diff --git a/example.yapp b/example.yapp
new file mode 100644
index 0000000..30e5ac3
--- /dev/null
+++ b/example.yapp
@@ -0,0 +1,11 @@
+
+
+fn b() {
+    a();
+}
+
+fn a() {
+
+}
+
+
diff --git a/src/checked.rs b/src/checked.rs
new file mode 100644
index 0000000..ae77e83
--- /dev/null
+++ b/src/checked.rs
@@ -0,0 +1,63 @@
+#[derive(Clone, PartialEq, Debug)]
+pub struct Node {
+    pub kind: NodeKind,
+    pub typ: Type,
+}
+
+#[derive(Clone, PartialEq, Debug)]
+pub enum NodeKind {
+    Error,
+    Id(u64),
+    Int(i64),
+    String(String),
+    Group(Box<Node>),
+    Block(Vec<Node>),
+    Call {
+        subject: Box<Node>,
+        args: Vec<Node>,
+    },
+    If {
+        cond: Box<Node>,
+        truthy: Box<Node>,
+        falsy: Option<Box<Node>>,
+    },
+    Loop {
+        body: Box<Node>,
+    },
+    Break,
+    Assign {
+        subject: Box<Node>,
+        value: Box<Node>,
+    },
+    Let {
+        subject: Box<Node>,
+        value: Box<Node>,
+    },
+    Fn {
+        subject: Box<Node>,
+        params: Vec<Node>,
+        return_typ: Box<Node>,
+        body: Box<Node>,
+    },
+    Return {
+        value: Option<Box<Node>>,
+    },
+    Param {
+        subject: Box<Node>,
+        typ: Option<Type>,
+    },
+}
+
+#[derive(Clone, PartialEq, Debug)]
+pub enum Type {
+    Error,
+    Unit,
+    I32,
+    U32,
+    String,
+    Fn {
+        id: u64,
+        params: Vec<Node>,
+        return_typ: Box<Type>,
+    },
+}
diff --git a/src/checker.rs b/src/checker.rs
new file mode 100644
index 0000000..42b1700
--- /dev/null
+++ b/src/checker.rs
@@ -0,0 +1,383 @@
+#![allow(unused_variables)]
+
+use crate::{
+    checked::{Node, NodeKind, Type},
+    hash::hash,
+    itertewls::Itertewls,
+    parsed,
+    sym::Syms,
+};
+
+pub struct Checker {}
+
+impl Checker {
+    pub fn new() -> Self {
+        Self {}
+    }
+
+    pub fn check(&mut self, ast: &Vec<parsed::Node>) -> Vec<Node> {
+        let mut syms = Syms::new();
+        ast.into_iter()
+            .map(|stmt| self.check_expr(stmt, &mut syms))
+            .collect()
+    }
+
+    fn fn_scan<'syms>(
+        &mut self,
+        ast: &Vec<parsed::Node>,
+        syms: &mut Syms<'syms>,
+    ) -> Result<(), ()> {
+        for node in ast {
+            match node {
+                parsed::Node::Fn {
+                    subject,
+                    params,
+                    return_typ,
+                    body,
+                } => {
+                    let params = params.into_iter().map(|param| {
+                        let parsed::Node::Param { subject, typ } = param else { unreachable!() };
+                        let parsed::Node::Id(id) = subject.as_ref() else { unreachable!() };
+                        let typ = self.check_type(typ.as_ref().ok_or(())?);
+                        Ok((*id, self.node(NodeKind::Param { subject: Box::new(self.node(NodeKind::Id(*id), Type::Unit)), typ: Some(typ) }, Type::Unit)))
+                    }).collect::<Result<Vec<_>, _>>()?;
+
+                    if let Some(id) = params.iter().map(|(id, _)| *id).find_first_duplicate() {
+                        self.error("redefinition param");
+                        return Err(());
+                    }
+
+                    let parsed::Node::Id(id) = subject.as_ref() else { unreachable!() };
+
+                    if syms.defined_locally(*id) {
+                        self.error("redefinition fn");
+                        return Err(());
+                    }
+                    //syms.define(*id, typ.clone());
+                }
+                _ => {}
+            }
+        }
+        Ok(())
+    }
+
+    fn check_expr<'syms>(&mut self, node: &parsed::Node, syms: &mut Syms<'syms>) -> Node {
+        match node {
+            parsed::Node::Error => self.node(NodeKind::Error, Type::Unit),
+            parsed::Node::Id(id) => {
+                let Some(sym) = syms.get(*id) else {
+                    self.error("undefined >~<");
+                    return self.node(NodeKind::Error, Type::Error);
+                };
+                self.node(NodeKind::Id(*id), sym.typ)
+            }
+            parsed::Node::Int(value) => self.node(
+                NodeKind::Int(*value),
+                if *value as i32 > i32::MAX {
+                    Type::U32
+                } else {
+                    Type::I32
+                },
+            ),
+            parsed::Node::String(value) => self.node(NodeKind::String(value.clone()), Type::String),
+            parsed::Node::Group(expr) => {
+                let expr = self.check_expr(expr, syms);
+                let typ = expr.typ.clone();
+                self.node(NodeKind::Group(Box::new(expr)), typ)
+            }
+            parsed::Node::Block(stmts) => {
+                let mut child_syms = syms.child();
+                let stmts = stmts
+                    .into_iter()
+                    .map(|stmt| self.check_expr(stmt, &mut child_syms))
+                    .collect::<Vec<_>>();
+                let typ = stmts
+                    .last()
+                    .map(|stmt| stmt.typ.clone())
+                    .unwrap_or(Type::Unit);
+                self.node(NodeKind::Block(stmts), typ)
+            }
+            parsed::Node::Call { subject, args } => {
+                let subject = Box::new(self.check_expr(subject, syms));
+
+                let args = args
+                    .into_iter()
+                    .map(|arg| self.check_expr(arg, syms))
+                    .collect::<Vec<_>>();
+                let typ = 'br: {
+                    match subject.typ.clone() {
+                        Type::Fn {
+                            id: _,
+                            params,
+                            return_typ,
+                        } => {
+                            if args.len() != params.len() {
+                                self.error("too few/many args");
+                                break 'br Type::Error;
+                            }
+                            if args
+                                .iter()
+                                .zip(params)
+                                .map(|(arg, param)| self.compatible(&arg.typ, &param.typ))
+                                .any(|is_compatible| !is_compatible)
+                            {
+                                self.error("incorrect args");
+                                break 'br Type::Error;
+                            }
+                            *return_typ
+                        }
+                        _ => {
+                            self.error("not a function");
+                            Type::Error
+                        }
