runtime/doc/usr_41.txt

*usr_41.txt*	For Vim version 8.2.  Last change: 2022 Jun 03

		     VIM USER MANUAL - by Bram Moolenaar

			      Write a Vim script


The Vim script language is used for the startup vimrc file, syntax files, and
many other things.  This chapter explains the items that can be used in a Vim
script.  There are a lot of them, therefore this is a long chapter.

|41.1|	Introduction
|41.2|	Variables
|41.3|	Expressions
|41.4|	Conditionals
|41.5|	Executing an expression
|41.6|	Using functions
|41.7|	Defining a function
|41.8|	Lists and Dictionaries
|41.9|	Exceptions
|41.10|	Various remarks

     Next chapter: |usr_42.txt|  Add new menus
 Previous chapter: |usr_40.txt|  Make new commands
Table of contents: |usr_toc.txt|

==============================================================================
*41.1*	Introduction				*vim-script-intro* *script*

Your first experience with Vim scripts is the vimrc file.  Vim reads it when
it starts up and executes the commands.  You can set options to the values you
prefer, define mappings, select plugins and much more.   You can use any colon
command in it (commands that start with a ":"; these are sometimes referred to
as Ex commands or command-line commands).

Syntax files are also Vim scripts.  As are files that set options for a
specific file type.  A complicated macro can be defined by a separate Vim
script file.  You can think of other uses yourself.

Vim script comes in two flavors: legacy and |Vim9|.  Since this help file is
for new users, we'll teach you the newer and more convenient |Vim9| syntax.
While legacy script is particularly for Vim, |Vim9| script looks more like
other languages, such as JavaScript and TypeScript.

To try out Vim script the best way is to edit a script file and source it.
Basically: >
	:edit test.vim
	[insert the script lines you want]
	:w
	:source %

Let's start with a simple example: >

	vim9script
	var i = 1
	while i < 5
	  echo "count is" i
	  i += 1
	endwhile
<
The output of the example code is:

	count is 1 ~
	count is 2 ~
	count is 3 ~
	count is 4 ~

In the first line the `vim9script` command makes clear this is a new, |Vim9|
script file.  That matters for how the rest of the file is used.
							*vim9-declarations*
The `var i = 1` command declares the "i" variable and initializes it.  The
generic form is: >

	var {name} = {expression}

In this case the variable name is "i" and the expression is a simple value,
the number one.

The `while` command starts a loop.  The generic form is: >

	while {condition}
	  {statements}
	endwhile

The statements until the matching `endwhile` are executed for as long as the
condition is true.  The condition used here is the expression "i < 5".  This
is true when the variable i is smaller than five.
	Note:
	If you happen to write a while loop that keeps on running, you can
	interrupt it by pressing CTRL-C (CTRL-Break on MS-Windows).

The `echo` command prints its arguments.  In this case the string "count is"
and the value of the variable i.  Since i is one, this will print:

	count is 1 ~

Then there is the `i += 1` command.  This does the same thing as "i = i + 1",
it adds one to the variable i and assigns the new value to the same variable.

The example was given to explain the commands, but would you really want to
make such a loop, it can be written much more compact: >

	for i in range(1, 4)
	  echo $"count is {i}"
	endfor

We won't explain how `for`, `range()`and `$"string"` work until later.  Follow
the links if you are impatient.


TRYING OUT EXAMPLES

You can easily try out most examples in these help files without saving the
commands in a file.  For example, to try out the "for" loop above do this:
1. position the cursor on the "for"
2. start Visual mode with "v"
3. move down to the "endfor"
4. press colon, then "so" and Enter

After pressing colon you will see ":'<,'>", which is the range of the Visually
selected text.

For some commands it matters they are executed as in |Vim9| script.  But typed
commands normally use legacy script syntax, such as the example below that
causes the E1004 error.  For that use this fourth step:
4. press colon, then "vim9 so" and Enter

"vim9" is short for `vim9cmd`, which is a command modifier to execute the
following command in |Vim9| syntax.

Note that this won't work for examples that require a script context.


FOUR KINDS OF NUMBERS

Numbers can be decimal, hexadecimal, octal and binary.

A hexadecimal number starts with "0x" or "0X".  For example "0x1f" is decimal
31 and 0x1234 is decimal 4660.

An octal number starts with "0o", "0O".  "0o17" is decimal 15.

A binary number starts with "0b" or "0B".  For example "0b101" is decimal 5.

A decimal number is just digits.  Careful: In legacy script don't put a zero
before a decimal number, it will be interpreted as an octal number!  That's
one reason to use |Vim9| script.

The `echo` command evaluates its argument and when it is a number always
prints the decimal form.  Example: >

	echo 0x7f 0o36
<	127 30 ~

A number is made negative with a minus sign.  This also works for hexadecimal,
octal and binary numbers: >

	echo -0x7f
<	-127 ~

A minus sign is also used for subtraction.  This can sometimes lead to
confusion.  If we put a minus sign before both numbers we get an error: >

	echo -0x7f -0o36
<	E1004: White space required before and after '-' at "-0o36" ~

Note: if you are not using a |Vim9| script to try out these commands but type
them directly, they will be executed as legacy script.  Then the echo command
sees the second minus sign as subtraction.  To get the error, prefix the
command with `vim9cmd`: >

	vim9cmd echo -0x7f -0o36
<	E1004: White space required before and after '-' at "-0o36" ~

White space in an expression is often required to make sure it is easy to read
and avoid errors.  Such as thinking that the "-0o36" above makes the number
negative, while it is actually seen as a subtraction.

To actually have the minus sign be used for negation, you can put the second
expression in parentheses: >

	echo -0x7f (-0o36)
<	-127 -30 ~

==============================================================================
*41.2*	Variables

A variable name consists of ASCII letters, digits and the underscore.  It
cannot start with a digit.  Valid variable names are:

	counter
	_aap3
	very_long_variable_name_with_underscores
	CamelCaseName
	LENGTH

Invalid names are "foo+bar" and "6var".

Some variables are global.  To see a list of currently defined global
variables type this command: >

	:let

You can use global variables everywhere.  However, it is too easy to use the
same name in two unrelated scripts.  Therefore variables declared in a script
are local to that script.  For example, if you have this in "script1.vim": >

	vim9script
	var counter = 5
	echo counter
<	5 ~

And you try to use the variable in "script2.vim": >

	vim9script
	echo counter
<	E121: Undefined variable: counter ~

Using a script-local variable means you can be sure that it is only changed in
that script and not elsewhere.

If you do want to share variables between scripts, use the "g:" prefix and
assign the value directly, do not use `var`.  And use a specific name to avoid
mistakes.  Thus in "script1.vim": >

	vim9script
	g:mash_counter = 5
	echo g:mash_counter
<	5 ~

And then in "script2.vim": >

	vim9script
	echo g:mash_counter
<	5 ~

Global variables can also be accessed on the command line, E.g. typing this: >
	echo g:mash_counter
That will not work for a script-local variable.

More about script-local variables here: |script-variable|.

There are more kinds of variables, see |internal-variables|.  The most often
used ones are:

	b:name		variable local to a buffer
	w:name		variable local to a window
	g:name		global variable (also in a function)
	v:name		variable predefined by Vim


DELETING VARIABLES

Variables take up memory and show up in the output of the `let` command.  To
delete a global variable use the `unlet` command.  Example: >

	unlet g:counter

This deletes the global variable "g:counter" to free up the memory it uses.
If you are not sure if the variable exists, and don't want an error message
when it doesn't, append !: >

	unlet! g:counter

You cannot `unlet` script-local variables in |Vim9| script, only in legacy
script.

