Add evaluate

packages/events/src/events.ts

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+import { IDisposable } from "@coder/disposable";
+
+export interface Event<T> {
+	(listener: (e: T) => void): IDisposable;
+}
+
+/**
+ * Emitter typecasts for a single event type
+ */
+export class Emitter<T> {
+
+	private listeners: Array<(e: T) => void> | undefined;
+
+	public constructor() {
+		this.listeners = [];
+	}
+
+	public get event(): Event<T> {
+		return (cb: (e: T) => void): IDisposable => {
+			if (this.listeners) {
+				this.listeners.push(cb);
+			}
+
+			return {
+				dispose: (): void => {
+					if (this.listeners) {
+						const i = this.listeners.indexOf(cb);
+						if (i !== -1) {
+							this.listeners.splice(i, 1);
+						}
+					}
+				},
+			};
+		};
+	}
+
+	/**
+	 * Emit a value
+	 */
+	public emit(value: T): void {
+		if (this.listeners) {
+			this.listeners.forEach((t) => t(value));
+		}
+	}
+
+	/**
+	 * Disposes the event emitter
+	 */
+	public dispose(): void {
+		this.listeners = undefined;
+	}
+
+	/**
+	 * Whether the event has listeners.
+	 */
+	public get hasListeners(): boolean {
+		return !!this.listeners && this.listeners.length > 0;
+	}
+
+}

packages/events/src/index.ts

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+export * from "./events";