การประเมินแบบขี้เกียจด้วยโมดูล Stream

Enum is eager: each step builds a full intermediate list. Stream is lazy: it composes operations and computes only when needed.

Chaining several Enum calls walks the whole collection multiple times and allocates a list at each stage.

Swap Enum for Stream to defer work. Nothing runs until a consuming function is called.

A stream stays inert until an Enum function (like take or to_list) pulls values through it.

Lazy pipelines fuse the steps and stop as soon as enough elements are produced, avoiding huge intermediate lists.

Stream.iterate/2 creates endless sequences that are safe because evaluation is lazy.

Stream.cycle repeats a finite list forever, useful for assigning rotating values.

Stream.unfold/2 builds a stream from a state and a function returning the next value and new state.

File.stream!/1 reads a file lazily, one line at a time, so you can process huge files with constant memory.

Group a stream into batches lazily, handy for paginating work without loading everything.

Use Stream for large datasets, multi-step pipelines, infinite sequences, or IO. Use Enum for small collections where simplicity wins.

You learned lazy evaluation:

• Enum is eager; Stream is lazy and composable
• Streams compute only when consumed by an Enum function
• They enable infinite sequences and constant-memory file processing
• Prefer streams for large/multi-step pipelines, Enum for small data