diff --git a/main.go b/main.go
index f8bdf08993..d299a48abb 100644
--- a/main.go
+++ b/main.go
@@ -3,6 +3,8 @@ package main
 import (
 	"crypto/md5"
 	"encoding/hex"
+	"flag"
+	"fmt"
 	"github.com/golang/protobuf/proto"
 	"github.com/ry/v8worker2"
 	"io"
@@ -17,6 +19,10 @@ import (
 	"time"
 )
 
+var flagReload = flag.Bool("reload", false, "Reload cached remote source code.")
+var flagV8Options = flag.Bool("v8-options", false, "Print V8 command line options.")
+var flagDebug = flag.Bool("debug", false, "Enable debug output.")
+
 var DenoDir string
 var CompileDir string
 var SrcDir string
@@ -44,12 +50,14 @@ func IsRemote(filename string) bool {
 
 // Fetches a remoteUrl but also caches it to the localFilename.
 func FetchRemoteSource(remoteUrl string, localFilename string) ([]byte, error) {
+	//println("FetchRemoteSource", remoteUrl)
 	Assert(strings.HasPrefix(localFilename, SrcDir), localFilename)
 	var sourceReader io.Reader
 
 	file, err := os.Open(localFilename)
-	if os.IsNotExist(err) {
+	if *flagReload || os.IsNotExist(err) {
 		// Fetch from HTTP.
+		println("Downloading", remoteUrl)
 		res, err := http.Get(remoteUrl)
 		if err != nil {
 			return nil, err
@@ -100,6 +108,7 @@ func ResolveModule(moduleSpecifier string, containingFile string) (
 const assetPrefix string = "/$asset$/"
 
 func HandleSourceCodeFetch(moduleSpecifier string, containingFile string) (out []byte) {
+	Assert(moduleSpecifier != "", "moduleSpecifier shouldn't be empty")
 	res := &Msg{}
 	var sourceCodeBuf []byte
 	var err error
@@ -117,6 +126,9 @@ func HandleSourceCodeFetch(moduleSpecifier string, containingFile string) (out [
 		return
 	}
 
+	//println("HandleSourceCodeFetch", "moduleSpecifier", moduleSpecifier,
+	//		"containingFile", containingFile, "filename", filename)
+
 	if IsRemote(moduleName) {
 		sourceCodeBuf, err = FetchRemoteSource(moduleName, filename)
 	} else if strings.HasPrefix(moduleName, assetPrefix) {
@@ -249,7 +261,14 @@ func recv(buf []byte) []byte {
 }
 
 func main() {
-	args := v8worker2.SetFlags(os.Args)
+	flag.Parse()
+	args := flag.Args()
+	if *flagV8Options {
+		args = append(args, "--help")
+		fmt.Println(args)
+	}
+	args = v8worker2.SetFlags(args)
+
 	createDirs()
 	worker := v8worker2.New(recv)
 	loadAsset(worker, "dist/main.js")
@@ -262,8 +281,9 @@ func main() {
 	out, err := proto.Marshal(&Msg{
 		Payload: &Msg_Start{
 			Start: &StartMsg{
-				Cwd:  cwd,
-				Argv: args,
+				Cwd:       cwd,
+				Argv:      args,
+				DebugFlag: *flagDebug,
 			},
 		},
 	})
diff --git a/main.ts b/main.ts
index 9fe002d7e3..ac0b4d3292 100644
--- a/main.ts
+++ b/main.ts
@@ -2,10 +2,16 @@ import { main as pb } from "./msg.pb";
 import "./util";
 import * as runtime from "./runtime";
 import * as timers from "./timers";
+import * as util from "./util";
 
