Lazy Sequences in Clojure

Many Clojure functions return lazy sequences: they describe a computation, but do not perform all the work immediately. Work happens as you consume the sequence.

This is powerful:

• You can build streaming pipelines (transform as you go).
• You can represent infinite sequences safely when you take only what you need.

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

The gotchas to learn early

• If you keep a reference to the head of a lazy sequence, you can accidentally retain memory.
• Side effects inside lazy pipelines can be surprising because evaluation time is deferred.

Java mental model: laziness is closer to an iterator/stream that executes on demand, but it composes like plain functions.

In this section

• How Lazy Sequences Work in Clojure
  Learn how Clojure lazy sequences defer work, compose transformations, and differ from Java iterators and streams in evaluation timing.
• Creating Lazy Sequences in Clojure
  Create lazy sequences with lazy-seq, repeat, range, iterate, and sequence transformations while keeping realization and memory retention visible.
• Infinite Sequences in Clojure
  Work with unbounded Clojure sequences safely by pairing lazy producers with bounded consumers such as take, take-while, and finite reductions.