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0.1.3 #2

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Thilawyn merged 4 commits from next into master 2026-03-28 21:13:30 +01:00
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3 changed files with 119 additions and 3 deletions
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2
packages/effect-lens/package.json
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@@ -1,7 +1,7 @@
{
"name": "effect-lens",
"description": "An effectful Lens type to easily manage nested state",
"version": "0.1.2",
"version": "0.1.3",
"type": "module",
"files": [
"./README.md",

52
packages/effect-lens/src/Lens.test.ts
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@@ -1,9 +1,59 @@
import { describe, expect, test } from "bun:test"
import { Chunk, Effect, SubscriptionRef } from "effect"
import { Chunk, Effect, Option, SubscriptionRef } from "effect"
import * as Lens from "./Lens.js"
describe("Lens", () => {
test("mapOption transforms Some values and preserves None", async () => {
const result = await Effect.runPromise(
Effect.flatMap(
SubscriptionRef.make<Option.Option<number>>(Option.some(42)),
parent => {
const lens = Lens.mapOption(
Lens.fromSubscriptionRef(parent),
n => n * 2,
(_n, doubled) => doubled / 2,
)
return Effect.flatMap(
Lens.get(lens),
value => Effect.flatMap(
Lens.set(lens, Option.some(100)),
() => Effect.map(parent.get, parentValue => [value, parentValue] as const),
),
)
},
),
)
expect(result[0]).toEqual(Option.some(84)) // 42 * 2
expect(result[1]).toEqual(Option.some(50)) // 100 / 2
})
test("mapOptionEffect transforms Some values with effects", async () => {
const result = await Effect.runPromise(
Effect.flatMap(
SubscriptionRef.make<Option.Option<number>>(Option.some(42)),
parent => {
const lens = Lens.mapOptionEffect(
Lens.fromSubscriptionRef(parent),
n => Effect.succeed(n * 2),
(_n, doubled) => Effect.succeed(doubled / 2),
)
return Effect.flatMap(
Lens.get(lens),
value => Effect.flatMap(
Lens.set(lens, Option.some(100)),
() => Effect.map(parent.get, parentValue => [value, parentValue] as const),
),
)
},
),
)
expect(result[0]).toEqual(Option.some(84)) // 42 * 2
expect(result[1]).toEqual(Option.some(50)) // 100 / 2
})
test("focusObjectField focuses a nested property without touching other fields", async () => {
const [initialCount, updatedState] = await Effect.runPromise(
Effect.flatMap(

68
packages/effect-lens/src/Lens.ts
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@@ -1,4 +1,4 @@
import { Array, Chunk, Effect, Function, Pipeable, Predicate, Readable, Stream, type SubscriptionRef, type SynchronizedRef } from "effect"
import { Array, Chunk, Effect, Function, Option, Pipeable, Predicate, Readable, Stream, type SubscriptionRef, type SynchronizedRef } from "effect"
import type { NoSuchElementException } from "effect/Cause"
import * as Subscribable from "./Subscribable.js"
@@ -183,6 +183,72 @@ export const mapEffect: {
)),
}))
/**
* Derives a new `Lens` by applying synchronous getters and setters over the value inside an `Option`.
*
* Similar to `Option.map`, this preserves the `Option` structure:
* - If the `Option` is `Some(a)`, applies the getter and setter to the inner value
* - If the `Option` is `None`, it remains `None`
*/
export const mapOption: {
<A, ER, EW, RR, RW, B>(
self: Lens<Option.Option<A>, ER, EW, RR, RW>,
get: (a: NoInfer<A>) => B,
set: (a: NoInfer<A>, b: B) => NoInfer<A>,
): Lens<Option.Option<B>, ER, EW, RR, RW>
<A, ER, EW, RR, RW, B>(
get: (a: NoInfer<A>) => B,
set: (a: NoInfer<A>, b: B) => NoInfer<A>,
): (self: Lens<Option.Option<A>, ER, EW, RR, RW>) => Lens<Option.Option<B>, ER, EW, RR, RW>
} = Function.dual(3, <A, ER, EW, RR, RW, B>(
self: Lens<Option.Option<A>, ER, EW, RR, RW>,
get: (a: NoInfer<A>) => B,
set: (a: NoInfer<A>, b: B) => NoInfer<A>,
): Lens<Option.Option<B>, ER, EW, RR, RW> => map(
self,
Option.map(get),
(opt, newOpt) => Option.match(opt, {
onSome: a => Option.map(newOpt, b => set(a, b)),
onNone: () => Option.none(),
}),
))
/**
* Derives a new `Lens` by applying effectful getters and setters over the value inside an `Option`.
*
* Similar to `Option.map`, this preserves the `Option` structure:
* - If the `Option` is `Some(a)`, applies the effectful getter and setter to the inner value
* - If the `Option` is `None`, it remains `None`
*/
export const mapOptionEffect: {
<A, ER, EW, RR, RW, B, EGet = never, RGet = never, ESet = never, RSet = never>(
self: Lens<Option.Option<A>, ER, EW, RR, RW>,
get: (a: NoInfer<A>) => Effect.Effect<B, EGet, RGet>,
set: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
): Lens<Option.Option<B>, ER | EGet, EW | ESet, RR | RGet, RW | RSet>
<A, ER, EW, RR, RW, B, EGet = never, RGet = never, ESet = never, RSet = never>(
get: (a: NoInfer<A>) => Effect.Effect<B, EGet, RGet>,
set: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
): (self: Lens<Option.Option<A>, ER, EW, RR, RW>) => Lens<Option.Option<B>, ER | EGet, EW | ESet, RR | RGet, RW | RSet>
} = Function.dual(3, <A, ER, EW, RR, RW, B, EGet = never, RGet = never, ESet = never, RSet = never>(
self: Lens<Option.Option<A>, ER, EW, RR, RW>,
get: (a: NoInfer<A>) => Effect.Effect<B, EGet, RGet>,
set: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
): Lens<Option.Option<B>, ER | EGet, EW | ESet, RR | RGet, RW | RSet> => mapEffect(
self,
Option.match({
onSome: a => Effect.map(get(a), Option.some),
onNone: () => Effect.succeed(Option.none()),
}),
(opt, newOpt) => Option.match(opt, {
onSome: a => Option.match(newOpt, {
onSome: b => Effect.map(set(a, b), Option.some),
onNone: () => Effect.succeed(Option.none()),
}),
onNone: () => Effect.succeed(Option.none()),
}),
))
/**
* Allows transforming only the `changes` stream of a `Lens` while keeping the focus type intact.
*/