2 files changed, 96 insertions, 6 deletions
diff --git a/js/main.ts b/js/main.ts
index 50de2c26c..0ed45aaec 100644
--- a/js/main.ts
+++ b/js/main.ts
@@ -8,6 +8,7 @@ import { libdeno } from "./libdeno";
 import { args } from "./deno";
 import { sendSync, handleAsyncMsgFromRust } from "./dispatch";
 import { promiseErrorExaminer, promiseRejectHandler } from "./promise_util";
+import { replLoop } from "./repl";
 import { version } from "typescript";
 
 function sendStart(): msg.StartRes {
@@ -77,13 +78,13 @@ export default function denoMain() {
   }
   log("args", args);
   Object.freeze(args);
-
   const inputFn = args[0];
-  if (!inputFn) {
-    console.log("No input script specified.");
-    os.exit(1);
-  }
 
   compiler.recompile = startResMsg.recompileFlag();
-  compiler.run(inputFn, `${cwd}/`);
+
+  if (inputFn) {
+    compiler.run(inputFn, `${cwd}/`);
+  } else {
+    replLoop();
+  }
 }
diff --git a/js/repl.ts b/js/repl.ts
new file mode 100644
index 000000000..b7c516110
--- /dev/null
+++ b/js/repl.ts
@@ -0,0 +1,89 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import * as msg from "gen/msg_generated";
+import * as flatbuffers from "./flatbuffers";
+import { assert } from "./util";
+import * as deno from "./deno";
+import { close } from "./files";
+import * as dispatch from "./dispatch";
+import { exit } from "./os";
+import { window } from "./globals";
+
+function startRepl(historyFile: string): number {
+  const builder = flatbuffers.createBuilder();
+  const historyFile_ = builder.createString(historyFile);
+
+  msg.ReplStart.startReplStart(builder);
+  msg.ReplStart.addHistoryFile(builder, historyFile_);
+  const inner = msg.ReplStart.endReplStart(builder);
+
+  const baseRes = dispatch.sendSync(builder, msg.Any.ReplStart, inner);
+  assert(baseRes != null);
+  assert(msg.Any.ReplStartRes === baseRes!.innerType());
+  const innerRes = new msg.ReplStartRes();
+  assert(baseRes!.inner(innerRes) != null);
+  const rid = innerRes.rid();
+  return rid;
+}
+
+// @internal
+export function readline(rid: number, prompt: string): string {
+  const builder = flatbuffers.createBuilder();
+  const prompt_ = builder.createString(prompt);
+  msg.ReplReadline.startReplReadline(builder);
+  msg.ReplReadline.addRid(builder, rid);
+  msg.ReplReadline.addPrompt(builder, prompt_);
+  const inner = msg.ReplReadline.endReplReadline(builder);
+
+  // TODO use async?
+  const baseRes = dispatch.sendSync(builder, msg.Any.ReplReadline, inner);
+
+  assert(baseRes != null);
+  assert(msg.Any.ReplReadlineRes === baseRes!.innerType());
+  const innerRes = new msg.ReplReadlineRes();
+  assert(baseRes!.inner(innerRes) != null);
+  const line = innerRes.line();
+  assert(line !== null);
+  return line || "";
+}
+
+// @internal
+export function replLoop(): void {
+  window.deno = deno; // FIXME use a new scope (rather than window).
+
+  const historyFile = "deno_history.txt";
+  const prompt = "> ";
+
+  const rid = startRepl(historyFile);
+
+  let line = "";
+  while (true) {
+    try {
+      line = readline(rid, prompt);
+      line = line.trim();
+    } catch (err) {
+      if (err.message === "EOF") {
+        break;
+      }
+      console.error(err);
+      exit(1);
+    }
+    if (!line) {
+      continue;
+    }
+    if (line === ".exit") {
+      break;
+    }
+    try {
+      const result = eval.call(window, line); // FIXME use a new scope.
+      console.log(result);
+    } catch (err) {
+      if (err instanceof Error) {
+        console.error(`${err.constructor.name}: ${err.message}`);
+      } else {
+        console.error("Thrown:", err);
+      }
+    }
+  }
+
+  close(rid);
+}