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vim9script.md

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+---
+name: Vim9script
+filename: learn9vimscript.vim
+contributors:
+    - ["HiPhish", "http://hiphish.github.io/"]
+---
+
+```vim
+# ##############
+#  Introduction
+# ##############
+
+# Vim9 script is a modernized version of Vim's scripting language, offering features like variables, functions, and loops.
+# Accoding to `:help vim9-differences`, the principal differences from legacy Vim script are as follows:
+# 
+# - Comments start with #, not ": >
+# 	echo "hello"   # comment
+# - Using a backslash for line continuation is hardly ever needed: >
+# 	echo "hello "
+# 	     .. yourName
+# 	     .. ", how are you?"
+# - White space is required in many places to improve readability.
+# - Assign values without `:let` *E1126* , declare variables with `:var`: >
+# 	var count = 0
+# 	count += 3
+# - Constants can be declared with `:final` and `:const`: >
+# 	final matches = []		  # add to the list later
+# 	const names = ['Betty', 'Peter']  # cannot be changed
+# - `:final` cannot be used as an abbreviation of `:finally`.
+# - Variables and functions are script-local by default.
+# - Functions are declared with argument types and return type: >
+# 	def CallMe(count: number, message: string): bool
+# - Call functions without `:call`: >
+# 	writefile(['done'], 'file.txt')
+# - You cannot use old Ex commands:
+# 	`:Print`
+# 	`:append`
+# 	`:change`
+# 	`:d`  directly followed by 'd' or 'p'.
+# 	`:insert`
+# 	`:k`
+# 	`:mode`
+# 	`:open`
+# 	`:s`  with only flags
+# 	`:t`
+# 	`:xit`
+# - Some commands, especially those used for flow control, cannot be shortened.
+#   E.g., `:throw` cannot be written as `:th`.  *vim9-no-shorten*
+# - You cannot use curly-braces names.
+# - A range before a command must be prefixed with a colon: >
+# 	:%s/this/that
+# - Executing a register with "@r" does not work, you can prepend a colon or use
+#   `:exe`: >
+# 	:exe @a
+# - Unless mentioned specifically, the highest |scriptversion| is used.
+# - When defining an expression mapping, the expression will be evaluated in the
+#   context of the script where it was defined.
+# - When indexing a string the index is counted in characters, not bytes:
+#   |vim9-string-index|
+# - Some possibly unexpected differences: |vim9-gotchas|.
+#
+# You can run Vim9 script commands in command-line mode or write them to a file and source it in Vim.
+# This guide assumes familiarity with ex-commands and focuses on scripting.
+
+# Comments start with #
+# The vertical line '|' separates commands
+echo 'Hello' | echo 'world!'
+
+# Putting a comment after a command usually works
+pwd  # Displays the current working directory
+
+# Line continuation is rarely needed
+echo "Hello "
+     .. "world"
+
+echo [1, 2]
+
+echo {
+    'a': 1,
+    'b': 2
+}
+
+# #######
+#  Types
+# #######
+
+# Numbers
+echo 123         # Decimal
+echo 0b1111011   # Binary
+echo 0173        # Octal
+echo 0x7B        # Hexadecimal
+echo 123.0       # Floating-point
+echo 1.23e2      # Floating-point (scientific notation)
+
+# Booleans
+echo true      # Evaluates to true
+echo false     # Evaluates to false
+
+# Boolean values from comparison
+echo x == y      # Equality by value
+echo x != y      # Inequality
+echo x > y       # Greater than
+echo x >= y      # Greater than or equal
+echo x < y       # Smaller than
+echo x <= y      # Smaller than or equal
+echo x is y      # Instance identity
+echo x isnot y   # Instance non-identity
+
+# Strings
+echo 'a' < 'B'   # True or false depending on 'ignorecase'
+echo 'a' <? 'B'  # True
+echo 'a' <# 'B'  # False
+
+# Regular expression matching
+echo "hi" =~ "hello"    # Regular expression match
+echo "hi" =~# "hello"   # Case sensitive
+echo "hi" =~? "hello"   # Case insensitive
+echo "hi" !~ "hello"    # Regular expression unmatch
+echo "hi" !~# "hello"   # Case sensitive
+echo "hi" !~? "hello"   # Case insensitive
+
+# Boolean operations
+echo true && false  # Logical AND
+echo true || false  # Logical OR
+echo !true            # Logical NOT
+echo true ? 'yes' : 'no'  # Ternary operator
+
+# Strings
+echo "Hello world\n"   # Newline
+echo 'Hello world\n'   # Literal
