Lazy Evaluation

Source: src/hql/lib/stdlib/js/internal/seq-protocol.js, src/hql/lib/stdlib/js/core.js, src/hql/lib/stdlib/stdlib.hql

HQL implements Clojure-inspired lazy sequences built on a Symbol-based protocol system. Lazy sequences defer computation until values are needed, enable infinite data structures, and provide memory-efficient processing.

Summary

• SEQ Protocol: Symbol-based protocol (hql.seq) with first(), rest(), seq() methods
• lazy-seq: Creates lazy sequences from thunks, memoized and trampolined
• Cons cells: Immutable pairs via (cons head tail)
• seq function: Converts collections to lazy sequences with nil-punning
• delay/force/realized: Deferred computation primitives
• Infinite sequences: range, repeat, cycle, iterate
• Chunked sequences: ArrayChunk/ChunkBuffer/ChunkedCons for batch optimization

Quick Examples

;; Infinite lazy sequence
(take 5 (range))           ;; => (0 1 2 3 4)

;; Lazy transformations (nothing computed until consumed)
(take 3 (filter isOdd (range)))  ;; => (1 3 5)

;; Infinite fibonacci
(fn fib-seq [a b]
  (lazy-seq (cons a (fib-seq b (+ a b)))))
(take 10 (fib-seq 0 1))  ;; => (0 1 1 2 3 5 8 13 21 34)

;; Cons cells
(cons 1 (cons 2 (cons 3 null)))  ;; => (1 2 3)

;; Nil-punning
(seq [])    ;; => null
(seq [1])   ;; => ArraySeq(1)

;; Delay/Force
(let d (delay (expensive-computation)))
(force d)      ;; evaluates and caches
(realized d)   ;; => true

Core Types

See Also

• spec.md - Technical specification
• examples.hql - More examples