Nvim documentation: if_lua

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*if_lua.txt*    Nvim


Lua engine						*lua* *Lua*

                                      Type |gO| to see the table of contents.


Introduction						*lua-intro*

The Lua 5.1 language is builtin and always available.  Try this command to get
an idea of what lurks beneath:

    :lua print(vim.inspect(package.loaded))

Nvim includes a "standard library" |lua-stdlib| for Lua.  It complements the
"editor stdlib" (|functions| and Ex commands) and the |API|, all of which can
be used from Lua code.

Module conflicts are resolved by "last wins".  For example if both of these
are on 'runtimepath':
then `require('foo')` loads "~/.config/nvim/lua/foo.lua", and
"runtime/lua/foo.lua" is not used.  See |lua-require| to understand how Nvim
finds and loads Lua modules.  The conventions are similar to VimL plugins,
with some extra features.  See |lua-require-example| for a walkthrough.


Importing Lua modules					*lua-require*

Nvim automatically adjusts `package.path` and `package.cpath` according to
effective 'runtimepath' value.  Adjustment happens whenever 'runtimepath' is
changed.  `package.path` is adjusted by simply appending `/lua/?.lua` and
`/lua/?/init.lua` to each directory from 'runtimepath' (`/` is actually the
first character of `package.config`).

Similarly to `package.path`, modified directories from 'runtimepath' are also
added to `package.cpath`.  In this case, instead of appending `/lua/?.lua` and
`/lua/?/init.lua` to each runtimepath, all unique `?`-containing suffixes of
the existing `package.cpath` are used.  Example:

1. Given that
   - 'runtimepath' contains `/foo/bar,/xxx;yyy/baz,/abc`;
   - initial (defined at compile-time or derived from 
     `$LUA_CPATH`/`$LUA_INIT`) `package.cpath` contains 
2. It finds `?`-containing suffixes `/?.so`, `/a?d/j/g.elf` and `/?.so`, in 
   order: parts of the path starting from the first path component containing 
   question mark and preceding path separator.
3. The suffix of `/def/?.so`, namely `/?.so` is not unique, as it’s the same 
   as the suffix of the first path from `package.path` (i.e. `./?.so`).  Which 
   leaves `/?.so` and `/a?d/j/g.elf`, in this order.
4. 'runtimepath' has three paths: `/foo/bar`, `/xxx;yyy/baz` and `/abc`.  The 
   second one contains semicolon which is a paths separator so it is out, 
   leaving only `/foo/bar` and `/abc`, in order.
5. The cartesian product of paths from 4. and suffixes from 3. is taken, 
   giving four variants. In each variant `/lua` path segment is inserted 
   between path and suffix, leaving

   - `/foo/bar/lua/?.so`
   - `/foo/bar/lua/a?d/j/g.elf`
   - `/abc/lua/?.so`
   - `/abc/lua/a?d/j/g.elf`

6. New paths are prepended to the original `package.cpath`.

The result will look like this:

    `/foo/bar,/xxx;yyy/baz,/abc` ('runtimepath')
    × `./?.so;/def/ghi/a?d/j/g.elf;/def/?.so` (`package.cpath`)

    = `/foo/bar/lua/?.so;/foo/bar/lua/a?d/j/g.elf;/abc/lua/?.so;/abc/lua/a?d/j/g.elf;./?.so;/def/ghi/a?d/j/g.elf;/def/?.so`


- To track 'runtimepath' updates, paths added at previous update are
  remembered and removed at the next update, while all paths derived from the
  new 'runtimepath' are prepended as described above.  This allows removing
  paths when path is removed from 'runtimepath', adding paths when they are
  added and reordering `package.path`/`package.cpath` content if 'runtimepath'
  was reordered.

- Although adjustments happen automatically, Nvim does not track current
  values of `package.path` or `package.cpath`.  If you happen to delete some
  paths from there you can set 'runtimepath' to trigger an update:
      let &runtimepath = &runtimepath

- Skipping paths from 'runtimepath' which contain semicolons applies both to
  `package.path` and `package.cpath`.  Given that there are some badly written
  plugins using shell which will not work with paths containing semicolons it
  is better to not have them in 'runtimepath' at all.


