improve REPL feedback.

src/repl.mjs

@@ -1,29 +1,72 @@
 import Line from "./Line.mjs";
+import Expr from "./Expr.mjs";
+
 import { parse_line } from "./parse.mjs";
 import { compile_line } from "./compile.mjs";
 import { execute } from "./execute.mjs";
 
+import readline from "node:readline";
 
+const rl = readline.createInterface({
+	input: process.stdin,
+	output: process.stdout,
+});
+
+
+
+let running = true;
 
 let env = new Map();
 
+function print (str) {
+	console.log(str);
+}
+
+
+
+const specials = new Map();
+
+specials.set("!.exit", _ => running = false);
+
+specials.set("!.env", _ => {
+	print(env);
+});
+
+
+
 function run (line) {
+	if (specials.has(line)) {
+		specials.get(line)();
+		return;
+	}
+
 	const parsed = parse_line(line);
 	const type = parsed.type;
 
 	const compiled = compile_line(env, parsed);
 
 	if (!compiled.valid) {
-		console.log("invalid line!");
+		print("invalid line!");
 		return;
 	}
 
 	env = compiled.env;
 
 	if (type === Line.Expression) {
-		console.log(prettify(evaluate(compiled.value)));
+		const expr_type = parsed.value.type;
+
+		if (expr_type === Expr.Token || expr_type === Expr.Fn) {
+			print(prettify(compiled.value));
+		} else if (expr_type === Expr.Application) {
+			const result = evaluate(compiled.value);
+			if (typeof result === "function") {
+				print(prettify(compiled.value));
+			} else {
+				print(prettify(result));
+			}
+		}
 	} else {
-		console.log(env);
+		print(parsed.name + " = " + prettify(compiled.fn));
 	}
 }
 
@@ -32,14 +75,30 @@ function evaluate (fn) {
 }
 
 function prettify (code) {
-	if (Array.isArray(code)) {
-		return prettify(code[0]).concat(" ", prettify(code[1]));
+	if (typeof code === "number") {
+		return code.toString();
+	} else if (code[0] === 0) {
+		return "(λ" + prettify(code[1]) + ")";
+	} else {
+		return prettify(code[0]) + " " + prettify(code[1]);
 	}
-	if (code === 0) {
-		return "λ";
-	}
-	return code.toString();
 }
 
-run("id = a → a");
-run("id id");
+function read (callback) {
+	rl.question("> ", callback);
+}
+
+function repl () {
+	read(line => {
+		run(line);
+		if (running) {
+			setImmediate(repl);
+		} else {
+			rl.close();
+		}
+	});
+}
+
+print("welcome to catgirl calculus!");
+print("uwu");
+repl();