Records & Enums

1. Records as product values

Records are literal field bundles:

person = { name: "Ada", born: 1906 }
print(person.name)
print(person["born"])

Field order is ignored for structural equality.

2. Updates are immutable by default

p = { x: 1, y: 2 }
p2 = set(p, "x", 99)
print(p, p2)

set returns a new record. The original p is unchanged.

3. Records as maps

The same {} shape is used as a dynamic map with string keys.

mut counts = {}
counts = set(counts, "cat", 1)
counts = set(counts, "cat", get_or(counts, "cat", 0) + 1)
print(get(counts, "cat"))
print(has(counts, "dog"), has(counts, "cat"))
print(keys(counts), values(counts))

Map APIs:

• get(m, key)
• set(m, key, value)
• get_or(m, key, default)
• has(m, key)
• del(m, key)
• keys(m)
• values(m)

These are available in Stage-0 and documented in REFERENCE.md.

4. Map operations are immutable

set/del return new maps, so update loops normally rebind:

mut m = {}
for w in split("a b a", " "):
    m = set(m, w, get_or(m, w, 0) + 1)
print(m)

5. Mutable collections

When mutability is required, Stage-0 has:

• dict() for mutable string-keyed maps with dict_set, dict_get, dict_len, etc.
• array() / array_from for mutable growable sequences.

d = dict()
dict_set(d, "mode", "fast")
print(dict_get(d, "mode"), dict_len(d))

arr = array_from([1, 2])
array_push(arr, 3)
print(to_list(arr))

6. Enums (tagged unions)

type declarations provide sum types / tagged unions.

type Option:
    Some(v)
    None

type Result:
    Ok(v)
    Err(e)

Match arms destructure constructor fields.