LUA PLUGIN EXAMPLE					*lua-require-example*

The following example plugin adds a command `:MakeCharBlob` which transforms 
current buffer into a long `unsigned char` array.  Lua contains transformation 
function in a module `lua/charblob.lua` which is imported in 
`autoload/charblob.vim` (`require("charblob")`).  Example plugin is supposed 
to be put into any directory from 'runtimepath', e.g. `~/.config/nvim` (in 
this case `lua/charblob.lua` means `~/.config/nvim/lua/charblob.lua`).


    function charblob#encode_buffer()
      call setline(1, luaeval(
      \    'require("charblob").encode(unpack(_A))',
      \    [getline(1, '$'), &textwidth, '  ']))


    if exists('g:charblob_loaded')
    let g:charblob_loaded = 1

    command MakeCharBlob :call charblob#encode_buffer()


    local function charblob_bytes_iter(lines)
      local init_s = {
        next_line_idx = 1,
        next_byte_idx = 1,
        lines = lines,
      local function next(s, _)
        if lines[s.next_line_idx] == nil then
          return nil
        if s.next_byte_idx > #(lines[s.next_line_idx]) then
          s.next_line_idx = s.next_line_idx + 1
          s.next_byte_idx = 1
          return ('\n'):byte()
        local ret = lines[s.next_line_idx]:byte(s.next_byte_idx)
        if ret == ('\n'):byte() then
          ret = 0  -- See :h NL-used-for-NUL.
        s.next_byte_idx = s.next_byte_idx + 1
        return ret
      return next, init_s, nil

    local function charblob_encode(lines, textwidth, indent)
      local ret = {
        'const unsigned char blob[] = {',
      for byte in charblob_bytes_iter(lines) do
        --                .- space + number (width 3) + comma
        if #(ret[#ret]) + 5 > textwidth then
          ret[#ret + 1] = indent
          ret[#ret] = ret[#ret] .. ' '
        ret[#ret] = ret[#ret] .. (('%3u,'):format(byte))
      ret[#ret + 1] = '};'
      return ret

    return {
      bytes_iter = charblob_bytes_iter,
      encode = charblob_encode,


Commands						*lua-commands*

:[range]lua {chunk}
			Execute Lua chunk {chunk}.


    :lua vim.api.nvim_command('echo "Hello, Nvim!"')
To see the Lua version:
    :lua print(_VERSION)

To see the LuaJIT version:
    :lua print(jit.version)

:[range]lua << {endmarker}
			Execute Lua script {script}.

{endmarker} must NOT be preceded by any white space.  If {endmarker} is
omitted from after the "<<", a dot '.' must be used after {script}, like
for the |:append| and |:insert| commands.
This form of the |:lua| command is mainly useful for including Lua code
in Vim scripts.


    function! CurrentLineInfo()
    lua << EOF
    local linenr = vim.api.nvim_win_get_cursor(0)[1]
    local curline = vim.api.nvim_buf_get_lines(
            0, linenr, linenr + 1, false)[1]
    print(string.format("Current line [%d] has %d bytes",
            linenr, #curline))

Note that the `local` variables will disappear when block finishes. This is
not the case for globals.

:[range]luado {body}	Execute Lua function "function (line, linenr) {body}
			end" for each line in the [range], with the function
			argument being set to the text of each line in turn,
			without a trailing <EOL>, and the current line number.
			If the value returned by the function is a string it
			becomes the text of the line in the current turn. The
			default for [range] is the whole file: "1,$".


    :luado return string.format("%s\t%d", line:reverse(), #line)

    :lua require"lpeg"
    :lua -- balanced parenthesis grammar:
    :lua bp = lpeg.P{ "(" * ((1 - lpeg.S"()") + lpeg.V(1))^0 * ")" }
    :luado if bp:match(line) then return "-->\t" .. line end

:[range]luafile {file}
			Execute Lua script in {file}.
			The whole argument is used as a single file name.


    :luafile script.lua
    :luafile %

All these commands execute a Lua chunk from either the command line (:lua and
:luado) or a file (:luafile) with the given line [range]. Similarly to the Lua
interpreter, each chunk has its own scope and so only global variables are
shared between command calls. All Lua default libraries are available. In
addition, Lua "print" function has its output redirected to the Nvim message
area, with arguments separated by a white space instead of a tab.

Lua uses the "vim" module (see |lua-vim|) to issue commands to Nvim. However,
procedures that alter buffer content, open new buffers, and change cursor
position are restricted when the command is executed in the |sandbox|.


luaeval()						*lua-eval* *luaeval()*

The (dual) equivalent of "vim.eval" for passing Lua values to Nvim is
"luaeval". "luaeval" takes an expression string and an optional argument used 
for _A inside expression and returns the result of the expression. It is 
semantically equivalent in Lua to:

    local chunkheader = "local _A = select(1, ...) return "
    function luaeval (expstr, arg)
        local chunk = assert(loadstring(chunkheader .. expstr, "luaeval"))
        return chunk(arg) -- return typval

Lua nils, numbers, strings, tables and booleans are converted to their
respective VimL types. An error is thrown if conversion of any other Lua types
is attempted.