+                    }
+                };
+                self.node(NodeKind::Call { subject, args }, typ)
+            }
+            parsed::Node::If {
+                cond,
+                truthy,
+                falsy,
+            } => {
+                let cond = Box::new(self.check_expr(cond, syms));
+                let truthy = Box::new(self.check_expr(truthy, syms));
+                let falsy = falsy
+                    .as_ref()
+                    .map(|block| Box::new(self.check_expr(block, syms)));
+                let typ = 'br: {
+                    match falsy.as_ref().map(|block| block.typ.clone()) {
+                        Some(falsy_typ) => {
+                            if !self.compatible(&truthy.typ, &falsy_typ) {
+                                self.error("incompatible types #2");
+                                break 'br Type::Error;
+                            }
+                            falsy_typ
+                        }
+                        None => Type::Unit,
+                    }
+                };
+                self.node(
+                    NodeKind::If {
+                        cond,
+                        truthy,
+                        falsy,
+                    },
+                    typ,
+                )
+            }
+            parsed::Node::Loop { body } => {
+                let body = Box::new(self.check_expr(body, &mut syms.child()));
+                let typ = body.typ.clone();
+                self.node(NodeKind::Loop { body }, typ)
+            }
+            parsed::Node::Break => self.node(NodeKind::Break, Type::Unit),
+            parsed::Node::Assign { subject, value } => {
+                let subject = Box::new(self.check_expr(subject, syms));
+                let value = Box::new(self.check_expr(value, syms));
+
+                let typ = if !self.compatible(&subject.typ, &value.typ) {
+                    self.error("incompatible types #3");
+                    Type::Error
+                } else {
+                    subject.typ.clone()
+                };
+                self.node(NodeKind::Assign { subject, value }, typ)
+            }
+            parsed::Node::Let { subject, value } => {
+                let (subject, subject_typ) = match subject.as_ref() {
+                    parsed::Node::Param { subject, typ } => {
+                        (subject, typ.as_ref().map(|typ| self.check_type(typ)))
+                    }
+                    _ => unreachable!(),
+                };
+
+                let value = Box::new(self.check_expr(value, syms));
+                let typ = value.typ.clone();
+
+                if subject_typ
+                    .as_ref()
+                    .map(|subject_typ| !self.compatible(subject_typ, &typ))
+                    .unwrap_or(false)
+                {
+                    self.error("incompatible types #1");
+                    return self.node(NodeKind::Error, Type::Error);
+                }
+
+                let subject = match subject.as_ref() {
+                    parsed::Node::Id(id) => {
+                        if syms.defined_locally(*id) {
+                            self.error("redefinition");
+                            return self.node(NodeKind::Error, Type::Error);
+                        }
+                        syms.define(*id, typ.clone());
+                        Box::new(self.node(
+                            NodeKind::Param {
+                                subject: Box::new(self.node(NodeKind::Id(*id), Type::Unit)),
+                                typ: Some(Type::Unit),
+                            },
+                            Type::Unit,
+                        ))
+                    }
+                    _ => unreachable!(),
+                };
+
+                self.node(NodeKind::Let { subject, value }, typ)
+            }
+            parsed::Node::Fn {
+                subject,
+                params,
+                return_typ,
+                body,
+            } => {
+                todo!("symbol lookup");
+            }
+            parsed::Node::Return { value } => {
+                let value = value
+                    .as_ref()
+                    .map(|value| Box::new(self.check_expr(value, syms)));
+                let typ = value
+                    .as_ref()
+                    .map(|value| value.typ.clone())
+                    .unwrap_or(Type::Unit);
+                self.node(NodeKind::Return { value }, typ)
+            }
+            parsed::Node::Param { .. } => unreachable!("handle elsewhere"),
+        }
+    }
+
+    fn check_type(&self, node: &parsed::Node) -> Type {
+        match node {
+            parsed::Node::Error => Type::Error,
+            parsed::Node::Id(value) => {
+                if *value == hash("i32") {
+                    Type::I32
+                } else if *value == hash("u32") {
+                    Type::U32
+                } else {
+                    todo!("symbol lookup idk")
+                }
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    fn compatible(&self, typ_a: &Type, typ_b: &Type) -> bool {
+        typ_a == typ_b
+    }
+
+    fn node(&self, kind: NodeKind, typ: Type) -> Node {
+        Node { kind, typ }
+    }
+
+    fn error<S: Into<String>>(&mut self, msg: S) {
+        let msg = msg.into();
+        println!("checker error: {msg}");
+    }
+}
+
+#[test]
+fn test_checker() {
+    use crate::parser::Parser;
+    use NodeKind::{Block, Id, Int, Let, Param};
+    use Type::{Unit, I32};
+
+    let check = |text| Checker::new().check(&Parser::new(text).parse());
+
+    assert_eq!(
+        check("let a = 5; a;"),
+        vec![
+            Node {
+                kind: Let {
+                    subject: Box::new(Node {
+                        kind: Param {
+                            subject: Box::new(Node {
+                                kind: Id(hash("a")),
+                                typ: Unit
+                            }),
+                            typ: Some(Unit)
+                        },
+                        typ: Unit
+                    }),
+                    value: Box::new(Node {
+                        kind: Int(5),
+                        typ: I32
+                    })
+                },
+                typ: I32
+            },
+            Node {
+                kind: Id(hash("a")),
+                typ: I32
+            }
+        ]
+    );
+
+    assert_eq!(
+        check("let a = 5; a; { a; let b = 5; b; } a; b;"),
+        vec![
+            Node {
+                kind: Let {
+                    subject: Box::new(Node {
+                        kind: Param {
+                            subject: Box::new(Node {
