diff --git a/parser/src/lib.rs b/parser/src/lib.rs
index f7b488bd9..2ace33281 100644
--- a/parser/src/lib.rs
+++ b/parser/src/lib.rs
@@ -1,7 +1,7 @@
 #[macro_use]
 extern crate log;
 
-mod parser;
+pub mod parser;
 mod python;
 pub mod ast;
 mod token;
diff --git a/src/main.rs b/src/main.rs
index 76949bb3d..7e32ee56d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,7 +11,11 @@ mod compile;
 use clap::{Arg, App};
 use std::path::Path;
 use rustpython_parser::parse;
+use rustpython_parser::parser::parse_source;
 use rustpython_vm::evaluate;
+use rustpython_vm::pyobject::PyObjectRef;
+use std::io;
+use std::io::prelude::*;
 
 
 fn main() {
@@ -21,7 +25,7 @@ fn main() {
       .author(crate_authors!())
       .about("Rust implementation of the Python language")
       .arg(Arg::with_name("script")
-          .required(true)
+          .required(false)
           .index(1))
       .arg(Arg::with_name("v")
           .short("v")
@@ -29,10 +33,16 @@ fn main() {
           .help("Give the verbosity"))
       .get_matches();
 
-  // Figure out the filename:
-  let script_file = matches.value_of("script").unwrap_or("foo");
-  debug!("Running file {}", script_file);
+  // Figure out if a script was passed:
+  match matches.value_of("script") {
+      None => run_shell(),
+      Some(filename) => run_script(&filename.to_string()),
+  }
 
+}
+
+fn run_script(script_file: &String) {
+  debug!("Running file {}", script_file);
   // Parse an ast from it:
   let filepath = Path::new(script_file);
   match parse(filepath) {
@@ -49,3 +59,31 @@ fn main() {
   }
 }
 
