*vim9.txt* For Vim version 8.2. Last change: 2020 Feb 21 VIM REFERENCE MANUAL by Bram Moolenaar THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE Vim9 script commands and expressions. Most expression help is in |eval|. This file is about the new syntax and features in Vim9 script. THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE 1 What is Vim9 script? |vim9-script| 2. Differences |vim9-differences| 3. New style functions |fast-functions| 4. Types |vim9-types| 5. Namespace, Import and Export |vim9script| 9. Rationale |vim9-rationale|
1. What is Vim9 script? *vim9-script* THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE Vim script has been growing over time, while keeping backwards compatibility. That means bad choices from the past often can't be changed. Execution is quite slow, every line is parsed every time it is executed. The main goal of Vim9 script is to drastically improve performance. An increase in execution speed of 10 to 100 times can be expected. A secondary goal is to avoid Vim-specific constructs and get closer to commonly used programming languages, such as JavaScript, TypeScript and Java. The performance improvements can only be achieved by not being 100% backwards compatible. For example, in a function the arguments are not available in the "a:" dictionary, as creating that dictionary adds quite a lot of overhead. Other differences are more subtle, such as how errors are handled. The Vim9 script syntax and semantics are used in: - a function defined with the `:def` command - a script file where the first command is `vim9script` When using `:function` in a Vim9 script file the legacy syntax is used. However, this is discouraged. Vim9 script and legacy Vim script can be mixed. There is no need to rewrite old scripts, they keep working as before.
2. Differences from legacy Vim script *vim9-differences* THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGEVim9 functions`:def` has no extra arguments like `:function` does: "range", "abort", "dict" or "closure". A `:def` function always aborts on an error, does not get a range passed and cannot be a "dict" function. In the function body: - Arguments are accessed by name, without "a:". - There is no "a:" dictionary or "a:000" list. Variable arguments are defined with a name and have a list type:def MyFunc(...itemlist: list<type>)for item in itemlist...Variable declarations with :let and :constLocal variables need to be declared with `:let`. Local constants need to be declared with `:const`. We refer to both as "variables". Variables can be local to a script, function or code block:vim9scriptlet script_var = 123def SomeFunc()let func_var = script_varif condlet block_var = func_var...The variables are only visible in the block where they are defined and nested blocks. Once the block ends the variable is no longer accessible:if condlet inner = 5elselet inner = 0endifecho inner " Error!The declaration must be done earlier:let inner: numberif condinner = 5elseinner = 0endifecho innerTo intentionally use a variable that won't be available later, a block can be used:{let temp = 'temp'...}echo temp " Error!An existing variable cannot be assigned to with `:let`, since that implies a declaration. An exception is global variables: these can be both used with and without `:let`, because there is no rule about where they are declared. Variables cannot shadow previously defined variables. Variables may shadow Ex commands, rename the variable if needed. Since "&opt = value" is now assigning a value to option "opt", ":&" cannot be used to repeat a `:substitute` command.Omitting :call and :evalFunctions can be called without `:call`:writefile(lines, 'file')Using `:call` is still possible, but this is discouraged. A method call without `eval` is possible, so long as the start is an identifier or can't be an Ex command. It does NOT work for string constants:myList->add(123) " worksg:myList->add(123) " works[1, 2, 3]->Process() " works#{a: 1, b: 2}->Process() " works{'a': 1, 'b': 2}->Process() " works"foobar"->Process() " does NOT work("foobar")->Process() " works'foobar'->Process() " does NOT work('foobar')->Process() " worksIn case there is ambiguity between a function name and an Ex command, use ":" to make clear you want to use the Ex command. For example, there is both the `:substitute` command and the `substitute()` function. When the line starts with `substitute(` this will use the function, prepend a colon to use the command instead::substitute(pattern (replacement (No curly braces expansion|curly-braces-names| cannot be used.No :append, :change or :insertThese commands are too quickly confused with local variable names.ComparatorsThe 'ignorecase' option is not used for comparators that use strings.White spaceVim9 script enforces proper use of white space. This is no longer allowed:let var=234 " Error!let var= 234 " Error!let var =234 " Error!There must be white space before and after the "=":let var = 234 " OKWhite space is required around most operators. White space is not allowed: - Between a function name and the "(":call Func (arg) " Error!call Func\ (arg) " Error!call Func(arg) " OKcall Func(\ arg) " OKcall Func(\ arg " OK\ )Conditions and expressionsConditions and expression are mostly working like they do in JavaScript. A difference is made where JavaScript does not work like most people expect. Specifically, an empty list is falsey. Any type of variable can be used as a condition, there is no error, not even for using a list or job. This is very much like JavaScript, but there are a few exceptions.type TRUE whenbool v:true number non-zero float non-zero string non-empty blob non-empty list non-empty (different from JavaScript) dictionary non-empty (different from JavaScript) funcref when not NULL partial when not NULL special v:true job when not NULL channel when not NULL class when not NULL object when not NULL (TODO: when isTrue() returns v:true) The boolean operators "||" and "&&" do not change the value:8 || 2 == 80 || 2 == 20 || '' == ''8 && 2 == 20 && 2 == 0[] && 2 == []When using `..` for string concatenation the arguments are always converted to string.'hello ' .. 123 == 'hello 123''hello ' .. v:true == 'hello true'In Vim9 script one can use "true" for v:true and "false" for v:false.
