Lykn

Destructuring and Immutable Updates

Destructuring (taking apart) and assoc/dissoc/conj (putting together differently) are complementary tools. Both are immutable operations — neither mutates the original.

Extract, Transform, Reassemble

(bind (object name age) user)
(bind updated (obj
  :name (name:to-upper-case)
  :age (+ age 1)))

Destructuring extracts the parts; obj builds a new object from transformed parts. The original user is unchanged.

assoc Preserves What You Don’t Touch

(bind updated (assoc user :name (user:name:to-upper-case)))

assoc (Ch 13) produces a shallow copy with overrides. Properties you don’t mention are preserved. Destructuring + obj builds from scratch; assoc copies and modifies. Choose based on whether you want to keep the other properties.

The Pattern

The idiomatic flow in surface Lykn:

1. Destructure — extract the parts you need
2. Transform — apply functions to the extracted values
3. Reassemble — build a new value with obj or assoc

No mutation at any step. The original value survives. The new value has the changes. The functional update pattern, expressed through s-expressions.