kakoune/doc/design.asciidoc

Kakoune design
==============

This document describes the design goals for Kakoune, including rationales.

Interactivity
-------------

Unlike Vim, Kakoune does not have an underlying line-oriented editor, and
is always expected to be used in an interactive (i.e. with the edited text
being displayed in real time) fashion. That should not prevent Kakoune from
being used non interactively (executing macro for example), but priority
should be given to ease of interactive use.

Limited scope
-------------

Kakoune is a code editor. It is not an IDE, not a file browser, not a word
processor and not a window manager. It should be very efficient at editing code,
and should, as a side effect, be very efficient at editing text in general.

Composability
-------------

Being limited in scope to code edition should not isolate Kakoune from its
environment. On the contrary, Kakoune is expected to run on a Unix-like
system, along with a lot of text-based tools, and should make it easy to
interact with these tools.

For example, sorting lines should be done using the Unix sort command, not
with an internal implementation. Kakoune should make it easy to do that,
hence the +|+ command for piping selected text through a filter.

The modern Unix environment is not limited to text filters, most people use
a graphical interface nowadays, and Kakoune should be able to take advantage
of that, without hindering text mode support. For example Kakoune supports
multiple clients on the same editing session, so that multiple windows can
be used, letting the system window manager handle its responsibilities such
as tiling or tabbing.

Orthogonality
-------------

Kakoune features should be as orthogonal as possible, for example, in Vim,
there are multiple ways for modifying the buffer: Through normal/insert
mode, command mode, and Vim scripts. In Kakoune, modifying the buffer is the
normal/insert mode job.

That means there should be clear separation of concerns between modes:

 * normal mode is for manipulating the selection and the selection contents.

 * insert mode is for interactive insertion into the buffer.

 * command mode is for non-editing features (opening a file, setting
   options...).

Orthogonality is an ideal, and should not prevent common sense pragmatism,
the +gf+ and +ga+ commands are not strictly selection manipulation ones,
but fit nicely with other +goto+ commands, and hence are acceptable in
normal mode even though they could arguably be moved to command mode.

Modes should be orthogonal, and commands in modes should be as well. For
example, Vim uses +d+ and +x+ for very similar things: deleting text. In
Kakoune only +d+ exists, and the design ensures that +x+ is not needed.

Speed
-----

Kakoune should be fast, fast to use, as in a lot of editing in a few
keystrokes, and fast to execute.

 * Vim is the benchmark here, most editing tasks should be doable in less
   or the same number of keys.

 * Kakoune be designed with asynchronicity in mind, launching a background
   process and using its result when available should not block the editor.

 * Kakoune should be implemented with speed in mind, a slow editor is a
   useless one.

Simplicity
----------

Simplicity is nice, simplicity correlates with orthogonality and speed, and makes
things easier to understand, bugs easier to fix, and code easier to change.

 * *No threading*: multithreading is a hard problem, and is not well suited
   to a text editor:

   - Either we want a direct result, and we need to be synchronous with
     the user, so getting a 4x speed up is meaningless, we need to have an
     algorithm which appears instantaneous the user.

   - Or we want an asynchronous result, and then the processing is best left
     to a helper command which can be reused with other Unix tools.

 * *No binary plugins*: shared object by themselves add a lot of
   complexity. Plugins add another interface to Kakoune, and goes against
   orthogonality. The +%sh{ ... }+ and socket interface should be made good
   enough for most plugin use cases.
  
   - It is better to write Kakoune-independent helper tools (intelligent
     code completer, source code navigation programs) that can interact with
     Kakoune through the shell than write them in a plugin.

 * *No integrated scripting language*: for the same reason as binary plugins.

 * *Limited smartness*: Kakoune should not try to be too smart, being smart
   is often unpredictable for the user, and makes things context dependent.
   When Kakoune tries to be smart, it should provide the alternative, 'non
   smart' version (+\*+ tries to detect word boundaries on the selection, but
   +alt-*+ permits to avoid this behavior).

Unified interactive use and scripting
-------------------------------------

As both an effect of Orthogonality and Simplicity, normal mode is *not*
a layer on top of a text editing language layer (normal mode keys are
*not* bound to text editing commands), normal mode *is* the text editing
language.

That means there is no +delete-selected-text+ command that +d+ is bound
to, +d+ *is* the +delete selected text+ command.

This permits to have scripting use case and interactive use cases share
the same text editing language. Both use normal mode to express complex
edition.

Besides promoting simplicity by avoiding the introduction of another
layer, this helps ensure the interactive editing language is as expressive
as possible as we need to make it able to handle complex use cases,
such as indentation hooks.

Language agnostic
-----------------

Kakoune should not be tailored for writing in a specific programming
language. Support for different languages should be provided by a kak script
file, built-in language support should be avoided.

Self documenting
----------------

Kakoune should be able to document its features, live documentation along
with an extensive suggestion/completion system provides the discoverability
which is often lacking in non GUI tools. Documentation should as much as
possible be integrated with the code so that it stays up to date.

Vim compatibility
-----------------

Kakoune is inspired by Vim, and should try to keep its commands close to
Vim's if there are no compelling reasons to change. However self-consistency
is more important than Vim compatibility.