Variables

Variables in Rune store data values. Rune is dynamically typed, meaning a variable can hold any type of value and change its type over time.

Declaration & Assignment

Variables are declared and assigned using the set keyword:

set name = "Rune"
set score = 100
set active = yes

There is no separate keyword for declaring a variable and reassigning it; the set keyword is used for both.

set score = 0
# Reassignment:
set score = score + 10
write(score) # 10

Scoping Rules

Rune uses lexical scoping through a chain of parent-linked environments:

• Local Scope — Spells (functions) and loops introduce a new local scoping frame.
• Innermost Binding — The set statement defines the variable on the current innermost environment scope frame.
• Hoisting / Variable Lookup — When looking up a variable (e.g. write(x)), the interpreter searches the current scope. If not found, it traverses up the parent chain until the global environment is reached.
• Assignment Limitation — Because set always defines the variable on the current scope, assigning to a captured variable from an outer scope inside a spell defines a new local variable in the inner scope instead of modifying the outer scope.

set x = 10

spell check() {
    # This reads x from the outer scope:
    write(x) # 10

    # This creates a NEW local x inside check():
    set x = 20
    write(x) # 20
}

check()
write(x) # 10 (outer x remains unchanged)