+echo 'Let''s go!'      # Two single quotes become one
+
+# String concatenation
+echo 'Hello ' .. 'world'  # String concatenation
+
+# String indexing
+echo 'Hello'[0]           # First character
+echo 'Hello'[1]           # Second character
+echo 'Hellö'[4]           # Returns a character
+
+# Substrings
+echo 'Hello'[:]           # Copy of entire string
+echo 'Hello'[1:3]         # Substring
+echo 'Hello'[1:-2]        # Substring until second to last character
+echo 'Hello'[1:]          # Substring with starting index
+echo 'Hello'[:2]          # Substring with ending index
+echo 'Hello'[-2:]         # Substring relative to end
+
+# Lists
+echo []                   # Empty list
+echo [1, 2, 'Hello']      # List with elements
+echo [1, 2, 'Hello', ]    # Trailing comma permitted
+echo [[1, 2], 'Hello']    # Nested lists
+
+# List concatenation
+echo [1, 2] + [3, 4]      # Creates a new list
+
+# List indexing
+echo [1, 2, 3, 4][2]      # Third element
+echo [1, 2, 3, 4][-1]     # Last element
+
+# List slicing
+echo [1, 2, 3, 4][:]      # Shallow copy
+echo [1, 2, 3, 4][:2]     # Sublist until third item
+echo [1, 2, 3, 4][2:]     # Sublist from third item
+echo [1, 2, 3, 4][:-2]    # Sublist until second-to-last item
+
+# Dictionaries
+echo {}                       # Empty dictionary
+echo {'a': 1, 'b': 2}         # Dictionary literal
+echo {'a': 1, 'b': 2, }       # Trailing comma permitted
+echo {'x': {'a': 1, 'b': 2}}  # Nested dictionary
+
+# Indexing a dictionary
+echo {'a': 1, 'b': 2}['a']    # Literal index
+echo {'a': 1, 'b': 2}.a       # Syntactic sugar
+
+# Funcref
+echo function('type')         # Reference to function type()
+echo {x -> x * x}             # Anonymous function
+
+# Regular expression
+substitute/hello/Hello/
+
+# ###########################
+#  Implicit type conversions
+# ###########################
+
+echo "1" + 1         # Number
+echo "1" .. 1        # String
+echo "0xA" + 1       # Number
+
+# ###########
+#  Variables
+# ###########
+
+var b:my_var = 1        # Local to current buffer
+var w:my_var = 1        # Local to current window
+var t:my_var = 1        # Local to current tab page
+var g:my_var = 1        # Global variable
+
+# Access special Vim memory like variables
+var @a = 'Hello'        # Register
+var $PATH=''            # Environment variable
+var &textwidth = 79     # Option
+var &l:textwidth = 79   # Local option
+var &g:textwidth = 79   # Global option
+
+# Access scopes as dictionaries
+echo b:                # All buffer variables
+echo w:                # All window variables
+echo t:                # All tab page variables
+echo g:                # All global variables
+echo v:                # All Vim variables
+
+# Constant variables
+const x = 10            # Constant
+
+# Function reference variables
+var IsString = {x -> type(x) == type('')}    # Global
+var isNumber = {x -> type(x) == type(0)}   # Local
+
+# Multiple value binding
+var [x, y] = [1, 2]
+
+# Assign the remainder to a rest variable
+var [mother, father; children] = ['Alice', 'Bob', 'Carol', 'Dennis', 'Emily']
+
+# ##############
+#  Flow control
+# ##############
+
+# Conditional
+var condition = true
+
+if condition
+    echo 'First condition'
+elseif another_condition
+    echo 'Second condition'
+else
+    echo 'Fail'
+endif
+
+# Loops
+
+# For-loop
+for person in ['Alice', 'Bob', 'Carol', 'Dennis', 'Emily']
+    echo 'Hello ' .. person
+endfor
+
+# Iterate over a nested list
+for [x, y] in [[1, 0], [0, 1], [-1, 0], [0, -1]]
+    echo 'Position: x =' .. x .. ', y = ' .. y
+endfor
+
+# Iterate over a range of numbers
+for i in range(10, 0, -1)
+    echo 'T minus' .. i
+endfor
+
+# Iterate over the keys of a dictionary
+for symbol in keys({'π': 3.14, 'e': 2.71})
+    echo 'The constant ' .. symbol .. ' is a transcendent number'
+endfor
+
+# Iterate over the values of a dictionary
+for value in values({'π': 3.14, 'e': 2.71})
+    echo 'The value ' .. value .. ' approximates a transcendent number'
+endfor
+
+# Iterate over the keys and values of a dictionary
+for [symbol, value] in items({'π': 3.14, 'e': 2.71})
+    echo 'The number ' .. symbol .. ' is approximately ' .. value
+endfor
+
+# While-loops
+var there_yet = true
+while !there_yet
+    echo 'Are we there yet?'
