diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..a824679
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,41 @@
+use std::{error::Error, fmt::Display};
+
+#[derive(Debug)]
+pub struct ParseError {
+    message: String
+}
+
+impl ParseError {
+    pub fn new(message: impl Into<String>) -> Self {
+        Self { message: message.into() }
+    }
+}
+
+impl Display for ParseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "parse error: {}", self.message)
+    }
+}
+
+impl Error for ParseError {}
+
+
+
+#[derive(Debug)]
+pub struct LexError {
+    message: String
+}
+
+impl LexError {
+    pub fn new(message: impl Into<String>) -> Self {
+        Self { message: message.into() }
+    }
+}
+
+impl Display for LexError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "lex error: {}", self.message)
+    }
+}
+
+impl Error for LexError {}
\ No newline at end of file
diff --git a/src/lexer.rs b/src/lexer.rs
index 32d806a..f862a54 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -1,4 +1,6 @@
-use crate::token::Token;
+use crate::{error::LexError, token::Token};
+
+type LexResult<T> = Result<T, LexError>;
 
 pub struct Lexer {
     source: Vec<u8>,
@@ -27,7 +29,7 @@ impl Lexer {
         self.source.get(self.pos).copied()
     }
 
-    fn number(&mut self) -> Option<Token> {
+    fn number(&mut self) -> LexResult<Token> {
         let mut num = String::new();
 
         while matches!(self.peek(), Some(b'0' ..= b'9')) {
@@ -35,42 +37,97 @@ impl Lexer {
             self.advance();
         }
 
-        Some(Token::Number(num.parse().unwrap()))
+        Ok(Token::Number(num.parse().unwrap()))
     }
 
-    fn ident(&mut self) -> Option<Token> {
+    fn ident(&mut self) -> LexResult<Token> {
         let mut ident = String::new();
 
-        while matches!(self.peek(), Some(b'a' ..= b'z' | b'A' ..= b'Z')) {
+        while matches!(self.peek(), Some(b'a' ..= b'z' | b'A' ..= b'Z' | b'0' ..= b'9' | b'_')) {
             ident.push(self.peek().unwrap() as char);
+            self.advance();
         }
 
-        Some(Token::Ident(ident))
+        let tok = match ident.as_str() {
+            "mov"        => Token::Mov,
+            "if"         => Token::If,
+            "else"       => Token::Else,
+            "loop"       => Token::Loop,
+            "while"      => Token::While,
+            "for"        => Token::For,
+            "in"         => Token::In,
+            "fun"        => Token::Fun,
+            "call"       => Token::Call,
+            "break"      => Token::Break,
+            "continue"   => Token::Continue,
+            "true"       => Token::True,
+            "false"      => Token::False,
+
+            "eq"         => Token::Eq,
+            "new"        => Token::Neq,
+            "lt"         => Token::Lt,
+            "gt"         => Token::Gt,
+            "lte"        => Token::Lte,
+            "gte"        => Token::Gte,
+
+            _            => Token::Ident(ident)
+        };
+
+        Ok(tok)
     }
 
-    pub fn next(&mut self) -> Option<Token> {
+    fn string(&mut self) -> LexResult<Token> {
+        self.advance();
+        let mut s = String::new();
+
+        loop {
+            match self.peek() {
+                Some(b'"') => { self.advance(); break; },
+                Some(c) => { s.push(c as char); self.advance(); }
+                None => { return Err(LexError::new(format!(
+                    "expected closing \""
+                ))); }
+            }
+        }
+
+        Ok(Token::StringLit(s))
+    }
+
+    pub fn next(&mut self) -> LexResult<Token> {
         self.skip_whitespace();
         match self.peek() {
             Some(b'0' ..= b'9') => self.number(),
             Some(b'a' ..= b'z' | b'A' ..= b'Z') => self.ident(),
 
-            Some(b'+') => {self.advance(); Some(Token::Plus)},
-            Some(b'-') => {self.advance(); Some(Token::Minus)},
-            Some(b'*') => {self.advance(); Some(Token::Asterisk)},
-            Some(b'/') => {self.advance(); Some(Token::Slash)},
-            Some(b'%') => {self.advance(); Some(Token::Percent)},
-            Some(b'^') => {self.advance(); Some(Token::Caret)},
+            Some(b'+') => {self.advance(); Ok(Token::Plus)},
+            Some(b'-') => {self.advance(); Ok(Token::Minus)},
+            Some(b'*') => {self.advance(); Ok(Token::Asterisk)},
+            Some(b'/') => {self.advance(); Ok(Token::Slash)},
+            Some(b'%') => {self.advance(); Ok(Token::Percent)},
+            Some(b'^') => {self.advance(); Ok(Token::Caret)},
 
-            Some(b'(') => {self.advance(); Some(Token::LParen)},
-            Some(b')') => {self.advance(); Some(Token::RParen)},
-            Some(b'[') => {self.advance(); Some(Token::LBracket)},
-            Some(b']') => {self.advance(); Some(Token::RBracket)},
-            Some(b'{') => {self.advance(); Some(Token::LBrace)},
-            Some(b'}') => {self.advance(); Some(Token::RBrace)},
+            Some(b'(') => {self.advance(); Ok(Token::LParen)},
+            Some(b')') => {self.advance(); Ok(Token::RParen)},
+            Some(b'[') => {self.advance(); Ok(Token::LBracket)},
+            Some(b']') => {self.advance(); Ok(Token::RBracket)},
+            Some(b'{') => {self.advance(); Ok(Token::LBrace)},
+            Some(b'}') => {self.advance(); Ok(Token::RBrace)},
 
