Femto

Femto is an extended version of Atto Emacs with a Tiny Lisp extension languauge

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

Goals of Femto Emacs

• 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).

What does Femto bring to the party of Text Editors

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.

Why the name Femto?

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 languauge

History

• 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 Georg Lehner refactored the Lisp infrastructure.

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

Comparisons with Other Emacs Implementations

Femto has almost the same level of functionality as MicroEmacs 3.10 for a codebase 1/10 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     108408     6.7k     18/31 **
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 files count are the C-files plus the minimal required femto.rc Lisp file. The second number includes all provided Lisp files.

Femto Key Bindings

C-A   begining-of-line
C-B   backward-character
C-D   delete-char
C-E   end-of-line
C-F   forward Character
C-G	  Abort (at prompts)
C-H   backspace
C-I   handle-tab
C-J   newline
C-K   kill-to-eol
C-L   refresh display
C-M   Carrage Return
C-N   next line
C-P   previous line
C-R   search-backwards
C-S	  search-forwards
C-U   Undo
C-V   Page Down
C-W   Kill Region (Cut)
C-X   CTRL-X command prefix
C-Y   Yank (Paste)

M-<   Start of file
M->   End of file
M-v   Page Up
M-f   Forward Word
M-b   Backwards Word
M-g   goto-line
M-r   Search and Replace
M-w   copy-region

C-<spacebar> Set mark at current position.

^X^B  List Buffers
^X^C  Exit. Any unsaved files will require confirmation.
^X^F  Find file; read into a new buffer created from filename.
^X^S  Save current buffer to disk, using the filename associated with the buffer
^X^W  Write current buffer to disk. Type in a new filename at the prompt
^X@   shell-command (prompted for a command which is sent to the shell
^Xi   Insert file at point
^X=   Show Character at position
^X^N  next-buffer
^Xn   next-buffer
^Xk   kill-buffer
^X1   delete-other-windows
^X2   split-window
^Xo   other-window

Home  Beginning-of-line
End   End-of-line
Del   Delete character under cursor
Ins   Toggle Overwrite Mode
Left  Move left
Right Move point right
Up    Move to the previous line
Down  Move to the next line
Backspace delete caharacter on the left
Ctrl+Up      beginning of file
Ctrl+Down    end of file
Ctrk+Left    Page Down
Ctrl+Right   Page Up

Copying and moving

C-<spacebar> Set mark at current position
^W   Delete region
^Y   Yank back kill buffer at cursor
M-w  Copy Region

A region is defined as the area between this mark and the current cursor position. The kill buffer is the text which has been most recently deleted or copied.

Generally, the procedure for copying or moving text is:

1. Mark out region using M- at the beginning and move the cursor to the end.
2. Delete it (with ^W) or copy it (with M-W) into the kill buffer.
3. Move the cursor to the desired location and yank it back (with ^Y).

Searching

C-S or C-R enters the search prompt, where you type the search string
BACKSPACE - will reduce the search string, any other character will extend it
C-S at the search prompt will search forward, will wrap at end of the buffer
C-R at the search prompt will search backwards, will wrap at start of the buffer
ESC will escape from the search prompt and return to the point of the match
C-G abort the search and return to point before the search started

Lisp Interaction

There are two ways to interract with Tiny-Lisp within Femto.

• You can use C-] to find the last s-expression above the cursor and send it to be evaluated.
• You can mark a region and send the whole region to be evaluated with ESC-].

Lisp Interaction - finding and evaluating the last s-expression

This works in almost the same way as GNU Emacs in the scratch buffer.

Lisp Interaction - mark and evaluating a region

Type a lisp function into the editor.

for example:

1: --------------
2: (defun factorial (n)
3:   (cond ((= n 0) 1)
4:     (t (* n (factorial (- n 1))))))
5:--------------

Place the cursor at the beginning of line 1 and set a mark (hit control-spacebar).