+                                kind: Id(hash("a")),
+                                typ: Unit
+                            }),
+                            typ: Some(Unit)
+                        },
+                        typ: Unit
+                    }),
+                    value: Box::new(Node {
+                        kind: Int(5),
+                        typ: I32
+                    })
+                },
+                typ: I32
+            },
+            Node {
+                kind: Id(hash("a")),
+                typ: I32
+            },
+            Node {
+                kind: Block(vec![
+                    Node {
+                        kind: Id(hash("a")),
+                        typ: I32
+                    },
+                    Node {
+                        kind: Let {
+                            subject: Box::new(Node {
+                                kind: Param {
+                                    subject: Box::new(Node {
+                                        kind: Id(hash("b")),
+                                        typ: Unit
+                                    }),
+                                    typ: Some(Unit)
+                                },
+                                typ: Unit
+                            }),
+                            value: Box::new(Node {
+                                kind: Int(5),
+                                typ: I32
+                            })
+                        },
+                        typ: I32
+                    },
+                    Node {
+                        kind: Id(hash("b")),
+                        typ: I32
+                    }
+                ]),
+                typ: I32
+            },
+            Node {
+                kind: Id(hash("a")),
+                typ: I32
+            },
+            Node {
+                kind: NodeKind::Error,
+                typ: Type::Error
+            }
+        ]
+    );
+}
diff --git a/src/hash.rs b/src/hash.rs
new file mode 100644
index 0000000..4164ef7
--- /dev/null
+++ b/src/hash.rs
@@ -0,0 +1,7 @@
+use std::hash::{DefaultHasher, Hash, Hasher};
+
+pub fn hash<H: Hash>(value: H) -> u64 {
+    let mut hasher = DefaultHasher::new();
+    value.hash(&mut hasher);
+    hasher.finish()
+}
diff --git a/src/itertewls.rs b/src/itertewls.rs
new file mode 100644
index 0000000..76db65f
--- /dev/null
+++ b/src/itertewls.rs
@@ -0,0 +1,29 @@
+enum Duplicate<T: std::hash::Hash> {
+    None(std::collections::HashMap<T, T>),
+    Found(T),
+}
+
+pub trait Itertewls<T>
+where
+    Self: Iterator<Item = T> + Sized,
+{
+    fn find_first_duplicate(self) -> Option<T>;
+}
+
+impl<I, Item> Itertewls<Item> for I
+where
+    I: Iterator<Item = Item> + Sized,
+    Item: std::cmp::PartialEq + Clone,
+{
+    fn find_first_duplicate(mut self) -> Option<Item> {
+        self.try_fold(Vec::new(), |mut used, item| {
+            if used.contains(&item) {
+                Err(item)
+            } else {
+                used.push(item);
+                Ok(used)
+            }
+        })
+        .err()
+    }
+}
diff --git a/src/lexer.rs b/src/lexer.rs
new file mode 100644
index 0000000..e074eb5
--- /dev/null
+++ b/src/lexer.rs
@@ -0,0 +1,279 @@
+use crate::{
+    hash::hash,
+    token::{Token, TokenKind, TokenValue},
+};
+use std::{collections::HashMap, str::Chars};
+
+pub struct Lexer<'a> {
+    text: &'a str,
+    chars: Chars<'a>,
+    current: Option<char>,
+    index: usize,
+    line: i32,
+    col: i32,
+    symbols: HashMap<u64, String>,
+    keywords: HashMap<String, TokenKind>,
+}
+
+impl<'a> Lexer<'a> {
+    pub fn new(text: &'a str) -> Self {
+        let mut chars = text.chars();
+        let current = chars.next();
+        Self {
+            text,
+            chars,
+            current,
+            index: 0,
+            line: 1,
+            col: 1,
+            symbols: HashMap::new(),
+            keywords: Self::make_keywords(),
+        }
+    }
+
+    fn make_keywords() -> HashMap<String, TokenKind> {
+        let mut keywords = HashMap::new();
+        keywords.insert("if".to_string(), TokenKind::If);
+        keywords.insert("else".to_string(), TokenKind::Else);
+        keywords.insert("loop".to_string(), TokenKind::Loop);
+        keywords.insert("break".to_string(), TokenKind::Break);
+        keywords.insert("let".to_string(), TokenKind::Let);
+        keywords.insert("fn".to_string(), TokenKind::Fn);
+        keywords.insert("return".to_string(), TokenKind::Return);
+        keywords
+    }
+
+    pub fn symbols(self) -> HashMap<u64, String> {
+        self.symbols
+    }
+
+    fn next_token(&mut self) -> Option<Token> {
+        match self.current {
+            None => None,
+            Some(' ' | '\t' | '\n') => {
+                self.step();
+                self.next_token()
+            }
+            Some(ch @ ('a'..='z' | 'A'..='Z' | '_')) => {
+                let mut value = String::new();
+                value.push(ch);
+                self.step();
+                loop {
+                    match self.current {
+                        Some(ch @ ('a'..='z' | 'A'..='Z' | '0'..='9' | '_')) => {
+                            value.push(ch);
+                            self.step();
+                        }
+                        _ => {
+                            if let Some(kind) = self.keywords.get(&value) {
+                                return self.token(kind.clone());
+                            }
+                            let id = hash(&value);
+                            self.symbols.insert(id, value);
+                            break self.token_with_value(TokenKind::Id, TokenValue::Id(id));
+                        }
+                    }
+                }
+            }
+            Some(ch @ ('1'..='9')) => {
+                let mut value = String::new();
+                value.push(ch);
+                self.step();
+                loop {
+                    match self.current {
+                        Some(ch @ ('0'..='9' | '_')) => {
+                            value.push(ch);
+                            self.step();
+                        }
+                        _ => {
+                            let value = value.replace('_', "").parse::<i64>().unwrap();
+                            break self.token_with_value(TokenKind::Int, TokenValue::Int(value));
+                        }
+                    }
+                }
+            }
+            Some('"') => {
+                self.step();
+                let mut value = String::new();
+                loop {
+                    match self.current {
+                        Some('\\') => {
