Vim conceal indentation. Replace indentation spaces with utf-8 chars

Question

I use four spaces for indent. I would like to replace the indentation with some UTF-8 chars.

What I have:

1.

def foo(bar):
    for jaffa in bar:
        print jaffa

2.

var foo = function(bar){
    bar.forEach(function(jaffa){
        console.log(jaffa);
    });
}

What I want:

1.

def foo(bar):
►for jaffa in bar:
►►print jaffa

2.

var foo = function(bar){
►bar.forEach(function(jaffa){
►►console.log(jaffa);
►});
}

I tried using conceal myself, but I couldn't come up with a pattern to match the indentation spaces.

How would I accomplish changing the indentation to UTF-8 chars using vim conceal as described in the examples?

@Muru gave the answer for this question. But what if I want to conceal the last 'block' of the indentation spaces differently than the ones before it? Example:

var foo = function(bar){
►bar.forEach(function(jaffa){
◼►console.log(jaffa);
►});
}

Answer 1

With the following:

set conceallevel=2
syn match IndentWS '\v(^( {4}|\t)*)@<=( {4}|\t)' conceal cchar=▶

I get:

The regex \v(^( {4}|\t)*)@<=( {4}|\t):

• uses very magic \v
• matches a sets of 4 spaces ( {4}) or a tab \t, at the beginning of the line, with zero width \@<=
• and then a set of 4 spaces or a tab.

Of course, if you use only tabs or spaces, you can simplify the regex accordingly.

For the update, with:

set conceallevel=2
syn match IndentWS '\v^( {4}|\t)+\S@=' contains=IndentEndWS,IndentStartWS
syn match IndentStartWS '\v( {4}|\t)' conceal cchar== 
syn match IndentEndWS '\v( {4}|\t)\S@=' conceal cchar=▶

I get:

Making ends highlight differently would need a region, or contained matches. In this case I used two contained matches, one for general indentation whitespace, and one for indentation just before a non-whitespace character (\S).

Answer 2

This could be used call matchadd('Conceal', '\s\{'.&ts.'\}', 10, -1, {'conceal': '►'})

This uses the matchadd() function to conceal parts of your text, which needs a 7.4.500 release or something. This has the advantage, that the match functions can override syntax rules, the other way around might not be always possible.