Weekly Emacs tip #14: Highlighting parentheses and the region they enclose

One of the features that Emacs has to help you with your code is show-paren-mode. By default this global minor-mode is turned on, which means that Emacs will highlight matching parentheses. Take the following R expression, for example:

myfun <- function(parA, parB) {
  paste("Doing nothing")
}

Here, if the cursor is between the last n of function and the opening parenthesis, it will highlight the closing parenthesis following parB. Similarly, if the cursor is positioned directly after the }, the opening { will be highlighted, see the light blue background colour in the screenshot.

But there is more! The variable show-paren-style accepts three values, each of which change the way the expression between the matching parentheses should be highlighted (or not). The three styles are parenthesis, expression and mixed. The first one is the default and acts as discussed above. The second, expression doesn’t just highlight the two parentheses, but the whole expression between them, and mixed is indeed a sort of mix of the other two: it highlights the parentheses if the whole expression fits in the current window. If, however, the opening or closing parenthesis is off-screen, it will highlight the expression.

In my Emacs config file, I explicitly set show-paren-mode to t (this might be a left-over from older versions of Emacs where t wasn’t the default) and set the style to mixed. As these are part of Emacs itself, I have put them in the use-package call for emacs (together with a bunch of other settings that, for clarity, I haven’t shown here).

(use-package emacs
  :custom
  ;; Code display options (highlight parens)
  (show-paren-mode 1)
  ;; Three options for paren-style: 'expression, 'parenthesis, and
  ;; 'mixed The first one highlights the complete region between
  ;; parens, the second only highlights the matching paren, the third
  ;; does 'expression when the matching paren is not visible.
  (show-paren-style 'mixed)
)