+                            self.step();
+                            match self.current {
+                                Some('n') => value.push('\n'),
+                                Some('r') => value.push('\r'),
+                                Some('t') => value.push('\t'),
+                                Some('0') => value.push('\0'),
+                                Some(ch) => value.push(ch),
+                                None => {
+                                    self.error("malformed string");
+                                    break self.token(TokenKind::Error);
+                                }
+                            }
+                        }
+                        Some('"') => {
+                            self.step();
+                            break self
+                                .token_with_value(TokenKind::String, TokenValue::String(value));
+                        }
+                        Some(ch) => {
+                            value.push(ch);
+                        }
+                        _ => {
+                            self.error("malformed string");
+                            break self.token(TokenKind::Error);
+                        }
+                    }
+                    self.step()
+                }
+            }
+            Some('/') => {
+                self.step();
+                match self.current {
+                    Some('/') => {
+                        self.step();
+                        loop {
+                            match self.current {
+                                None | Some('\n') => break self.next_token(),
+                                _ => {
+                                    self.step();
+                                }
+                            }
+                        }
+                    }
+                    Some('*') => {
+                        self.step();
+                        let mut lch = self.current;
+                        loop {
+                            match (lch, self.current) {
+                                (Some('*'), Some('/')) => break self.next_token(),
+                                (_, Some(ch)) => {
+                                    lch = Some(ch);
+                                    self.step();
+                                }
+                                (_, None) => {
+                                    self.error("malformed /**/ comment");
+                                    break self.token(TokenKind::Error);
+                                }
+                            }
+                        }
+                    }
+                    _ => todo!(),
+                }
+            }
+            Some('-') => {
+                self.step();
+                match self.current {
+                    Some('>') => {
+                        self.step();
+                        self.token(TokenKind::MinusLt)
+                    }
+                    _ => todo!(),
+                }
+            }
+            Some(ch @ ('0' | '(' | ')' | '{' | '}' | ':' | ',' | ';' | '=')) => {
+                self.step();
+                match ch {
+                    '0' => self.token_with_value(TokenKind::Int, TokenValue::Int(0)),
+                    '(' => self.token(TokenKind::LParen),
+                    ')' => self.token(TokenKind::RParen),
+                    '{' => self.token(TokenKind::LBrace),
+                    '}' => self.token(TokenKind::RBrace),
+                    ':' => self.token(TokenKind::Colon),
+                    ',' => self.token(TokenKind::Comma),
+                    ';' => self.token(TokenKind::Semicolon),
+                    '=' => self.token(TokenKind::Equal),
+                    _ => unreachable!(),
+                }
+            }
+            Some(ch) => {
+                self.error(format!("unknown char '{ch}'"));
+                self.token(TokenKind::Error)
+            }
+        }
+    }
+
+    fn step(&mut self) {
+        match self.current {
+            Some('\n') => {
+                self.line += 1;
+                self.col = 1;
+            }
+            Some(_) => {
+                self.col += 1;
+            }
+            _ => {}
+        }
+        self.current = self.chars.next();
+        if self.current.is_some() {
+            self.index += 1;
+        }
+    }
+
+    fn token(&self, kind: TokenKind) -> Option<Token> {
+        Some(Token {
+            kind,
+            value: TokenValue::None,
+            index: self.index,
+            line: self.line,
+            col: self.col,
+        })
+    }
+
+    fn token_with_value(&self, kind: TokenKind, value: TokenValue) -> Option<Token> {
+        Some(Token {
+            kind,
+            value,
+            index: self.index,
+            line: self.line,
+            col: self.col,
+        })
+    }
+
+    fn error<S: Into<String>>(&mut self, msg: S) {
+        let msg = msg.into();
+        println!("lexer error: {msg}, line {}", self.line)
+    }
+
+    fn done(&self) -> bool {
+        self.current.is_none()
+    }
+}
+
+impl Iterator for Lexer<'_> {
+    type Item = Token;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.next_token()
+    }
+}
+
+#[test]
+fn test_lexer() {
+    use TokenKind as TK;
+    use TokenValue as TV;
+
+    let lex = |text| {
+        Lexer::new(text)
+            .map(|token| (token.kind, token.value))
+            .collect::<Vec<_>>()
+    };
+
+    assert_eq!(lex("abc"), vec![(TK::Id, TV::Id(hash("abc")))]);
+    assert_eq!(lex("123"), vec![(TK::Int, TV::Int(123))]);
+    assert_eq!(lex("\"\""), vec![(TK::String, TV::String("".to_string()))]);
+    assert_eq!(
+        lex("\"hello\""),
+        vec![(TK::String, TV::String("hello".to_string()))]
+    );
+    assert_eq!(
+        lex("\"new\\nline\""),
+        vec![(TK::String, TV::String("new\nline".to_string()))]
+    );
+    assert_eq!(
+        lex("\"backslash\\\\\""),
+        vec![(TK::String, TV::String("backslash\\".to_string()))]
+    );
+    assert_eq!(lex("->"), vec![(TK::MinusLt, TV::None)]);
+    assert_eq!(lex("let"), vec![(TK::Let, TV::None)]);
+}
diff --git a/src/main.rs b/src/main.rs
index eeaf413..b2fe783 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,503 +1,14 @@
 #![allow(dead_code)]
 
-use std::{collections::HashMap, str::Chars};
-
-#[derive(Clone, PartialEq, Debug)]
-enum Expr {
-    Error,
-    Id(u64),
-    Int(i64),
-    String(String),
-    Block(Vec<Expr>),
-    Call {
-        subject: Box<Expr>,
-        args: Vec<Expr>,
-    },
-    If {
-        cond: Box<Expr>,
-        truthy: Box<Expr>,
-        falsy: Option<Box<Expr>>,
-    },
-    Loop {