When a script finishes, the local variables declared there will not be
deleted.  Functions defined in the script can use them.  Example:
>
	vim9script
	var counter = 0
	def g:GetCount(): number
	  s:counter += 1
	  return s:counter
	enddef

Every time you call the function it will return the next count: >
	:echo g:GetCount()
<	1 ~
>
	:echo g:GetCount()
<	2 ~

If you are worried a script-local variable is consuming too much memory, set
it to an empty or null value after you no longer need it.  Example: >
	var lines = readfile(...)
	...
	lines = []

Note: below we'll leave out the `vim9script` line from examples, so we can
concentrate on the relevant commands, but you'll still need to put it at the
top of your script file.


STRING VARIABLES AND CONSTANTS

So far only numbers were used for the variable value.  Strings can be used as
well.  Numbers and strings are the basic types of variables that Vim supports.
Example: >

	var name = "Peter"
	echo name
<	Peter ~

Every variable has a type.  Very often, as in this example, the type is
defined by assigning a value.  This is called type inference.  If you do not
want to give the variable a value yet, you need to specify the type: >

	var name: string
	var age: number
	if male
	   name = "Peter"
	   age = 42
	else
	   name = "Elisa"
	   age = 45
	endif

If you make a mistake and try to assign the wrong type of value you'll get an
error: >
	
	age = "Peter"
<	E1012: Type mismatch; expected number but got string ~

More about types in |41.8|.

To assign a string value to a variable, you can use a string constant.  There
are two types of these.  First the string in double quotes, as we used
already.  If you want to include a double quote inside the string, put a
backslash in front of it: >

	var name = "he is \"Peter\""
	echo name
<	he is "Peter" ~

To avoid the need for backslashes, you can use a string in single quotes: >

	var name = 'he is "Peter"'
	echo name
<	he is "Peter" ~

Inside a single-quote string all the characters are as they are.  Only the
single quote itself is special: you need to use two to get one.  A backslash
is taken literally, thus you can't use it to change the meaning of the
character after it: >

	var name = 'P\e''ter'''
	echo name
<	P\e'ter' ~

In double-quote strings it is possible to use special characters.  Here are a
few useful ones:

	\t		<Tab>
	\n		<NL>, line break
	\r		<CR>, <Enter>
	\e		<Esc>
	\b		<BS>, backspace
	\"		"
	\\		\, backslash
	\<Esc>		<Esc>
	\<C-W>		CTRL-W

The last two are just examples.  The  "\<name>" form can be used to include
the special key "name".

See |expr-quote| for the full list of special items in a string.

==============================================================================
*41.3*	Expressions

Vim has a fairly standard way to handle expressions.  You can read the
definition here: |expression-syntax|.  Here we will show the most common
items.

The numbers, strings and variables mentioned above are expressions by
themselves.  Thus everywhere an expression is expected, you can use a number,
string or variable.  Other basic items in an expression are:

	$NAME		environment variable
	&name		option value
	@r		register contents

Examples: >

	echo "The value of 'tabstop' is" &ts
	echo "Your home directory is" $HOME
	if @a == 'text'

The &name form can also be used to set an option value, do something and
restore the old value.  Example: >

	var save_ic = &ic
	set noic
	s/The Start/The Beginning/
	&ic = save_ic

This makes sure the "The Start" pattern is used with the 'ignorecase' option
off.  Still, it keeps the value that the user had set.  (Another way to do
this would be to add "\C" to the pattern, see |/\C|.)


MATHEMATICS

It becomes more interesting if we combine these basic items.  Let's start with
mathematics on numbers:

	a + b		add
	a - b		subtract
	a * b		multiply
	a / b		divide
	a % b		modulo

The usual precedence is used.  Example: >

	echo 10 + 5 * 2
<	20 ~

Grouping is done with parentheses.  No surprises here.  Example: >

	echo (10 + 5) * 2
<	30 ~


OTHERS

Strings can be concatenated with ".." (see |expr6|).  Example: >

	echo "Name: " .. name
	Name: Peter

When the "echo" command gets multiple arguments, it separates them with a
space.  In the example the argument is a single expression, thus no space is
inserted.

If you don't like the concatenation you can use the $"string" form, which
accepts an expression in curly braces: >
	echo $"Name: {name}"

See |interp-string| for more information.

Borrowed from the C language is the conditional expression: >

	a ? b : c

If "a" evaluates to true "b" is used, otherwise "c" is used.  Example: >

	var nr = 4
	echo nr > 5 ? "nr is big" : "nr is small"
<	nr is small ~

The three parts of the constructs are always evaluated first, thus you could
see it works as: >

	(a) ? (b) : (c)

There is also the falsy operator: >
	echo name ?? "No name given"
See |??|.

==============================================================================
*41.4*	Conditionals

The `if` commands executes the following statements, until the matching
`endif`, only when a condition is met.  The generic form is:

	if {condition}
	   {statements}
	endif

Only when the expression {condition} evaluates to true or one will the
{statements} be executed.  If they are not executed they must still be valid
commands.  If they contain garbage, Vim won't be able to find the matching
`endif`.

You can also use `else`.  The generic form for this is:

	if {condition}
	   {statements}
	else
	   {statements}
	endif

The second {statements} block is only executed if the first one isn't.

Finally, there is `elseif`

	if {condition}
	   {statements}
	elseif {condition}
	   {statements}
	endif

This works just like using `else` and then `if`, but without the need for an
extra `endif`.

A useful example for your vimrc file is checking the 'term' option and doing
something depending upon its value: >

	if &term == "xterm"
	  # Do stuff for xterm
	elseif &term == "vt100"
	  # Do stuff for a vt100 terminal
	else
	  # Do something for other terminals
	endif

This uses "#" to start a comment, more about that later.


LOGIC OPERATIONS

We already used some of them in the examples.  These are the most often used
ones:

	a == b		equal to
	a != b		not equal to
	a >  b		greater than
	a >= b		greater than or equal to
	a <  b		less than
	a <= b		less than or equal to

The result is true if the condition is met and false otherwise.  An example: >

	if v:version >= 800
	  echo "congratulations"
	else
	  echo "you are using an old version, upgrade!"
	endif

Here "v:version" is a variable defined by Vim, which has the value of the Vim
version.  800 is for version 8.0, version 8.1 has the value 801.  This is
useful to write a script that works with multiple versions of Vim.
See |v:version|.  You can also check for a specific feature with `has()` or a
specific patch, see |has-patch|.

The logic operators work both for numbers and strings.  When comparing two
strings, the mathematical difference is used.  This compares byte values,
which may not be right for some languages.

If you try to compare a string with a number you will get an error.

For strings there are two more useful items:

	str =~ pat		matches with
	str !~ pat		does not match with

The left item "str" is used as a string.  The right item "pat" is used as a
pattern, like what's used for searching.  Example: >

	if str =~ " "
	  echo "str contains a space"
	endif
	if str !~ '\.$'
	  echo "str does not end in a full stop"
	endif

Notice the use of a single-quote string for the pattern.  This is useful,
because patterns tend to contain many backslashes and backslashes need to be
doubled in a double-quote string.

The match is not anchored, if you want to match the whole string start with
"^" and end with "$".

