Provided by: elvish_0.13+ds1-2ubuntu0.1_amd64 
Overview
Modes and Submodules
The Elvish editor has different modes, and exactly one mode is active at the same time. Each mode has
its own UI and keybindings. For instance, the default insert mode lets you modify the current command.
The completion mode (triggered by Tab by default) shows you all candidates for completion, and you can
use arrow keys to navigate those candidates.
@ttyshot completion-mode
Each mode has its own submodule under edit:. For instance, builtin functions and configuration variables
for the completion mode can be found in the edit:completion: module.
The primary modes supported now are insert, completion, navigation, history, histlist, location, and
lastcmd. The last 4 are "listing modes", and their particularity is documented below.
Prompts
Elvish has two prompts: the (normal) left-hand prompt and the right-side prompt (rprompt). Most of this
section only documents the left-hand prompt, but API for rprompt is the same other than the variable
name: just replace prompt with rprompt.
To customize the prompt, assign a function to edit:prompt. The function may write value outputs or byte
outputs. Value outputs may be either strings or styled values; they are joiend with no spaces in
between. Byte outputs are output as-is, including any newlines, but control characters will be escaped:
you should use styled to output styled text. If you mix value and byte outputs, the order in which they
appear is non-deterministic.
The default prompt and rprompt are equivalent to:
edit:prompt = { tilde-abbr $pwd; put '> ' }
edit:rprompt = (constantly (styled (whoami)@(hostname) inverse))
More prompt functions:
~> edit:prompt = { tilde-abbr $pwd; styled '> ' green }
~> # ">" is now green
~> edit:prompt = { echo '$' }
$
# Cursor will be on the next line as `echo` outputs a trailing newline
Stale Prompt
Elvish never waits for the prompt function to finish. Instead, the prompt function is always executed on
a separate thread, and Elvish updates the screen when the function finishes.
However, this can be misleading when the function is slow: this means that the prompt on the screen may
not contain the latest information. To deal with this, if the prompt function does not finish within a
certain threshold - by default 0.2 seconds, Elvish marks the prompt as stale: it still shows the old
stale prompt content, but transforms it using a stale transformer. The default stale transformer applies
reverse-video to the whole prompt.
The threshold is customizable with $edit:prompt-stale-threshold; it specifies the threshold in seconds.
The transformer is customizable with $edit:prompt-stale-transform. It is a function; the function is
called with no arguments, and styled values as inputs, and the output is interpreted in the same way as
prompt functions. Since styled values can be used as outputs in prompt functions, a function that simply
passes all the input values through as outputs is a valid stale transformer.
As an example, try running following code:
n = 0
edit:prompt = { sleep 2; put $n; n = (+ $n 1); put ': ' }
edit:-prompt-eagerness = 10 # update prompt on each keystroke
edit:prompt-stale-threshold = 0.5
And then start typing. Type one character; the prompt becomes inverse after 0.5 second: this is when
Elvish starts to consider the prompt as stale. The prompt will return normal after 2 seconds, and the
counter in the prompt is updated: this is when the prompt function finishes.
Another thing you will notice is that, if you type a few characters quickly (in less than 2 seconds, to
be precise), the prompt is only updated twice. This is because Elvish never does two prompt updates in
parallel: prompt updates are serialized. If a prompt update is required when the prompt function is
still running, Elvish simply queues another update. If an update is already queued, Elvish does not
queue another update. The reason why exactly two updates happen in this case, and how this algorithm
ensures freshness of the prompt is left as an exercise to the reader.
Prompt Eagerness
The occassions when the prompt should get updated can be controlled with $edit:-prompt-eagerness:
• The prompt is always updated when the editor becomes active -- when Elvish starts, or a command
finishes execution, or when the user presses Enter.
• If $edit-prompt-eagerness >= 5, it is updated when the working directory changes.
• If $edit-prompt-eagerness >= 10, it is updated on each keystroke.
The default value is 5.
RPrompt Persistency
By default, the rprompt is only shown while the editor is active: as soon as you press Enter, it is
erased. If you want to keep it, simply set $edit:rprompt-persistent to $true:
edit:rprompt-persistent = $true
Keybindings
Each mode has its own keybinding, accessible as the binding variable in its module. For instance, the
binding table for insert mode is $edit:insert:binding. To see current bindings, simply print the binding
table: pprint $edit:insert:binding (replace insert with any other mode).
A binding tables is simply a map that maps keys to functions. For instance, to bind Alt-x in insert mode
to exit Elvish, simply do:
edit:insert:binding[Alt-x] = { exit }
Outputs from a bound function always appear above the Elvish prompt. You can see this by doing the
following:
edit:insert:binding[Alt-x] = { echo 'output from a bound function!' }
and press Alt-x in insert mode. It allows you to put debugging outputs in bound functions without
messing up the terminal.
Internally, this is implemented by connecting their output to a pipe. This does the correct thing in
most cases, but if you are sure you want to do something to the terminal, redirect the output to
/dev/tty. For instance, the following binds Ctrl-L to clearing the terminal:
edit:insert:binding[Ctrl-L] = { clear > /dev/tty }
Bound functions have their inputs redirected to /dev/null.
Format of Keys
TBD
Listing Modes
The modes histlist, loc and lastcmd are all listing modes: They all show a list, and you can filter items
and accept items.
Because they are very similar, you may want to change their bindings at the same time. This is made
possible by the $edit:listing:binding binding table (listing is not a "real" mode but an "abstract"
mode). These modes still have their own binding tables like $edit:histlist:binding, and bindings there
have highter precedence over those in the shared $edit:listing:binding table.
Moreover, there are a lot of builtin functions in the edit:listing module like edit:listing:down (for
moving down selection). They always apply to whichever listing mode is active.