-        body: Box<Expr>,
-    },
-    Break,
-    Assign {
-        subject: Box<Expr>,
-        value: Box<Expr>,
-    },
-    Let {
-        subject: Box<Expr>,
-        value: Box<Expr>,
-    },
-    Fn {
-        subject: Box<Expr>,
-        value: Box<Expr>,
-    },
-    Return {
-        value: Option<Box<Expr>>,
-    },
-}
-
-struct Parser<'a> {
-    lexer: Lexer<'a>,
-    current: Option<Token>,
-}
-
-impl<'a> Parser<'a> {
-    pub fn new(text: &'a str) -> Self {
-        let mut lexer = Lexer::new(text);
-        let current = lexer.next();
-        Self { lexer, current }
-    }
-
-    pub fn parse(&mut self) -> Vec<Expr> {
-        self.parse_file()
-    }
-
-    fn parse_file(&mut self) -> Vec<Expr> {
-        let mut stmts = Vec::new();
-        loop {
-            match self.current {
-                Some(_) => stmts.push(self.parse_stmt()),
-                None => break stmts,
-            }
-        }
-    }
-
-    fn parse_stmt(&mut self) -> Expr {
-        match self.curr_kind() {
-            Some(TokenKind::If) => todo!(),
-            Some(TokenKind::Loop) => todo!(),
-            Some(TokenKind::Fn) => todo!(),
-            _ => {
-                let stmt = match self.curr_kind() {
-                    Some(TokenKind::Let) => todo!(),
-                    Some(TokenKind::Break) => {
-                        self.step();
-                        Expr::Break
-                    }
-                    Some(TokenKind::Return) => {
-                        self.step();
-                        let value = match self.curr_kind() {
-                            Some(TokenKind::Semicolon) => None,
-                            _ => Some(Box::new(self.parse_expr())),
-                        };
-                        Expr::Return { value }
-                    }
-                    _ => self.parse_assign(),
-                };
-                match self.curr_kind() {
-                    Some(TokenKind::Semicolon) => {
-                        self.step();
-                        stmt
-                    }
-                    _ => {
-                        self.error("expected ';'");
-                        Expr::Error
-                    }
-                }
-            }
-        }
-    }
-
-    fn parse_assign(&mut self) -> Expr {
-        let subject = self.parse_expr();
-        match self.curr_kind() {
-            Some(TokenKind::Equal) => {
-                self.step();
-                let value = self.parse_expr();
-                Expr::Assign {
-                    subject: Box::new(subject),
-                    value: Box::new(value),
-                }
-            }
-            _ => subject,
-        }
-    }
-
-    fn parse_expr(&mut self) -> Expr {
-        self.parse_call()
-    }
-
-    fn parse_call(&mut self) -> Expr {
-        let mut subject = self.parse_value();
-        loop {
-            match self.curr_kind() {
-                Some(TokenKind::LParen) => {
-                    self.step();
-                    let mut args = Vec::new();
-                    match self.curr_kind() {
-                        None | Some(TokenKind::LParen) => {}
-                        Some(_) => {
-                            args.push(self.parse_expr());
-                            while let Some(TokenKind::Comma) = self.curr_kind() {
-                                self.step();
-                                if let Some(TokenKind::RParen) = self.curr_kind() {
-                                    break;
-                                }
-                                args.push(self.parse_expr());
-                            }
-                        }
-                    }
-                    match self.curr_kind() {
-                        Some(TokenKind::RParen) => {}
-                        _ => {
-                            self.error("expected ')'");
-                            return Expr::Error;
-                        }
-                    }
-                    self.step();
-                    subject = Expr::Call {
-                        subject: Box::new(subject),
-                        args,
-                    };
-                }
-                _ => break subject,
-            }
-        }
-    }
-
-    fn parse_value(&mut self) -> Expr {
-        match self.curr_kind() {
-            Some(TokenKind::Id) => {
-                let Some(Token {
-                    value: TokenValue::Id(value),
-                    ..
-                }) = self.current
-                else {
-                    unreachable!()
-                };
-                self.step();
-                Expr::Id(value)
-            }
-            Some(TokenKind::Int) => {
-                let Some(Token {
-                    value: TokenValue::Int(value),
-                    ..
-                }) = self.current
-                else {
-                    unreachable!()
-                };
-                self.step();
-                Expr::Int(value)
-            }
-            Some(TokenKind::String) => {
-                self.step();
-                let Some(Token {
-                    value: TokenValue::String(value),
-                    ..
-                }) = self.current.clone()
-                else {
-                    unreachable!()
-                };
-                Expr::String(value.clone())
-            }
-            _ => {
-                self.step();
-                self.error("expected value");
-                Expr::Error
-            }
-        }
-    }
-
-    fn error<S: Into<String>>(&mut self, msg: S) {
-        let msg = msg.into();
-        println!(
-            "parser error: {msg}, line {}",
-            self.current
-                .as_ref()
-                .map(|t| t.line.to_string())
-                .unwrap_or_else(|| "-".to_string())
-        )
-    }
-
-    fn step(&mut self) {
-        self.current = self.lexer.next();
-    }
-
-    fn curr_kind(&self) -> Option<TokenKind> {
-        self.current.as_ref().map(|t| t.kind.clone())
-    }
-}
-
-#[test]
-fn test_parser() {
-    use Expr::*;
-    assert_eq!(Parser::new("abc;").parse(), vec![Id(0)]);
-    assert_eq!(Parser::new("123;").parse(), vec![Int(123)]);
-    assert_eq!(Parser::new("0;").parse(), vec![Int(0)]);
-    assert_eq!(Parser::new("0;abc;").parse(), vec![Int(0), Id(0)]);
-    assert_eq!(
-        Parser::new("add(mul(12, 34), 56);").parse(),
-        vec![Call {
-            subject: Box::new(Id(0)),
-            args: vec![
-                Call {
-                    subject: Box::new(Id(1)),
-                    args: vec![Int(12), Int(34)]
-                },
-                Int(56)
-            ]
-        }]
-    );
