Functions

Functions in Faber are declared with functio, using type-first parameter syntax and a glyph return type.

Basic syntax

functio twice(numerus n) → numerus {
    redde n
}

With an error channel:

functio parse(textus input) → numerus ⇥ textus {
    redde 0
}

Examples

# No parameters, no return
functio saluta() {
    nota "Salve, Mundus!"
}

# Parameter, no explicit return
functio dic(textus verbum) {
    nota verbum
}

# Parameter and return type
functio duplica(numerus n) → numerus {
    redde n * 2
}

# Multiple parameters
functio adde(numerus a, numerus b) → numerus {
    redde a + b
}

Return values

Use redde for normal returns:

functio porta(numerus x) → numerus {
    si x < 0 ∴ redde 0
    redde x * 2
}

Bare redde for vacuum return type:

functio tace() → vacuum {
    redde
}

Borrowing and mutability (de, in, ex)

Faber marks how a value is passed with short prepositions on parameters:

Marker	Intent	Typical Rust lowering
(none)	Owned value	`T` by value
`de`	Shared borrow (read-only)	`&T`
`in`	Mutable borrow	`&mut T`
`ex`	Consume (move into callee)	`T` by move

# Shared borrow
functio imprime(de textus label) → vacuum {
    nota label
}

# Mutable borrow
functio duplica(in numerus value) → vacuum {
    value ← value * 2
}

# Consume
functio consume(ex textus buffer) → textus {
    redde buffer
}

# Owned
functio salve(textus nomen) → textus {
    redde "Salve, §!"(nomen)
}

The same words (de, ex) are reused in other constructs — do not read every ex as "consume":

Surface	Role
`de textus name` on parameter	Shared borrow
`in numerus count` on parameter	Mutable borrow
`ex textus buffer` on parameter	Move into callee
`itera ex items fixum item`	Iterate values
`itera de tabula fixum key`	Iterate keys
`ex source fixum x, ceteri rest`	Destructure fields
`importa ex "path"`	Import from module

Entry point

The program entry point is incipit:

incipit {
    nota "ingressus"
}

CLI entry point

For CLI programs, incipit argumenta receives parsed command arguments:

@ cli "echo"
@ descriptio "Prints text"
@ operandus ceteri textus words
incipit argumenta args {
    itera ex args.words fixum word {
        nota word
    }
}

Passing mode — `sponte`

sponte marks a parameter that may be omitted by the caller:

functio connect(textus host, numerus port sponte) → vacuum {
    nota host
}