Femto

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

Femto screenshot

Femto screenshot

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

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.

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.

History

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 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     141456  9.3k/6.6k 22/33 **
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.

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-T   transpose-chars
C-U   Undo
C-V   Page Down
C-W   Kill Region (Cut)
C-X   CTRL-X command prefix
C-Y   Yank (Paste)
C-Z   suspend

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.

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 screenshot

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.

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 implements a simple library loader and handles batch mode. It provides the 'core' functionality.

Standard Lisp function:

Lisp library functions:

flisp.lsp complements commonly known standard lisp functions:

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

startup.lsp loads extensions, creates key bindings for them, shows the startup message, loads the user specified configuration file and processes the command line arguments. ~/.config/femto/femto.rc. It defines the following functions:

Femto Extensions

Additional extensions loaded by femto.rc

Femto screenshot

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.

Known Issues

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

Adding a line at the bottom of a window will hide the line until the cursor moves up and down again or the screen is refreshed.

Coding Style

See STYLE.MD

Copying

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

References