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Retabbing files using VIM

Recently I've made a mistake of using 2 spaces to indent my F# program. After some thought I decided to stick to 4 spaces like everyone else does.

Here is how it looked:

module foomodule
  let foo = 
    let bar = 
      get_file_names()
      |> Seq.filter (f -> f.EndsWith(".cs")
    let bar2 = do_something_with_bar bar
    bar2

And here is how I wanted it to look

module foomodule
    let foo = 
        let bar = 
            get_file_names()
            |> Seq.filter (f -> f.EndsWith(".cs")
        let bar2 = do_something_with_bar bar
        bar2

What to do? This is not as trivial as it may look. But not if use use VIM!

Here is how to retab everything using VIM:

Step 0. (Optional) Tell VIM to show whitespace:

:set list

Step 1. Tell VIM what the the current tabsize is:

:set tabstop=2      " Tab size is 2 spaces

Step 2. Convert spaces to real tabs:

:set noexpandtab    " Use real tab instead of space
:retab!             " Replace all space-tabs with real tabs

Step 3. Convert real tabs back to spaces, using tabsize 4

:set expandtab      " User spaces instead ot tab
:set tabstop=4      " 4 spaces for each tab
:retab              " Reformat using new tabbing policy

It's possible to get all this on one line:

:set ts=2 noet | retab! | set et ts=4 | retab