3. New style functions *fast-functions* THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE *:def* :def[!]{name}([arguments])[:{return-type}Define a new function by the name{name}. The body of the function follows in the next lines, until the matching `:enddef`. When{return-type}is omitted the function is not expected to return anything.{arguments}is a sequence of zero or more argument declarations. There are three forms:{name}:{type}{name}={value}{name}:{type}={value}The first form is a mandatory argument, the caller must always provide them. The second and third form are optional arguments. When the caller omits an argument the{value}is used.NOTE:It is possible to nest `:def` inside another `:def`, but it is not possible to nest `:def` inside `:function`, for backwards compatibility. [!] is used as with `:function`. *:enddef* :enddef End of a function defined with `:def`. If the script the function is defined in is Vim9 script, then script-local variables can be accessed without the "s:" prefix. They must be defined before the function. If the script the function is defined in is legacy script, then script-local variables must be accessed with the "s:" prefix. *:disa* *:disassemble* :disa[ssemble]{func}Show the instructions generated for{func}. This is for debugging and testing.
4. Types *vim9-types* THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE The following builtin types are supported: bool number float string blob list<type>dict<type>(a: type, b: type): type job channel Not supported yet: tuple<a: type, b: type, ...>These types can be used in declarations, but no variable will have this type: type|type void any There is no array type, use list<type>instead. For a list constant an efficient implementation is used that avoids allocating lot of small pieces of memory. A function defined with `:def` must declare the return type. If there is no type then the function doesn't return anything. "void" is used in type declarations. Custom types can be defined with `:type`::type MyList list<string>{not implemented yet}And classes and interfaces can be used as types::class MyClass:let mine: MyClass:interface MyInterface:let mine: MyInterface:class MyTemplate<Targ>:let mine: MyTemplate<number>:let mine: MyTemplate<string>:class MyInterface<Targ>:let mine: MyInterface<number>:let mine: MyInterface<string>{not implemented yet}Type inference *type-inference* In general: Whenever the type is clear it can be omitted. For example, when declaring a variable and giving it a value:let var = 0 " infers number typelet var = 'hello' " infers string type
5. Namespace, Import and Export *vim9script* *vim9-export* *vim9-import* THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE A Vim9 script can be written to be imported. This means that everything in the script is local, unless exported. Those exported items, and only those items, can then be imported in another script.Namespace*:vim9script* *:vim9* To recognize a file that can be imported the `vim9script` statement must appear as the first statement in the file. It tells Vim to interpret the script in its own namespace, instead of the global namespace. If a file starts with:vim9scriptlet myvar = 'yes'Then "myvar" will only exist in this file. While without `vim9script` it would be available as `g:myvar` from any other script and function. The variables at the file level are very much like the script-local "s:" variables in legacy Vim script, but the "s:" is omitted. In Vim9 script the global "g:" namespace can still be used as before. A side effect of `:vim9script` is that the 'cpoptions' option is set to the Vim default value, like with::set cpo&vimOne of the effects is that |line-continuation| is always enabled. The original value of 'cpoptions' is restored at the end of the script.Export*:export* *:exp* Exporting one item can be written as:export const EXPORTED_CONST = 1234export let someValue = ...export def MyFunc() ...export class MyClass ...As this suggests, only constants, variables, `:def` functions and classes can be exported. Alternatively, an export statement can be used to export several already defined (otherwise script-local) items:export{EXPORTED_CONST, someValue, MyFunc, MyClass}Import*:import* *:imp* The exported items can be imported individually in another Vim9 script:import EXPORTED_CONST from "thatscript.vim"import MyClass from "myclass.vim"To import multiple items at the same time:import{someValue, MyClass}from "thatscript.vim"In case the name is ambiguous, another name can be specified:import MyClass as ThatClass from "myclass.vim"import{someValue, MyClass as ThatClass}from "myclass.vim"To import all exported items under a specific identifier:import * as That from 'thatscript.vim'Then you can use "That.EXPORTED_CONST", "That.someValue", etc. You are free to choose the name "That", but it is highly recommended to use the name of the script file to avoid confusion. The script name after `import` can be: - A relative path, starting "." or "..". This finds a file relative to the location of the script file itself. This is useful to split up a large plugin into several files. - An absolute path, starting with "/" on Unix or "D:/" on MS-Windows. This will be rarely used. - A path not being relative or absolute. This will be found in the "import" subdirectories of 'runtimepath' entries. The name will usually be longer and unique, to avoid loading the wrong file. Once a vim9 script file has been imported, the result is cached and used the next time the same script is imported. It will not be read again. *:import-cycle* The `import` commands are executed when encountered. If that script (directly or indirectly) imports the current script, then items defined after the `import` won't be processed yet. Therefore cyclic imports can exist, but may result in undefined items.Import in an autoload scriptFor optimal startup speed, loading scripts should be postponed until they are actually needed. A recommended mechanism: 1. In the plugin define user commands, functions and/or mappings that refer to an autoload script.command -nargs=1 SearchForStuff call searchfor#Stuff(<f-args>)This goes in .../plugin/anyname.vim. "anyname.vim" can be freely chosen. 2. In the autocommand script do the actual work. You can import items from other files to split up functionality in appropriate pieces.vim9scriptimport FilterFunc from "../import/someother.vim"def searchfor#Stuff(arg: string)let filtered = FilterFunc(arg)...This goes in .../autoload/searchfor.vim. "searchfor" in the file name must be exactly the same as the prefix for the function name, that is how Vim finds the file. 3. Other functionality, possibly shared between plugins, contains the exported items and any private items.vim9scriptlet localVar = 'local'export def FilterFunc(arg: string): string...This goes in .../import/someother.vim.Import in legacy Vim scriptIf an `import` statement is used in legacy Vim script, for identifier the script-local "s:" namespace will be used, even when "s:" is not specified.