The 'ignorecase' option is not used when comparing strings.  When you do want
to ignore case append "?".  Thus "==?" compares two strings to be equal while
ignoring case.  For the full table see |expr-==|.


MORE LOOPING

The `while` command was already mentioned.  Two more statements can be used in
between the `while` and the `endwhile`:

	continue		Jump back to the start of the while loop; the
				loop continues.
	break			Jump forward to the `endwhile`; the loop is
				discontinued.

Example: >

	var counter = 1
	while counter < 40
	  if skip_number(counter)
	    continue
	  endif
	  if last_number(counter)
	    break
	  endif
	  sleep 50m
	  ++counter
	endwhile

The `sleep` command makes Vim take a nap.  The "50m" specifies fifty
milliseconds.  Another example is `sleep 4`, which sleeps for four seconds.

`continue` and `break` can also be used in between `for` and `endfor`.
Even more looping can be done with the `for` command, see below in |41.8|.

==============================================================================
*41.5*	Executing an expression

So far the commands in the script were executed by Vim directly.  The
`execute` command allows executing the result of an expression.  This is a
very powerful way to build commands and execute them.

An example is to jump to a tag, which is contained in a variable: >

	execute "tag " .. tag_name

The ".." is used to concatenate the string "tag " with the value of variable
"tag_name".  Suppose "tag_name" has the value "get_cmd", then the command that
will be executed is: >

	tag get_cmd

The `execute` command can only execute Ex commands.  The `normal` command
executes Normal mode commands.  However, its argument is not an expression but
the literal command characters.  Example: >

	normal gg=G

This jumps to the first line with "gg" and formats all lines with the "="
operator and the "G" movement.

To make `normal` work with an expression, combine `execute` with it.
Example: >

	execute "normal " .. count .. "j"

This will move the cursor "count" lines down.

Make sure that the argument for `normal` is a complete command.  Otherwise
Vim will run into the end of the argument and silently abort the command.  For
example, if you start the delete operator, you must give the movement command
also.  This works: >
	
	normal d$

This does nothing: >

	normal d

If you start Insert mode and do not end it with Esc, it will end anyway.  This
works to insert "new text": >

	execute "normal inew text"

If you want to do something after inserting text you do need to end Insert
mode: >

	execute "normal inew text\<Esc>b"

This inserts "new text" and puts the cursor on the first letter of "text".
Notice the use of the special key "\<Esc>".  This avoids having to enter a
real <Esc> character in your script.  That is where `execute` with a
double-quote string comes in handy.

If you don't want to execute a string as a command but evaluate it to get the
result of the expression, you can use the eval() function: >

	var optname = "path"
	var optvalue = eval('&' .. optname)

A "&" character is prepended to "path", thus the argument to eval() is
"&path".  The result will then be the value of the 'path' option.

==============================================================================
*41.6*	Using functions

Vim defines many functions and provides a large amount of functionality that
way.  A few examples will be given in this section.  You can find the whole
list below: |function-list|.

A function is called with the parameters in between parentheses, separated by
commas.  Example: >

	search("Date: ", "W")

This calls the search() function, with arguments "Date: " and "W".  The
search() function uses its first argument as a search pattern and the second
one as flags.  The "W" flag means the search doesn't wrap around the end of
the file.

Using the  `call` command is optional in |Vim9| script.  This works the same
way and also works in legacy script and on the command line: >

	call search("Date: ", "W")

A function can be called in an expression.  Example: >

	var line = getline(".")
	var repl = substitute(line, '\a', "*", "g")
	setline(".", repl)

The getline() function obtains a line from the current buffer.  Its argument
is a specification of the line number.  In this case "." is used, which means
the line where the cursor is.

The substitute() function does something similar to the `:substitute` command.
The first argument "line" is the string on which to perform the substitution.
The second argument '\a' is the pattern, the third "*" is the replacement
string.  Finally, the last argument "g" is the flags.

The setline() function sets the line, specified by the first argument, to a
new string, the second argument.  In this example the line under the cursor is
replaced with the result of the substitute().  Thus the effect of the three
statements is equal to: >

	:substitute/\a/*/g

Using the functions becomes more interesting when you do more work before and
after the substitute() call.


FUNCTIONS						*function-list*

There are many functions.  We will mention them here, grouped by what they are
used for.  You can find an alphabetical list here: |builtin-function-list|.
Use CTRL-] on the function name to jump to detailed help on it.

String manipulation:					*string-functions*
	nr2char()		get a character by its number value
	list2str()		get a character string from a list of numbers
	char2nr()		get number value of a character
	str2list()		get list of numbers from a string
	str2nr()		convert a string to a Number
	str2float()		convert a string to a Float
	printf()		format a string according to % items
	escape()		escape characters in a string with a '\'
	shellescape()		escape a string for use with a shell command
	fnameescape()		escape a file name for use with a Vim command
	tr()			translate characters from one set to another
	strtrans()		translate a string to make it printable
	tolower()		turn a string to lowercase
	toupper()		turn a string to uppercase
	charclass()		class of a character
	match()			position where a pattern matches in a string
	matchend()		position where a pattern match ends in a string
	matchfuzzy()		fuzzy matches a string in a list of strings
	matchfuzzypos()		fuzzy matches a string in a list of strings
	matchstr()		match of a pattern in a string
	matchstrpos()		match and positions of a pattern in a string
	matchlist()		like matchstr() and also return submatches
	stridx()		first index of a short string in a long string
	strridx()		last index of a short string in a long string
	strlen()		length of a string in bytes
	strcharlen()		length of a string in characters
	strchars()		number of characters in a string
	strwidth()		size of string when displayed
	strdisplaywidth()	size of string when displayed, deals with tabs
	setcellwidths()		set character cell width overrides
	substitute()		substitute a pattern match with a string
	submatch()		get a specific match in ":s" and substitute()
	strpart()		get part of a string using byte index
	strcharpart()		get part of a string using char index
	slice()			take a slice of a string, using char index in
				Vim9 script
	strgetchar()		get character from a string using char index
	expand()		expand special keywords
	expandcmd()		expand a command like done for `:edit`
	iconv()			convert text from one encoding to another
	byteidx()		byte index of a character in a string
	byteidxcomp()		like byteidx() but count composing characters
	charidx()		character index of a byte in a string
	repeat()		repeat a string multiple times
	eval()			evaluate a string expression
	execute()		execute an Ex command and get the output
	win_execute()		like execute() but in a specified window
	trim()			trim characters from a string
	gettext()		lookup message translation

List manipulation:					*list-functions*
	get()			get an item without error for wrong index
	len()			number of items in a List
	empty()			check if List is empty
	insert()		insert an item somewhere in a List
	add()			append an item to a List
	extend()		append a List to a List
	extendnew()		make a new List and append items
	remove()		remove one or more items from a List
	copy()			make a shallow copy of a List
	deepcopy()		make a full copy of a List
	filter()		remove selected items from a List
	map()			change each List item
	mapnew()		make a new List with changed items
	reduce()		reduce a List to a value
	slice()			take a slice of a List
	sort()			sort a List
	reverse()		reverse the order of a List
	uniq()			remove copies of repeated adjacent items
	split()			split a String into a List
	join()			join List items into a String
	range()			return a List with a sequence of numbers
	string()		String representation of a List
	call()			call a function with List as arguments
	index()			index of a value in a List
	max()			maximum value in a List
	min()			minimum value in a List
	count()			count number of times a value appears in a List
	repeat()		repeat a List multiple times
	flatten()		flatten a List
	flattennew()		flatten a copy of a List

