1.20 Interactive embedded development with uLisp, Arduino and Emacs
===================================================================

2017-08-04

   AS I MENTIONED IN MY *note 'POST ABOUT ADA': Arduino Programming with
Ada, LISP HAS A COMPLETELY DIFFERENT APPROACH in terms of...  well, just
about everything, beginning with the type system.  One important feature
of Lisp environments is the high degree if interaction they provide:
Lisp Systems allowed for interaction with every part of the system (OS,
applications, window manager...)  and to a smaller degree this is what
the read-eval-print-loop approach (REPL) provides in, say, Emacs with
SLIME.

   One interesting language I found recently was uLisp, a Lisp language
for the Arduino and MSP430 platforms.  It is based on a subset of Common
Lisp and provides a different approach to development: it installs an
interpreter which is programmed via the serial interface, thus allowing
for a much more interactive development style (at a certain cost in
terms of available space).

   The interaction is normally made with the Arduino IDE, via the Serial
Monitor; uLisp contains a minimal editor as well, but using Emacs makes
more sense and it's actually easy to configure to that end; before going
into the details this is the end result (zoom in the image if necessary
to start the animation).

++++++++++++=+++++++++++=+++++++++++++++++++++++++++++++++++++++++++++
::::::::.:::::.::::::.............:::::::::::::::::..................:
............:.....................::..................................
::................................:::::::::::........................:
::::::::........:......:..........:-::::::::..:...::.................:
.:-::.............................:::::-:-::::.::....................:
.:::-::::::::::...................::.::::::.::.:.:.::................:
:.:::.....:.......................::.................................:
:.................................::.................................:
..................................::.................................:
:.................................::.................................:
:.................................::.................................:
:.................................::.................................:
:.................................::.................................:
:.................................::.................................:
:.................................::.................................:
..................................::..................................
:...::::.::::::::::::::::::.......::.....:........:::::::::::........:
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

   The main thing to consider is that inferior-lisp-mode is actually
based on comint-mode, which simplifies things: we just need a way to
replace the buffer created by calling inferior-lisp with a buffer that
communicates via the serial port.  This is, in turn, something which can
be done using Emacs term-mode.

   Combining all of this the following Emacs Lisp code will connect to
the Arduino via the serial port, rename the resulting buffer and change
to line mode.

     ;; Arduino LED blink
     ;;
     ;; Based on the example at http://www.ulisp.com/show?1LG8
     ;;
     ;; 2017, Frederico Munoz <fsmunoz@     sdf.org>


     (defun b (x s d)
       "Slowly increases and decreases the blinking interval in a loop"
       (pinmode 13 t)
       (digitalwrite 13 x)
       (delay s)
       (cond
        ((< s 100) (b (not x) (+ s 50) 50))
        ((> s 1000) (b (not x) (- s 50) -50))
        (t (b (not x) (+ s d) d))))

     (b t 500 50)

   Gist
(https://gist.github.com/fsmunoz/ef4a04c5f4eb117087a923d2555563af#file-arduino-serial-el)

   Creating a new Lisp file (like test.lisp) will by default enter
lisp-mode; in this mode we can use C-x C-e to send the s-expression to
the uLisp interpreter and get the result, as seen in the previous
screencast

     ;; Arduino LED blink
     ;;
     ;; Based on the example at http://www.ulisp.com/show?1LG8
     ;;
     ;; 2017, Frederico Munoz <fsmunoz@sdf.org>


     (defun b (x s d)
       "Slowly increases and decreases the blinking interval in a loop"
       (pinmode 13 t)
       (digitalwrite 13 x)
       (delay s)
       (cond
        ((< s 100) (b (not x) (+ s 50) 50))
        ((> s 1000) (b (not x) (- s 50) -50))
        (t (b (not x) (+ s d) d))))

     (b t 500 50)

   I've put the Lisp code on Github as well (1))

   ---------- Footnotes ----------

   (1) I've put the Lisp code on Github as well
(https://gist.github.com/fsmunoz/424b052e1848cdda3bee043386bdc7bd#file-blink-lisp)