You have to explicitly declare your function a closure by adding closure after the function arguments.

function Hi()
  let a = "hi"
  function s:inside() closure
    echo a
  endfunction
  call s:inside()
endfunction

Without closure, :call Hi() will print out an error.

We use s:inside to make the function script local, rather than global.

The dot concatenates strings: let str = "one thing" . "another".

let pos = match("one thing", "thing") returns 4, the point where thing starts.

let str1 = str[0:pos] splits the string from position 0 until 4 (as above). It returns one .

With a string slice as above, you can use negative numbers, i.e. -1 means the end of the string.

function Hi()
  let str = "one thing " . "another"
  let pos = match(str, "thing")
  let str = str[pos:-1]
  echo str 
endfunction

:call Hi() will print thing another.

getline() can take two parameters: the start position in a file, and an end position in a file.

getline(1, '$') will get all the lines from line 1 until the end. And it puts this in an array/list.

We can use the previously learnt filter() function and regex operator to filter all the lines with a word in them:

let bicycles = getline(1, '$')->filter({ _,line -> line =~ '.*bicycle.*' })

Then you'd loop over this as normal.

You can use getline() to get the current line as a string with getline(".") or pass it a line number to get that line.

=~ matches strings with regular expressions.

You use single quotes so you don't need to double escape escape sequences like \s etc.

function Hi()
  if "hello" =~ 'hel.o'
    echo "you said hello"
  else
    echo "you didn't say hello"
  endif
endfunction

:call Hi() will print you said hello.

list_name->filter() filters the list list_name.

The filter function takes an inline function as a filter. The inline function syntax is { param1, param2 -> ... }

The filter function has the list index and value as parameters.

This example filters and gives you only the 2nd index of a list:

function Aa()
  let alist = ["one", "two", "three"]
  let alist = alist->filter({ i, line -> i == 1 })
  echo alist
endfunction

:call Aa() will output ["two"].