packages/effect-lens/src/Lens.ts

@@ -29,7 +29,14 @@ export const isLens = (u: unknown): u is Lens<unknown, unknown, unknown, unknown
 
 
 export const LensStepTypeId: unique symbol = Symbol.for("@effect-fc/Lens/LensStep")
-export type LensStepTypeId = typeof LensTypeId
+export type LensStepTypeId = typeof LensStepTypeId
+
+export interface LensFrame<in out A, in out EW = never, in out RW = never> {
+    readonly value: A
+    readonly commit: <E = never, R = never>(
+        next: Effect.Effect<A, E, R>
+    ) => Effect.Effect<void, EW | E, RW | R>
+}
 
 export interface LensStep<
     in out A,
@@ -44,9 +51,8 @@ export interface LensStep<
     in out RSW = never,
 > {
     readonly [LensStepTypeId]: LensStepTypeId
-    readonly transform: (effect: Effect.Effect<B, ESR, RSR>) => Effect.Effect<A, ER, RR>
+    readonly access: (effect: Effect.Effect<LensFrame<B, ESW, RSW>, ESR, RSR>) => Effect.Effect<LensFrame<A, EW, RW>, ER, RR>
     readonly transformStream: (stream: Stream.Stream<B, ESR, RSR>) => Stream.Stream<A, ER, RR>
-    readonly update: (next: Effect.Effect<A, ESW, RSW>, parent: B) => Effect.Effect<B, EW, RW>
 }
 
 export const isLensStep = (u: unknown): u is LensStep<unknown, unknown, unknown, unknown, unknown, unknown, unknown, unknown, unknown, unknown> => Predicate.hasProperty(u, LensStepTypeId)
@@ -89,11 +95,23 @@ extends Pipeable.Class() implements Lens<A, ER, EW, RR, RW> {
     abstract readonly sourceCommit: (b: B) => Effect.Effect<void, ESW, RSW>
     abstract readonly withLock: <A1, E1, R1>(self: Effect.Effect<A1, E1, R1>) => Effect.Effect<A1, EW | E1, RW | R1>
 
-    get get(): Effect.Effect<A, ER, RR> {
+    private get access(): Effect.Effect<LensFrame<A, EW, RW>, ER, RR> {
-        let effect: Effect.Effect<unknown, unknown, unknown> = this.sourceGet
+        let effect: Effect.Effect<LensFrame<unknown, unknown, unknown>, unknown, unknown> = Effect.map(
+            this.sourceGet,
+            value => ({
+                value,
+                commit: next => Effect.flatMap(next, value => this.sourceCommit(value as B)),
+            }),
+        )
+
         for (const step of this.steps)
-            effect = step.transform(effect)
+            effect = step.access(effect as never) as Effect.Effect<LensFrame<unknown, unknown, unknown>, unknown, unknown>
-        return effect as Effect.Effect<A, ER, RR>
+
+        return effect as Effect.Effect<LensFrame<A, EW, RW>, ER, RR>
+    }
+
+    get get(): Effect.Effect<A, ER, RR> {
+        return Effect.map(this.access, frame => frame.value)
     }
 
     get changes(): Stream.Stream<A, ER, RR> {
@@ -107,38 +125,12 @@ extends Pipeable.Class() implements Lens<A, ER, EW, RR, RW> {
         f: (a: A) => Effect.Effect<readonly [C, A], E1, R1>,
     ): Effect.Effect<C, ER | EW | E1, RR | RW | R1> {
         return this.withLock(Effect.flatMap(
-            this.sourceGet,
+            this.access,
-            source => {
+            frame => Effect.flatMap(
-                const parents: unknown[] = []
+                f(frame.value),
-                let current: Effect.Effect<unknown, unknown, unknown> = Effect.succeed(source)
+                ([c, next]) => Effect.as(frame.commit(Effect.succeed(next)), c),
-
+            ),
-                for (const step of this.steps)
-                    current = Effect.flatMap(current, parent => {
-                        parents.push(parent)
-                        return step.transform(Effect.succeed(parent))
-                    })
-
-                return Effect.flatMap(current, a => Effect.flatMap(
-                    f(a as A),
-                    ([c, next]) => {
-                        let rebuilt: Effect.Effect<unknown, unknown, unknown> = Effect.succeed(next)
-
-                        for (let i = this.steps.length - 1; i >= 0; i--) {
-                            // biome-ignore lint/style/noNonNullAssertion: won't throw
-                            const step = this.steps[i]!
-                            // biome-ignore lint/style/noNonNullAssertion: won't throw
-                            const parent = parents[i]!
-                            rebuilt = step.update(rebuilt, parent)
-                        }
-
-                        return Effect.as(
-                            Effect.flatMap(rebuilt, b => this.sourceCommit(b as B)),
-                            c,
-                        )
-                    },
         ))
-            },
-        )) as Effect.Effect<C, ER | EW | E1, RR | RW | R1>
     }
 }