-    assert_eq!(Parser::new("break;").parse(), vec![Break]);
-    assert_eq!(Parser::new("return;").parse(), vec![Return { value: None }]);
-    assert_eq!(
-        Parser::new("return add(1, 2);").parse(),
-        vec![Return {
-            value: Some(Box::new(Call {
-                subject: Box::new(Id(0)),
-                args: vec![Int(1), Int(2)]
-            }))
-        }]
-    );
-}
-
-#[derive(Clone, PartialEq, Debug)]
-struct Token {
-    kind: TokenKind,
-    value: TokenValue,
-    index: usize,
-    line: i32,
-    col: i32,
-}
-
-#[derive(Clone, PartialEq, Debug)]
-enum TokenKind {
-    Error,
-    Id,
-    Int,
-    String,
-    If,
-    Loop,
-    Break,
-    Let,
-    Fn,
-    Return,
-    LParen,
-    RParen,
-    LBrace,
-    RBrace,
-    Comma,
-    Semicolon,
-    Equal,
-}
-
-#[derive(Clone, PartialEq, Debug)]
-enum TokenValue {
-    None,
-    Id(u64),
-    Int(i64),
-    String(String),
-}
-
-struct Lexer<'a> {
-    text: &'a str,
-    chars: Chars<'a>,
-    current: Option<char>,
-    index: usize,
-    line: i32,
-    col: i32,
-    symbol_counter: u64,
-    symbols: HashMap<String, u64>,
-    keywords: HashMap<String, TokenKind>,
-}
-
-impl<'a> Lexer<'a> {
-    pub fn new(text: &'a str) -> Self {
-        let mut chars = text.chars();
-        let current = chars.next();
-        Self {
-            text,
-            chars,
-            current,
-            index: 0,
-            line: 1,
-            col: 1,
-            symbol_counter: 0,
-            symbols: HashMap::new(),
-            keywords: Self::make_keywords(),
-        }
-    }
-
-    fn make_keywords() -> HashMap<String, TokenKind> {
-        let mut keywords = HashMap::new();
-        keywords.insert("if".to_string(), TokenKind::If);
-        keywords.insert("loop".to_string(), TokenKind::Loop);
-        keywords.insert("break".to_string(), TokenKind::Break);
-        keywords.insert("let".to_string(), TokenKind::Let);
-        keywords.insert("fn".to_string(), TokenKind::Fn);
-        keywords.insert("return".to_string(), TokenKind::Return);
-        keywords
-    }
-
-    fn next_token(&mut self) -> Option<Token> {
-        match self.current {
-            None => None,
-            Some(' ' | '\t' | '\n') => {
-                self.step();
-                self.next_token()
-            }
-            Some(ch @ ('a'..='z' | 'A'..='Z' | '_')) => {
-                let mut value = String::new();
-                value.push(ch);
-                self.step();
-                loop {
-                    match self.current {
-                        Some(ch @ ('a'..='z' | 'A'..='Z' | '0'..='9' | '_')) => {
-                            value.push(ch);
-                            self.step();
-                        }
-                        _ => {
-                            if let Some(kind) = self.keywords.get(&value) {
-                                return self.token(kind.clone());
-                            }
-                            let id = self.symbol_counter;
-                            self.symbol_counter += 1;
-                            self.symbols.insert(value, id);
-                            break self.token_with_value(TokenKind::Id, TokenValue::Id(id));
-                        }
-                    }
-                }
-            }
-            Some(ch @ ('1'..='9')) => {
-                let mut value = String::new();
-                value.push(ch);
-                self.step();
-                loop {
-                    match self.current {
-                        Some(ch @ ('0'..='9' | '_')) => {
-                            value.push(ch);
-                            self.step();
-                        }
-                        _ => {
-                            let value = value.replace('_', "").parse::<i64>().unwrap();
-                            break self.token_with_value(TokenKind::Int, TokenValue::Int(value));
-                        }
-                    }
-                }
-            }
-            Some('/') => {
-                self.step();
-                match self.current {
-                    Some('/') => {
-                        self.step();
-                        loop {
-                            match self.current {
-                                None | Some('\n') => break self.next_token(),
-                                _ => {
-                                    self.step();
-                                }
-                            }
-                        }
-                    }
-                    Some('*') => {
-                        self.step();
-                        let mut lch = self.current;
-                        loop {
-                            match (lch, self.current) {
-                                (Some('*'), Some('/')) => break self.next_token(),
-                                (_, Some(ch)) => {
-                                    lch = Some(ch);
-                                    self.step();
-                                }
-                                (_, None) => {
-                                    self.error("malformed /**/ comment");
-                                    break self.token(TokenKind::Error);
-                                }
-                            }
-                        }
-                    }
-                    _ => todo!(),
-                }
-            }
-            Some(ch @ ('0' | '(' | ')' | '{' | '}' | ',' | ';' | '=')) => {
-                self.step();
-                match ch {
-                    '0' => self.token_with_value(TokenKind::Int, TokenValue::Int(0)),
-                    '(' => self.token(TokenKind::LParen),
-                    ')' => self.token(TokenKind::RParen),
-                    '{' => self.token(TokenKind::LBrace),
-                    '}' => self.token(TokenKind::RBrace),
-                    ',' => self.token(TokenKind::Comma),
-                    ';' => self.token(TokenKind::Semicolon),
-                    '=' => self.token(TokenKind::Equal),
-                    _ => unreachable!(),
-                }
-            }
-            _ => todo!(),
-        }
-    }
-
-    fn step(&mut self) {
-        match self.current {
-            Some('\n') => {
-                self.line += 1;
-                self.col = 1;
-            }
-            Some(_) => {
-                self.col += 1;
-            }
-            _ => {}
-        }
-        self.current = self.chars.next();
-        if self.current.is_some() {
-            self.index += 1;
-        }
-    }
-
-    fn token(&self, kind: TokenKind) -> Option<Token> {
-        Some(Token {
-            kind,
-            value: TokenValue::None,