9. Rationale *vim9-rationale*The :def commandPlugin writers have asked for a much faster Vim script. Investigation have shown that keeping the existing semantics of function calls make this close to impossible, because of the overhead involved with calling a function, setting up the local function scope and executing lines. There are many details that need to be handled, such as error messages and exceptions. The need to create a dictionary for a: and l: scopes, the a:000 list and several others add too much overhead that cannot be avoided. Therefore the `:def` method to define a new-style function had to be added, which allows for a function with different semantics. Most things still work as before, but some parts do not. A new way to define a function was considered the best way to separate the old-style code from Vim9 script code. Using "def" to define a function comes from Python. Other languages use "function" which clashes with legacy Vim script.Type checkingWhen compiling lines of Vim commands into instructions as much as possible should be done at compile time. Postponing it to runtime makes the execution slower and means mistakes are found only later. For example, when encountering the "+" character and compiling this into a generic add instruction, at execution time the instruction would have to inspect the type of the arguments and decide what kind of addition to do. And when the type is dictionary throw an error. If the types are known to be numbers then an "add number" instruction can be used, which is faster. The error can be given at compile time, no error handling is needed at runtime. The syntax for types is similar to Java, since it is easy to understand and widely used. The type names are what was used in Vim before, with some additions such as "void" and "bool".JavaScript/TypeScript syntax and semanticsScript writers have complained that the Vim script syntax is unexpectedly different from what they are used to. To reduce this complaint popular languages will be used as an example. At the same time, we do not want to abandon the well-known parts of legacy Vim script. Since Vim already uses `:let` and `:const` and optional type checking is desirable, the JavaScript/TypeScript syntax fits best for variable declarations.const greeting = 'hello' " string type is inferredlet name: string...name = 'John'Expression evaluation was already close to what JavaScript and other languages are doing. Some details are unexpected and can be fixed. For example how the || and && operators work. Legacy Vim script:let result = 44...return result || 0 " returns 1Vim9 script works like JavaScript, keep the value:let result = 44...return result || 0 " returns 44On the other hand, overloading "+" to use both for addition and string concatenation goes against legacy Vim script and often leads to mistakes. For that reason we will keep using ".." for string concatenation. Lua also uses ".." this way.Import and ExportA problem of legacy Vim script is that by default all functions and variables are global. It is possible to make them script-local, but then they are not available in other scripts. In Vim9 script a mechanism very similar to the Javascript import and export mechanism is supported. It is a variant to the existing `:source` command that works like one would expect: - Instead of making everything global by default, everything is script-local, unless exported. - When importing a script the symbols that are imported are listed, avoiding name conflicts and failures if later functionality is added. - The mechanism allows for writing a big, long script with a very clear API: the exported function(s) and class(es). - By using relative paths loading can be much faster for an import inside of a package, no need to search many directories. - Once an import has been used, it can be cached and loading it again can be avoided. - The Vim-specific use of "s:" to make things script-local can be dropped.ClassesVim supports interfaces to Perl, Python, Lua, Tcl and a few others. But these have never become widespread. When Vim 9 was designed a decision was made to phase out these interfaces and concentrate on Vim script, while encouraging plugin authors to write code in any language and run it as an external tool, using jobs and channels. Still, using an external tool has disadvantages. An alternative is to convert the tool into Vim script. For that to be possible without too much translation, and keeping the code fast at the same time, the constructs of the tool need to be supported. Since most languages support classes the lack of class support in Vim is then a problem. Previously Vim supported a kind-of object oriented programming by adding methods to a dictionary. With some care this could be made to work, but it does not look like real classes. On top of that, it's very slow, because of the use of dictionaries. The support of classes in Vim9 script is a "minimal common functionality" of class support in most languages. It works mostly like Java, which is the most popular programming language. vim:tw=78:ts=8:noet:ft=help:norl:
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