Add mapStream

packages/effect-lens-next/src/View.ts

@@ -99,6 +99,25 @@ export const mapOptionEffect: {
     onNone: () => Effect.succeed(Option.none()),
 })))
 
+/**
+ * Allows transforming only the `changes` stream of a `View`.
+ */
+export const mapStream: {
+    <A, E, R>(
+        f: (changes: Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>) => Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>,
+    ): (self: View<A, E, R>) => View<A, E, R>
+    <A, E, R>(
+        self: View<A, E, R>,
+        f: (changes: Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>) => Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>,
+    ): View<A, E, R>
+} = Function.dual(2, <A, E, R>(
+    self: View<A, E, R>,
+    f: (changes: Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>) => Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>,
+): View<A, E, R> => make({
+    get get() { return self.get },
+    get changes() { return f(self.changes) },
+}))
+
 /** Converts typed failures from both channels into `Result` values. */
 export const result = <A, E, R>(
     self: View<A, E, R>,

packages/effect-lens/src/Subscribable.ts

@@ -40,6 +40,25 @@ export const mapOptionEffect: {
     onNone: () => Effect.succeed(Option.none()),
 })))
 
+/**
+ * Allows transforming only the `changes` stream of a `Subscribable`.
+ */
+export const mapStream: {
+    <A, E, R>(
+        f: (changes: Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>) => Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>,
+    ): (self: Subscribable.Subscribable<A, E, R>) => Subscribable.Subscribable<A, E, R>
+    <A, E, R>(
+        self: Subscribable.Subscribable<A, E, R>,
+        f: (changes: Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>) => Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>,
+    ): Subscribable.Subscribable<A, E, R>
+} = Function.dual(2, <A, E, R>(
+    self: Subscribable.Subscribable<A, E, R>,
+    f: (changes: Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>) => Stream.Stream<NoInfer<A>, NoInfer<E>, NoInfer<R>>,
+): Subscribable.Subscribable<A, E, R> => Subscribable.make({
+    get get() { return self.get },
+    get changes() { return f(self.changes) },
+}))
+
 /**
  * Combines the current values and streams of changes from multiple `Subscribable` values.
  */