Ensures errors are handled properly

Author: eamodio

src/system/lazy.ts

@@ -1,7 +1,12 @@
 /** Provides lazy initialization support */
 export class Lazy<T> {
+	private _evaluated: boolean = false;
+	get evaluated(): boolean {
+		return this._evaluated;
+	}
+
+	private _exception: Error | undefined;
 	private _value?: T;
-	private _initialized: boolean = false;
 
 	/**
 	 * Creates a new instance of Lazy<T> that uses the specified initialization function.
@@ -11,11 +16,19 @@ export class Lazy<T> {
 
 	/** Gets the lazily initialized value of the current Lazy<T> instance */
 	get value(): T {
-		if (!this._initialized) {
-			this._value = this.valueProvider();
-			this._initialized = true;
+		if (!this._evaluated) {
+			try {
+				this._value = this.valueProvider();
+			} catch (ex) {
+				this._exception = ex;
+				throw ex;
+			} finally {
+				this._evaluated = true;
+			}
 		}
 
+		if (this._exception) throw this._exception;
+
 		return this._value!;
 	}
 }