Dictionary manipulation:				*dict-functions*
	get()			get an entry without an error for a wrong key
	len()			number of entries in a Dictionary
	has_key()		check whether a key appears in a Dictionary
	empty()			check if Dictionary is empty
	remove()		remove an entry from a Dictionary
	extend()		add entries from one Dictionary to another
	extendnew()		make a new Dictionary and append items
	filter()		remove selected entries from a Dictionary
	map()			change each Dictionary entry
	mapnew()		make a new Dictionary with changed items
	keys()			get List of Dictionary keys
	values()		get List of Dictionary values
	items()			get List of Dictionary key-value pairs
	copy()			make a shallow copy of a Dictionary
	deepcopy()		make a full copy of a Dictionary
	string()		String representation of a Dictionary
	max()			maximum value in a Dictionary
	min()			minimum value in a Dictionary
	count()			count number of times a value appears

Floating point computation:				*float-functions*
	float2nr()		convert Float to Number
	abs()			absolute value (also works for Number)
	round()			round off
	ceil()			round up
	floor()			round down
	trunc()			remove value after decimal point
	fmod()			remainder of division
	exp()			exponential
	log()			natural logarithm (logarithm to base e)
	log10()			logarithm to base 10
	pow()			value of x to the exponent y
	sqrt()			square root
	sin()			sine
	cos()			cosine
	tan()			tangent
	asin()			arc sine
	acos()			arc cosine
	atan()			arc tangent
	atan2()			arc tangent
	sinh()			hyperbolic sine
	cosh()			hyperbolic cosine
	tanh()			hyperbolic tangent
	isinf()			check for infinity
	isnan()			check for not a number

Blob manipulation:					*blob-functions*
	blob2list()		get a list of numbers from a blob
	list2blob()		get a blob from a list of numbers

Other computation:					*bitwise-function*
	and()			bitwise AND
	invert()		bitwise invert
	or()			bitwise OR
	xor()			bitwise XOR
	sha256()		SHA-256 hash
	rand()			get a pseudo-random number
	srand()			initialize seed used by rand()

Variables:						*var-functions*
	type()			type of a variable as a number
	typename()		type of a variable as text
	islocked()		check if a variable is locked
	funcref()		get a Funcref for a function reference
	function()		get a Funcref for a function name
	getbufvar()		get a variable value from a specific buffer
	setbufvar()		set a variable in a specific buffer
	getwinvar()		get a variable from specific window
	gettabvar()		get a variable from specific tab page
	gettabwinvar()		get a variable from specific window & tab page
	setwinvar()		set a variable in a specific window
	settabvar()		set a variable in a specific tab page
	settabwinvar()		set a variable in a specific window & tab page
	garbagecollect()	possibly free memory

Cursor and mark position:		*cursor-functions* *mark-functions*
	col()			column number of the cursor or a mark
	virtcol()		screen column of the cursor or a mark
	line()			line number of the cursor or mark
	wincol()		window column number of the cursor
	winline()		window line number of the cursor
	cursor()		position the cursor at a line/column
	screencol()		get screen column of the cursor
	screenrow()		get screen row of the cursor
	screenpos()		screen row and col of a text character
	virtcol2col()		byte index of a text character on screen
	getcurpos()		get position of the cursor
	getpos()		get position of cursor, mark, etc.
	setpos()		set position of cursor, mark, etc.
	getmarklist()		list of global/local marks
	byte2line()		get line number at a specific byte count
	line2byte()		byte count at a specific line
	diff_filler()		get the number of filler lines above a line
	screenattr()		get attribute at a screen line/row
	screenchar()		get character code at a screen line/row
	screenchars()		get character codes at a screen line/row
	screenstring()		get string of characters at a screen line/row
	charcol()		character number of the cursor or a mark
	getcharpos()		get character position of cursor, mark, etc.
	setcharpos()		set character position of cursor, mark, etc.
	getcursorcharpos()	get character position of the cursor
	setcursorcharpos()	set character position of the cursor

Working with text in the current buffer:		*text-functions*
	getline()		get a line or list of lines from the buffer
	setline()		replace a line in the buffer
	append()		append line or list of lines in the buffer
	indent()		indent of a specific line
	cindent()		indent according to C indenting
	lispindent()		indent according to Lisp indenting
	nextnonblank()		find next non-blank line
	prevnonblank()		find previous non-blank line
	search()		find a match for a pattern
	searchpos()		find a match for a pattern
	searchcount()		get number of matches before/after the cursor
	searchpair()		find the other end of a start/skip/end
	searchpairpos()		find the other end of a start/skip/end
	searchdecl()		search for the declaration of a name
	getcharsearch()		return character search information
	setcharsearch()		set character search information

Working with text in another buffer:
	getbufline()		get a list of lines from the specified buffer
	setbufline()		replace a line in the specified buffer
	appendbufline()		append a list of lines in the specified buffer
	deletebufline()		delete lines from a specified buffer

					*system-functions* *file-functions*
System functions and manipulation of files:
	glob()			expand wildcards
	globpath()		expand wildcards in a number of directories
	glob2regpat()		convert a glob pattern into a search pattern
	findfile()		find a file in a list of directories
	finddir()		find a directory in a list of directories
	resolve()		find out where a shortcut points to
	fnamemodify()		modify a file name
	pathshorten()		shorten directory names in a path
	simplify()		simplify a path without changing its meaning
	executable()		check if an executable program exists
	exepath()		full path of an executable program
	filereadable()		check if a file can be read
	filewritable()		check if a file can be written to
	getfperm()		get the permissions of a file
	setfperm()		set the permissions of a file
	getftype()		get the kind of a file
	isabsolutepath()	check if a path is absolute
	isdirectory()		check if a directory exists
	getfsize()		get the size of a file
	getcwd()		get the current working directory
	haslocaldir()		check if current window used |:lcd| or |:tcd|
	tempname()		get the name of a temporary file
	mkdir()			create a new directory
	chdir()			change current working directory
	delete()		delete a file
	rename()		rename a file
	system()		get the result of a shell command as a string
	systemlist()		get the result of a shell command as a list
	environ()		get all environment variables
	getenv()		get one environment variable
	setenv()		set an environment variable
	hostname()		name of the system
	readfile()		read a file into a List of lines
	readblob()		read a file into a Blob
	readdir()		get a List of file names in a directory
	readdirex()		get a List of file information in a directory
	writefile()		write a List of lines or Blob into a file

Date and Time:				*date-functions* *time-functions*
	getftime()		get last modification time of a file
	localtime()		get current time in seconds
	strftime()		convert time to a string
	strptime()		convert a date/time string to time
	reltime()		get the current or elapsed time accurately
	reltimestr()		convert reltime() result to a string
	reltimefloat()		convert reltime() result to a Float

Autocmds:					*autocmd-functions*
	autocmd_add()		add a list of autocmds and groups
	autocmd_delete()	delete a list of autocmds and groups
	autocmd_get()		return a list of autocmds

