Vimscript function to eval the contents of the current file or only the selected lines based on file extension

eval_file.vim

function! GetSelectedLines(type, ...) range
  let sel_save = &selection
  let &selection = "inclusive"
  let reg_save = @@
  if a:type == 'n'
    silent exe a:firstline . "," . a:lastline . "y"
  elseif a:type == 'c'
    silent exe a:1 . "," . a:2 . "y"
  else
    silent exe "normal! `<" . a:type . "`>y"
  endif

  let lines = split(@@,"\n")
  let &selection = sel_save
  let @@ = reg_save
  return lines
endfunction

function! EvalMyFile(type, ...) range
  let full_path = expand('%:p')
  let file_ext  = expand('%:e')
  let file_handlers = {
      \   'exs'   : 'elixir',
      \   'ex'    : 'elixir',
      \   'rb'    : 'ruby',
      \}
  let handler = file_handlers[file_ext]
  let selected_lines = GetSelectedLines(a:type)
  let tmpfile = tempname()

  if len(selected_lines) >= 1
    call writefile(selected_lines, tmpfile)
    execute "!" . handler . " " . tmpfile
  else
    execute "!" . handler . " " . full_path
  endif
endfunction

vnoremap <D-r> :call EvalMyFile(visualmode(), 1)<cr>
nnoremap <D-r> :call EvalMyFile('n', 1)<cr>