Download uLisp

Version 4.3

Version 4.3 now includes integral documentation for all the built-in functions, which you can display in the Arduino Serial Monitor or a terminal used with uLisp. You can also add documentation to the functions you define in uLisp, in the same format as the built-in documentation.

For more information see Built-in documentation.

In addition, with Version 4.3 the AVR version of uLisp has been split into two versions:

  • The full AVR Version 4.3 now includes the new documentation features, and also includes the multi-dimensional array handling previously only included in the 32-bit versions of uLisp.
  • An AVR-Nano Version 4.3 excludes these new features, allowing it to continue supporting the smallest AVR platforms, the Arduino Uno, Arduino Nano, and Arduino Nano Every.

Latest versions

There are now five actively maintained versions of uLisp. Download the correct one for your platform:

AVR version

Download the AVR version of uLisp for the Arduino Mega 2560, ATmega1284, and AVR DA/DB-series platforms, or the AVR-Nano version for the Arduino Uno, Arduino Nano, and Arduino Nano Every:

AVR Version 4.3 - 15th September 2022

AVR-Nano Version 4.3 - 15th September 2022

or get them from GitHub at

ARM version

Download the latest ARM version of uLisp for the Arduino Zero, Arduino MKRZero, Adafruit M0 boards, Adafruit M4 boards, Adafruit PyBadge/PyGamer, Adafruit nRF52840 boards, BBC Micro Bit, Calliope mini, MAX32620FTHR, Teensy 4.0/4.1, and RP2040-based boards here:

ARM Version 4.3a - 18th September 2022

or get it from GitHub at

ESP version

Download the latest ESP version of uLisp for the ESP8266 and ESP32 platforms here:

ESP Version 4.3a - 25th September 2022

or get it from GitHub at

RISC-V version

Download the latest RISC-V version of uLisp for the Sipeed Maixduino, MAiX One Dock, and MAiX BiT boards here:

RISC-V Version 4.3a - 26th September 2022

or get it from GitHub at

Commented versions

These are identical to the above source files, but include comments to explain the C functions.

AVR Version 4.3 - 16th September 2022

ARM Version 4.3a - 18th September 2022

ESP Version 4.3a - 25th September 2022

RISC-V Version 4.3a - 26th September 2022

Other platforms

These versions are also available, but are not currently up to date with the newer features:

MSP430 version

Download the version of uLisp for the Energia MSP430 platforms here:

MSP430 Version 2.7c - 20th June 2019

or get it from GitHub at

STM32 version

Download the STM32 version of uLisp for the Maple Mini and Blue Pill platforms here:

STM32 Version 3.0b - 11th January 2020

or get it from GitHub at

Installing uLisp

The download is a single text file. To compile it in the Arduino IDE either save it as a text file and rename it to a .cpp file, or copy and paste the text into a new empty project file. You can download the latest Arduino IDE from

Select the correct Board option for your platform on the Tools menu, select the USB port from the Port menu, and upload uLisp. You should then be able to select Serial Monitor from the Tools menu, and interact with uLisp.

The following pages give specific advice for installing uLisp on these platforms:

AVR DA and DB series boards

BBC Micro:bit

Calliope mini

Maxim MAX32620FTHR

RP2040 boards

Sipeed MAiX RISC-V boards

Teensy 4.0 and 4.1

If you're using uLisp with the Arduino IDE on Debian or OpenBSD see these threads on GitHub: and

Note that saved images are not generally compatible between different versions of uLisp.

Compile options

The uLisp sources provide the following compile options:

Option Default Description
checkoverflow * enabled Generates an error if underflow/overflow occurs in arithmetic operations.
resetautorun disabled Loads, and optionally runs, an image using load-image on reset.
printfreespace enabled Prints the number of free objects before the uLisp prompt.
printgcs disabled Prints the amount of space reclaimed after each garbage collection.
sdcardsupport disabled Provides SD card support using with-sd-card.
gfxsupport ** disabled Provides graphics extensions for use with a suitable display.
lisplibrary disabled Evaluates the Lisp definitions provided in the Lisp Library on reset.
assemblerlist *** enabled Generates an assembler listing from defcode.
lineeditor disabled Provides a line editor for use when using uLisp from a terminal.
vt100 disabled Provides parenthesis matching on VT100-compatible terminals.

* Not applicable to the versions with floating point.
** Only applicable to the versions with graphics extensions; currently ARM, ESP, and RISC-V.
*** Only applicable to versions with defcode; currently ARM, RISC-V, and AVR. 

Older versions

See Older versions.

Test suites

The following files contains test suites I use for testing each release of uLisp. You may find these useful if you are porting uLisp to another platform:

Test suite - 8/16-bit version (AVR uLisp)

Test suite - 32-bit version (ARM, ESP, and RISC-V uLisp)

Test suite - Floating point (ARM, ESP, and RISC-V uLisp)