Gen context (#2857)

Co-authored-by: maksim.khramtsov <maksim.khramtsov@btsdigital.kz>

.changeset/rare-spiders-occur.md

@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Support `this` argument for `{STM, Either, Option}.gen`

packages/effect/src/Either.ts

@@ -700,7 +700,10 @@ const adapter = Gen.adapter<EitherTypeLambda>()
  * @category generators
  * @since 2.0.0
  */
-export const gen: Gen.Gen<EitherTypeLambda, Gen.Adapter<EitherTypeLambda>> = (f) => {
+export const gen: Gen.Gen<EitherTypeLambda, Gen.Adapter<EitherTypeLambda>> = (...args) => {
+  const f = (args.length === 1)
+    ? args[0]
+    : args[1].bind(args[0])
   const iterator = f(adapter)
   let state: IteratorYieldResult<any> | IteratorReturnResult<any> = iterator.next()
   if (state.done) {

packages/effect/src/Option.ts

@@ -1345,7 +1345,13 @@ const adapter = Gen.adapter<OptionTypeLambda>()
  * @category generators
  * @since 2.0.0
  */
-export const gen: Gen.Gen<OptionTypeLambda, Gen.Adapter<OptionTypeLambda>> = (f) => {
+export const gen: Gen.Gen<OptionTypeLambda, Gen.Adapter<OptionTypeLambda>> = (...args) => {
+  let f: any
+  if (args.length === 1) {
+    f = args[0]
+  } else {
+    f = args[1].bind(args[0])
+  }
   const iterator = f(adapter)
   let state: IteratorYieldResult<any> | IteratorReturnResult<any> = iterator.next()
   if (state.done) {

packages/effect/src/STM.ts

@@ -1065,8 +1065,13 @@ export interface Adapter {
  * @since 2.0.0
  * @category constructors
  */
-export const gen: <Eff extends YieldWrap<STM<any, any, any>>, AEff>(
-  f: (resume: Adapter) => Generator<Eff, AEff, never>
+export const gen: <Self, Eff extends YieldWrap<STM<any, any, any>>, AEff>(
+  ...args:
+    | [
+      self: Self,
+      body: (this: Self, resume: Adapter) => Generator<Eff, AEff, never>
+    ]
+    | [body: (resume: Adapter) => Generator<Eff, AEff, never>]
 ) => STM<
   AEff,
   [Eff] extends [never] ? never : [Eff] extends [YieldWrap<STM<infer _A, infer E, infer _R>>] ? E : never,

packages/effect/src/Utils.ts

@@ -172,17 +172,20 @@ export interface Variance<in out F extends TypeLambda, in R, out O, out E> {
   readonly _E: Types.Covariant<E>
 }
 
-/**
- * @category models
- * @since 2.0.0
- */
 /**
  * @category models
  * @since 2.0.0
  */
 export interface Gen<F extends TypeLambda, Z> {
-  <K extends Variance<F, any, any, any> | YieldWrap<Kind<F, any, any, any, any>>, A>(
-    body: (resume: Z) => Generator<K, A, never>
+  <Self, K extends Variance<F, any, any, any> | YieldWrap<Kind<F, any, any, any, any>>, A>(
+    ...args:
+      | [
+        self: Self,
+        body: (this: Self, resume: Z) => Generator<K, A, never>
+      ]
+      | [
+        body: (resume: Z) => Generator<K, A, never>
+      ]
   ): Kind<
     F,
     [K] extends [Variance<F, infer R, any, any>] ? R

packages/effect/src/internal/stm/stm.ts

@@ -618,8 +618,11 @@ export const fromOption = <A>(option: Option.Option<A>): STM.STM<A, Option.Optio
  * Inspired by https://github.com/tusharmath/qio/pull/22 (revised)
  * @internal
  */
-export const gen: typeof STM.gen = (f) =>
+export const gen: typeof STM.gen = (...args) =>
   suspend(() => {
+    const f = (args.length === 1)
+      ? args[0]
+      : args[1].bind(args[0])
     const iterator = f(pipe)
     const state = iterator.next()
     const run = (

packages/effect/test/Either.test.ts

@@ -42,12 +42,16 @@ describe("Either", () => {
     const f = Either.gen(function*($) {
       yield* $(Either.left("err"))
     })
+    const g = Either.gen({ context: "testContext" as const }, function*($) {
+      return yield* $(Either.right(this.context))
+    })
     expect(a).toEqual(Either.right(3))
     expect(b).toEqual(Either.right(10))
     expect(c).toEqual(Either.right(undefined))
     expect(d).toEqual(Either.right(2))
     expect(e).toEqual(Either.left("err"))
     expect(f).toEqual(Either.left("err"))
+    expect(g).toEqual(Either.right("testContext"))
   })
 
   it("exports", () => {

packages/effect/test/Option.test.ts

@@ -46,12 +46,17 @@ describe("Option", () => {
     const f = Option.gen(function*($) {
       yield* $(Option.none())
     })
+
+    const g = Option.gen({ ctx: "testContext" as const }, function*() {
+      return yield* Option.some(this.ctx)
+    })
     expect(a).toEqual(Option.some(3))
     expect(b).toEqual(Option.some(10))
     expect(c).toEqual(Option.some(undefined))
     expect(d).toEqual(Option.some(2))
     expect(e).toEqual(Option.none())
     expect(f).toEqual(Option.none())
+    expect(g).toEqual(Option.some("testContext"))
   })
 
   it("toString", () => {

packages/effect/test/STM.test.ts

@@ -957,6 +957,12 @@ describe("STM", () => {
       assert.strictEqual(result, "test")
     }))
 
+  it.effect("gen with context", () =>
+    STM.gen({ context: "Context" as const }, function*() {
+      const result = yield* STM.succeed(this.context)
+      assert.strictEqual(result, "Context")
+    }))
+
   it.effect("summarized - returns summary and value", () =>
     Effect.gen(function*($) {
       const transaction = STM.gen(function*($) {