Variables and binding

Faber has three variable keywords and a dedicated assignment glyph. The key distinction is between fixum (write-once) and varia (freely reassignable), and between ← (runtime flow) and = (structural field shape).

fixum — immutable binding

fixum bindings are write-once. They may be declared with or without an initializer; if declared without, they must be assigned exactly once before reading. A second assignment is rejected.

fixum numerus count ← 0
fixum textus name ← "Marcus"
fixum _ inferred ← [1, 2, 3]

Deferred initialisation:

incipit {
    fixum numerus factor
    si verum {
        factor ← 10
    } secus {
        factor ← 100
    }
    nota factor
}

varia — mutable binding

varia bindings are freely reassignable:

incipit {
    varia numerus count ← 0
    count ← count + 1
    count ← count * 2
}

sit — inferred immutable sugar

sit is sugar for fixum _ — an immutable binding with inferred type:

incipit {
    sit salve ← "Salve"
    sit nomen ← "Marcus"
    sit x ← 42

    # Deferred form
    sit label
    label ← "deferred"
}

Runtime binding vs structural definition

Faber splits what most languages collapse into =:

genus Point {
    numerus x
    numerus y
}

incipit {
    # Runtime: ← attaches a value to a name at execution time
    varia numerus count ← 0
    varia textus label ← "ready"
    count ← count + 1

    # Structural: = defines field values inside a type literal
    fixum _ p ← Point {
        x = 10,
        y = 20
    }
}

Ex field extraction

ex extracts fields from a value into local bindings:

genus Persona {
    textus nomen
    numerus aetas
}

incipit {
    fixum _ p ← Persona { nomen = "Marcus", aetas = 30 }
    ex p fixum nomen, aetas
    # prints "Marcus"
    nota nomen
}

Postfix increment and decrement

⊕ and ⊖ are postfix increment/decrement statements for mutable numerus places. They are statement-only — no expression value, no prefix forms:

incipit {
    varia numerus i ← 0
    # i becomes 1
    i ⊕
    # i becomes 0
    i ⊖
}