diff --git a/Cargo.lock b/Cargo.lock
index 3ef61c2..14bb9f2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,127 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "codespan-reporting"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3538270d33cc669650c4b093848450d380def10c331d38c768e34cac80576e6e"
+dependencies = [
+ "termcolor",
+ "unicode-width",
+]
+
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613f8cc01fe9cf1a3eb3d7f488fd2fa8388403e97039e2f73692932e291a770d"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.8.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "248e3bacc7dc6baa3b21e405ee045c3047101a49145e7e9eca583ab4c2ca5345"
+
+[[package]]
+name = "either"
+version = "1.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a26ae43d7bcc3b814de94796a5e736d4029efb0ee900c12e2d54c993ad1a1e07"
+
+[[package]]
+name = "itertools"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "25db6b064527c5d482d0423354fcd07a89a2dfe07b67892e62411946db7f07b0"
+dependencies = [
+ "either",
+]
+
+[[package]]
+name = "rayon"
+version = "1.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa7237101a77a10773db45d62004a272517633fbcc3df19d96455ede1122e051"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1465873a3dfdaa8ae7cb14b4383657caab0b3e8a0aa9ae8e04b044854c8dfce2"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "riscv_interpreter"
 version = "0.1.0"
+dependencies = [
+ "codespan-reporting",
+ "itertools",
+ "rayon",
+]
+
+[[package]]
+name = "termcolor"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06794f8f6c5c898b3275aebefa6b8a1cb24cd2c6c79397ab15774837a0bc5755"
+dependencies = [
+ "winapi-util",
+]
+
+[[package]]
+name = "unicode-width"
+version = "0.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e51733f11c9c4f72aa0c160008246859e340b00807569a0da0e7a1079b27ba85"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-util"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f29e6f9198ba0d26b4c9f07dbe6f9ed633e1f3d5b8b414090084349e46a52596"
+dependencies = [
+ "winapi",
+]
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
diff --git a/Cargo.toml b/Cargo.toml
index 883d84e..db2436e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,3 +2,8 @@
 name = "riscv_interpreter"
 version = "0.1.0"
 edition = "2021"
+
+[dependencies]
+codespan-reporting = { version = "0.11.1", features = ["ascii-only"] }
+itertools = "0.12.0"
+rayon = "1.8.1"
diff --git a/src/env.rs b/src/env.rs
index 8c9dc18..87adf33 100644
--- a/src/env.rs
+++ b/src/env.rs
@@ -1,3 +1,79 @@
+use std::collections::HashMap;
 
+#[derive(Debug)]
+pub struct Env {
+    register_alias: HashMap<String, usize>,
+    labels: HashMap<String, usize>,
+    registers: [i64; 32],
+    stack: Vec<i64>, // TODO: Find the size of the stack
+}
 
-pub enum Env {}
+impl Env {
+    pub fn new() -> Self {
+        // alias -> xN
+        let register_alias = [
+            ("zero", 0),
+            ("ra", 1),
+            ("sp", 2),
+            ("gp", 3),
+            ("tp", 4),
+            ("t0", 5),
+            ("t1", 6),
+            ("t2", 7),
+            ("s0", 8),
+            ("s1", 9),
+            ("a0", 10),
+            ("a1", 11),
+            ("a2", 12),
+            ("a3", 13),
+            ("a4", 14),
+            ("a5", 15),
+            ("a6", 16),
+            ("a7", 17),
+            ("s2", 18),
+            ("s3", 19),
+            ("s4", 20),
+            ("s5", 21),
+            ("s6", 22),
+            ("s7", 23),
+            ("s8", 24),
+            ("s9", 25),
+            ("s10", 26),
+            ("s11", 27),
+            ("t3", 28),
+            ("t4", 29),
+            ("t5", 30),
+            ("t6", 31),
+        ]
+        .iter()
+        .map(|(k, v)| (k.to_string(), v.to_owned()))
+        .collect::<HashMap<_, _>>();
+
+        Self {
+            register_alias,
+            labels: HashMap::new(),
+            registers: [0; 32],
+            stack: Vec::new(),
+        }
+    }
+
+    pub fn set_register(&mut self, reg: usize, value: i64) {
+        self.registers[reg] = value;
+    }
+
+    pub fn get_register(&self, reg: usize) -> i64 {
+        self.registers[reg]
+    }
+
+    pub fn alias_to_register(&self, reg: &str) -> Option<usize> {
+        self.register_alias.get(reg).copied()
+    }
+
+    pub fn add_label(&mut self, label: &str, value: usize) {
+        self.labels.insert(label.to_string(), value);
+    }
+
+    pub fn get_label(&self, label: &str) -> Option<usize> {
+        self.labels.get(label).copied()
+    }
+}
diff --git a/src/err.rs b/src/err.rs
index 83ede89..efe1608 100644
--- a/src/err.rs
+++ b/src/err.rs
@@ -1,19 +1,26 @@
 use std::fmt::{self, Display, Formatter};
 
