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+*userfunc.txt*	For Vim version 9.0.  Last change: 2022 Jun 17
+
+
+		  VIM REFERENCE MANUAL	  by Bram Moolenaar
+
+
+Defining and using functions.
+
+This is introduced in section |41.7| of the user manual.
+
+1. Defining a fuction			|define-function|
+2. Calling a fuction			|:call|
+3. Cleaning up in a function		|:defer|
+4. Automatically loading functions	|autoload-functions|
+
+==============================================================================
+
+1. Defining a fuction ~
+						*define-function*
+New functions can be defined.  These can be called just like builtin
+functions.  The function executes a sequence of Ex commands.  Normal mode
+commands can be executed with the |:normal| command.
+
+The function name must start with an uppercase letter, to avoid confusion with
+builtin functions.  To prevent from using the same name in different scripts
+make them script-local.  If you do use a global function the avoid obvious,
+short names.  A good habit is to start the function name with the name of the
+script, e.g., "HTMLcolor()".
+
+In legacy script it is also possible to use curly braces, see
+|curly-braces-names|.
+
+The |autoload| facility is useful to define a function only when it's called.
+
+							*local-function*
+A function local to a legacy script must start with "s:".  A local script
+function can only be called from within the script and from functions, user
+commands and autocommands defined in the script.  It is also possible to call
+the function from a mapping defined in the script, but then |<SID>| must be
+used instead of "s:" when the mapping is expanded outside of the script.
+There are only script-local functions, no buffer-local or window-local
+functions.
+
+In |Vim9| script functions are local to the script by default, prefix "g:" to
+define a global function.
+
+				*:fu* *:function* *E128* *E129* *E123* *E454*
+:fu[nction]		List all functions and their arguments.
+
+:fu[nction] {name}	List function {name}.
+			{name} can also be a |Dictionary| entry that is a
+			|Funcref|: >
+				:function dict.init
+
+:fu[nction] /{pattern}	List functions with a name matching {pattern}.
+			Example that lists all functions ending with "File": >
+				:function /File$
+<
+							*:function-verbose*
+When 'verbose' is non-zero, listing a function will also display where it was
+last defined. Example: >
+
+    :verbose function SetFileTypeSH
+	function SetFileTypeSH(name)
+	    Last set from /usr/share/vim/vim-7.0/filetype.vim
+<
+See |:verbose-cmd| for more information.
+
+						*E124* *E125* *E853* *E884*
+:fu[nction][!] {name}([arguments]) [range] [abort] [dict] [closure]
+			Define a new function by the name {name}.  The body of
+			the function follows in the next lines, until the
+			matching |:endfunction|.
+								*E1267*
+			The name must be made of alphanumeric characters and
+			'_', and must start with a capital or "s:" (see
+			above).  Note that using "b:" or "g:" is not allowed.
+			(since patch 7.4.260 E884 is given if the function
+			name has a colon in the name, e.g. for "foo:bar()".
+			Before that patch no error was given).
+
+			{name} can also be a |Dictionary| entry that is a
+			|Funcref|: >
+				:function dict.init(arg)
+<			"dict" must be an existing dictionary.  The entry
+			"init" is added if it didn't exist yet.  Otherwise [!]
+			is required to overwrite an existing function.  The
+			result is a |Funcref| to a numbered function.  The
+			function can only be used with a |Funcref| and will be
+			deleted if there are no more references to it.
+								*E127* *E122*
+			When a function by this name already exists and [!] is
+			not used an error message is given.  There is one
+			exception: When sourcing a script again, a function
+			that was previously defined in that script will be
+			silently replaced.
+			When [!] is used, an existing function is silently
+			replaced.  Unless it is currently being executed, that
+			is an error.
+			NOTE: Use ! wisely.  If used without care it can cause
+			an existing function to be replaced unexpectedly,
+			which is hard to debug.
+			NOTE: In Vim9 script script-local functions cannot be
+			deleted or redefined.
+
+			For the {arguments} see |function-argument|.
+
+					*:func-range* *a:firstline* *a:lastline*
+			When the [range] argument is added, the function is
+			expected to take care of a range itself.  The range is
+			passed as "a:firstline" and "a:lastline".  If [range]
+			is excluded, ":{range}call" will call the function for
+			each line in the range, with the cursor on the start
+			of each line.  See |function-range-example|.
+			The cursor is still moved to the first line of the
+			range, as is the case with all Ex commands.
+								*:func-abort*
+			When the [abort] argument is added, the function will
+			abort as soon as an error is detected.
+								*:func-dict*
+			When the [dict] argument is added, the function must
+			be invoked through an entry in a |Dictionary|.  The
+			local variable "self" will then be set to the
+			dictionary.  See |Dictionary-function|.
