FP #1 — compose() & pipe()

Function composition is the core of functional programming — combining simple functions to build complex transformations. compose runs right-to-left, pipe runs left-to-right. This article implements both and shows real-world transformation pipelines.

Prerequisites: Functions #2 — Currying

1. compose() — Right-to-Left

compose(f, g)(x) means f(g(x)) — apply g first, then f:

2. pipe() — Left-to-Right (More Readable)

pipe(f, g)(x) means g(f(x)) — execution order matches reading order:

3. Handling Multiple Arguments — Pipe with First Function

4. Async Pipe — Chain Async Functions

5. Pipe with Error Handling — Railway Pattern

Key Takeaways

• compose(f, g, h)(x) = f(g(h(x))) — right-to-left execution.
• pipe(f, g, h)(x) = h(g(f(x))) — left-to-right, reads in natural order.
• Use reduce/reduceRight for the implementation — concise and correct.
• Async pipe chains promise-returning functions sequentially.
• Safe pipe stops on error — the foundation of the Either monad and railway-oriented programming.

Next: FP #2 — transduce() — Map + Filter in One Pass — fuse map and filter into a single reduction for better performance.