			*buffer-functions* *window-functions* *arg-functions*
Buffers, windows and the argument list:
	argc()			number of entries in the argument list
	argidx()		current position in the argument list
	arglistid()		get id of the argument list
	argv()			get one entry from the argument list
	bufadd()		add a file to the list of buffers
	bufexists()		check if a buffer exists
	buflisted()		check if a buffer exists and is listed
	bufload()		ensure a buffer is loaded
	bufloaded()		check if a buffer exists and is loaded
	bufname()		get the name of a specific buffer
	bufnr()			get the buffer number of a specific buffer
	tabpagebuflist()	return List of buffers in a tab page
	tabpagenr()		get the number of a tab page
	tabpagewinnr()		like winnr() for a specified tab page
	winnr()			get the window number for the current window
	bufwinid()		get the window ID of a specific buffer
	bufwinnr()		get the window number of a specific buffer
	winbufnr()		get the buffer number of a specific window
	listener_add()		add a callback to listen to changes
	listener_flush()	invoke listener callbacks
	listener_remove()	remove a listener callback
	win_findbuf()		find windows containing a buffer
	win_getid()		get window ID of a window
	win_gettype()		get type of window
	win_gotoid()		go to window with ID
	win_id2tabwin()		get tab and window nr from window ID
	win_id2win()		get window nr from window ID
	win_move_separator()	move window vertical separator
	win_move_statusline()	move window status line
	win_splitmove()		move window to a split of another window
	getbufinfo()		get a list with buffer information
	gettabinfo()		get a list with tab page information
	getwininfo()		get a list with window information
	getchangelist()		get a list of change list entries
	getjumplist()		get a list of jump list entries
	swapinfo()		information about a swap file
	swapname()		get the swap file path of a buffer

Command line:					*command-line-functions*
	getcmdcompltype()	get the type of the current command line
				completion
	getcmdline()		get the current command line
	getcmdpos()		get position of the cursor in the command line
	getcmdscreenpos()	get screen position of the cursor in the
				command line
	setcmdpos()		set position of the cursor in the command line
	getcmdtype()		return the current command-line type
	getcmdwintype()		return the current command-line window type
	getcompletion()		list of command-line completion matches
	fullcommand()		get full command name

Quickfix and location lists:			*quickfix-functions*
	getqflist()		list of quickfix errors
	setqflist()		modify a quickfix list
	getloclist()		list of location list items
	setloclist()		modify a location list

Insert mode completion:				*completion-functions*
	complete()		set found matches
	complete_add()		add to found matches
	complete_check()	check if completion should be aborted
	complete_info()		get current completion information
	pumvisible()		check if the popup menu is displayed
	pum_getpos()		position and size of popup menu if visible

Folding:					*folding-functions*
	foldclosed()		check for a closed fold at a specific line
	foldclosedend()		like foldclosed() but return the last line
	foldlevel()		check for the fold level at a specific line
	foldtext()		generate the line displayed for a closed fold
	foldtextresult()	get the text displayed for a closed fold

Syntax and highlighting:	  *syntax-functions* *highlighting-functions*
	clearmatches()		clear all matches defined by |matchadd()| and
				the |:match| commands
	getmatches()		get all matches defined by |matchadd()| and
				the |:match| commands
	hlexists()		check if a highlight group exists
	hlget()			get highlight group attributes
	hlset()			set highlight group attributes
	hlID()			get ID of a highlight group
	synID()			get syntax ID at a specific position
	synIDattr()		get a specific attribute of a syntax ID
	synIDtrans()		get translated syntax ID
	synstack()		get list of syntax IDs at a specific position
	synconcealed()		get info about concealing
	diff_hlID()		get highlight ID for diff mode at a position
	matchadd()		define a pattern to highlight (a "match")
	matchaddpos()		define a list of positions to highlight
	matcharg()		get info about |:match| arguments
	matchdelete()		delete a match defined by |matchadd()| or a
				|:match| command
	setmatches()		restore a list of matches saved by
				|getmatches()|

Spelling:					*spell-functions*
	spellbadword()		locate badly spelled word at or after cursor
	spellsuggest()		return suggested spelling corrections
	soundfold()		return the sound-a-like equivalent of a word

History:					*history-functions*
	histadd()		add an item to a history
	histdel()		delete an item from a history
	histget()		get an item from a history
	histnr()		get highest index of a history list

Interactive:					*interactive-functions*
	browse()		put up a file requester
	browsedir()		put up a directory requester
	confirm()		let the user make a choice
	getchar()		get a character from the user
	getcharstr()		get a character from the user as a string
	getcharmod()		get modifiers for the last typed character
	getmousepos()		get last known mouse position
	echoraw()		output characters as-is
	feedkeys()		put characters in the typeahead queue
	input()			get a line from the user
	inputlist()		let the user pick an entry from a list
	inputsecret()		get a line from the user without showing it
	inputdialog()		get a line from the user in a dialog
	inputsave()		save and clear typeahead
	inputrestore()		restore typeahead

GUI:						*gui-functions*
	getfontname()		get name of current font being used
	getwinpos()		position of the Vim window
	getwinposx()		X position of the Vim window
	getwinposy()		Y position of the Vim window
	balloon_show()		set the balloon content
	balloon_split()		split a message for a balloon
	balloon_gettext()	get the text in the balloon

Vim server:					*server-functions*
	serverlist()		return the list of server names
	remote_startserver()	run a server
	remote_send()		send command characters to a Vim server
	remote_expr()		evaluate an expression in a Vim server
	server2client()		send a reply to a client of a Vim server
	remote_peek()		check if there is a reply from a Vim server
	remote_read()		read a reply from a Vim server
	foreground()		move the Vim window to the foreground
	remote_foreground()	move the Vim server window to the foreground

Window size and position:			*window-size-functions*
	winheight()		get height of a specific window
	winwidth()		get width of a specific window
	win_screenpos()		get screen position of a window
	winlayout()		get layout of windows in a tab page
	winrestcmd()		return command to restore window sizes
	winsaveview()		get view of current window
	winrestview()		restore saved view of current window

Mappings and Menus:			    *mapping-functions*
	digraph_get()		get |digraph|
	digraph_getlist()	get all |digraph|s
	digraph_set()		register |digraph|
	digraph_setlist()	register multiple |digraph|s
	hasmapto()		check if a mapping exists
	mapcheck()		check if a matching mapping exists
	maparg()		get rhs of a mapping
	maplist()		get list of all mappings
	mapset()		restore a mapping
	menu_info()		get information about a menu item
	wildmenumode()		check if the wildmode is active

Testing:				    *test-functions*
	assert_equal()		assert that two expressions values are equal
	assert_equalfile()	assert that two file contents are equal
	assert_notequal()	assert that two expressions values are not equal
	assert_inrange()	assert that an expression is inside a range
	assert_match()		assert that a pattern matches the value
	assert_notmatch()	assert that a pattern does not match the value
	assert_false()		assert that an expression is false
	assert_true()		assert that an expression is true
	assert_exception()	assert that a command throws an exception
	assert_beeps()		assert that a command beeps
	assert_nobeep()		assert that a command does not cause a beep
	assert_fails()		assert that a command fails
	assert_report()		report a test failure
	test_alloc_fail()	make memory allocation fail
	test_autochdir()	enable 'autochdir' during startup
	test_override()		test with Vim internal overrides
	test_garbagecollect_now()   free memory right now
	test_garbagecollect_soon()  set a flag to free memory soon
	test_getvalue()		get value of an internal variable
	test_gui_event()	generate a GUI event for testing
	test_ignore_error()	ignore a specific error message
	test_null_blob()	return a null Blob
	test_null_channel()	return a null Channel
	test_null_dict()	return a null Dict
	test_null_function()	return a null Funcref
	test_null_job()		return a null Job
	test_null_list()	return a null List
	test_null_partial()	return a null Partial function
	test_null_string()	return a null String
	test_settime()		set the time Vim uses internally
	test_setmouse()		set the mouse position
	test_feedinput()	add key sequence to input buffer
	test_option_not_set()	reset flag indicating option was set
	test_refcount()		return an expression's reference count
	test_srand_seed()	set the seed value for srand()
	test_unknown()		return a value with unknown type
	test_void()		return a value with void type