+						*:func-closure* *E932*
+			When the [closure] argument is added, the function
+			can access variables and arguments from the outer
+			scope.  This is usually called a closure.  In this
+			example Bar() uses "x" from the scope of Foo().  It
+			remains referenced even after Foo() returns: >
+				:function! Foo()
+				:  let x = 0
+				:  function! Bar() closure
+				:    let x += 1
+				:    return x
+				:  endfunction
+				:  return funcref('Bar')
+				:endfunction
+
+				:let F = Foo()
+				:echo F()
+<				1 >
+				:echo F()
+<				2 >
+				:echo F()
+<				3
+
+						*function-search-undo*
+			The last used search pattern and the redo command "."
+			will not be changed by the function.  This also
+			implies that the effect of |:nohlsearch| is undone
+			when the function returns.
+
+			*:endf* *:endfunction* *E126* *E193* *W22* *E1151*
+:endf[unction] [argument]
+			The end of a function definition.  Best is to put it
+			on a line by its own, without [argument].
+
+			[argument] can be:
+				| command	command to execute next
+				\n command	command to execute next
+				" comment	always ignored
+				anything else	ignored, warning given when
+						'verbose' is non-zero
+			The support for a following command was added in Vim
+			8.0.0654, before that any argument was silently
+			ignored.
+
+			To be able to define a function inside an `:execute`
+			command, use line breaks instead of |:bar|: >
+				:exe "func Foo()\necho 'foo'\nendfunc"
+<
+				*:delf* *:delfunction* *E131* *E933* *E1084*
+:delf[unction][!] {name}
+			Delete function {name}.
+			{name} can also be a |Dictionary| entry that is a
+			|Funcref|: >
+				:delfunc dict.init
+<			This will remove the "init" entry from "dict".  The
+			function is deleted if there are no more references to
+			it.
+			With the ! there is no error if the function does not
+			exist.
+							*:retu* *:return* *E133*
+:retu[rn] [expr]	Return from a function.  When "[expr]" is given, it is
+			evaluated and returned as the result of the function.
+			If "[expr]" is not given, the number 0 is returned.
+			When a function ends without an explicit ":return",
+			the number 0 is returned.
+			In a :def function *E1095* is given if unreachable
+			code follows after the `:return`.
+			In legacy script there is no check for unreachable
+			lines, thus there is no warning if commands follow
+			`:return`.
+
+			If the ":return" is used after a |:try| but before the
+			matching |:finally| (if present), the commands
+			following the ":finally" up to the matching |:endtry|
+			are executed first.  This process applies to all
+			nested ":try"s inside the function.  The function
+			returns at the outermost ":endtry".
+
+						*function-argument* *a:var*
+An argument can be defined by giving its name.  In the function this can then
+be used as "a:name" ("a:" for argument).
+					*a:0* *a:1* *a:000* *E740* *...*
+Up to 20 arguments can be given, separated by commas.  After the named
+arguments an argument "..." can be specified, which means that more arguments
+may optionally be following.  In the function the extra arguments can be used
+as "a:1", "a:2", etc.  "a:0" is set to the number of extra arguments (which
+can be 0).  "a:000" is set to a |List| that contains these arguments.  Note
+that "a:1" is the same as "a:000[0]".
+							*E742* *E1090*
+The a: scope and the variables in it cannot be changed, they are fixed.
+However, if a composite type is used, such as |List| or |Dictionary| , you can
+change their contents.  Thus you can pass a |List| to a function and have the
+function add an item to it.  If you want to make sure the function cannot
+change a |List| or |Dictionary| use |:lockvar|.
+
+It is also possible to define a function without any arguments.  You must
+still supply the () then.
+
+It is allowed to define another function inside a function body.
+
+						*optional-function-argument*
+You can provide default values for positional named arguments.  This makes
+them optional for function calls.  When a positional argument is not
+specified at a call, the default expression is used to initialize it.
+This only works for functions declared with `:function` or `:def`, not for
+lambda expressions |expr-lambda|.
+
+Example: >
+  function Something(key, value = 10)
+     echo a:key .. ": " .. a:value
+  endfunction
+  call Something('empty')	"empty: 10"
+  call Something('key', 20)	"key: 20"
+
+The argument default expressions are evaluated at the time of the function
+call, not definition.  Thus it is possible to use an expression which is
+invalid the moment the function is defined.  The expressions are also only
+evaluated when arguments are not specified during a call.
+						*none-function_argument*
+You can pass |v:none| to use the default expression.  Note that this means you
+cannot pass v:none as an ordinary value when an argument has a default
+expression.
+
+Example: >
+  function Something(a = 10, b = 20, c = 30)
+  endfunction
+  call Something(1, v:none, 3)	    " b = 20
+<
+								*E989*
+Optional arguments with default expressions must occur after any mandatory
+arguments.  You can use "..." after all optional named arguments.
