Add liftNow and performComponent

src/component.ts

@@ -79,7 +79,6 @@ export abstract class Component<O, A> implements Monad<A> {
     }
     // return new OutputComponent(remaps, this);
   }
-  // explicitOutput: string[] | undefined;
   static multi: boolean = false;
   multi: boolean = false;
   abstract run(
@@ -103,6 +102,27 @@ class OfComponent<A> extends Component<{}, A> {
   }
 }
 
+class PerformComponent<A> extends Component<{}, A> {
+  constructor(private cb: () => A) {
+    super();
+  }
+  run(_1: Node, _2: Future<boolean>): { explicit: {}; output: A } {
+    return { explicit: {}, output: this.cb() };
+  }
+}
+
+/**
+ * Takes a callback, potentially with side-effects. The callback is invoked when
+ * the component is run and the return value becomes the components output.
+ */
+export function performComponent<A>(callback: () => A): Component<{}, A> {
+  return new PerformComponent(callback);
+}
+
+export function liftNow<A>(now: Now<A>): Component<{}, A> {
+  return performComponent(() => runNow(now));
+}
+
 class OutputComponent extends Component<any, any> {
   constructor(
     private remaps: Record<string, string>,

test/component.spec.ts

@@ -19,13 +19,35 @@ import {
   list,
   runComponent,
   output,
-  merge
+  merge,
+  performComponent,
+  liftNow
 } from "../src";
 const { span, div, button, input } = elements;
 
 const supportsProxy = "Proxy" in window;
 
 describe("component specs", () => {
+  describe("performComponent", () => {
+    it("invokes callback", () => {
+      let result: number | undefined = undefined;
+      const c = performComponent(() => (result = 12));
+      assert.strictEqual(result, undefined);
+      const { out: actual } = testComponent(c);
+      assert.strictEqual(result, 12);
+      assert.strictEqual(actual, 12);
+    });
+  });
+  describe("liftNow", () => {
+    it("runs now", () => {
+      let result: number | undefined = undefined;
+      const c = liftNow(H.perform(() => (result = 12)));
+      assert.strictEqual(result, undefined);
+      const { out: actual } = testComponent(c);
+      assert.strictEqual(result, 12);
+      assert.strictEqual(actual, 12);
+    });
+  });
   describe("toComponent", () => {
     it("converts a behavior of a string to a component", () => {
       const b = H.sinkBehavior("Hello");
@@ -36,7 +58,7 @@ describe("component specs", () => {
       expect(dom).to.have.text("world");
     });
     it("converts a behavior of a boolean to a component", () => {
-      const b = H.sinkBehavior(true)
+      const b = H.sinkBehavior(true);
       const component = toComponent(b);
       const { dom } = testComponent(component);
       expect(dom).to.have.text("true");
@@ -279,10 +301,7 @@ describe("modelView", () => {
         fromView = args;
         return H.Now.of({});
       },
-      (): Child<FromView> => [
-        span("Hello"),
-        input().output({ value: "value" })
-      ]
+      (): Child<FromView> => [span("Hello"), input().output({ value: "value" })]
     )();
     const { dom } = testComponent(c);
     expect(dom.querySelector("span")).to.exist;