lunar_wave/src/main.rs

use std::collections::BTreeMap;

enum Instruction {
	VarArgPrep (i32),
	GetTabUp (u8, u8, u8),
	GetI (u8, u8, u8),
	EqK (u8, u8, u8),
	Jmp (i32),
	LoadK (u8, i32),
	Call (u8, u8, u8),
	Closure (u8, i32),
	Return (u8, u8, u8),
}

#[derive (Clone, Debug, PartialEq)]
enum Value {
	Nil,
	False,
	True,
	Float (f64),
	String (String),
	
	// These are all bogus, I haven't figured out how to implement
	// tables and function pointers yet
	
	BogusArg (Vec <String>),
	BogusEnv (BTreeMap <String, Value>),
	BogusPrint,
}

impl Default for Value {
	fn default () -> Self {
		Self::Nil
	}
}

impl From <String> for Value {
	fn from (x: String) -> Self {
		Self::String (x)
	}
}

impl From <&str> for Value {
	fn from (x: &str) -> Self {
		Self::from (String::from (x))
	}
}

struct Chunk {
	instructions: Vec <Instruction>,
	constants: Vec <Value>,
}

struct VirtualMachine {
	registers: Vec <Value>,
	
	// i32 makes it a little easier to implement jumps
	program_counter: i32,
}

impl Default for VirtualMachine {
	fn default () -> Self {
		Self {
			registers: vec! [Value::Nil; 256],
			program_counter: 0,
		}
	}
}

impl VirtualMachine {
	fn execute_chunk (&mut self, chunk: &Chunk, upvalues: &Vec <Value>) {
		let max_iters = 2000;
		
		for _ in 0..max_iters {
			let instruction = chunk.instructions.get (usize::try_from (self.program_counter).unwrap ()).unwrap ();
			
			let r = &mut self.registers;
			let k = &chunk.constants;
			
			match instruction {
				Instruction::Call (a, b, c) => {
					// Take arguments from registers [a + 1, a + b)
					// Call the function in register [a]
					// Return values in registers [a, a + c - 1)
					// 
					// That is, call a with b - 1 arguments and expect c returns
					// 
					// e.g. CALL 0 2 1 mean "Call 0 with 1 argument, return 1 value", like for printing a constant
					
					// TODO: Only implement printing constants for now
					
					let a = usize::try_from (*a).unwrap ();
					
					assert_eq! (*b, 2);
					assert_eq! (*c, 1);
					
					println! ("{:?}", r [a + 1]);
				},
				Instruction::EqK (a, b, c_k) => {
					let a = usize::try_from (*a).unwrap ();
					let b = usize::try_from (*b).unwrap ();
					
					let equal = r [a] == k [b];
					
					match (equal, c_k) {
						(true, 0) => self.program_counter += 1,
						(false, 1) => self.program_counter += 1,
						_ => (),
					}
				},
				Instruction::GetTabUp (a, b, c) => {
					let a = usize::try_from (*a).unwrap ();
					let b = usize::try_from (*b).unwrap ();
					let c = usize::try_from (*c).unwrap ();
					
					let env = match upvalues.get (b).unwrap () {
						Value::BogusEnv (x) => x,
						_ => panic! ("Only allowed upvalue is BogusEnv"),
					};
					
					let key = match k.get (c).unwrap () {
						Value::String (s) => s,
						_ => panic! ("GetTabUp only supports string keys"),
					};
					
					
					let value = env.get (key).unwrap ();
					
					r [a] = value.clone ();
				},
				Instruction::GetI (a, b, c) => {
					let a = usize::try_from (*a).unwrap ();
					let b = usize::try_from (*b).unwrap ();
					let c = usize::try_from (*c).unwrap ();
					
					let table = r.get (b).unwrap ();
					let value = match table {
						Value::BogusArg (arg) => arg.get (c).unwrap ().as_str().into (),
						_ => unimplemented!(),
					};
					
					r [a] = value;
				},
				Instruction::Jmp (sJ) => self.program_counter += sJ,
				Instruction::LoadK (a, bx) => {
					let a  = usize::try_from  (*a).unwrap ();
					let bx = usize::try_from (*bx).unwrap ();
					
					r [a] = k [bx].clone ();
				},
				Instruction::Return (_a, _b, _c) => {
					break;
				},
				Instruction::VarArgPrep (_) => (),
				_ => (),
			}
			
			self.program_counter += 1;
		}
	}
}

fn main() {
	let arg: Vec <_> = std::env::args ().collect ();
	
	let chunk = Chunk {
		instructions: vec! [
			Instruction::VarArgPrep (0),
			Instruction::GetTabUp (0, 0, 0),
			Instruction::GetI (0, 0, 1),
			Instruction::EqK (0, 1, 0),
			Instruction::Jmp (4),
			Instruction::GetTabUp (0, 0, 2),
			Instruction::LoadK (1, 3),
			Instruction::Call (0, 2, 1),
			Instruction::Jmp (3),
			Instruction::GetTabUp (0, 0, 2),
			Instruction::LoadK (1, 4),
			Instruction::Call (0, 2, 1),
			Instruction::Return (1, 1, 1),
		],
		constants: vec! [
			"arg",
			"93",
			"print",
			"it's 93",
			"it's not 93",
		].into_iter ().map (|s| Value::from (s)).collect (),
	};
	
	let env = BTreeMap::from_iter ([
		("arg", Value::BogusArg (arg.clone ())),
		("print", Value::BogusPrint),
	].map (|(k, v)| (k.to_string (), v)).into_iter ());
	
	let upvalues = vec! [
		Value::BogusEnv (env),
	];
	
	let mut vm = VirtualMachine::default ();
	vm.execute_chunk (&chunk, &upvalues);
}