Variables are places to store values. They can be declared with the following syntax:
"let" ID "=" expr
ID is any valid identifier ([A-Za-z_$][A-Za-z0-9_$]* i.e. alphanumerics, underscores, and dollar-signs, and not starting with a number) and expr is any valid expression.
examples:
# declare new variable x, set its value to 64
let x = 64
Constants are similar to variables, but the value cannot be reassigned once it has been set. Note that if the value set is mutable, such as a list or an array, it can still be mutated. Constants can be declared and initialized with the following syntax:
"const" ID "=" expr
Note that constants must be initialized, unlike variables.
examples:
# declare new constant pi, set its value to 3.14159.
# trying to reassign pi is an error
const pi = 3.14159
# error, because tau was not initialised
const tau