Inter-process communication:		    *channel-functions*
	ch_canread()		check if there is something to read
	ch_open()		open a channel
	ch_close()		close a channel
	ch_close_in()		close the in part of a channel
	ch_read()		read a message from a channel
	ch_readblob()		read a Blob from a channel
	ch_readraw()		read a raw message from a channel
	ch_sendexpr()		send a JSON message over a channel
	ch_sendraw()		send a raw message over a channel
	ch_evalexpr()		evaluate an expression over channel
	ch_evalraw()		evaluate a raw string over channel
	ch_status()		get status of a channel
	ch_getbufnr()		get the buffer number of a channel
	ch_getjob()		get the job associated with a channel
	ch_info()		get channel information
	ch_log()		write a message in the channel log file
	ch_logfile()		set the channel log file
	ch_setoptions()		set the options for a channel
	json_encode()		encode an expression to a JSON string
	json_decode()		decode a JSON string to Vim types
	js_encode()		encode an expression to a JSON string
	js_decode()		decode a JSON string to Vim types

Jobs:						*job-functions*
	job_start()		start a job
	job_stop()		stop a job
	job_status()		get the status of a job
	job_getchannel()	get the channel used by a job
	job_info()		get information about a job
	job_setoptions()	set options for a job

Signs:						*sign-functions*
	sign_define()		define or update a sign
	sign_getdefined()	get a list of defined signs
	sign_getplaced()	get a list of placed signs
	sign_jump()		jump to a sign
	sign_place()		place a sign
	sign_placelist()	place a list of signs
	sign_undefine()		undefine a sign
	sign_unplace()		unplace a sign
	sign_unplacelist()	unplace a list of signs

Terminal window:				*terminal-functions*
	term_start()		open a terminal window and run a job
	term_list()		get the list of terminal buffers
	term_sendkeys()		send keystrokes to a terminal
	term_wait()		wait for screen to be updated
	term_getjob()		get the job associated with a terminal
	term_scrape()		get row of a terminal screen
	term_getline()		get a line of text from a terminal
	term_getattr()		get the value of attribute {what}
	term_getcursor()	get the cursor position of a terminal
	term_getscrolled()	get the scroll count of a terminal
	term_getaltscreen()	get the alternate screen flag
	term_getsize()		get the size of a terminal
	term_getstatus()	get the status of a terminal
	term_gettitle()		get the title of a terminal
	term_gettty()		get the tty name of a terminal
	term_setansicolors()	set 16 ANSI colors, used for GUI
	term_getansicolors()	get 16 ANSI colors, used for GUI
	term_dumpdiff()		display difference between two screen dumps
	term_dumpload()		load a terminal screen dump in a window
	term_dumpwrite()	dump contents of a terminal screen to a file
	term_setkill()		set signal to stop job in a terminal
	term_setrestore()	set command to restore a terminal
	term_setsize()		set the size of a terminal
	term_setapi()		set terminal JSON API function name prefix

Popup window:					*popup-window-functions*
	popup_create()		create popup centered in the screen
	popup_atcursor()	create popup just above the cursor position,
				closes when the cursor moves away
	popup_beval()		at the position indicated by v:beval_
				variables, closes when the mouse moves away
	popup_notification()	show a notification for three seconds
	popup_dialog()		create popup centered with padding and border
	popup_menu()		prompt for selecting an item from a list
	popup_hide()		hide a popup temporarily
	popup_show()		show a previously hidden popup
	popup_move()		change the position and size of a popup
	popup_setoptions()	override options of a popup
	popup_settext()		replace the popup buffer contents
	popup_close()		close one popup
	popup_clear()		close all popups
	popup_filter_menu()	select from a list of items
	popup_filter_yesno()	block until 'y' or 'n' is pressed
	popup_getoptions()	get current options for a popup
	popup_getpos()		get actual position and size of a popup
	popup_findinfo()	get window ID for popup info window
	popup_findpreview()	get window ID for popup preview window
	popup_list()		get list of all popup window IDs
	popup_locate()		get popup window ID from its screen position

Timers:						*timer-functions*
	timer_start()		create a timer
	timer_pause()		pause or unpause a timer
	timer_stop()		stop a timer
	timer_stopall()		stop all timers
	timer_info()		get information about timers

Tags:						*tag-functions*
	taglist()		get list of matching tags
	tagfiles()		get a list of tags files
	gettagstack()		get the tag stack of a window
	settagstack()		modify the tag stack of a window

Prompt Buffer:					*promptbuffer-functions*
	prompt_getprompt()	get the effective prompt text for a buffer
	prompt_setcallback()	set prompt callback for a buffer
	prompt_setinterrupt()	set interrupt callback for a buffer
	prompt_setprompt()	set the prompt text for a buffer

Text Properties:				*text-property-functions*
	prop_add()		attach a property at a position
	prop_add_list()		attach a property at multiple positions
	prop_clear()		remove all properties from a line or lines
	prop_find()		search for a property
	prop_list()		return a list of all properties in a line
	prop_remove()		remove a property from a line
	prop_type_add()		add/define a property type
	prop_type_change()	change properties of a type
	prop_type_delete()	remove a text property type
	prop_type_get()		return the properties of a type
	prop_type_list()	return a list of all property types

Sound:							*sound-functions*
	sound_clear()		stop playing all sounds
	sound_playevent()	play an event's sound
	sound_playfile()	play a sound file
	sound_stop()		stop playing a sound

Various:					*various-functions*
	mode()			get current editing mode
	state()			get current busy state
	visualmode()		last visual mode used
	exists()		check if a variable, function, etc. exists
	exists_compiled()	like exists() but check at compile time
	has()			check if a feature is supported in Vim
	changenr()		return number of most recent change
	cscope_connection()	check if a cscope connection exists
	did_filetype()		check if a FileType autocommand was used
	eventhandler()		check if invoked by an event handler
	getpid()		get process ID of Vim
	getimstatus()		check if IME status is active
	interrupt()		interrupt script execution
	windowsversion()	get MS-Windows version
	terminalprops()		properties of the terminal

	libcall()		call a function in an external library
	libcallnr()		idem, returning a number

	undofile()		get the name of the undo file
	undotree()		return the state of the undo tree

	getreg()		get contents of a register
	getreginfo()		get information about a register
	getregtype()		get type of a register
	setreg()		set contents and type of a register
	reg_executing()		return the name of the register being executed
	reg_recording()		return the name of the register being recorded

	shiftwidth()		effective value of 'shiftwidth'

	wordcount()		get byte/word/char count of buffer

	luaeval()		evaluate |Lua| expression
	mzeval()		evaluate |MzScheme| expression
	perleval()		evaluate Perl expression (|+perl|)
	py3eval()		evaluate Python expression (|+python3|)
	pyeval()		evaluate Python expression (|+python|)
	pyxeval()		evaluate |python_x| expression
	rubyeval()		evaluate |Ruby| expression

	debugbreak()		interrupt a program being debugged

==============================================================================
*41.7*	Defining a function

Vim enables you to define your own functions.  The basic function declaration
begins as follows: >

	def {name}({var1}, {var2}, ...): return-type
	  {body}
	enddef
<
	Note:
	Function names must begin with a capital letter.

