Learn to Program MCUs with uLISP

Part 1: Crash Course Offers Insight Into Pioneering Language

- Raul Alvarez Torrico

Lisp is a Turing-complete programming language, based on Alonso Church's lambda calculus. It was designed by John McCarthy and published in his 1960 paper, "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I" [1]. Of its many dialects, Common Lisp and Scheme are the best known, along with the newer Racket and Clojure.

Lisp pioneered many programming language ideas now commonly in use [2], such as higher order functions, recursion, lexical closures, dynamic typing, tree data structures, automatic garbage collection, and the read-eval-print loop (REPL). I've been programming in Common Lisp and Scheme as a hobby for many years. Recently, I discovered uLisp, a version designed to run on microcontrollers (MCUs) [3]. As a fan of Lisp and embedded systems, for the past few years, I've been willing to try the uLisp platform and write about it.

In this article I begin by discussing very simple uLisp examples that showcase basic syntax and programming concepts. Then, I discuss some extensions to the language that deal specifically with MCU-related functionalities, such as general-purpose input/ output and I2C serial data communications. I present some hardware examples using Seeed Studio's Wio Terminal development board and the Sensirion SGP30 gas sensor. Nevertheless, uLisp support as well a few other MCU platforms.

To follow the topics discussed here, you just need a basic knowledge of microcontrollers and the Arduino platform.

ULISP CRASH COURSE

uLisp is available for many MCU boards in five versions [4]. The version of uLisp that you wish to use can be downloaded free from uLisp.​com:

1) AVR: for Arduino Mega 2560, ATmega 1284, and AVR DA/DB series.

2) AVR-Nano: for Arduino UNO, Arduino Nano, and Arduino Every.

3) ARM: for Arduino Zero and MKTZero, Adafruit MO, M4, PyBadge/PyGamer, nrf52840 and Clue, BBC Micro Bit, Teensy 40/4.1, RP2040-based boards, and others.