ion-sound/tests/optional_assignment.ion

let a ?= 5
echo $a
let a ?= 10
echo $a

let b ?= [ 1 2 3 ]
echo @b
let b ?= [ 4 5 6 ]
echo @b

let c d e ?= [ 1 2 3 ] hello 5
echo @c
echo $d
echo $e
let c d e ?= [ 4 5 6 ] world 10
echo @c
echo $d
echo $e