Let's define a short function to return the smaller of two numbers.  It starts
with this line: >

	def Min(num1: number, num2: number): number

This tells Vim that the function is named "Min", it takes two arguments that
are numbers: "num1" and "num2" and returns a number.

The first thing you need to do is to check to see which number is smaller:
   >
	if num1 < num2

Let's assign the variable "smaller" the value of the smallest number: >

	var smaller: number
	if num1 < num2
	  smaller = num1
	else
	  smaller = num2
	endif

The variable "smaller" is a local variable.  Variables used inside a function
are local unless prefixed by something like "g:", "w:", or "s:".

	Note:
	To access a global variable from inside a function you must prepend
	"g:" to it.  Thus "g:today" inside a function is used for the global
	variable "today", and "today" is another variable, local to the
	function or the script.

You now use the `return` statement to return the smallest number to the user.
Finally, you end the function: >

	  return smaller
	enddef

The complete function definition is as follows: >

	def Min(num1: number, num2: number): number
	  var smaller: number
	  if num1 < num2
	    smaller = num1
	  else
	    smaller = num2
	  endif
	  return smaller
	enddef

Obviously this is a verbose example.  You can make it shorter by using two
return commands: >

	def Min(num1: number, num2: number): number
	  if num1 < num2
	    return num1
	  endif
	  return num2
	enddef

And if you remember the conditional expression, you need only one line: >

	def Min(num1: number, num2: number): number
	  return num1 < num2 ? num1 : num2
	enddef

A user defined function is called in exactly the same way as a built-in
function.  Only the name is different.  The Min function can be used like
this: >

	echo Min(5, 8)

Only now will the function be executed and the lines be parsed by Vim.
If there are mistakes, like using an undefined variable or function, you will
now get an error message.  When defining the function these errors are not
detected.  To get the errors sooner you can tell Vim to compile all the
functions in the script: >

	defcompile

Compiling functions takes a little time, but does report errors early.  You
could use `:defcompile` at the end of your script while working on it, and
comment it out when everything is fine.

For a function that does not return anything simply leave out the return type: >

	def SayIt(text: string)
	  echo text
	enddef

It is also possible to define a legacy function with `function` and
`endfunction`.  These do not have types and are not compiled.  Therefore they
execute much slower.


USING A RANGE

A line range can be used with a function call.  The function will be called
once for every line in the range, with the cursor in that line.  Example: >

	def Number()
	  echo "line " .. line(".") .. " contains: " .. getline(".")
	enddef

If you call this function with: >

	:10,15call Number()

The function will be called six times, starting on line 10 and ending on line
15.


VARIABLE NUMBER OF ARGUMENTS

Vim enables you to define functions that have a variable number of arguments.
The following command, for instance, defines a function that must have 1
argument (start) and can have up to 20 additional arguments: >

	def Show(start: string, ...items: list<string>)

The variable "items" will be a list in the function containing the extra
arguments.  You can use it like any list, for example: >

	def Show(start: string, ...items: list<string>)
	  echohl Title
	  echo "start is " .. start
	  echohl None
	  for index in range(len(items))
	    echon $"  Arg {index} is {items[index]}"
	  endfor
	  echo
	enddef

You can call it like this: >

	Show('Title', 'one', 'two', 'three')
<	start is Title  Arg 0 is one  Arg 1 is two  Arg 2 is three ~
	
This uses the `echohl` command to specify the highlighting used for the
following `echo` command.  `echohl None` stops it again.  The `echon` command
works like `echo`, but doesn't output a line break.

If you call it with one argument the "items" list will be empty.
`range(len(items))` returns a list with the indexes, what `for` loops over,
we'll explain that further down.


LISTING FUNCTIONS

The `function` command lists the names and arguments of all user-defined
functions: >

	:function
<	def <SNR>86_Show(start: string, ...items: list<string>) ~
	function GetVimIndent() ~
	function SetSyn(name) ~

The "<SNR>" prefix means that a function is script-local.  |Vim9| functions
wil start with "def" and include argument and return types.  Legacy functions
are listed with "function".

To see what a function does, use its name as an argument for `function`: >

	:function SetSyn
<	1     if &syntax == '' ~
	2       let &syntax = a:name ~
	3     endif ~
	   endfunction ~

To see the "Show" function you need to include the script prefix, since
multiple "Show" functions can be defined in different scripts.  To find
the exact name you can use `function`, but the result may be a very long list.
To only get the functions matching a pattern you can use the `filter` prefix:
>
	:filter Show function
<	def <SNR>86_Show(start: string, ...items: list<string>) ~
>
	:function <SNR>86_Show
<	1    echohl Title ~
	2    echo "start is " .. start ~
	etc.


DEBUGGING

The line number is useful for when you get an error message or when debugging.
See |debug-scripts| about debugging mode.

You can also set the 'verbose' option to 12 or higher to see all function
calls.  Set it to 15 or higher to see every executed line.


DELETING A FUNCTION

To delete the SetSyn() function: >

	:delfunction SetSyn

Deleting only works for global functions and functions in legacy script, not
for functions defined in a |Vim9| script.

You get an error when the function doesn't exist or cannot be deleted.


FUNCTION REFERENCES

Sometimes it can be useful to have a variable point to one function or
another.  You can do it with a function reference variable.  Often shortened
to "funcref".  Example: >

	def Right(): string
	  return 'Right!'
	enddef
	def Wrong(): string
	  return 'Wrong!'
	enddef
	
	var Afunc = g:result == 1 ? Right : Wrong
	echo Afunc()
<	Wrong! ~

This assumes "g:result" is not one.  See |Funcref| for details.

Note that the name of a variable that holds a function reference must start
with a capital.  Otherwise it could be confused with the name of a builtin
function.

More information about defining your own functions here: |user-functions|.

==============================================================================
*41.8*	Lists and Dictionaries

So far we have used the basic types String and Number.  Vim also supports two
composite types: List and Dictionary.

A List is an ordered sequence of items.  The items can be any kind of value,
thus you can make a List of numbers, a List of Lists and even a List of mixed
items.  To create a List with three strings: >

	var alist = ['aap', 'noot', 'mies']

The List items are enclosed in square brackets and separated by commas.  To
create an empty List: >

	var alist = []

You can add items to a List with the add() function: >

	var alist = []
	add(alist, 'foo')
	add(alist, 'bar')
	echo alist
<	['foo', 'bar'] ~

List concatenation is done with +: >

	var alist = ['foo', 'bar']
	alist = alist + ['and', 'more']
	echo alist
<	['foo', 'bar', 'and', 'more'] ~

Or, if you want to extend a List with a function, use `extend()`: >

	var alist = ['one']
	extend(alist, ['two', 'three'])
	echo alist
<	['one', 'two', 'three'] ~

Notice that using `add()` will have a different effect than `extend()`: >

	var alist = ['one']
	add(alist, ['two', 'three'])
	echo alist
<	['one', ['two', 'three']] ~

The second argument of add() is added as an item, now you have a nested list.


