functional

functional is a set of utility modules in the vein of Ramda and fp-ts. It uses a lightweight higher kinded type encoding to implement reusable high level interfaces. These interfaces are called Type Classes or Algebraic Structures in other languages. The usefulness of these interfaces comes from their ability to describe common operations across different data structures and concrete data types without referencing any specific data type. Intuitively one can think of these higher kinded types as a generic type that itself has a Generic parameter. ie type Apply<A, B> = A<B>. This is not valid typescript code but it illuminates the cored idea of higher kinder types.

The functional library is written as a first class Deno library. Some effort might be made to release Deno into npm but NodeJS is not a first class target for support. If you want a functional library for NodeJS fp-ts is definitely the way to go!

The primary goals of functional are to be:

• Pragmatic: The API surface of functional should favor ease-of-use and consistency over cleverness or purity. This project is ultimately for getting work done.
• Understandable: The higher kinded type and TypeClass implementations are meant to be as simple as possible so their logic can be easily audited. We have also chosen descriptive names for TypeClass implementations instead of ones pulled from Category Theory.
• Performant: Once the first two goals are satisfied, the long term changes within functional are likely going to be beneath the API surface and aimed at speeding things up where possible.

Some non-goals of functional are:

• To be an exact port of fp-ts. Many changes have been implemented throughout functional that diverge sharply from fp-ts, this is often on purpose.

Documentation

Documentation is generated for each github tagged release. The latest documentation can be found here.

Versions

History

functional started as an exploratory project in late 2020 to learn more about higher kinded type implementations in TypeScript and to assess how much effort it would take to port fp-ts to a Deno-native format. Through that process it became clear that the things I had learned could serve as both a useful tool and as a learning resource in and of itself. At various times functional has used multiple hkt encodings, type class definitions, and implementation methods. Some of the key history moments of functional are in the hkts history. Specifically, the hkts implementation in the initial commit and the last major type system rewrite might be interesting. Now, however, the API for version 1.0.0 is set and will only change between major versions (which should be extremely rare).

This project is incredibly indebted to gcanti, pelotom, and the TypeScript community at large. There is nothing new in this project, it’s all a reimaginings of ideas that already existed.

For anyone getting started with functional programming I highly recommend writing your own implementation of an ADT such as Option or Either. From Functor to IndexedTraversable with everything inbetween, there is a lot to learn about the mechanics of programming in general by taking these small pieces apart and putting them back together.

Contributions

Contributions are welcome! Currently, the only maintainer for functional is baetheus. If you want to add to functional or change something, open an issue and ask away. The guidelines for contribution are:

1. We are kind to others
2. We use conventional commit messages
3. We use semantic versioning
4. We try to keep test coverage at 100%
5. We try not to break APIs between major releases

Since there is little churn in this library releases are infrequent. If you wish to contribute I would prefer that you start with documentation. It is one of my long term goals to have a few sentences of description and an example for every export. After that, if I’m behind on test coverage that is a great place to start. Last, if you wish to add a feature it’s good to start a discussion about the feature with a few concrete use cases before submitting a PR. This will allow for others to chime in without crowding the issues section.

Also, primary development takes places on one of my servers where I use fossil instead of git as a VCS. I still use github for interfacing with users and for releases, but if you wish to become a long term contributor learning to get around with fossil is a must.

Thanks for you interest!