HN Explorer

Show HN: FP-pack – Functional pipelines in TypeScript without monads (github.com)

14 points by superlucky84 ↗ HN
Hi HN,

I built fp-pack, a small TypeScript functional utility library focused on pipe-first composition.

The goal is to keep pipelines simple and readable, while still supporting early exits and side effects — without introducing monads like Option or Either.

Most code uses plain pipe/pipeAsync. For the few cases that need early termination, fp-pack provides a SideEffect-based pipeline that short-circuits safely.

I also wrote an “AI agent skills” document to help LLMs generate consistent fp-pack-style code.

Feedback, criticism, or questions are very welcome.

9 comments

[ 0.26 ms ] story [ 28.9 ms ] thread
superlucky84
One thing I’d especially like feedback on is the SideEffect approach.

It’s intentionally not a monad, and I’m curious how others feel about this trade-off compared to Option/Either in real-world TypeScript codebases.

epgui
How is this not a monad? It might be trying really hard not to reify the core concept of a monad, but it seems to me like it ends up being essentially a complicated monad.
superlucky84
It’s definitely monad-adjacent.

The main difference is that SideEffect isn’t a compositional context — there’s no bind/flatMap, and composition intentionally stops once it appears. It’s meant as an explicit early-exit signal in pipe-first code, not a general computation container.

eterps
While I like the concept, the side-effect pattern might be difficult for the average developer to understand (without fp-pack knowledge) in a shared codebase:

https://github.com/superlucky84/fp-pack?tab=readme-ov-file#s...

Still, this approach is very useful for most business logic, too bad most programming languages don't provide a nice syntax for this.

superlucky84
That’s a fair point, and I agree.

The SideEffect pattern is intentionally explicit, so without fp-pack context it can look unfamiliar at first. The trade-off is making early exits visible in the code, rather than hiding them in conditionals or exceptions.

In practice, most code stays in plain pipe/pipeAsync. SideEffect is meant for a small number of boundary cases only.

And I agree — better language-level syntax for this kind of pattern would make it much easier to adopt.

wk_end
The default any return type from pipelines is kind of brutal. Seems like a real footgun. Is that fixable?
superlucky84
That’s a fair point — it can definitely become a footgun if you’re not careful.

This happens because `runPipeResult` defaults its generic parameter to `R = any`. When type safety matters, the intended solution is to use `pipeSideEffectStrict`, which preserves all possible SideEffect result types as a precise union throughout the pipeline.

The default version prioritizes ergonomics and simplicity, while the strict version prioritizes type safety.

Also, fp-pack is still in an early stage, so the usability and API choices haven’t been fully validated yet. That’s why feedback like this is especially helpful in shaping the direction of the library.

almosthere
Every time I introduce something like this teams complain. RX is a brain antipattern
mrkeen
Haskell does not have nulls. Java 8 introduced Options, and now there are nulls and Options.

Please tell me you didn't just add SideEffects to a language full of side-effects.