FOR LOOP

One of the nice things you can do with a List is iterate over it: >

	var alist = ['one', 'two', 'three']
	for n in alist
	  echo n
	endfor
<	one ~
	two ~
	three ~

This will loop over each element in List "alist", assigning each value to
variable "n".  The generic form of a for loop is: >

	for {varname} in {list-expression}
	  {commands}
	endfor

To loop a certain number of times you need a List of a specific length.  The
range() function creates one for you: >

	for a in range(3)
	  echo a
	endfor
<	0 ~
	1 ~
	2 ~

Notice that the first item of the List that range() produces is zero, thus the
last item is one less than the length of the list.  Detail: Internally range()
does not actually create the list, so that a large range used in a for loop
works efficiently.  When used elsewhere, the range is turned into an actual
list, which takes more time for a long ist.

You can also specify the maximum value, the stride and even go backwards: >

	for a in range(8, 4, -2)
	  echo a
	endfor
<	8 ~
	6 ~
	4 ~

A more useful example, looping over all the lines in the buffer: >

	for line in getline(1, 50)
	  if line =~ "Date: "
	    echo line
	  endif
	endfor

This looks into lines 1 to 50 (inclusive) and echoes any date found in there.

For further reading see |Lists|.


DICTIONARIES

A Dictionary stores key-value pairs.  You can quickly lookup a value if you
know the key.  A Dictionary is created with curly braces: >

	var uk2nl = {one: 'een', two: 'twee', three: 'drie'}

Now you can lookup words by putting the key in square brackets: >

	echo uk2nl['two']
<	twee ~

If the key does not have special characters, you can use the dot notation: >

	echo uk2nl.two
<	twee ~

The generic form for defining a Dictionary is: >

	{<key> : <value>, ...}

An empty Dictionary is one without any keys: >

	{}

The possibilities with Dictionaries are numerous.  There are various functions
for them as well.  For example, you can obtain a list of the keys and loop
over them: >

	for key in keys(uk2nl)
	  echo key
	endfor
<	three ~
	one ~
	two ~

You will notice the keys are not ordered.  You can sort the list to get a
specific order: >

	for key in sort(keys(uk2nl))
	  echo key
	endfor
<	one ~
	three ~
	two ~

But you can never get back the order in which items are defined.  For that you
need to use a List, it stores items in an ordered sequence.

For further reading see |Dictionaries|.

==============================================================================
*41.9*	Exceptions

Let's start with an example: >

	try
	   read ~/templates/pascal.tmpl
	catch /E484:/
	   echo "Sorry, the Pascal template file cannot be found."
	endtry

The `read` command will fail if the file does not exist.  Instead of
generating an error message, this code catches the error and gives the user a
message with more information.

For the commands in between `try` and `endtry` errors are turned into
exceptions.  An exception is a string.  In the case of an error the string
contains the error message.  And every error message has a number.  In this
case, the error we catch contains "E484:".  This number is guaranteed to stay
the same (the text may change, e.g., it may be translated).

Besides being able to give a nice error message, Vim will also continue
executing commands after the `:endtry`.  Otherwise, once an uncaught error is
encountered, execution of the script/function/mapping will be aborted.

When the `read` command causes another error, the pattern "E484:" will not
match in it.  Thus this exception will not be caught and result in the usual
error message and excecution is aborted.

You might be tempted to do this: >

	try
	   read ~/templates/pascal.tmpl
	catch
	   echo "Sorry, the Pascal template file cannot be found."
	endtry

This means all errors are caught.  But then you will not see an error that
would indicate a completely different problem, such as "E21: Cannot make
changes, 'modifiable' is off".  Think twice before you catch any error!

Another useful mechanism is the `finally` command: >

	var tmp = tempname()
	try
	   exe ":.,$write " .. tmp
	   exe "!filter " .. tmp
	   :.,$delete
	   exe ":$read " .. tmp
	finally
	   delete(tmp)
	endtry

This filters the lines from the cursor until the end of the file through the
"filter" command, which takes a file name argument.  No matter if the
filtering works, if something goes wrong in between `try` and `finally` or the
user cancels the filtering by pressing CTRL-C, the `delete(tmp)` call is
always executed.  This makes sure you don't leave the temporary file behind.

The `finally` does not catch the exception, the error will still abort
further execution.

More information about exception handling can be found in the reference
manual: |exception-handling|.

==============================================================================
*41.10*	Various remarks

Here are a few items that are useful to know when writing Vim scripts.


FILEFORMAT

The end-of-line character depends on the system.  For Vim scripts it is
recommended to always use the Unix fileformat.  This also works on any other
system.  That way you can copy your Vim scripts from MS-Windows to Unix and
they still work.  See |:source_crnl|.  To be sure it is set right, do this
before writing the file: >

	:setlocal fileformat=unix


WHITE SPACE

Blank lines are allowed and ignored.

Leading whitespace characters (blanks and TABs) are always ignored.

Trailing whitespace is often ignored, but not always.  One command that
includes it is `map`.

To include a whitespace character in the value of an option, it must be
escaped by a "\" (backslash)  as in the following example: >

	:set tags=my\ nice\ file

If it would be written as: >

	:set tags=my nice file

This will issue an error, because it is interpreted as: >

	:set tags=my
	:set nice
	:set file

|Vim9| script is very picky when it comes to white space.  This was done
intentionally to make sure scripts are easy to read and to avoid mistakes.
If you use white space sensibly it will just work.  When not you will get an
error message telling you where white space is missing or should be removed.


COMMENTS

In |Vim9| script the character # starts a comment.  That character and
everything after it until the end-of-line is considered a comment and
is ignored, except for commands that don't consider comments, as shown in
examples below.  A comment can start on any character position on the line,
but not when it is part of the command, e.g. inside a string.

The character " (the double quote mark) starts a comment in legacy script.  
This involves some cleverness to make sure double quoted strings are not
recognized as comments (just one reason to prefer |Vim9| script).

There is a little "catch" with comments for some commands.  Examples: >

	abbrev dev development	# shorthand
	map <F3> o#include	# insert include
	execute cmd		# do it
	!ls *.c			# list C files

- The abbreviation 'dev' will be expanded to 'development  # shorthand'.
- The mapping of <F3> will actually be the whole line after the 'o# ....'
  including the '# insert include'.
- The `execute` command will give an error.
- The `!` command will send everything after it to the shell, most likely
  causing an error.

There can be no comment after `map`, `abbreviate`, `execute` and `!` commands
(there are a few more commands with this restriction).  For the `map`,
`abbreviate` and `execute` commands there is a trick: >

	abbrev dev development|# shorthand
	map <F3> o#include|# insert include
	execute '!ls *.c'	|# do it

With the '|' character the command is separated from the next one.  And that
next command is only a comment.  The last command, using `execute` is a
general solution, it works for all commands that do not accept a comment or a
'|' to separate the next command.

Notice that there is no white space before the '|' in the abbreviation and
mapping.  For these commands, any character until the end-of-line or '|' is
included.  As a consequence of this behavior, you don't always see that
trailing whitespace is included: >

	map <F4> o#include  

Here it is intended, in other cases it might be accidental.  To spot these
problems, you can highlight trailing spaces: >
	match Search /\s\+$/

For Unix there is one special way to comment a line, that allows making a Vim
script executable, and it also works in legacy script: >
	#!/usr/bin/env vim -S
	echo "this is a Vim script"
	quit


Advance information about writing Vim script is in |usr_50.txt|.

==============================================================================

Next chapter: |usr_42.txt|  Add new menus

Copyright: see |manual-copyright|  vim:tw=78:ts=8:noet:ft=help:norl: