Effect.mapAccum & Array.mapAccum preserve non-emptiness (#3675)

Co-authored-by: maksim.khramtsov <maksim.khramtsov@btsdigital.kz>
Effect-TS · Oct 6, 2024 · 0779681 · 0779681
1 parent 9237ac6
commit 0779681
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diff --git a/.changeset/healthy-dogs-judge.md b/.changeset/healthy-dogs-judge.md
@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Effect.mapAccum & Array.mapAccum preserve non-emptiness
diff --git a/packages/effect/dtslint/Array.ts b/packages/effect/dtslint/Array.ts
@@ -1504,3 +1504,24 @@ pipe(
     _n // $ExpectType 1 | 2
   ) => "a" as const)
 )
+
+// -------------------------------------------------------------------------------------
+// mapAccum
+// -------------------------------------------------------------------------------------
+
+// $ExpectType [state: number, mappedArray: string[]]
+Array.mapAccum(strings, 0, (s, a, i) => [s + i, a])
+
+// $ExpectType [state: number, mappedArray: [string, ...string[]]]
+Array.mapAccum(nonEmptyReadonlyStrings, 0, (s, a, i) => [s + i, a])
+
+// $ExpectType [state: number, mappedArray: string[]]
+pipe(
+  strings,
+  Array.mapAccum(0, (s, a, i) => [s + i, a])
+)
+// $ExpectType [state: number, mappedArray: [string, ...string[]]]
+pipe(
+  nonEmptyReadonlyStrings,
+  Array.mapAccum(0, (s, a, i) => [s + i, a])
+)
diff --git a/packages/effect/dtslint/Effect.ts b/packages/effect/dtslint/Effect.ts
@@ -1263,3 +1263,28 @@ pipe(
     ) => "b" as const
   )
 )
+
+// -------------------------------------------------------------------------------------
+// mapAccum
+// -------------------------------------------------------------------------------------
+
+declare const nonEmptyReadonlyStrings: NonEmptyReadonlyArray<string>
+declare const strings: Array<string>
+
+// $ExpectType Effect<[number, string[]], never, never>
+Effect.mapAccum(strings, 0, (s, a, i) => Effect.succeed([s + i, a]))
+
+// $ExpectType Effect<[number, [string, ...string[]]], never, never>
+Effect.mapAccum(nonEmptyReadonlyStrings, 0, (s, a, i) => Effect.succeed([s + i, a]))
+
+// $ExpectType Effect<[number, string[]], never, never>
+pipe(
+  strings,
+  Effect.mapAccum(0, (s, a, i) => Effect.succeed([s + i, a]))
+)
+
+// $ExpectType Effect<[number, [string, ...string[]]], never, never>
+pipe(
+  nonEmptyReadonlyStrings,
+  Effect.mapAccum(0, (s, a, i) => Effect.succeed([s + i, a]))
+)
diff --git a/packages/effect/src/Array.ts b/packages/effect/src/Array.ts
@@ -2859,11 +2859,15 @@ export const join: {
  * @category folding
  */
 export const mapAccum: {
-  <S, A, B>(
+  <S, A, B, I extends Iterable<A> = Iterable<A>>(
     s: S,
-    f: (s: S, a: A, i: number) => readonly [S, B]
-  ): (self: Iterable<A>) => [state: S, mappedArray: Array<B>]
-  <S, A, B>(self: Iterable<A>, s: S, f: (s: S, a: A, i: number) => readonly [S, B]): [state: S, mappedArray: Array<B>]
+    f: (s: S, a: ReadonlyArray.Infer<I>, i: number) => readonly [S, B]
+  ): (self: I) => [state: S, mappedArray: ReadonlyArray.With<I, B>]
+  <S, A, B, I extends Iterable<A> = Iterable<A>>(
+    self: I,
+    s: S,
+    f: (s: S, a: ReadonlyArray.Infer<I>, i: number) => readonly [S, B]
+  ): [state: S, mappedArray: ReadonlyArray.With<I, B>]
 } = dual(
   3,
   <S, A, B>(self: Iterable<A>, s: S, f: (s: S, a: A, i: number) => [S, B]): [state: S, mappedArray: Array<B>] => {

diff --git a/packages/effect/src/Effect.ts b/packages/effect/src/Effect.ts
@@ -2365,15 +2365,15 @@ export const map: {
  * @category mapping
  */
 export const mapAccum: {
-  <S, A, B, E, R>(
+  <S, A, B, E, R, I extends Iterable<A> = Iterable<A>>(
     zero: S,
-    f: (s: S, a: A, i: number) => Effect<readonly [S, B], E, R>
-  ): (elements: Iterable<A>) => Effect<[S, Array<B>], E, R>
-  <A, S, B, E, R>(
-    elements: Iterable<A>,
+    f: (s: S, a: RA.ReadonlyArray.Infer<I>, i: number) => Effect<readonly [S, B], E, R>
+  ): (elements: I) => Effect<[S, RA.ReadonlyArray.With<I, B>], E, R>
+  <A, S, B, E, R, I extends Iterable<A> = Iterable<A>>(
+    elements: I,
     zero: S,
-    f: (s: S, a: A, i: number) => Effect<readonly [S, B], E, R>
-  ): Effect<[S, Array<B>], E, R>
+    f: (s: S, a: RA.ReadonlyArray.Infer<I>, i: number) => Effect<readonly [S, B], E, R>
+  ): Effect<[S, RA.ReadonlyArray.With<I, B>], E, R>
 } = effect.mapAccum
 
 /**

diff --git a/packages/effect/src/internal/core-effect.ts b/packages/effect/src/internal/core-effect.ts
@@ -1055,17 +1055,17 @@ const loopDiscard = <S, X, E, R>(
 
 /* @internal */
 export const mapAccum: {
-  <S, A, B, E, R>(
+  <S, A, B, E, R, I extends Iterable<A> = Iterable<A>>(
     zero: S,
     f: (s: S, a: A, i: number) => Effect.Effect<readonly [S, B], E, R>
-  ): (elements: Iterable<A>) => Effect.Effect<[S, Array<B>], E, R>
-  <A, S, B, E, R>(
-    elements: Iterable<A>,
+  ): (elements: I) => Effect.Effect<[S, Arr.ReadonlyArray.With<I, B>], E, R>
+  <A, S, B, E, R, I extends Iterable<A> = Iterable<A>>(
+    elements: I,
     zero: S,
     f: (s: S, a: A, i: number) => Effect.Effect<readonly [S, B], E, R>
-  ): Effect.Effect<[S, Array<B>], E, R>
-} = dual(3, <A, S, B, E, R>(
-  elements: Iterable<A>,
+  ): Effect.Effect<[S, Arr.ReadonlyArray.With<I, B>], E, R>
+} = dual(3, <A, S, B, E, R, I extends Iterable<A> = Iterable<A>>(
+  elements: I,
   zero: S,
   f: (s: S, a: A, i: number) => Effect.Effect<readonly [S, B], E, R>
 ): Effect.Effect<[S, Array<B>], E, R> =>