-            index: self.index,
-            line: self.line,
-            col: self.col,
-        })
-    }
-
-    fn token_with_value(&self, kind: TokenKind, value: TokenValue) -> Option<Token> {
-        Some(Token {
-            kind,
-            value,
-            index: self.index,
-            line: self.line,
-            col: self.col,
-        })
-    }
-
-    fn error<S: Into<String>>(&mut self, msg: S) {
-        let msg = msg.into();
-        println!("lexer error: {msg}, line {}", self.line)
-    }
-
-    fn done(&self) -> bool {
-        self.current.is_none()
-    }
-}
-
-impl Iterator for Lexer<'_> {
-    type Item = Token;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.next_token()
-    }
-}
-
-#[test]
-fn test_lexer() {
-    assert_eq!(
-        Lexer::new("123").collect::<Vec<_>>(),
-        vec![Token {
-            kind: TokenKind::Int,
-            value: TokenValue::Int(123),
-            index: 2,
-            line: 1,
-            col: 4
-        }]
-    );
-}
+mod checked;
+mod checker;
+mod hash;
+mod itertewls;
+mod lexer;
+mod parsed;
+mod parser;
+mod sym;
+mod token;
 
 fn main() {
     println!("Hello, world!");
diff --git a/src/parsed.rs b/src/parsed.rs
new file mode 100644
index 0000000..7074005
--- /dev/null
+++ b/src/parsed.rs
@@ -0,0 +1,43 @@
+#[derive(Clone, PartialEq, Debug)]
+pub enum Node {
+    Error,
+    Id(u64),
+    Int(i64),
+    String(String),
+    Group(Box<Node>),
+    Block(Vec<Node>),
+    Call {
+        subject: Box<Node>,
+        args: Vec<Node>,
+    },
+    If {
+        cond: Box<Node>,
+        truthy: Box<Node>,
+        falsy: Option<Box<Node>>,
+    },
+    Loop {
+        body: Box<Node>,
+    },
+    Break,
+    Assign {
+        subject: Box<Node>,
+        value: Box<Node>,
+    },
+    Let {
+        subject: Box<Node>,
+        value: Box<Node>,
+    },
+    Fn {
+        subject: Box<Node>,
+        params: Vec<Node>,
+        return_typ: Box<Node>,
+        body: Box<Node>,
+    },
+    Return {
+        value: Option<Box<Node>>,
+    },
+    Param {
+        subject: Box<Node>,
+        typ: Option<Box<Node>>,
+    },
+}
diff --git a/src/parser.rs b/src/parser.rs
new file mode 100644
index 0000000..82bd0a1
--- /dev/null
+++ b/src/parser.rs
@@ -0,0 +1,478 @@
+use std::collections::HashMap;
+
+use crate::{
+    lexer::Lexer,
+    parsed::Node,
+    token::{Token, TokenKind, TokenValue},
+};
+
+pub struct Parser<'a> {
+    lexer: Lexer<'a>,
+    current: Option<Token>,
+}
+
+impl<'a> Parser<'a> {
+    pub fn new(text: &'a str) -> Self {
+        let mut lexer = Lexer::new(text);
+        let current = lexer.next();
+        Self { lexer, current }
+    }
+
+    pub fn parse(&mut self) -> Vec<Node> {
+        self.parse_file()
+    }
+
+    pub fn symbols(self) -> HashMap<u64, String> {
+        self.lexer.symbols()
+    }
+
+    fn parse_file(&mut self) -> Vec<Node> {
+        let mut stmts = Vec::new();
+        loop {
+            match self.current {
+                Some(_) => stmts.push(self.parse_stmt()),
+                None => break stmts,
+            }
+        }
+    }
+
+    fn parse_stmt(&mut self) -> Node {
+        match self.curr_kind() {
+            Some(TokenKind::LBrace) => self.parse_block(),
+            Some(TokenKind::If) => self.parse_if(),
+            Some(TokenKind::Loop) => self.parse_loop(),
+            Some(TokenKind::Fn) => self.parse_fn(),
+            _ => {
+                let stmt = match self.curr_kind() {
+                    Some(TokenKind::Let) => self.parse_let(),
+                    Some(TokenKind::Break) => {
+                        self.step();
+                        Node::Break
+                    }
+                    Some(TokenKind::Return) => {
+                        self.step();
+                        let value = match self.curr_kind() {
+                            Some(TokenKind::Semicolon) => None,
+                            _ => Some(Box::new(self.parse_expr())),
+                        };
+                        Node::Return { value }
+                    }
+                    _ => self.parse_assign(),
+                };
+                match self.curr_kind() {
+                    Some(TokenKind::Semicolon) => {
+                        self.step();
+                        stmt
+                    }
+                    _ => {
+                        self.error("expected ';'");
+                        Node::Error
+                    }
+                }
+            }
+        }
+    }
+
+    fn parse_fn(&mut self) -> Node {
+        self.step();
+        if !self.curr_is(TokenKind::Id) {
+            self.error("expected id");
+            return Node::Error;
+        }
+        let subject = Box::new(self.parse_id());
+        if !self.curr_is(TokenKind::LParen) {
+            self.error("expected '('");
+            return Node::Error;
+        }
+        let params = match self.parse_fn_params() {
+            Ok(params) => params,
+            Err(expr) => return expr,
+        };
+        if !self.curr_is(TokenKind::MinusLt) {
+            self.error("expected '->'");
+            return Node::Error;
+        }
+        self.step();
+        let return_typ = Box::new(self.parse_typ());
+        if !self.curr_is(TokenKind::LBrace) {
+            self.error("expected '{'");
+            return Node::Error;
+        }
+        let body = Box::new(self.parse_block());
+        Node::Fn {
+            subject,
+            params,
+            return_typ,
+            body,
+        }
+    }
+
+    fn parse_fn_params(&mut self) -> Result<Vec<Node>, Node> {
+        self.step();
+        let mut params = Vec::new();
+        if !self.curr_is(TokenKind::RParen) {
+            if !self.curr_is(TokenKind::RParen) {
+                self.error("expected ')'");
+                return Err(Node::Error);
+            }
+            if !self.curr_is(TokenKind::Id) {
+                self.error("expected id");
+                return Err(Node::Error);
+            }
+            params.push(self.parse_param());
+            while let Some(TokenKind::Comma) = self.curr_kind() {
+                self.step();
+                if self.curr_is(TokenKind::RParen) {
+                    self.error("expected ')'");
+                    break;
+                }
+                params.push(self.parse_param());
+            }
+        }
+        if !self.curr_is(TokenKind::RParen) {
+            self.error("expected ')'");
+            return Err(Node::Error);
+        }
+        self.step();
+        Ok(params)
+    }
+
+    fn parse_let(&mut self) -> Node {
+        self.step();
+        if !self.curr_is(TokenKind::Id) {
+            self.error("expected id");