Caveat: Bindings to Start Modes
Note that keybindings to start modes live in the binding table of the insert mode, not the target mode.
For instance, if you want to be able to use Alt-l to start location mode, you should modify
$edit:insert:binding[Alt-l]:
edit:insert:binding[Alt-l] = { edit:location:start }
One tricky case is the history mode. You can press ▲︎ to start searching for history, and continue
pressing it to search further. However, when the first press happens, the editor is in insert mode,
while with subsequent presses, the editor is in history mode. Hence this binding actually relies on two
entries, $edit:insert:binding[Up] and $edit:history:binding[Up].
So for instance if you want to be able to use Ctrl-P for this, you need to modify both bindings:
edit:insert:binding[Ctrl-P] = { edit:history:start }
edit:history:binding[Ctrl-P] = { edit:history:up }
Completion API
Argument Completer
There are two types of completions in Elvish: completion for internal data and completion for command
arguments. The former includes completion for variable names (e.g. echo $Tab) and indicies (e.g. echo
$edit:insert:binding[Tab). These are the completions that Elvish can provide itself because they only
depend on the internal state of Elvish.
The latter, in turn, is what happens when you type e.g. catTab. Elvish cannot provide completions for
them without full knowledge of the command.
Command argument completions are programmable via the $edit:completion:arg-completer variable. When
Elvish is completing an argument of command $x, it will call the value stored in
$edit:completion:arg-completer[$x], with all the existing arguments, plus the command name in the front.
For example, if the user types man 1Tab, Elvish will call:
$edit:completion:arg-completer[man] man 1
If the user is starting a new argument when hitting Tab, Elvish will call the completer with a trailing
empty string. For instance, if you do man 1SpaceTab, Elvish will call:
$edit:completion:arg-completer[man] man 1 ""
The output of this call becomes candidates. There are several ways of outputting candidates:
• Writing byte output, e.g. "echo cand1; echo cand2". Each line becomes a candidate. This has the
drawback that you cannot put newlines in candidates. Only use this if you are sure that you candidates
will not contain newlines -- e.g. package names, usernames, but not file names, etc..
• Write strings to value output, e.g. "put cand1 cand2". Each string output becomes a candidate.
• Use the edit:complex-candidate command:
edit:complex-candidate &code-suffix='' &display-suffix='' &style='' $stem
TODO: Document this.
After receiving your candidates, Elvish will match your candidates against what the user has typed.
Hence, normally you don't need to (and shouldn't) do any matching yourself.
That means that in many cases you can (and should) simpy ignore the last argument to your completer.
However, they can be useful for deciding what kind of things to complete. For instance, if you are to
write a completer for ls, you want to see whether the last argument starts with - or not: if it does,
complete an option; and if not, complete a filename.
Here is a very basic example of configuring a completer for the apt command. It only supports completing
the install and remove command and package names after that:
all-packages = [(apt-cache search '' | eawk [0 1 @rest]{ put $1 })]
edit:completion:arg-completer[apt] = [@args]{
n = (count $args)
if (== $n 2) {
# apt x<Tab> -- complete a subcommand name
put install uninstall
} elif (== $n 3) {
put $@all-packages
}
}
Here is another slightly more complex example for the git command. It supports completing some common
subcommands and then branch names after that:
fn all-git-branches {
# Note: this assumes a recent version of git that supports the format
# string used.
git branch -a --format="%(refname:strip=2)" | eawk [0 1 @rest]{ put $1 }
}
common-git-commands = [
add branch checkout clone commit diff init log merge
pull push rebase reset revert show stash status
]
edit:arg-completer[git] = [@args]{
n = (count $args)
if (== $n 2) {
put $@common-git-commands
} elif (>= $n 3) {
all-git-branches
}
}
Matcher
As stated above, after the completer outputs candidates, Elvish matches them with them with what the user
has typed. For clarity, the part of the user input that is relevant to tab completion is called for the
seed of the completion. For instance, in echo xTab, the seed is x.
Elvish first indexes the matcher table -- $edit:completion:matcher -- with the completion type to find a
matcher. The completion type is currently one of variable, index, command, redir or argument. If the
$edit:completion:matcher lacks the suitable key, $edit:completion:matcher[''] is used.
Elvish then calls the matcher with one argument -- the seed, and feeds the text of all candidates to the
input. The mather must output an identical number of booleans, indicating whether the candidate should
be kept.
As an example, the following code configures a prefix matcher for all completion types:
edit:completion:matcher[''] = [seed]{ each [cand]{ has-prefix $cand $seed } }
Elvish provides three builtin matchers, edit:match-prefix, edit:match-substr and edit:match-subseq. In
addition to conforming to the matcher protocol, they accept two options &ignore-case and &smart-case.
For example, if you want completion of arguments to use prefix matching and ignore case, use:
edit:completion:matcher[argument] = [seed]{ edit:match-prefix $seed &ignore-case=$true }
The default value of $edit:completion:matcher is [&''=$edit:match-prefix~], hence that candidates for all
completion types are matched by prefix.
Hooks
Hooks are functions that are executed at certain points in time. In Elvish, this functionality is
provided by lists of functions.
There are current two hooks:
• $edit:before-readline, whose elements are called before the editor reads code, with no arguments.
• $edit:after-readline, whose elements are called, after the editor reads code, with a sole element --
the line just read.
Example usage:
edit:before-readline = [{ echo 'going to read' }]
edit:after-readline = [[line]{ echo 'just read '$line }]
Then every time you accept a chunk of code (and thus leaving the editor), just read followed by the code
is printed; and at the very beginning of an Elvish session, or after a chunk of code is executed, going
to read is printed.
@elvdoc -ns edit: -dir ../pkg/edit