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The Lizard Language


Statements are input via the command-line interface or stored in the startup script on the microcontroller. The following statement types are currently supported.


An expression can be a constant value, a variable, a module property, an arithmetic or logical expression as well as various combinations:

"Hello world"
1 + (2 - 3 * 4)**5
1 == 2 or (x == 4 and button.level == 0)

Expressions can be assigned to variables, used in conditions and passed to constructors, method calls or routine calls. Plain expression statements print their result to the command line.

Variables: declaration and assignment

New variables need to be explicitly declared with a data type:

int i

They can be immediately initialized:

int i = 1

Otherwise they have an initial value of false, 0, 0.0 or "", respectively.

Variables can be assigned a new value of compatible data type:

i = 2

Modules: constructors, method calls and property assignments

Constructors are used to create module instances:

led = Output(15)

See the module reference for more details about individual modules and their argument lists.

Constructors can also be used with expander modules to instantiate a remote module that can be controlled from the main microcontroller:

led = expander.Output(15)

You can call module methods as follows:


Some module properties are meant to be written to:

motor.ratio = 9

Routines: definition and call

Routines have a name and contain a list of actions:

let all_on do

They can be called similar to module methods:


Rules: definition

Rules execute a list of actions when a condition is met:

when button.level == 0 then

In contrast to an if-statement known from other languages a when-condition is checked in every cycle of Lizard's main loop. Whenever the condition is true, the actions are executed.

Note that actions can be asynchronous. If there are still actions running asynchronously, a truthy condition is ignored.


Routines and rules contain a list of actions.

Method and routine calls

Like with a method call statement, you can call methods and routines with an action:

when clicked then

Property and variable assignments

Like with the corresponding assignment statements, you can assign properties and variables with an action as well:

when i > 0 then
    i = 0
    core.debug = true

Await conditions and routines

In contrast to statements, actions can await conditions, causing the execution of subsequent actions to wait until the condition is met.

int t
let blink do
    t = core.millis
    await core.millis > t + 1000

Similarly, actions can await asynchronous routines, causing subsequent actions to wait until a routine is completed.

when button.level == 0 then
    await blink()

Data types

Lizard currently supports five data types:

Data type Example Range
boolean bool b = true false, true
integer number int i = 0 64-bit unsigned integer
floating point number float f = 0.0 64-bit float
string str s = "foo"
identifier led = Output(15)

Note that identifiers cannot be created via variable declarations, but only via constructors.

Implicit conversion only happens from integers to floating point numbers:

int i = 42
float f = i + 3.14

Whitespace, comments and line breaks

Tabs and spaces are treated as whitespace.

Blank lines are interpreted as no-op and do nothing.

Line comments start with #.

Multiple statements or actions are separated with ; or a newline.

Control commands

Lines with a leading ! can indicate one of the following control commands.

Command Meaning
!+abc Add abc to the startup script
!-abc Remove lines starting with abc from the startup script
!? Print the startup script
!. Write the startup script to non-volatile storage
!!abc Interpret abc as Lizard code
!"abc Print abc to the command-line

Note that the commands !+, !- and !? affect the startup script in RAM, which is only written to non-volatile storage with the !. command.

Input from the default command-line interface UART0 is usually interpreted as Lizard code; input from a port expander is usually printed to the command-line on UART0. This behavior can be changed using !! and !".