+endwhile
+
+# Exception handling
+try
+    source path/to/file
+catch /Cannot open/
+    echo 'Looks like that file does not exist'
+catch /.*/
+    echo 'Something went wrong, but I do not know what'
+finally
+    echo 'I am done trying'
+endtry
+
+# ##########
+#  Functions
+# ##########
+
+# Defining functions
+def AddNumbersLoudly(x: number, y: number): number
+    echo 'Adding' .. x .. 'and' .. y
+    return x + y
+enddef
+
+def s:addNumbersLoudly(x: number, y: number): number
+    echo 'Adding' .. x .. 'and' .. y
+    return x + y
+enddef
+
+# Range functions
+def FirstAndLastLine() range
+    echo [a:firstline, a:lastline]
+enddef
+
+# Aborting functions
+def SourceMyFile() abort
+    source my-file.vim
+    echo 'This will never be printed'
+enddef
+
+# Closures
+def MakeAdder(x: number)
+    def Adder(n: number) closure
+        return n + x
+    enddef
+    return funcref('Adder')
+enddef
+var AddFive = MakeAdder(5)
+echo AddFive(3)  # Prints 8
+
+# Dictionary functions
+def Mylen() dict
+    return len(self.data)
+enddef
+var mydict = {'data': [0, 1, 2, 3], 'len': function("Mylen")}
+echo mydict.len()
+
+# Alternatively, more concise
+var mydict = {'data': [0, 1, 2, 3]}
+def mydict.len()
+    return len(self.data)
+enddef
+
+# Calling functions
+var animals = keys({'cow': 'moo', 'dog': 'woof', 'cat': 'meow'})
+
+# Call a function for its side effects only
+call sign_undefine()
+
+# The call() function
+echo call(function('get'), [{'a': 1, 'b': 2}, 'c', 3])  # Prints 3
+
+# Function namespaces
+def foo#bar#log(value: string)
+    echomsg value
+enddef
+
+call foo#bar#log('Hello')
+
+# #############################
+#  Frequently used ex-commands
+# #############################
+
+# Sourcing runtime files
+runtime plugin/my-plugin.vim
+
+# Defining new ex-commands
+command! SwapAdjacentLines normal! ddp
+
+command! -nargs=1 Error echoerr <args>
+
+# Defining auto-commands
+autocmd BufWritePost $MYVIMRC source $MYVIMRC
+
+# Auto groups
+augroup auto-source
+    autocmd!
+    autocmd BufWritePost $MYVIMRC source $MYVIMRC
+augroup END
+
+# Executing
+var line = 3
+execute line .. 'delete'
+
+# Executing normal-mode commands
+normal! ggddGp
+
+# Window commands
+wincmd L
+
+# ###########################
+#  Frequently used functions
+# ###########################
+
+# Feature check
+echo has('nvim')
+echo has('python3')
+echo has('unix')
+echo has('win32')
+
+# Test if something exists
+echo exists('&mouse')
+echo exists('+mouse')
+echo exists('$HOSTNAME')
+echo exists('*strftime')
+echo exists('**s:MyFunc')
+echo exists('bufcount')
+echo exists('my_dict["foo"]')
+echo exists(':Make')
+echo exists("#CursorHold")
+echo exists("#BufReadPre#*.gz")
+echo exists("#filetypeindent")
+echo exists("##ColorScheme")
+
+# Various dynamic values
+echo expand('%')
+echo expand('<cword>')
+echo expand('%:p')
+
+# Type tests
+echo type(my_var) == v:t_number
+echo type(my_var) == v:t_string
+echo type(my_var) == v:t_func
+echo type(my_var) == v:t_list
+echo type(my_var) == v:t_dict
+echo type(my_var) == v:t_float
+echo type(my_var) == v:t_bool
+echo my_var is v:null
+
+# Format strings
+echo printf('%d in hexadecimal is %X', 123, 123)
+
+# #####################
+#  Tricks of the trade
+# #####################
+
+# Source guard
+if exists('g:loaded_my_plugin')
+    finish
+endif
+var g_loaded_my_plugin = true
+
+# Default values
+var greeting = get(g:, 'my_plugin_greeting', 'Hello')
+```