effect-monocle

effect-monocle

Hey there! This is a library aiming to provide monocle-ts API for effect codebases. My motivation for creating it was to make transition from fp-ts to effect easier because we rely heavily on monocle-ts in our codebase.

The overall tendency in the effect ecosystem is to ditch the optics whatsoever. I'm mostly aligned with this view, so I'd like to emphasize that this library's main goal is to provide a smooth transition path for those who are already using monocle-ts and want to switch to effect. The goal is NOT to promote the use of optics.

The API

This library exposes a very small subset of the monocle-ts API. I basically rewrote parts I use personally. If you need more, feel free to open an issue or a PR.

Along the way, I've made some changes to the API to make it more effect-friendly. Also, I've included some changes to the API that I either wish were in the monocle-ts or have implemented as a custom in-app code.

Notably,

• multi-parameter functions are implemented and exposed as duals, thus there are always both data-first and data-last variants,
• the index module exposes a fully named Lens and Optional modules, so the expected usage is e.g Lens.prop instead of L.prop,
• I included a Lens.extract / Optional.extract combinators, they are the moral equivalents of type-level Extract<A, { [K in keyof A]: B } and are useful when creating an optional from a discriminated union,
• I included Lens.append / Lens.appendAll / Optional.append / Optional.appendAll combinators that work on lenses / optionals focusing an array and they create a function performing an append / extend on the focused array,
• I modified the signature of Lens.prop / Optional.prop to accept multiple keys at once, so one can write Lens.prop(lens, 'a', 'b', 'c') instead of pipe(lens, Lens.prop('a'), Lens.prop('b'), Lens.prop('c')).
• I renamed Lens.props / Optional.props to Lens.pick / Optional.pick to unify the naming with @effect/schema, effect/Struct, etc.
• The Lens<S, A> has a modify method so it should be used insteadf of L.modify

Please refer to the monocle-ts README and the effect-monocle API docs for more information.