+#[derive(Debug, Clone)]
 pub enum SyntaxErr {
     TraillingComma,
-    UnmatchedParen,
+    /// false for '(' true for ')'
+    UnmatchedParen(bool),
+    UnexpectedChar,
+    OutsideOp(String),
 }
 
 impl Display for SyntaxErr {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
             SyntaxErr::TraillingComma => write!(f, "trailling comma"),
-            SyntaxErr::UnmatchedParen => write!(f, "unmatched parenthesis"),
+            SyntaxErr::UnmatchedParen(_) => write!(f, "unmatched parenthesis"),
+            SyntaxErr::UnexpectedChar => write!(f, "unexpected character"),
+            SyntaxErr::OutsideOp(kind) => write!(f, "{kind} before opcode"),
         }
     }
 }
 
+#[derive(Debug, Clone)]
 pub enum RuntimeErr {
     InvalidRegister(String),
     UnexpectedImmediate,
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..9c14777 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,9 @@
+use rayon::prelude::*;
+use riscv_interpreter::parser::{parse, Token};
+
 fn main() {
-    println!("Hello, world!");
+    let input = std::fs::read_to_string("test.s").unwrap();
+    let tokens = parse(&input);
+    // println!("{:#?} -> {:#?}", input, tokens.into_par_iter().filter(|(token, _)| !matches!(token, Token::Spacing)).collect::<Vec<_>>());
+    println!("{:#?} -> {:#?}", input, tokens);
 }
diff --git a/src/parser.rs b/src/parser.rs
index ab0197d..6cfda23 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,23 +1,245 @@
-pub enum Expr {
+/// TODO: Strings, Symbols
+use crate::err::SyntaxErr;
+use itertools::Itertools;
+use rayon::prelude::*;
+
+#[derive(Debug, Clone)]
+pub enum Token {
+    /// ' ', '\t', '\r'
+    Spacing,
+    /// \# blablabla,
+    Comment,
     /// 1, 2, -1
     Immediate(i64),
     /// zero, r1, pc
+    ///
+    /// Technically also label references and symbols, but we'll handle those later
     Register(String),
     /// add, xor, j
-    Op(Vec<Expr>),
+    Op(String, Vec<(Token, Loc)>),
     /// <label>:
     LabelDef(String),
-    /// j <label>
-    LabelRef(String),
+    /// 0(a0)
+    Memory(Box<Token>, Option<Box<Token>>),
+    /// symbol
+    Symbol(String),
+    /// "string"
+    String(String),
+
+    /// Error token
+    Error(ParseErr),
 }
 
-pub struct Location {
+impl Token {
+    pub fn kind(&self) -> &'static str {
+        use Token::*;
+        match self {
+            Spacing => "spacing",
+            Comment => "comment",
+            Immediate(_) => "immediate",
+            Register(_) => "register",
+            Op(_, _) => "op",
+            LabelDef(_) => "label def",
+            Memory(_, _) => "memory",
+            Symbol(_) => "symbol",
+            String(_) => "string",
+            Error(_) => "error",
+        }
+    }
+}
+
+type ParseErr = (SyntaxErr, Loc, Vec<(Token, Loc)>, Option<String>);
+
+#[derive(Debug, Clone, Copy)]
+pub struct Loc {
     pub line: usize,
     pub col: usize,
     pub start: usize,
     pub end: usize,
 }
 
