track signal dependencies

src/lang/eval/signal.ts

@@ -65,12 +65,13 @@ export function eval_signal_expression(program: Program, env: Env, e: SignalExpr
       // Setup a subscription to each dependency, when it changes, poll every signal and re-evaluate
       // TODO: This is extremely inefficient.
       for (const { signal } of signalBindings) {
-        signal.subscribe(() => {
+        const cancelSignal = signal.subscribe(() => {
           letSignal.set(() => {
             const value = eval_expr_in_signal_bindings(program, env, signalBindings, e.body);
             return value;
           });
         });
+        letSignal.dependencies.push(cancelSignal);
       }
 
       return letSignal;
@@ -117,16 +118,20 @@ export interface Signal<T> {
   observers: Observer<T>[],
   set(transform: (state: T) => T): void,
   read(): T,
-  subscribe(observer: Observer<T>): void,
+  subscribe(observer: Observer<T>): UnsubscribeCapability,
   map<S>(transform: (state: T) => S): Signal<S>,
+  dependencies: UnsubscribeCapability[],
+  dropDependencies(): void,
 };
 
 export type Observer<T> = (state: T) => void;
+export type UnsubscribeCapability = () => void;
 
 export function signal<T>(initState: T): Signal<T> {
   return {
     state: initState,
     observers: [],
+    dependencies: [],
     set(transform: (state: T) => T) {
       const state = transform(this.state);
       this.state = state;
@@ -138,27 +143,39 @@ export function signal<T>(initState: T): Signal<T> {
       return this.state;
     },
     subscribe(observer: Observer<T>) {
-      // TODO: This needs to return `cancellation`
       this.observers.push(observer);
+      const that = this;
+      return () => {
+        that.observers = that.observers.filter(sub => sub !== observer);
+      };
+    },
+    dropDependencies() {
+      for (const cancel of this.dependencies) {
+        cancel()
+      }
+      this.dependencies = [];
     },
     map<S>(transform: (state: T) => S): Signal<S> {
       const Y = signal(transform(this.state));
-      this.subscribe((state: T) => {
+      const cancelY = this.subscribe((state: T) => {
         Y.set(() => transform(state));
       });
+      Y.dependencies.push(cancelY);
       return Y;
-    }
+    },
   };
 }
 
 function pair<A, B>(X: Signal<A>, Y: Signal<B>): Signal<[A, B]> {
   const Z = signal([X.read(), Y.read()] as [A, B]);
-  X.subscribe(x => {
+  const cancelX = X.subscribe(x => {
     Z.set(() => [x, Y.read()]);
   });
-  Y.subscribe(y => {
+  Z.dependencies.push(cancelX);
+  const cancelY = Y.subscribe(y => {
     Z.set(() => [X.read(), y]);
   });
+  Z.dependencies.push(cancelY);
   return Z;
 }
 
@@ -167,9 +184,10 @@ function tupleThen<A, B>(Xs: Signal<A>[], f: (values: A[]) => B): Signal<B> {
 
   // TODO: This is just preliminary. Has the glitch bug. Also has insane quadratic behaviour.
   Xs.forEach((X, i) => {
-    X.subscribe(_ => {
+    const cancelX = X.subscribe(_ => {
       Z.set(() => f(Xs.map(X => X.read())));
     });
+    Z.dependencies.push(cancelX);
   });
 
   return Z;
@@ -183,7 +201,7 @@ function tupleThen<A, B>(Xs: Signal<A>[], f: (values: A[]) => B): Signal<B> {
 
 // console.log(count.read())
 
-// count.subscribe(x => {
+// const _ = count.subscribe(x => {
 //   console.log("count is now", x);
 // });
 
@@ -194,7 +212,7 @@ function tupleThen<A, B>(Xs: Signal<A>[], f: (values: A[]) => B): Signal<B> {
 // console.log("DOUBLE EXISTS");
 
 
-// double.subscribe(x => {
+// const _ = double.subscribe(x => {
 //   console.log("double is now", x);
 // });
 
@@ -204,7 +222,7 @@ function tupleThen<A, B>(Xs: Signal<A>[], f: (values: A[]) => B): Signal<B> {
 // const WTF = pair(count, double)
 // console.log("-> WTF EXISTS");
 
-// WTF.subscribe(([x, y]) => {
+// const _ = WTF.subscribe(([x, y]) => {
 //   console.log("WTF is now ", [x, y]);
 // });
 

src/ui/Digith/Signal/SignalDigith.tsx

@@ -51,13 +51,11 @@ export function SignalDigith(props: { signal: Digith.Signal }) {
 
       // TODO: Not sure about this one. Setting a signal in `setValue` is discouraged.
       setTimeout(() => setValue(signal.read()), 0);
-      // TODO: Handle cancelation...
+
-      signal.subscribe((newValue) => {
+      const cancel = signal.subscribe((newValue) => {
         setValue(newValue);
       });
-      onCleanup(() => {
+      onCleanup(cancel);
-        // TODO:
-      });
     } catch (e) {
       // TODO: setErrors... but how? Shouldn't this be independent of `errors`?
       console.log("Failed to link Signal: ", e);