://ned.rubyforge.org/doc/editor-101.txt
• [6] Anthony Howe, http://ned.rubyforge.org/doc/editor-102.txt
• [7] Tiny-Lisp, https://github.com/matp/tiny-lisp
• [8] FemtoEmacs, https://github.com/FemtoEmacs/Femto-Emacs
• [9] FemtoEmacs, https://github.com/hughbarney/Femto-Emacs
• [10] Femtolisp, https://github.com/JeffBezanson/femtolisp