Vi and Vim Stack Exchange is a question and answer site for people using the vi and Vim families of text editors. It only takes a minute to sign up.
Sign up to join this community
I found this useful setting form this post, which highlights trailing whitespaces :
highlight ExtraWhitespace ctermbg=grey guibg=grey
noremap <F10> :match ExtraWhitespace /\s\+$/<CR>
This works when I tap F10 but I also want the highlighting to go away when I tap F10 again.
Typing :match works but I was wondering if this could be done from this keymap itself. I tried putting ! after match but that is not allowed.
You can get a List of all matches previously defined for the current window with the getmatches() function. By using an <expr> mapping, you can dynamically set a mapping based on the size of the List returned by getmatches() with a conditional expression.
Conditional expressions in Vimscript (often called ternary expressions in other languages) take the following form:
a ? b : c
where a, b, and c are expressions. If a evaluates to true, then the conditional expression as a whole evaluates to b, otherwise, it evaluates to c.
The following expression evaluates to ':match<CR>' if the length of the List returned by getmatches() is greater than zero, otherwise it will evaluate to ':match ExtraWhitespace /\s\+$/<CR>'.
len(getmatches()) > 0 ? ':match<CR>' : ':match ExtraWhitespace /\s\+$/<CR>'
Using an <expr> mapping allows you to evaluate an expression to determine the function of the mapping, rather than a static value. The result of the expression should be a string representation of the desired Ex commands.
So, putting our conditional expression together with our <expr> mapping, we can do the following:
noremap <expr> <F10> len(getmatches()) > 0 ? ':match<CR>' : ':match ExtraWhitespace /\s\+$/<CR>'
Relevant help:
:h :map-<expr>
:h getmatches()
