While developing Ruby script using Vim I frequently want to execute the script. This is easy to do by calling :!ruby % in Vim, but that’s rather a lot of typing. With a Vim mapping I shortened this:

noremap <Leader>rx :!ruby %<CR>

Now I just have to hit \rx in Vim to execute the current buffer. (NB: I’m using the default Vim leader \.) Of course, sometimes I want to pass arguments to the script on the command line. This was easy to accomplish by omitting the carriage return at the end of the mapping:

" note the trailing white space on the next line
noremap <Leader>re :!ruby %

Now I can hit \re, and before the script executes, I can enter the desired arguments and hit enter to execute the contents of the buffer. (Note the trailing white space at the end of the mapping. This is deliberate. With it, I don’t remember to add a space before entering any optional arguments. I have a simple mind, and it delights in simple things.)

Recently I started working with Python, and I wanted the same ability. My first iteration defined new mappings for Python:

" note the trailing white space on the next line
noremap <Leader>pe :!python % 
noremap <Leader>px :!python %<CR>

This gave me \pe and \px mappings similar to the originals.

But this placed an awkward load on my right pinky finger using a QWERTY keyboard layout. Moreover, now I had the extra cognitive overhead of of choosing a mapping based on my the type of file I was working with. What am I to do when I add another language to the arsenal? More mappings? This isn’t what I wanted. What I really wanted was to continue using the \rx mapping. Let’s just rewrite the original mapping and have it run a function.

function! RunFile()
  if match(@%, '.rb$') != -1
    let argv = input('!ruby % ')
    exec '!ruby % ' . argv
  elseif match(@%, '.py$') != -1
    let argv = input('!python % ')
    exec '!python % ' . argv
  else
    echo '<< ERROR >> RunFile() only supports ruby and python'
  endif
endfunction

noremap <Leader>rx :call RunFile()<CR>

This version introduces a slight change to my workflow. Now when I hit \rx Vim prompts me for any additional arguments I want to pass to the script on execution — this is what \re and \pe did before. The original behavior of \rx and \px is gone. This means an extra carriage return when I’m executing the script without arguments, but it’s easier to type and less to remember overall. When it’s time to support a new language, I can just add an elseif branch to RunFile()