perf: Add benchmark and speedup (#37)

Fixes #36 at least to some extent!

Throwing a non-`Error` subclass makes the Fibonacci benchmark ~6x
faster:

    -Time elapsed (ms): 60459
    +Time elapsed (ms): 10152

The difference for the 40th Fibonacci number is even more dramatic,
~2000s → 200s. Still slower than jlox's 27 seconds, but at least within
an order of magnitude.

Thanks to https://github.com/davidhfriedman/jslox for the inspiration.

bench/fib.lox

@@ -0,0 +1,10 @@
+fun fib(n) {
+  if (n < 2) return n;
+  return fib(n - 1) + fib(n - 2);
+}
+
+var before = clock();
+print fib(40);
+var after = clock();
+print "Time elapsed (ms):";
+print after - before;

bench/fib33.lox

@@ -0,0 +1,10 @@
+fun fib(n) {
+  if (n < 2) return n;
+  return fib(n - 1) + fib(n - 2);
+}
+
+var before = clock();
+print fib(33);
+var after = clock();
+print "Time elapsed (ms):";
+print after - before;

package.json

@@ -20,6 +20,7 @@
 		"README.md"
 	],
 	"scripts": {
+		"benchmark": "pnpm --silent run repl bench/fib33.lox",
 		"build": "tsup",
 		"coverage": "pnpm test -- --coverage --no-watch",
 		"format": "prettier \"**/*\" --ignore-unknown",

src/interpreter.ts

@@ -8,10 +8,9 @@ import { CurrencyValue, LoxValue, isCurrency } from "./lox-value.js";
 import { runtimeError } from "./main.js";
 import { Token } from "./token.js";
 
-export class ReturnCall extends Error {
+export class ReturnCall {
 	value: LoxValue;
 	constructor(value: LoxValue) {
-		super();
 		this.value = value;
 	}
 }
@@ -286,6 +285,9 @@ export class Interpreter {
 
 			case "return": {
 				const value = stmt.value && this.evaluate(stmt.value);
+				// While it's bad practice to throw something other than an Error subclass,
+				// doing so here result in a ~5x speedup on the Fibonacci benchmark.
+				// eslint-disable-next-line @typescript-eslint/no-throw-literal
 				throw new ReturnCall(value);
 			}