The magic global "_A" contains the second argument to luaeval().

    :echo luaeval('_A[1] + _A[2]', [40, 2])
    :echo luaeval('string.match(_A, "[a-z]+")', 'XYXfoo123')

Lua tables are used as both dictionaries and lists, so it is impossible to
determine whether empty table is meant to be empty list or empty dictionary.
Additionally lua does not have integer numbers. To distinguish between these
cases there is the following agreement:

0. Empty table is empty list.
1. Table with N incrementally growing integral numbers, starting from 1 and 
   ending with N is considered to be a list.
2. Table with string keys, none of which contains NUL byte, is considered to 
   be a dictionary.
3. Table with string keys, at least one of which contains NUL byte, is also 
   considered to be a dictionary, but this time it is converted to 
   a |msgpack-special-map|.

4. Table with `vim.type_idx` key may be a dictionary, a list or floating-point 
   - `{[vim.type_idx]=vim.types.float, [vim.val_idx]=1}` is converted to 
     a floating-point 1.0. Note that by default integral lua numbers are 
     converted to |Number|s, non-integral are converted to |Float|s. This 
     variant allows integral |Float|s.
   - `{[vim.type_idx]=vim.types.dictionary}` is converted to an empty 
     dictionary, `{[vim.type_idx]=vim.types.dictionary, [42]=1, a=2}` is 
     converted to a dictionary `{'a': 42}`: non-string keys are ignored. 
     Without `vim.type_idx` key tables with keys not fitting in 1., 2. or 3. 
     are errors.
   - `{[vim.type_idx]=vim.types.list}` is converted to an empty list. As well 
     as `{[vim.type_idx]=vim.types.list, [42]=1}`: integral keys that do not 
     form a 1-step sequence from 1 to N are ignored, as well as all 
     non-integral keys.


    :echo luaeval('math.pi')
    :function Rand(x,y) " random uniform between x and y
    :  return luaeval('(_A.y-_A.x)*math.random()+_A.x', {'x':a:x,'y':a:y})
    :  endfunction
    :echo Rand(1,10)

Note that currently second argument to `luaeval` undergoes VimL to lua 
conversion, so changing containers in lua do not affect values in VimL. Return 
value is also always converted. When converting, |msgpack-special-dict|s are 
treated specially.


Lua standard modules					*lua-stdlib*

The Nvim Lua "standard library" (stdlib) is the `vim` module, which exposes
various functions and sub-modules.  It is always loaded, thus require("vim")
is unnecessary.

You can peek at the module properties:

    :lua print(vim.inspect(vim))

Result is something like this:

      _os_proc_children = <function 1>,
      _os_proc_info = <function 2>,
      api = {
        nvim__id = <function 5>,
        nvim__id_array = <function 6>,
      deepcopy = <function 106>,
      gsplit = <function 107>,

To find documentation on e.g. the "deepcopy" function:

    :help vim.deepcopy

Note that underscore-prefixed functions (e.g. "_os_proc_children") are
internal/private and must not be used by plugins.


VIM.API							*lua-api*

`vim.api` exposes the full Nvim |API| as a table of Lua functions.

For example, to use the "nvim_get_current_line()" API function, call



VIM.LOOP							*lua-loop*

`vim.loop` exposes all features of the Nvim event-loop.  This is a lower-level
API that provides functionality for networking, filesystem, and process

 See	http://docs.libuv.org for complete documentation.
See https://github.com/luvit/luv/tree/master/examples for examples.

Example: repeating timer
    1. Save this code to a file.
    2. Execute it with ":luafile %".

    -- Create a timer handle (implementation detail: uv_timer_t).
    local timer = vim.loop.new_timer()
    local i = 0
    -- Waits 1000ms, then repeats every 750ms until timer:close().
    timer:start(1000, 750, function()
      print('timer invoked! i='..tostring(i))
      if i > 4 then
        timer:close()  -- Always close handles to avoid leaks.
      i = i + 1

Example: TCP echo-server				*tcp-server*
    1. Save this code to a file.
    2. Execute it with ":luafile %".
    3. Note the port number.
    4. Connect from any TCP client (e.g. "nc 36795"):

    local function create_server(host, port, on_connection)
      local server = vim.loop.new_tcp()
      server:bind(host, port)
      server:listen(128, function(err)
        assert(not err, err)  -- Check for errors.
        local sock = vim.loop.new_tcp()
        server:accept(sock)  -- Accept client connection.
        on_connection(sock)  -- Start reading messages.
      return server
    local server = create_server('', 0, function(sock)
      sock:read_start(function(err, chunk)
        assert(not err, err)  -- Check for errors.
        if chunk then
          sock:write(chunk)  -- Echo received messages to the channel.
        else  -- EOF (stream closed).
          sock:close()  -- Always close handles to avoid leaks.
    print('TCP echo-server listening on port: '..server:getsockname().port)