-            Some(b';') => {self.advance(); Some(Token::Semicolon)}
-            
-            _ => None
+            Some(b';') => {self.advance(); Ok(Token::Semicolon)},
+            Some(b',') => {self.advance(); Ok(Token::Comma)},
+            Some(b'.') => {
+                self.advance();
+
+                match self.peek() {
+                    Some(b'.') => { self.advance(); Ok(Token::DotDot) },
+                    c => Err(LexError::new(format!(
+                        "unexpected character after '.': {c:?}"
+                    )))
+                }
+            },
+            Some(b'"') => self.string(),
+
+            _ => Ok(Token::EOF)
         }
     }
 }
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index f0cd919..608fb86 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,6 +3,7 @@ use std::{fs::File, io::Read};
 mod token;
 mod expr;
 mod lexer;
+mod error;
 use lexer::Lexer;
 mod parser;
 use parser::Parser;
@@ -20,7 +21,8 @@ fn main() -> std::io::Result<()> {
     let mut lexer = Lexer::new(&source);
 
     let mut tokens = Vec::new();
-    while let Some(tok) = lexer.next() {
+    while let Ok(tok) = lexer.next() {
+        if tok == token::Token::EOF { break; }
         print!("{tok:?}, ");
         tokens.push(tok);
     }
@@ -29,7 +31,7 @@ fn main() -> std::io::Result<()> {
 
     let mut parser = Parser::new(tokens);
     loop {
-        let parsed = parser.parse();
+        let parsed = parser.parse().unwrap_or(expr::Expr::EOL);
         match parsed {
             expr::Expr::EOL => break,
             _ => {
diff --git a/src/parser.rs b/src/parser.rs
index 3afc6e0..181b4fa 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,5 +1,8 @@
 use crate::token::Token;
 use crate::expr::{Expr, UnaryOp, BinaryOp, infix_bp, prefix_bp};
+use crate::error::ParseError;
+
+type ParseResult<T> = Result<T, ParseError>;
 
 pub struct Parser {
     tokens: Vec<Token>,
@@ -28,39 +31,49 @@ impl Parser {
         tok
     }
 
-    fn parse_atom(&mut self) -> Expr {
+    fn expect(&mut self, expected: &Token) -> ParseResult<Token> {
         match self.next() {
-            Some(Token::Number(n)) => Expr::Number(n),
-            Some(Token::Ident(id)) => Expr::Ident(id),
-            Some(Token::LParen) => {
-                let expr = self.parse_expr(0);
-
-                match self.next() {
-                    Some(Token::RParen) => expr,
-                    _ => panic!("expected ')'")
-                }
-            },
-            tok => panic!("unknown token: {tok:?}")
+            Some(tok) if &tok == expected => Ok(tok),
+            other => Err(ParseError::new(format!(
+                "expected {expected:?}, got {other:?}"
+            )))
         }
     }
 
-    fn parse_prefix(&mut self) -> Expr {
+    fn parse_atom(&mut self) -> ParseResult<Expr> {
+        match self.next() {
+            Some(Token::Number(n)) => Ok(Expr::Number(n)),
+            Some(Token::Ident(id)) => Ok(Expr::Ident(id)),
+            Some(Token::LParen) => {
+                let expr = self.parse_expr(0)?;
+
+                self.expect(&Token::RParen)?;
+
+                Ok(expr)
+            },
+            tok => Err(ParseError::new(format!(
+                "unexpected token: {tok:?}"
+            )))
+        }
+    }
+
+    fn parse_prefix(&mut self) -> ParseResult<Expr> {
         match self.peek() {
             Some(Token::Minus) => {
                 self.advance();
                 let op = UnaryOp::Neg;
 
                 let bp = prefix_bp(&op);
-                let rhs = self.parse_expr(bp);
+                let rhs = self.parse_expr(bp)?;
 
-                Expr::Unary { op, right: Box::new(rhs) }
+                Ok(Expr::Unary { op, right: Box::new(rhs) })
             },
             _ => self.parse_atom()
         }
     }
 
-    fn parse_expr(&mut self, min_bp: u8) -> Expr {
-        let mut lhs = self.parse_prefix();
+    fn parse_expr(&mut self, min_bp: u8) -> ParseResult<Expr> {
+        let mut lhs = self.parse_prefix()?;
 
         loop {
             let op = match self.peek() {
@@ -81,16 +94,16 @@ impl Parser {
 
             self.advance();
 
-            let rhs = self.parse_expr(right_bp);
+            let rhs = self.parse_expr(right_bp)?;
 
             lhs = Expr::Binary { left: Box::new(lhs), op, right: Box::new(rhs) }
         }
 
-        lhs
+        Ok(lhs)
     }
 
-    pub fn parse(&mut self) -> Expr {
-        if self.peek().is_none() {return Expr::EOL}
+    pub fn parse(&mut self) -> ParseResult<Expr> {
+        if self.peek().is_none() {return Ok(Expr::EOL)}
         self.parse_expr(0)
     }
 }
\ No newline at end of file
diff --git a/src/token.rs b/src/token.rs
index c193fbe..f54fca0 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -2,6 +2,7 @@
 pub enum Token {
     Number(i64),
     Ident(String),
+    StringLit(String),
 
     // Operators
     Plus,
@@ -19,5 +20,33 @@ pub enum Token {
     LBracket,
     RBracket,
 
-    Semicolon
+    // Separators
+    Semicolon,
+    Comma,
+
+    // Keywords
+    Mov,
+    If,
+    Else,
+    Loop,
+    While,
+    For,
+    In,
+    Fun,
+    Call,
+    Break,
+    Continue,
+    True,
+    False,
+    DotDot,
+
+    // Conditionals
+    Eq,
+    Neq,
+    Lt,
+    Gt,
+    Lte,
+    Gte,
+
+    EOF
 }
\ No newline at end of file