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Experimental through version 1. Version 0 was alpha. This is the first language release: the interface is relatively stable, not frozen. Nothing is promised stable until version 2.

varia

Translation status: English reader-locale proof. Term names and code fences follow the en pack; supporting prose may still be English.

Declares a mutable binding.

Aliases: let, mutable

Syntax: mut <type|_> <pattern> [← <expression>]

Category#

binding

Examples#

radix/corpus/varia/varia.fab (canonical · keyword)#

Declares a mutable binding.

# =============================================================================
# mut — Declares a mutable binding.
# =============================================================================
#
# What this teaches:
#   • Mutable bindings — `mut` for values that can be reassigned after declaration
#   • Write-once bindings — `let` for values that cannot be reassigned
#
# Common mistakes:
#   • declaring mut when the binding is never reassigned — use let instead (WARN013)
#
# See also: const, ←, ↑
# =============================================================================




# Mutable and immutable variable declarations
#
# mut <name> ← <expr>   -- mutable binding (may reassign)
# let <name> ← <expr>     -- write-once binding (see let/sit.fab)
#
# GRAMMAR:
#   bindingStmt :← ('mut' | 'let') type? ident '←' expr
#
# EXPECTED OUTPUT:
#   0, 1, 11, "Salve, Mundus!", 30, "Vale"

main {
    # --- Mutable bindings with mut ---

    mut _ computus ← 0
    print computus

    computus ← 1
    print computus

    computus ← computus + 10
    print computus

    # --- Write-once bindings: let ---

    let _ salutatio ← "Salve, Mundus!"
    print salutatio

    # let infers the type of each local
    let _ x ← 10
    let _ y ← 20
    let _ sum ← x + y
    print sum

    # --- Reassign only mut bindings ---

    mut _ nuntius ← "Salve"
    nuntius ← "Vale"
    print nuntius
}

Expected output:

0
1
11
Salve, Mundus!
30
Vale