VIM							*lua-util*

vim.stricmp({a}, {b})					*vim.stricmp()*
        Compares strings case-insensitively.  Returns 0, 1 or -1 if strings
        are equal, {a} is greater than {b} or {a} is lesser than {b},

vim.schedule({callback})				*vim.schedule()*
        Schedules {callback} to be invoked soon by the main event-loop. Useful
        to avoid |textlock| or other temporary restrictions.

vim.type_idx						*vim.type_idx*
	Type index for use in |lua-special-tbl|.  Specifying one of the 
	values from |vim.types| allows typing the empty table (it is 
	unclear whether empty lua table represents empty list or empty array) 
	and forcing integral numbers to be |Float|.  See |lua-special-tbl| for 
	more details.

vim.val_idx						*vim.val_idx*
	Value index for tables representing |Float|s.  A table representing 
	floating-point value 1.0 looks like this:
              [vim.type_idx] = vim.types.float,
              [vim.val_idx] = 1.0,
 	See also |vim.type_idx| and |lua-special-tbl|.

vim.types						*vim.types*
	Table with possible values for |vim.type_idx|.  Contains two sets 
	of key-value pairs: first maps possible values for |vim.type_idx| 
	to human-readable strings, second maps human-readable type names to 
	values for |vim.type_idx|.  Currently contains pairs for `float`, 
	`array` and `dictionary` types.

	Note: one must expect that values corresponding to `vim.types.float`, 
	`vim.types.array` and `vim.types.dictionary` fall under only two 
	following assumptions:
	1. Value may serve both as a key and as a value in a table.  Given the 
	   properties of lua tables this basically means “value is not `nil`”.
	2. For each value in `vim.types` table `vim.types[vim.types[value]]` 
	   is the same as `value`.
	No other restrictions are put on types, and it is not guaranteed that 
	values corresponding to `vim.types.float`, `vim.types.array` and 
	`vim.types.dictionary` will not change or that `vim.types` table will 
	only contain values for these three types.


Lua module: vim                                                      *lua-vim*

inspect({object}, {options})                                   *vim.inspect()*
                Return a human-readable representation of the given object.

                See also: 

deepcopy({orig})                                              *vim.deepcopy()*
                Returns a deep copy of the given object. Non-table objects are
                copied as in a typical Lua assignment, whereas table objects
                are copied recursively.

                    {orig}  Table to copy

                    New table of copied keys and (nested) values.

gsplit({s}, {sep}, {plain})                                     *vim.gsplit()*
                Splits a string at each instance of a separator.

                    {s}      String to split
                    {sep}    Separator string or pattern
                    {plain}  If `true` use `sep` literally (passed to

                    Iterator over the split components

                See also: 

split({s}, {sep}, {plain})                                       *vim.split()*
                Splits a string at each instance of a separator.

                 split(":aa::b:", ":")     --> {'','aa','','bb',''}
                 split("axaby", "ab?")     --> {'','x','y'}
                 split(x*yz*o, "*", true)  --> {'x','yz','o'}

                    {s}      String to split
                    {sep}    Separator string or pattern
                    {plain}  If `true` use `sep` literally (passed to

                    List-like table of the split components.

                See also: 

tbl_contains({t}, {value})                                *vim.tbl_contains()*
                Checks if a list-like (vector) table contains `value` .

                    {t}      Table to check
                    {value}  Value to compare

                    true if `t` contains `value`

tbl_extend({behavior}, {...})                               *vim.tbl_extend()*
                Merges two or more map-like tables.

                    {behavior}  Decides what to do if a key is found in more
                                than one map:
                                • "error": raise an error
                                • "keep": use value from the leftmost map
                                • "force": use value from the rightmost map
                    {...}       Two or more map-like tables.

                See also: 

tbl_flatten({t})                                           *vim.tbl_flatten()*
                Creates a copy of a list-like table such that any nested
                tables are "unrolled" and appended to the result.

                    {t}  List-like table

                    Flattened copy of the given list-like table.

trim({s})                                                         *vim.trim()*
                Trim whitespace (Lua pattern "%s") from both sides of a

                    {s}  String to trim

                    String with whitespace removed from its beginning and end

                See also: 

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