Load partials in Vimscript

.vimrc

" Name your partials here.  We'll look in e.g. ~/.vimrc.bundles, ~/.vimrc.keymaps, etc
" Order matters!
function! SourceFiles()
  return ['bundles', 'functions', 'sets', 'aesthetics', 'keymaps', 'autocommands']
endfunction

" Looks in e.g. ~/.vimrc.bundles
for file in map(SourceFiles(), '"~/.vimrc." . (v:val)')
  if filereadable(expand(file))
    exec('source ' . file)
  else
    echoerr(string(file) . ' not readable but present in SourceFiles()')
  endif
endfor