Add Ref impl

packages/effect-lens/src/Lens.ts

@@ -175,6 +175,44 @@ export const derive: {
 ): Lens<A, ER2, EW2, RR2, RW2> => new DerivedLensImpl(asLensImpl(self), source))
 
 
+export class RefLensImpl<in out A>
+extends LensImpl<A, never, never, never, never> {
+    constructor(
+        readonly ref: Ref.Ref<A>,
+        readonly semaphore: Effect.Semaphore,
+    ) {
+        super()
+    }
+
+    get resolve(): Effect.Effect<LensImpl.Frame<A>, never, never> {
+        return Effect.map(
+            Ref.get(this.ref),
+            value => ({
+                value,
+                commit: next => Effect.flatMap(
+                    next,
+                    value => Ref.set(this.ref, value),
+                ),
+            }),
+        )
+    }
+    get changes() { return Stream.unwrap(Effect.map(Ref.get(this.ref), Stream.make)) }
+    get withLock() { return this.semaphore.withPermits(1) }
+}
+
+/**
+ * Creates a `Lens` that proxies a `Ref`.
+ *
+ * Note: since `Ref` does not provide any kind of reactivity mechanism, the produced `Lens` will be non-reactive.
+ * This means its `changes` stream will only emit the current value once when evaluated and nothing else.
+ */
+export const fromRef = Effect.fnUntraced(function* <A>(
+    ref: Ref.Ref<A>
+): Effect.fn.Return<Lens<A, never, never, never, never>, never, never> {
+    return new RefLensImpl(ref, yield* Effect.makeSemaphore(1))
+})
+
+
 export declare namespace SynchronizedRefLensImpl {
     export interface SynchronizedRefWithInternals<in out A>
     extends SynchronizedRef.SynchronizedRef<A> {