ref(s, i, @optional default = false)
Return the element at index i from the sequence s. If the index is out of bounds, return default.
Ref and ref_set are generic functions that can be overridden by a user-defined object.
Strings, lists, arrays and hash tables
implement them by default. Any object that implement these functions automatically starts working with the [] syntax.
let s = "heLLo, world"
ref(s, 10)
// \l
s[11]
// \d
ref(#{"one":1, "two":2}, "abc", 100)
// 100
ref(#{"one":1, "two":2}, "one")
// 1
// overriding ref and ref_set for a custom sequence:
function make_coll(xs)
let (len = array_length(xs)
coll_ref = ^(index) xs[index]
coll_ref_set = ^(index, value) xs[index] = value)
^(msg)
| 'first -> when (len > 0) array_at(xs, 0)
| 'rest -> when (len > 1) make_coll(subarray(xs, 1, len))
| 'count -> len
| 'ref -> coll_ref
| 'ref_set -> coll_ref_set
let b = make_coll(#[10, 20, 30])
b[0]
// 10
b[1] = 100
b[1]
// 100
ref(b, 2)
// 30
ref_set(b, 2, 200)
b[2]
// 200
// an object that responds to `ref` can be destructred as a list or a hash table:
let [x, y, z] = b
x + y + z
// 310
let #{0:i, 2:j, 1:k} = b;
[i, j, k]
// [10, 200, 100]