-pub fn parse(input: &str) -> Result<Expr, ()> {
-    todo!()
+fn parse_line(input: &str, line: usize) -> Result<Vec<(Token, Loc)>, ParseErr> {
+    let mut loc = Loc {
+        line,
+        col: 1,
+        start: 0,
+        end: 0,
+    };
+
+    let mut tokens: Vec<(Token, Loc)> = Vec::new();
+    let mut chars = input.chars().peekable();
+
+    use Token::*;
+
+    while let Some(c) = chars.next() {
+        let token = match c {
+            '\t' => {
+                // TODO: Make a flag to set the tab size
+                loc.col += 3;
+                Spacing
+            }
+            ' ' => Spacing,
+
+            '#' => {
+                while let Some(_) = chars.peek() {
+                    chars.next();
+                    loc.end += 1;
+                }
+                Comment
+            }
+
+            '0'..='9' => {
+                let mut num = c.to_string();
+                while let Some('0'..='9') = chars.peek() {
+                    num.push(chars.next().unwrap());
+                    loc.end += 1;
+                }
+                Immediate(num.parse().unwrap())
+            }
+            '-' => {
+                let mut num = c.to_string();
+                while let Some('0'..='9') = chars.peek() {
+                    num.push(chars.next().unwrap());
+                }
+                Immediate(num.parse().unwrap())
+            }
+            '(' => {
+                let imm;
+                if let Some((Immediate(_), _)) = tokens.last() {
+                    imm = Box::new(tokens.pop().unwrap());
+                    loc.start = imm.1.start;
+                    loc.col = imm.1.col;
+                } else {
+                    return Err((
+                        SyntaxErr::UnexpectedChar,
+                        loc.clone(),
+                        tokens.clone(),
+                        Some("a memory index must be of the form imm(reg) or imm".to_string()),
+                    ));
+                }
+
+                let mut reg = std::string::String::new();
+                while let Some(' ') | Some('0'..='9') | Some('a'..='z') | Some('A'..='Z') =
+                    chars.peek()
+                {
+                    reg.push(chars.next().unwrap());
+                }
+                if chars.next() != Some(')') {
+                    return Err((
+                        SyntaxErr::UnmatchedParen(false),
+                        loc.clone(),
+                        tokens.clone(),
+                        None,
+                    ));
+                }
+                loc.end += 2;
+
+                Memory(
+                    Box::new(imm.0),
+                    Some(Box::new(Register(reg.trim().to_string()))),
+                )
+            }
+            ')' => {
+                return Err((
+                    SyntaxErr::UnmatchedParen(true),
+                    loc.clone(),
+                    tokens.clone(),
+                    None,
+                ))
+            }
+
+            // Opcode or Label definition
+            'a'..='z' | 'A'..='Z' | '_' => {
+                dbg!("op");
+                let mut str = c.to_string();
+                while let Some('a'..='z') | Some('A'..='Z') | Some('_') | Some('0'..='9') =
+                    chars.peek()
+                {
+                    str.push(chars.next().unwrap());
+                    loc.end += 1;
+                }
+                if let Some(':') = chars.peek() {
+                    chars.next();
+                    loc.end += 1;
+                    LabelDef(str[..str.len()].to_string())
+                } else if let Some((Op(_, _), _)) = tokens.get(tokens.len() - 2) {
+                    // These Registers may actually be label references or symbols, but there's ambiguity
+                    // between them and registers, so we'll just assume they're registers for now
+                    Register(str)
+                } else {
+                    Op(str, vec![])
+                }
+            }
+            _ => return Err((SyntaxErr::UnexpectedChar, loc.clone(), tokens.clone(), None)),
+        };
+        tokens.push((token, loc.clone()));
+        loc.end += 1;
+        loc.col += loc.end - loc.start;
+        loc.col;
+        loc.start = loc.end;
+    }
+
+    Ok(tokens
+        .into_iter()
+        .filter(|(token, _)| !matches!(token, Token::Spacing))
+        .group_by(|(token, _)| {
+            matches!(
+                token,
+                Op(_, _) | Immediate(_) | Register(_) | Memory(_, _) | Symbol(_) | String(_)
+            )
+        })
+        .into_iter()
+        .flat_map(|group| {
+            let (is_op, group) = group;
+            if is_op {
+                let group = group.collect::<Vec<_>>();
+                let (op, loc) = dbg!(dbg!(group[0].clone()));
+                let (op, mut args) = match op {
+                    Op(op, args) => (op, args),
+                    _ => {
+                        return vec![(
+                            Token::Error((
+                                SyntaxErr::OutsideOp(op.kind().to_string()),
+                                loc.clone(),
+                                group.clone(),
+                                None,
+                            )),
+                            loc.clone(),
+                        )]
+                    }
+                };
+                args.extend_from_slice(&group[1..]);
+
+                vec![(Op(op, args), loc)]
+            } else {
+                group.collect::<Vec<_>>()
+            }
+        })
+        .collect::<Vec<_>>())
+}
+
+/// Parse the input
+///
+/// Returns a vector of tokens and their locations, if successful, or an error vector
+/// containing the error, the location of the error, the tokens parsed up to that point,
+/// and an optional message to display to the users
+pub fn parse(input: &str) -> Result<Vec<(Token, Loc)>, Vec<ParseErr>> {
+    let parsed_lines = input
+        .lines()
+        .enumerate()
+        .par_bridge()
+        .map(|(i, line)| parse_line(line, i + 1))
+        .collect::<Vec<_>>();
+
+    let (ok, err) = parsed_lines
+        .into_par_iter()
+        .partition::<Vec<Result<_, _>>, Vec<Result<_, _>>, _>(|line| matches!(line, Ok(_)));
+    dbg!(&err);
+
+    if err.is_empty() {
+        Ok(ok.into_par_iter().flat_map(|line| line.unwrap()).collect())
+    } else {
+        dbg!("err");
+        Err(err.into_par_iter().map(|line| line.unwrap_err()).collect())
+    }
 }
diff --git a/test.s b/test.s
index 098905d..780be8f 100644
--- a/test.s
+++ b/test.s
@@ -1 +1 @@
-    add r1 r2 r1
+a:  lw a0 1(sp)