Now move the cursot to line 5 and evaluate the block of code (hit escape followed by ])

Femto will pass the code to lisp for it to be evaluated.

<Lambda (n)>

Now call factorial in the same way (mark the start of the code, move to the end of the code and hit escape-])

(factorial 6)

720

Femto Startup

The Femto editor itself provides only basic buffer movement and edit functions, everything else is done by extending the user interface using the Lisp extension language.

The lisp subdirectory contains essential extensions to the Femto editor as well as examples. With make install these are copied to a system wide location, together with the femto.rc file.

When Femto starts it loads the femto.rc file, which in turn loads the extensions with their respective key bindings and then shows a startup message in the scratch buffer.

Just before showing the startup message a user specific femto.rc file is loaded from the directory .config/femto in your HOME directory, if available.

The femto.rc file and the extensions are loaded by default from /usr/local/share/femto. This path is made available in the Lisp interpreter as script_dir. This default directory can be changed at compile time by changing SCRIPTDIR. At startup femto overrides the default with the value of the environment variable FEMTOLIB if set.

Batch Mode

If the environment variable FEMTO_BATCH exists and is not set to 0 batch mode is enabled. In batch mode the GUI is not started up and all Lisp output is sent to stdout.

Debugging

If the environment variable FEMTO_DEBUG exists and is not set to 0 debug mode is enabled. In debug mode, some internal workings are logged to the file debug.out, as well as the arguments of the invocations of the log-debug Lisp primitive.

Basic Femto Extension

femto.rc and femto.lsp extend the Lisp editor and provide basic editor functionality.

• load-script file - load file from script directory.
• edit-config - open user specific configuration file in Femto.
• delete-next-word, delete-previous-word, kill-to-eol - For Emacs like key bindings
• describe-key, find_end_p, find_start_p, find_and_eval_sexp, show-startup-message
• concat args, string.trim.front s, string.trim.back s, string.trim s, shrink s - string operations
• max a b, min a b, repeat n func - Lisp functions
• is_ctl_g k, is_escape k, is_backspace k, is_ctl_s k, is_control_char k - helper functions
• shell-command - backwards compatibility wrapper for system.

Femto Extensions

Additional extensions loaded by femto.rc

• dired - enbles directory editing (Emacs style filemanager)

  • C-x C-d to invoke, then single character keystrokes provide menu options
  • f load file on current line
  • x exit dired (other features to be added)

• grep - enables searching for text in files and loading of the files at the location of the match into the editor.

  • C-x g to invoke, will request a search string and files to search
  • C-x ` to load the next matching file

• bufmenu - the classic Emacs buffer menu

  • C-x C-b to invoke, then single character keystrokes provide menu options
  • 1 loads the file on the current line in one window
  • 2 loads the file on the current line in a split window
  • s saves the file on the current line to disk
  • k unloads the file without saving
  • x exits bufmenu

• git - a simple interface to the git version control tool (similar to GNU Emacs magit).

  • C-x g to invoke, then single character keystrokes menu options

• oxo - a basic implementation of tick-tack-toe that runs in the Editor.

  • C-x C-o to invoke

Lisp Function Interface

The functionality of the embedded Lisp interpreter provides core Lisp functionality, and editor oriented extensions. Both are described in flisp.html or flisp.md respectively.

Building

Documentation

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

Building on Ubuntu (using UTF8 support in ncurse / ncursesw)

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

Future Enhancements

The following enhancements are envisaged.

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

• file-read-hook - function to be called when a file is loaded by the user

• Ability to configure the syntax highlighter to different languages based on file extension Add python triple quoted comments for python

• Buffer Mode flags that can be set to turn off single and double quote matching so that syntax hightlighting does not look messy when looking at a text file

• 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

Known Issues

Goto-line will fail to go to the very last line. This is a special case that could easily be fixed.

Coding Style

See STYLE.MD

Copying

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

References

• [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