Ignore specific characters in syntax matching

Question

I'm writing a vim syntax highlighting file for a specific language. For some keywords, specific characters are ignored (, and -and _). In other words, these are exactly the same:

foo f_oo f-o,o

Is there a way I can ignore these characters when using eg. syn match ?

Answer 1

There's no special option for this; you have you make a pattern which optionnally allows the specific chars between EACH char; example with foo:

f[,_-]*o[,_-]*o

Note that - has to be placed at the end of the [] block (see :h /[]).

As it is fastidious to write, you can create a function to make it for you:

func! CreatePattern(word)
    let l:s = ''
    let l:first = 1
    for i in range(len(a:word))
        if !l:first
            let l:s .= '[,_-]*'
        else
            let l:first = 0
        endif
        let l:s .= a:word[i]
    endfor
    return l:s
endf

After this, we have:

:echo CreatePattern('bar')
b[,_-]*a[,_-]*r

Then, you can use :syn match with the help of :execute :

:exe 'syn match MyHighlightGroup /'.CreatePattern('foo').'/'

or using matchadd() :

:call matchadd('MyHighlightGroup', CreatePattern('foo'))

Please note that the function above will only work with plain words, but it will break any pattern with contains special pattern chars. You may have to write a better function for such needs.