Mastering Vim

Map and filter

Vimscript supports map and filter—higher-order functions (aka functions that operate on functions). Both of these functions take either a list or a dictionary as a first argument, and a function as a second.

For instance, if we wanted to filter out every animal name that is not proper, we would write a filter function:

function IsProperName(name)  if a:name =~? '\(Mr\|Miss\) .\+'    return 1  endif  return 0endfunction

IsProperName will return 1 (true) if the name starts with Mr or Miss (which is, as we know, a proper form to address an animal), and 0 (false) otherwise.

Now, given the following dictionary:

let animal_names = {  \ 'cat': 'Miss Cattington',  \ 'dog': 'Mr Dogson',  \ 'parrot': 'Polly'  \ }

We will write a filter function ...