-function start(cwd: string, argv: string[]): void {
-  // TODO parse arguments.
-  const inputFn = argv[1];
+// To control internal logging output
+// Set with the -debug command-line flag.
+export let debug = false;
+
+function start(cwd: string, argv: string[], debugFlag: boolean): void {
+  debug = debugFlag;
+  util.log("start", { cwd, argv, debugFlag });
+  const inputFn = argv[0];
   const mod = runtime.resolveModule(inputFn, cwd + "/");
   mod.compileAndRun();
 }
@@ -14,7 +20,7 @@ V8Worker2.recv((ab: ArrayBuffer) => {
   const msg = pb.Msg.decode(new Uint8Array(ab));
   switch (msg.payload) {
     case "start":
-      start(msg.start.cwd, msg.start.argv);
+      start(msg.start.cwd, msg.start.argv, msg.start.debugFlag);
       break;
     case "timerReady":
       timers.timerReady(msg.timerReady.id, msg.timerReady.done);
diff --git a/modules_test.go b/modules_test.go
new file mode 100644
index 0000000000..ac94b5a3c5
--- /dev/null
+++ b/modules_test.go
@@ -0,0 +1,49 @@
+package main
+
+import (
+	"path"
+	"testing"
+)
+
+func AssertEqual(t *testing.T, actual string, expected string) {
+	if actual != expected {
+		t.Fatalf("not equal <<%s>> <<%s>>", actual, expected)
+	}
+}
+
+func TestResolveModule(t *testing.T) {
+	moduleName, filename, err := ResolveModule(
+		"http://localhost:4545/testdata/subdir/print_hello.ts",
+		"/Users/rld/go/src/github.com/ry/deno/testdata/006_url_imports.ts")
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	AssertEqual(t, moduleName,
+		"http://localhost:4545/testdata/subdir/print_hello.ts")
+	AssertEqual(t, filename,
+		path.Join(SrcDir, "localhost:4545/testdata/subdir/print_hello.ts"))
+
+	moduleName, filename, err = ResolveModule(
+		"./subdir/print_hello.ts",
+		"/Users/rld/go/src/github.com/ry/deno/testdata/006_url_imports.ts")
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	AssertEqual(t, moduleName,
+		"/Users/rld/go/src/github.com/ry/deno/testdata/subdir/print_hello.ts")
+	AssertEqual(t, filename,
+		"/Users/rld/go/src/github.com/ry/deno/testdata/subdir/print_hello.ts")
+
+	// In the case where the containingFile is a directory (indicated with a
+	// trailing slash)
+	moduleName, filename, err = ResolveModule(
+		"testdata/001_hello.js",
+		"/Users/rld/go/src/github.com/ry/deno/")
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	AssertEqual(t, moduleName,
+		"/Users/rld/go/src/github.com/ry/deno/testdata/001_hello.js")
+	AssertEqual(t, filename,
+		"/Users/rld/go/src/github.com/ry/deno/testdata/001_hello.js")
+}
diff --git a/msg.proto b/msg.proto
index 8524be2877..dba8cab942 100644
--- a/msg.proto
+++ b/msg.proto
@@ -17,6 +17,7 @@ message Msg {
 message StartMsg {
   string cwd = 1;
   repeated string argv = 2;
+  bool debug_flag = 3;
 }
 
 message SourceCodeFetchMsg {
diff --git a/runtime.ts b/runtime.ts
index 01dbf76ac2..7d6633ca9c 100644
--- a/runtime.ts
+++ b/runtime.ts
@@ -99,8 +99,10 @@ export function resolveModule(
   moduleSpecifier: string,
   containingFile: string
 ): FileModule {
+  util.assert(moduleSpecifier != null && moduleSpecifier.length > 0);
   // We ask golang to sourceCodeFetch. It will load the sourceCode and if
   // there is any outputCode cached, it will return that as well.
+  util.log("resolveModule", { moduleSpecifier, containingFile });
   const { filename, sourceCode, outputCode } = os.sourceCodeFetch(
     moduleSpecifier,
     containingFile
diff --git a/types.ts b/types.ts
new file mode 100644
index 0000000000..8631d2c843
--- /dev/null
+++ b/types.ts
@@ -0,0 +1,8 @@
+export type TypedArray = Uint8Array | Float32Array | Int32Array;
+
+export interface ModuleInfo {
+  moduleName?: string;
+  filename?: string;
+  sourceCode?: string;
+  outputCode?: string;
+}
diff --git a/util.go b/util.go
new file mode 100644
index 0000000000..851ee34753
--- /dev/null
+++ b/util.go
@@ -0,0 +1,7 @@
+package main
+
+func Assert(cond bool, msg string) {
+	if !cond {
+		panic(msg)
+	}
+}
diff --git a/util.ts b/util.ts
index 42163fb417..0b4b9adbcb 100644
--- a/util.ts
+++ b/util.ts
@@ -13,8 +13,7 @@ _global["window"] = _global; // Create a window object.
 
 const print = V8Worker2.print;
 
-// To control internal logging output
-const debug = false;
+import { debug } from "./main";
 
 // Internal logging for deno. Use the "debug" variable above to control
 // output.