+fn run_shell() {
+    println!("Welcome to the magnificent Rust Python interpreter");
+    // Read a single line:
+    loop {
+        let mut input = String::new();
+        print!(">>>");
+        io::stdout().flush().ok().expect("Could not flush stdout");
+        io::stdin().read_line(&mut input);
+        println!("You entered {:?}", input);
+        let result = eval(&input);
+        println!("{:?}", result);
+    }
+}
+
+fn eval(source: &String) -> Result<PyObjectRef, PyObjectRef> {
+  match parse_source(source) {
+    Ok(program) => {
+      debug!("Got ast: {:?}", program);
+      let bytecode = compile::compile(program);
+      debug!("Code object: {:?}", bytecode);
+      evaluate(bytecode)
+    },
+    Err(msg) => {
+        panic!("Parsing went horribly wrong: {}", msg);
+    },
+  }
+}
+
diff --git a/py_code_object/compile_code.py b/tests/compile_code.py
similarity index 100%
rename from py_code_object/compile_code.py
rename to tests/compile_code.py
diff --git a/tests/3.1.2.13.py b/tests/snippets/3.1.2.13.py
similarity index 100%
rename from tests/3.1.2.13.py
rename to tests/snippets/3.1.2.13.py
diff --git a/tests/3.1.2.16.py b/tests/snippets/3.1.2.16.py
similarity index 100%
rename from tests/3.1.2.16.py
rename to tests/snippets/3.1.2.16.py
diff --git a/tests/3.1.2.18.py b/tests/snippets/3.1.2.18.py
similarity index 100%
rename from tests/3.1.2.18.py
rename to tests/snippets/3.1.2.18.py
diff --git a/tests/3.1.2.19.py b/tests/snippets/3.1.2.19.py
similarity index 100%
rename from tests/3.1.2.19.py
rename to tests/snippets/3.1.2.19.py
diff --git a/tests/3.1.3.2.py b/tests/snippets/3.1.3.2.py
similarity index 100%
rename from tests/3.1.3.2.py
rename to tests/snippets/3.1.3.2.py
diff --git a/tests/3.1.3.4.py b/tests/snippets/3.1.3.4.py
similarity index 100%
rename from tests/3.1.3.4.py
rename to tests/snippets/3.1.3.4.py
diff --git a/tests/3.1.3.5.py b/tests/snippets/3.1.3.5.py
similarity index 100%
rename from tests/3.1.3.5.py
rename to tests/snippets/3.1.3.5.py
diff --git a/tests/append.py b/tests/snippets/append.py
similarity index 100%
rename from tests/append.py
rename to tests/snippets/append.py
diff --git a/tests/basic_types.py b/tests/snippets/basic_types.py
similarity index 100%
rename from tests/basic_types.py
rename to tests/snippets/basic_types.py
diff --git a/tests/builtin_len.py b/tests/snippets/builtin_len.py
similarity index 100%
rename from tests/builtin_len.py
rename to tests/snippets/builtin_len.py
diff --git a/tests/cast.py b/tests/snippets/cast.py
similarity index 100%
rename from tests/cast.py
rename to tests/snippets/cast.py
diff --git a/tests/floats.py b/tests/snippets/floats.py
similarity index 100%
rename from tests/floats.py
rename to tests/snippets/floats.py
diff --git a/tests/for.py b/tests/snippets/for.py
similarity index 100%
rename from tests/for.py
rename to tests/snippets/for.py
diff --git a/tests/function.py b/tests/snippets/function.py
similarity index 100%
rename from tests/function.py
rename to tests/snippets/function.py
diff --git a/tests/function_args.py b/tests/snippets/function_args.py
similarity index 100%
rename from tests/function_args.py
rename to tests/snippets/function_args.py
diff --git a/tests/function_nested.py b/tests/snippets/function_nested.py
similarity index 100%
rename from tests/function_nested.py
rename to tests/snippets/function_nested.py
diff --git a/tests/if.py b/tests/snippets/if.py
similarity index 100%
rename from tests/if.py
rename to tests/snippets/if.py
diff --git a/tests/intro/3.1.1.1.py b/tests/snippets/intro/3.1.1.1.py
similarity index 100%
rename from tests/intro/3.1.1.1.py
rename to tests/snippets/intro/3.1.1.1.py
diff --git a/tests/intro/3.1.1.2.py b/tests/snippets/intro/3.1.1.2.py
similarity index 100%
rename from tests/intro/3.1.1.2.py
rename to tests/snippets/intro/3.1.1.2.py
diff --git a/tests/intro/3.1.1.3.py b/tests/snippets/intro/3.1.1.3.py
similarity index 100%
rename from tests/intro/3.1.1.3.py
rename to tests/snippets/intro/3.1.1.3.py
diff --git a/tests/intro/3.1.1.4.py b/tests/snippets/intro/3.1.1.4.py
similarity index 100%
rename from tests/intro/3.1.1.4.py
rename to tests/snippets/intro/3.1.1.4.py
diff --git a/tests/intro/3.1.1.6.py b/tests/snippets/intro/3.1.1.6.py
similarity index 100%
rename from tests/intro/3.1.1.6.py
rename to tests/snippets/intro/3.1.1.6.py
diff --git a/tests/intro/3.1.2.1.py b/tests/snippets/intro/3.1.2.1.py
similarity index 100%
rename from tests/intro/3.1.2.1.py
rename to tests/snippets/intro/3.1.2.1.py
diff --git a/tests/intro/3.1.2.10.py b/tests/snippets/intro/3.1.2.10.py
similarity index 100%
rename from tests/intro/3.1.2.10.py
rename to tests/snippets/intro/3.1.2.10.py
diff --git a/tests/intro/3.1.2.3.py b/tests/snippets/intro/3.1.2.3.py
similarity index 100%
rename from tests/intro/3.1.2.3.py
rename to tests/snippets/intro/3.1.2.3.py
diff --git a/tests/intro/3.1.2.4.py b/tests/snippets/intro/3.1.2.4.py
similarity index 100%
rename from tests/intro/3.1.2.4.py
rename to tests/snippets/intro/3.1.2.4.py
diff --git a/tests/intro/3.1.2.5.py b/tests/snippets/intro/3.1.2.5.py
similarity index 100%
rename from tests/intro/3.1.2.5.py
rename to tests/snippets/intro/3.1.2.5.py
diff --git a/tests/intro/3.1.2.6.py b/tests/snippets/intro/3.1.2.6.py
similarity index 100%
rename from tests/intro/3.1.2.6.py
rename to tests/snippets/intro/3.1.2.6.py
diff --git a/tests/list.py b/tests/snippets/list.py
similarity index 100%
rename from tests/list.py
rename to tests/snippets/list.py
diff --git a/tests/loop.py b/tests/snippets/loop.py
similarity index 100%
rename from tests/loop.py
rename to tests/snippets/loop.py
diff --git a/tests/math.py b/tests/snippets/math.py
similarity index 100%
rename from tests/math.py
rename to tests/snippets/math.py
diff --git a/tests/minimum.py b/tests/snippets/minimum.py
similarity index 100%
rename from tests/minimum.py
rename to tests/snippets/minimum.py
diff --git a/tests/perf_add.py b/tests/snippets/perf_add.py
similarity index 100%
rename from tests/perf_add.py
rename to tests/snippets/perf_add.py
diff --git a/tests/perf_fib.py b/tests/snippets/perf_fib.py
similarity index 100%
rename from tests/perf_fib.py
rename to tests/snippets/perf_fib.py
diff --git a/tests/print_const.py b/tests/snippets/print_const.py
similarity index 100%
rename from tests/print_const.py
rename to tests/snippets/print_const.py
diff --git a/tests/tuple.py b/tests/snippets/tuple.py
similarity index 100%
rename from tests/tuple.py
rename to tests/snippets/tuple.py
diff --git a/tests/types.py b/tests/snippets/types.py
similarity index 100%
rename from tests/types.py
rename to tests/snippets/types.py
diff --git a/tests/variables.py b/tests/snippets/variables.py
similarity index 100%
rename from tests/variables.py
rename to tests/snippets/variables.py
diff --git a/tests/xfail_3.1.2.17.py b/tests/snippets/xfail_3.1.2.17.py
similarity index 100%
rename from tests/xfail_3.1.2.17.py
rename to tests/snippets/xfail_3.1.2.17.py
diff --git a/tests/xfail_assert.py b/tests/snippets/xfail_assert.py
similarity index 100%
rename from tests/xfail_assert.py
rename to tests/snippets/xfail_assert.py
diff --git a/py_code_object/test_snippets.py b/tests/test_snippets.py
similarity index 87%
rename from py_code_object/test_snippets.py
rename to tests/test_snippets.py
index 382d765a2..7acb8d66a 100644
--- a/py_code_object/test_snippets.py
+++ b/tests/test_snippets.py
@@ -3,6 +3,7 @@
 # in the tests folder.
 
 
+import sys
 import os
 import unittest
 import glob
@@ -15,7 +16,7 @@ import compile_code
 
 logger = logging.getLogger('tests')
 ROOT_DIR = '..'
-TEST_DIR = os.path.abspath(os.path.join(ROOT_DIR, 'tests'))
+TEST_DIR = os.path.abspath(os.path.join(ROOT_DIR, 'tests', 'snippets'))
 CPYTHON_RUNNER_DIR = os.path.abspath(os.path.join(ROOT_DIR, 'py_code_object'))
 RUSTPYTHON_RUNNER_DIR = os.path.abspath(os.path.join(ROOT_DIR))
 
@@ -32,6 +33,8 @@ def perform_test(filename, method):
     logger.info('Running %s via %s', filename, method)
     if method == 'cpython':
         run_via_cpython(filename)
+    elif method == 'cpython_bytecode':
+        run_via_cpython_bytecode(filename)
     elif method == 'rustpython':
         run_via_rustpython(filename)
     else:
@@ -39,6 +42,11 @@ def perform_test(filename, method):
 
 
 def run_via_cpython(filename):
+    """ Simply invoke python itself on the script """
+    subprocess.check_call([sys.executable, filename])
+
+
+def run_via_cpython_bytecode(filename):
     # Step1: Create bytecode file:
     bytecode_filename = filename + '.bytecode'
     with open(bytecode_filename, 'w') as f:
@@ -77,7 +85,7 @@ def create_test_function(cls, filename, method):
 
 def populate(cls):
     """ Decorator function which can populate a unittest.TestCase class """
-    for method in ['cpython', 'rustpython']:
+    for method in ['cpython', 'cpython_bytecode', 'rustpython']:
         for filename in get_test_files():
             create_test_function(cls, filename, method)
     return cls
diff --git a/vm/src/lib.rs b/vm/src/lib.rs
index 82e82a458..46f7f9d01 100644
--- a/vm/src/lib.rs
+++ b/vm/src/lib.rs
@@ -5,7 +5,7 @@ extern crate env_logger;
 //extern crate eval; use eval::eval::*;
 // use py_code_object::{Function, NativeType, PyCodeObject};
 
-mod pyobject;
+pub mod pyobject;
 pub mod bytecode;
 mod builtins;
 mod vm;
diff --git a/vm/src/pyobject.rs b/vm/src/pyobject.rs
index c2e29831c..8797269cb 100644
--- a/vm/src/pyobject.rs
+++ b/vm/src/pyobject.rs
@@ -47,6 +47,9 @@ pub enum PyObject {
         stop: Option<i32>,
         step: Option<i32>,
     },
+    NameError {  // TODO: improve python object and type system
+        name: String,
+    },
     Code {
         code: bytecode::CodeObject,
     },
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index 3f4f20067..4cbc8d51a 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -15,14 +15,14 @@ use super::pyobject::{PyObject, PyObjectRef};
 // use objects::objects;
 
 // Container of the virtual machine state:
-pub fn evaluate(code: bytecode::CodeObject) {
+pub fn evaluate(code: bytecode::CodeObject) -> Result<PyObjectRef, PyObjectRef> {
     let mut vm = VirtualMachine::new();
 
     // Register built in function:
     // vm.scope.insert(String::from("print"), PyObject::RustFunction { function: builtins::print }.into_ref());
 
     // { stack: Vec::new() };
-    vm.run(Rc::new(code));
+    vm.run(Rc::new(code))
 }
 
 // Objects are live when they are on stack, or referenced by a name (for now)
@@ -51,11 +51,6 @@ struct VirtualMachine {
     frames: Vec<Frame>,
 }
 
-enum ExeResult {
-    Value { value: PyObjectRef },
-    Exception,
-}
-
 impl Frame {
     pub fn new(code: Rc<bytecode::CodeObject>, callargs: HashMap<String, PyObjectRef>, globals: Option<HashMap<String, PyObjectRef>>) -> Frame {
         //populate the globals and locals
@@ -122,22 +117,25 @@ impl VirtualMachine {
         self.current_frame().pop_multiple(count)
     }
 
-    fn run(&mut self, code: Rc<bytecode::CodeObject>) {
+    fn run(&mut self, code: Rc<bytecode::CodeObject>) -> Result<PyObjectRef, PyObjectRef> {
         let frame = Frame::new(code, HashMap::new(), None);
-        self.run_frame(frame);
+        self.run_frame(frame)
     }
 
     // The Option<i32> is the return value of the frame, remove when we have implemented frame
     // TODO: read the op codes directly from the internal code object
-    fn run_frame(&mut self, mut frame: Frame) -> PyObjectRef {
+    fn run_frame(&mut self, mut frame: Frame) -> Result<PyObjectRef, PyObjectRef> {
         self.frames.push(frame);
 
         let value = loop {
             let result = self.execute_instruction();
             match result {
                 None => {},
-                Some(ExeResult::Value { value }) => { break value; },
-                Some(ExeResult::Exception) => { panic!("TODO"); }
+                Some(Ok(value)) => { break Ok(value); },
+                Some(Err(value)) => {
+                    // TODO: unwind stack on exception.
+                    panic!("TODO {:?}", value);
+                }
             }
             /*if curr_frame.blocks.len() > 0 {
               self.manage_block_stack(&why);
@@ -238,7 +236,7 @@ impl VirtualMachine {
     }
 
     // Execute a single instruction:
-    fn execute_instruction(&mut self) -> Option<ExeResult> {
+    fn execute_instruction(&mut self) -> Option<Result<PyObjectRef, PyObjectRef>> {
         // let frame = self.frames.last_mut().unwrap();
         let instruction = {
             let frame = self.current_frame();
@@ -268,9 +266,14 @@ impl VirtualMachine {
             },
             &bytecode::Instruction::LoadName { ref name } => {
                 // Lookup name in scope and put it onto the stack!
-                let obj = self.current_frame().locals[name].clone();
-                self.push_value(obj);
-                None
+                if self.current_frame().locals.contains_key(name) {
+                    let obj = self.current_frame().locals[name].clone();
+                    self.push_value(obj);
+                    None
+                } else {
+                    let name_error = PyObject::NameError { name: name.to_string() };
+                    Some(Err(name_error.into_ref()))
+                }
             },
             &bytecode::Instruction::StoreName { ref name } => {
                 // take top of stack and assign in scope:
@@ -342,7 +345,7 @@ impl VirtualMachine {
             },
             &bytecode::Instruction::ReturnValue => {
                 let value = self.pop_value();
-                Some(ExeResult::Value { value })
+                Some(Ok(value))
             },
             /*
             &bytecode::Instruction::PushBlock { start, end } => {
@@ -401,9 +404,9 @@ impl VirtualMachine {
                 let mut args: Vec<PyObjectRef> = self.pop_multiple(count);
                 let func_ref = self.pop_value();
                 let f = func_ref.borrow();// = &*func_ref.borrow();
-                let result = match *f {
+                let func_result = match *f {
                     PyObject::RustFunction { ref function } => {
-                        f.call(args)
+                        Ok(f.call(args))
                     }
                     PyObject::Function { ref code } => {
                         let frame = Frame::new(Rc::new(code.clone()), HashMap::new(), None);
@@ -414,11 +417,17 @@ impl VirtualMachine {
                         panic!("Not impl");
                     }
                 };
-                self.push_value(result);
+
+                match func_result {
+                    Ok(value) => { self.push_value(value); None },
+                    Err(value) => {
+                        // Ripple exception upwards:
+                        Some(Err(value))
+                    }
+                }
                 // call_stack.push();
                 // If a builtin function, then call directly, otherwise, execute it?
                 // execute(function.code);
-                None
             },
             /* TODO
             &bytecode::Instruction::Jump { target } => {