Implement simple REPL.

joke.js

@@ -1,37 +1,69 @@
 import JokeEngine from 'joke';
 import fs from 'fs';
-
-if (!process.argv[2]) {
-    console.log(`Usage: node joke.js sourceFile`);
-    process.exit(0);
-}
+import readline from 'readline';
 
 let debug = false;
 let argc = 2;
 while (true) {
-    if (process.argv[argc][0] != '-') {
+    if (!process.argv[argc] || process.argv[argc][0] != '-') {
         break;
     }
 
     switch (process.argv[argc]) {
     case '-d':
         debug = true;
         break;
+    case '-h':
+        console.log('Usage: node joke.js [options] [sourceFile]\n');
+        console.log('Options:');
+        console.group();
+        console.log('-d\tEnable debug mode (dump compiler output)')
+        console.groupEnd();
+        process.exit(0);
     }
     argc++;
 }
 
-const sourceFile = process.argv[argc];
-fs.readFile(sourceFile, 'utf8', (err, data) => {
-    if (err) {
-        console.error(err);
-        return;
-    }
+function runSourceFile(sourceFile) {
+    fs.readFile(sourceFile, 'utf8', (err, data) => {
+        if (err) {
+            console.error(err);
+            return;
+        }
+
+        try {
+            const joke = new JokeEngine(debug);
+            joke.run(sourceFile, data);
+        } catch (e) {
+            console.error(`${e.name}: ${e.message}`);
+        }
+    });
+}
 
-    try {
-        const joke = new JokeEngine(debug);
-        joke.run(sourceFile, data);
-    } catch (e) {
-        console.error(`${e.name}: ${e.message}`);
-    }
-});
+function executeRepl() {
+    const joke = new JokeEngine(debug);
+    const rl = readline.createInterface({
+        input: process.stdin,
+        output: process.stdout,
+        prompt: '> '
+    });
+    rl.on('line', (line) => {
+        try {
+            joke.run('<stdin>', line);
+        } catch (e) {
+            console.error(`${e.name}: ${e.message}`);
+        }
+        rl.prompt();
+    });
+    rl.on('close', () => {
+        process.exit(0);
+    })
+    rl.prompt();
+}
+
+const sourceFile = process.argv[argc];
+if (sourceFile) {
+    runSourceFile(sourceFile);    
+} else {
+    executeRepl();
+}

lib/joke.js

@@ -8,6 +8,17 @@ import { initializeGlobalScope } from './object.js';
 export default class JokeEngine {
     constructor(debug = false) {
         this.debug = debug;
+        // preserve scope for REPL
+        this.globalScope = initializeGlobalScope();
+    }
+
+    makeScopeForValidator() {
+        let names = this.globalScope.getObjectNames();
+        const scope = {};
+        for (const name of names) {
+            scope[name] = true;
+        }
+        return scope;
     }
 
     /*
@@ -37,7 +48,7 @@ export default class JokeEngine {
         }
 
         const validator = new Validator();
-        validator.validate(node);
+        validator.validate(node, this.makeScopeForValidator());
 
         const assembler = new Assembler();
         const insns = assembler.assemble(node);
@@ -50,7 +61,6 @@ export default class JokeEngine {
         }
 
         const vm = new Vm();
-        const globalScope = initializeGlobalScope();
-        vm.run(insns, globalScope);
+        vm.run(insns, this.globalScope);
     } 
 }

lib/object.js

@@ -1,9 +1,15 @@
 export function createScope() {
     return {
+        names: [],
+
+        getObjectNames() {
+            return this.names;
+        },
         getObject(name) {
             return this[name];
         },
         defineObject(name, declarationType) {
+            this.names.push(name);
             this[name] = {declarationType};
         },
         setObject(name, value, initialize=false) {
@@ -18,7 +24,7 @@ export function createScope() {
         }
     };
 }
- 
+
 export function createObject() {
     return {
         getProperty(name) {

lib/validator.js

@@ -30,8 +30,7 @@ function validateNode(node, scopes) {
 }
 
 export default class Validator {
-    validate(node) {
-        const scope = {};
+    validate(node, scope) {
         const scopes = [scope];
         validateNode(node, scopes);
     }

package.json

@@ -6,6 +6,7 @@
   "type": "module",
   "exports": "./lib/joke.js",
   "scripts": {
+    "joke": "node --experimental-modules joke.js",
     "test": "node --experimental-modules test.js"
   },
   "keywords": [],