interpolate Vim function arguments and shell commands

I've written a little .applescript file that can reload Safari. I've tried to hook it's execution into vim's BufWritePost event, (so Safari auto-reloads on file save). I've placed this in my .vimrc: ``` function! SaveAndReloadSafari(delay) " THIS IS WHERE MY PROBLEM IS>>>>>>>>>>>>>>> !osascript ~/MySrc/applescript/reloadSafari.APPLESCRIPT a:delay endfunction if !exists("b:my_autocommands_loaded") let b:matts_autocommands_loaded = 1 au BufWritePost *.html,*\.css,*.js call SaveAndReloadSafari(0) au BufWritePost *.scss call SaveAndReloadSafari(2) endif ``` As you can see, I want to add a 2 second delay after saving an .scss file (to allow my SCSS files to auto-compile to CSS) I've confirmed that the only piece of the puzzle missing is my syntax for interpolating the a:delay with the shell command. (Executing the command without a `delay` parameter works fine). What's wrong with my syntax?