[sedachv]

Very good question. A lot of the time "Write programs that do one thing and do it well" really means "I don't understand the difference between a procedure and a program." It is much easier to write procedures than it is to write programs, and it is often easier to turn a procedure into a program than vice-versa (emacsclient does the former especially well). Emacs is much better at "Writ[ing] programs to work together" - Emacs extensions usually work with each other without any extra effort, and deep integration is easy to achieve. "Write programs to handle text streams, because that is a universal interface" is the reason why Unix utilities do not integrate well.

To provide an example, I use mu4e[1] as an email client and reader, which uses a separate process running mu to operate on a Maildir. The Maildir is synchronized to multiple MDAs by OfflineIMAP, a command line program, which I set up to retrieve the IMAP passwords from an encrypted file using auth-source.el by execing emacsclient. With auth-source, all the credentials I need to access remote machines are in one GPG encrypted file, and Emacs takes care of handling communications with GPG, gpg-agent, and pinentry.

So Emacs provides both a better way to work with other standalone programs, and, via the emacsclient/server model, a better way for standalone programs to work with Elisp code.

[1] http://www.djcbsoftware.nl/code/mu/ [2] http://www.offlineimap.org/