+
+It is possible for later argument defaults to refer to prior arguments,
+but not the other way around.  They must be prefixed with "a:", as with all
+arguments.
+
+Example that works: >
+  :function Okay(mandatory, optional = a:mandatory)
+  :endfunction
+Example that does NOT work: >
+  :function NoGood(first = a:second, second = 10)
+  :endfunction
+<
+When not using "...", the number of arguments in a function call must be at
+least equal to the number of mandatory named arguments.  When using "...", the
+number of arguments may be larger than the total of mandatory and optional
+arguments.
+
+							*local-variables*
+Inside a function local variables can be used.  These will disappear when the
+function returns.  Global variables need to be accessed with "g:".
+Inside functions local variables are accessed without prepending anything.
+But you can also prepend "l:" if you like.  This is required for some reserved
+names, such as "count".
+
+Example: >
+  :function Table(title, ...)
+  :  echohl Title
+  :  echo a:title
+  :  echohl None
+  :  echo a:0 .. " items:"
+  :  for s in a:000
+  :    echon ' ' .. s
+  :  endfor
+  :endfunction
+
+This function can then be called with: >
+  call Table("Table", "line1", "line2")
+  call Table("Empty Table")
+
+To return more than one value, return a |List|: >
+  :function Compute(n1, n2)
+  :  if a:n2 == 0
+  :    return ["fail", 0]
+  :  endif
+  :  return ["ok", a:n1 / a:n2]
+  :endfunction
+
+This function can then be called with: >
+  :let [success, div] = Compute(102, 6)
+  :if success == "ok"
+  :  echo div
+  :endif
+<
+==============================================================================
+
+2. Calling a fuction ~
+						*:cal* *:call* *E107*
+:[range]cal[l] {name}([arguments])
+		Call a function.  The name of the function and its arguments
+		are as specified with `:function`.  Up to 20 arguments can be
+		used.  The returned value is discarded.
+		In |Vim9| script using `:call` is optional, these two lines do
+		the same thing: >
+			call SomeFunc(arg)
+			SomeFunc(arg)
+<		Without a range and for functions that accept a range, the
+		function is called once.  When a range is given the cursor is
+		positioned at the start of the first line before executing the
+		function.
+		When a range is given and the function doesn't handle it
+		itself, the function is executed for each line in the range,
+		with the cursor in the first column of that line.  The cursor
+		is left at the last line (possibly moved by the last function
+		call).  The arguments are re-evaluated for each line.  Thus
+		this works:
+						*function-range-example*  >
+	:function Mynumber(arg)
+	:  echo line(".") .. " " .. a:arg
+	:endfunction
+	:1,5call Mynumber(getline("."))
+<
+		The "a:firstline" and "a:lastline" are defined anyway, they
+		can be used to do something different at the start or end of
+		the range.
+
+		Example of a function that handles the range itself: >
+
+	:function Cont() range
+	:  execute (a:firstline + 1) .. "," .. a:lastline .. 's/^/\t\\ '
+	:endfunction
+	:4,8call Cont()
+<
+		This function inserts the continuation character "\" in front
+		of all the lines in the range, except the first one.
+
+		When the function returns a composite value it can be further
+		dereferenced, but the range will not be used then.  Example: >
+	:4,8call GetDict().method()
+<		Here GetDict() gets the range but method() does not.
+
+								*E117*
+When a function cannot be found the error "E117: Unknown function" will be
+given.  If the function was using an autoload path or an autoload import and
+the script is a |Vim9| script, this may also be caused by the function not
+being exported.
+
+								*E132*
+The recursiveness of user functions is restricted with the |'maxfuncdepth'|
+option.
+
+It is also possible to use `:eval`.  It does not support a range, but does
+allow for method chaining, e.g.: >
+	eval GetList()->Filter()->append('$')
+
+A function can also be called as part of evaluating an expression or when it
+is used as a method: >
+	let x = GetList()
+	let y = GetList()->Filter()
+
+==============================================================================
+
+3. Cleaning up in a function ~
+							*:defer*
+:defer {func}({args})	Call {func} when the current function is done.
+			{args} are evaluated here.
+
+Quite often a command in a function has a global effect, which must be undone
+when the function finishes.  Handling this in all kinds of situations can be a
+hassle.  Especially when an unexpected error is encountered.  This can be done
+with `try` / `finally` blocks, but this gets complicated when there is more
+than one.
