Variables & Values

Lumen is dynamically typed. A variable comes into existence the first time you assign to it — there’s no separate declaration syntax.

number = 42
result = number + 10

println result

Value types

Under the hood, every value carried on the stack or stored in a variable is tagged with one of three types:

You never annotate the type yourself — it’s inferred from the literal or the result of an expression, and it can change across the lifetime of a variable, since Lumen re-tags the value on every assignment.

x = 5        # integer
x = 'five'   # now a string — perfectly legal

Float literals

A numeric literal is a float if it contains a decimal point or an exponent (e/E); otherwise it’s an integer. This is a purely syntactic check (isFloatLiteral() in src/helpers.cpp) — it looks at how the literal is written, not its value:

a = 3        # integer
b = 3.0      # float
c = 3e2      # float (300)
d = -3.5     # float

Integer and float literals are pooled together into the same deduplicated constant table — see Bytecode Format.

Arithmetic between an integer and a float promotes the result to float; / (division) always produces a float result regardless of operand types. See Operators for the full rules.

Assignment

Assignment is a single =. The right-hand side can be a literal, another variable, or an arithmetic expression:

a = 10
b = a * 2
c = a + b - 1

Negative numbers work as you’d expect:

z = -20