i've written a _very_ simple one-line macro assigned to a function key, that
writes the file in the current buffer, compiles it using a certain program
and gets back to vim in normal mode. something like:
:map <F5> :w <CR> :!foo_command %:p <CR><CR>
now, i'd like to perform the :w command _only_ if the file has a "modified"
status (+), but i don't know how to do that. any pointers or a simple
example that would help me understand how to rewrite my macro?