+
+A much simpler solution is using `defer`.  It schedules a function call when
+the function is returning, no matter if there is an error.  Example: >
+	func Filter(text) abort
+	  call writefile(a:text, 'Tempfile')
+	  call system('filter < Tempfile > Outfile')
+	  call Handle('Outfile')
+	  call delete('Tempfile')
+	  call delete('Outfile')
+	endfunc
+
+Here 'Tempfile' and 'Outfile' will not be deleted if something causes the
+function to abort.  `:defer` can be used to avoid that: >
+	func Filter(text) abort
+	  call writefile(a:text, 'Tempfile')
+	  defer delete('Tempfile')
+	  defer delete('Outfile')
+	  call system('filter < Tempfile > Outfile')
+	  call Handle('Outfile')
+	endfunc
+
+Note that deleting "Outfile" is scheduled before calling system(), since it
+can be created even when `system()` fails.
+
+The deferred functions are called in reverse order, the last one added is
+executed first.  A useless example: >
+	func Useless() abort
+	  for s in range(3)
+	    defer execute('echomsg "number ' .. s .. '"')
+	  endfor
+	endfunc
+
+Now `:messages` shows:
+	number 2
+	number 1
+	number 0
+
+Any return value of the deferred function is discarded.  The function cannot
+be followed by anything, such as "->func" or ".member".  Currently `:defer
+GetArg()->TheFunc()` does not work, it may work in a later version.
+
+Errors are reported but do not cause aborting execution of deferred functions.
+
+No range is accepted.
+
+==============================================================================
+
+4. Automatically loading functions ~
+							*autoload-functions*
+When using many or large functions, it's possible to automatically define them
+only when they are used.  There are two methods: with an autocommand and with
+the "autoload" directory in 'runtimepath'.
+
+In |Vim9| script there is also an autoload mechanism for imported scripts, see
+|import-autoload|.
+
+
+Using an autocommand ~
+
+This is introduced in the user manual, section |51.4|.
+
+The autocommand is useful if you have a plugin that is a long Vim script file.
+You can define the autocommand and quickly quit the script with `:finish`.
+That makes Vim startup faster.  The autocommand should then load the same file
+again, setting a variable to skip the `:finish` command.
+
+Use the FuncUndefined autocommand event with a pattern that matches the
+function(s) to be defined.  Example: >
+
+	:au FuncUndefined BufNet* source ~/vim/bufnetfuncs.vim
+
+The file "~/vim/bufnetfuncs.vim" should then define functions that start with
+"BufNet".  Also see |FuncUndefined|.
+
+
+Using an autoload script ~
+							*autoload* *E746*
+This is introduced in the user manual, section |52.2|.
+
+Using a script in the "autoload" directory is simpler, but requires using
+exactly the right file name.  A function that can be autoloaded has a name
+like this: >
+
+	:call filename#funcname()
+
+These functions are always global, in Vim9 script "g:" needs to be used: >
+	:call g:filename#funcname()
+
+When such a function is called, and it is not defined yet, Vim will search the
+"autoload" directories in 'runtimepath' for a script file called
+"filename.vim".  For example "~/.vim/autoload/filename.vim".  That file should
+then define the function like this: >
+
+	function filename#funcname()
+	   echo "Done!"
+	endfunction
+
+The file name and the name used before the # in the function must match
+exactly, and the defined function must have the name exactly as it will be
+called.  In Vim9 script the "g:" prefix must be used: >
+	function g:filename#funcname()
+
+or for a compiled function: >
+	def g:filename#funcname()
+
+It is possible to use subdirectories.  Every # in the function name works like
+a path separator.  Thus when calling a function: >
+
+	:call foo#bar#func()
+
+Vim will look for the file "autoload/foo/bar.vim" in 'runtimepath'.
+
+This also works when reading a variable that has not been set yet: >
+
+	:let l = foo#bar#lvar
+
+However, when the autoload script was already loaded it won't be loaded again
+for an unknown variable.
+
+When assigning a value to such a variable nothing special happens.  This can
+be used to pass settings to the autoload script before it's loaded: >
+
+	:let foo#bar#toggle = 1
+	:call foo#bar#func()
+
+Note that when you make a mistake and call a function that is supposed to be
+defined in an autoload script, but the script doesn't actually define the
+function, you will get an error message for the missing function.  If you fix
+the autoload script it won't be automatically loaded again.  Either restart
+Vim or manually source the script.
+
+Also note that if you have two script files, and one calls a function in the
+other and vice versa, before the used function is defined, it won't work.
+Avoid using the autoload functionality at the toplevel.
+
+In |Vim9| script you will get error *E1263* if you define a function with
+a "#" character in the name.  You should use a name without "#" and use
+`:export`.
+
+Hint: If you distribute a bunch of scripts you can pack them together with the
+|vimball| utility.  Also read the user manual |distribute-script|.
+
+
+ vim:tw=78:ts=8:noet:ft=help:norl: