diff --git a/src/instruction.rs b/src/instruction.rs
index 36c815e..0ff3568 100644
--- a/src/instruction.rs
+++ b/src/instruction.rs
@@ -31,6 +31,8 @@ pub enum Instruction {
 	// Jump
 	Jmp (i32),
 	
+	Len (u8, u8),
+	
 	// Load F (Float?)
 	LoadF (u8, i32),
 	
diff --git a/src/loader.rs b/src/loader.rs
index 056eeef..ba67bbc 100644
--- a/src/loader.rs
+++ b/src/loader.rs
@@ -8,12 +8,35 @@ use crate::{
 	}
 };
 
+pub (crate) fn compile_bytecode_from_file (path: &str) -> Vec <u8> {
+	use std::{
+		process::{
+			Command,
+			Stdio,
+		},
+	};
+	
+	let child = Command::new ("luac5.4")
+	.arg ("-o") // Output to...
+	.arg ("-")  // Standard output
+	.arg (path) 
+	.stdout (Stdio::piped ())
+	.spawn ()
+	.expect ("failed to execute `luac5.4`. Is Lua installed?");
+	
+	let output = child
+	.wait_with_output ()
+	.expect ("failed to wait on child");
+	
+	output.stdout.as_slice ().to_vec ()
+}
+
 /// Invoke `luac` as a subprocess
 /// Luckily luac is single-pass, so we can just pipe in and out
 /// 
 /// `source` is a Vec because we move it to a worker thread
 
-pub (crate) fn compile_bytecode (source: Vec <u8>) -> Vec <u8> {
+pub (crate) fn compile_bytecode_from_stdin (source: Vec <u8>) -> Vec <u8> {
 	use std::{
 		io::Write,
 		process::{
@@ -87,6 +110,7 @@ pub fn parse_inst (buf: [u8; 4]) -> Option <Inst>
 		0x2e => Inst::MmBin (a, b, c),
 		0x30 => Inst::MmBinK (a, b, c, k),
 		0x33 => Inst::Not (a, b),
+		0x34 => Inst::Len (a, b),
 		0x3c => Inst::EqK (a, b, k),
 		0x3d => Inst::EqI (a, i_sb (buf)?, k),
 		0x38 => Inst::Jmp (s_j),
diff --git a/src/main.rs b/src/main.rs
index f007ec5..6291171 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,6 +11,7 @@ mod tests;
 fn main () {
 	use state::State;
 	
+	let mut list_bytecode = false;
 	let mut pipe_bytecode = false;
 	let mut script = None;
 	
@@ -19,6 +20,7 @@ fn main () {
 	
 	while let Some (arg) = args.next () {
 		match arg.as_str () {
+			"--list-bytecode" => list_bytecode = true,
 			"--pipe-bytecode" => pipe_bytecode = true,
 			"--script" => script = Some (args.next ().unwrap ()),
 			"--" => break,
@@ -26,9 +28,9 @@ fn main () {
 		}
 	}
 	
-	let lua_file = if let Some (script) = script {
-		let source = std::fs::read (script).expect ("couldn't load Lua source code");
-		let bytecode = loader::compile_bytecode(source);
+	let chunk = if let Some (script) = script {
+		let bytecode = loader::compile_bytecode_from_file (&script);
+		dbg! (&bytecode [0..48]);
 		let mut rdr = std::io::Cursor::new (bytecode);
 		loader::parse_chunk (&mut rdr).unwrap ()
 	}
@@ -40,6 +42,10 @@ fn main () {
 		unimplemented!();
 	};
 	
+	if list_bytecode {
+		dbg! (&chunk);
+	}
+	
 	let mut vm = State::default ();
 	if std::env::var("LUA_DEBUG").is_ok() {
 		vm.debug_print = true;
@@ -52,5 +58,5 @@ fn main () {
 		program_counter: 0,
 	});
 	
-	vm.execute_chunk (&lua_file, &upvalues);
+	vm.execute_chunk (&chunk, &upvalues);
 }
diff --git a/src/state.rs b/src/state.rs
index 58f6b75..7f953ce 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -8,12 +8,14 @@ use crate::{
 	},
 };
 
+#[derive (Debug)]
 pub struct Block {
 	pub instructions: Vec <Instruction>,
 	pub constants: Vec <Value>,
 	pub upvalue_count: usize,
 }
 
+#[derive (Debug)]
 pub struct Chunk {
 	pub blocks: Vec <Block>,
 }
@@ -338,6 +340,14 @@ impl State {
 					*self.reg_mut (*a) = upvalues [b].clone ();
 				},
 				Instruction::Jmp (s_j) => next_pc += s_j,
+				Instruction::Len (a, b) => {
+					let len = match self.reg (*b) {
+						Value::String (s) => s.len (),
+						_ => unimplemented!(),
+					};
+					
+					*self.reg_mut (*a) = len.into ();
+				}
 				Instruction::LoadF (a, sbx) => {
 					*self.reg_mut (*a) = Value::Float (*sbx as f64);
 				}
diff --git a/src/tests.rs b/src/tests.rs
index 05a425b..6c81843 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -42,7 +42,7 @@ fn run_bytecode (args: &[&str], bc: &[u8]) -> Vec <Value> {
 /// and returns the output
 
 fn run_source (args: &[&str], s: &str) -> Vec <Value> {
-	let bc = loader::compile_bytecode (s.as_bytes ().to_vec ());
+	let bc = loader::compile_bytecode_from_stdin (s.as_bytes ().to_vec ());
 	run_bytecode (args, &bc)
 }
 
@@ -289,7 +289,7 @@ fn is_93 () {
 	end
 	"#;
 	
-	let bc = loader::compile_bytecode (src.as_bytes ().to_vec ());
+	let bc = loader::compile_bytecode_from_stdin (src.as_bytes ().to_vec ());
 	let chunk = loader::parse_chunk_from_bytes (&bc).unwrap ();
 	
 	assert_eq! (chunk.blocks [0].instructions [3], Inst::EqK (0, 1, false));