+            return Node::Error;
+        }
+        let subject = self.parse_param();
+        if !self.curr_is(TokenKind::Equal) {
+            self.error("expected '='");
+            return Node::Error;
+        }
+        self.step();
+        let value = self.parse_expr();
+        Node::Let {
+            subject: Box::new(subject),
+            value: Box::new(value),
+        }
+    }
+
+    fn parse_param(&mut self) -> Node {
+        let subject = Box::new(self.parse_id());
+        let typ = if let Some(TokenKind::Comma) = self.curr_kind() {
+            self.step();
+            Some(Box::new(self.parse_typ()))
+        } else {
+            None
+        };
+        Node::Param { subject, typ }
+    }
+
+    fn parse_typ(&mut self) -> Node {
+        match self.curr_kind() {
+            Some(TokenKind::Id) => self.parse_id(),
+            _ => {
+                self.error("expected type");
+                self.step();
+                Node::Error
+            }
+        }
+    }
+
+    fn parse_assign(&mut self) -> Node {
+        let subject = self.parse_expr();
+        match self.curr_kind() {
+            Some(TokenKind::Equal) => {
+                self.step();
+                let value = self.parse_expr();
+                Node::Assign {
+                    subject: Box::new(subject),
+                    value: Box::new(value),
+                }
+            }
+            _ => subject,
+        }
+    }
+
+    fn parse_expr(&mut self) -> Node {
+        self.parse_call()
+    }
+
+    fn parse_call(&mut self) -> Node {
+        let mut subject = self.parse_value();
+        loop {
+            match self.curr_kind() {
+                Some(TokenKind::LParen) => {
+                    self.step();
+                    let mut args = Vec::new();
+                    match self.curr_kind() {
+                        None | Some(TokenKind::LParen) => {}
+                        Some(_) => {
+                            args.push(self.parse_expr());
+                            while let Some(TokenKind::Comma) = self.curr_kind() {
+                                self.step();
+                                if let Some(TokenKind::RParen) = self.curr_kind() {
+                                    break;
+                                }
+                                args.push(self.parse_expr());
+                            }
+                        }
+                    }
+                    match self.curr_kind() {
+                        Some(TokenKind::RParen) => {}
+                        _ => {
+                            self.error("expected ')'");
+                            return Node::Error;
+                        }
+                    }
+                    self.step();
+                    subject = Node::Call {
+                        subject: Box::new(subject),
+                        args,
+                    };
+                }
+                _ => break subject,
+            }
+        }
+    }
+
+    fn parse_value(&mut self) -> Node {
+        match self.curr_kind() {
+            Some(TokenKind::Id) => self.parse_id(),
+            Some(TokenKind::Int) => self.parse_int(),
+            Some(TokenKind::String) => self.parse_string(),
+            Some(TokenKind::LParen) => self.parse_group(),
+            Some(TokenKind::LBrace) => self.parse_block(),
+            Some(TokenKind::If) => self.parse_if(),
+            Some(TokenKind::Loop) => self.parse_loop(),
+            _ => {
+                self.error("expected value");
+                self.step();
+                Node::Error
+            }
+        }
+    }
+
+    fn parse_id(&mut self) -> Node {
+        let Some(Token {
+                kind: TokenKind::Id,
+                value: TokenValue::Id(value),
+                ..
+            }) = self.current
+            else {
+                unreachable!()
+            };
+        self.step();
+        Node::Id(value)
+    }
+
+    fn parse_int(&mut self) -> Node {
+        let Some(Token {
+                kind: TokenKind::Int,
+                value: TokenValue::Int(value),
+                ..
+            }) = self.current
+            else {
+                unreachable!()
+            };
+        self.step();
+        Node::Int(value)
+    }
+
+    fn parse_string(&mut self) -> Node {
+        let Some(Token {
+                kind: TokenKind::String,
+                    value: TokenValue::String(value),
+                    ..
+                }) = self.current.clone()
+                else {
+                    unreachable!()
+                };
+        self.step();
+        Node::String(value.clone())
+    }
+
+    fn parse_group(&mut self) -> Node {
+        self.step();
+        let expr = Box::new(self.parse_expr());
+        if !self.curr_is(TokenKind::RParen) {
+            self.error("expected ')'");
+            return Node::Error;
+        }
+        self.step();
+        Node::Group(expr)
+    }
+
+    fn parse_block(&mut self) -> Node {
+        self.step();
+        let mut stmts = Vec::new();
+        loop {
+            match self.curr_kind() {
+                Some(TokenKind::RBrace) => {
+                    self.step();
+                    break Node::Block(stmts);
+                }
+                _ => stmts.push(self.parse_stmt()),
+            }
+        }
+    }
+
+    fn parse_if(&mut self) -> Node {
+        self.step();
+        let cond = Box::new(self.parse_expr());
+        if !self.curr_is(TokenKind::LBrace) {
+            self.error("expected '}'");
+            return Node::Error;
+        }
+        let truthy = Box::new(self.parse_block());
+        let falsy = match self.curr_kind() {
+            Some(TokenKind::Else) => {
+                self.step();
+                if !self.curr_is(TokenKind::LBrace) {
+                    self.error("expected '}'");
+                    return Node::Error;
+                }
+                Some(Box::new(self.parse_block()))
+            }
+            _ => None,
+        };
+        Node::If {
+            cond,
+            truthy,
+            falsy,
+        }
+    }
+
+    fn parse_loop(&mut self) -> Node {
+        self.step();
+        if !self.curr_is(TokenKind::LBrace) {
+            self.error("expected '}'");
+            return Node::Error;
+        }
+        let body = Box::new(self.parse_block());
+        Node::Loop { body }
+    }
+
+    fn error<S: Into<String>>(&mut self, msg: S) {
+        let msg = msg.into();
+        println!(
+            "parser error: {msg}, line {}",
+            self.current
+                .as_ref()
+                .map(|t| t.line.to_string())
+                .unwrap_or_else(|| "-".to_string())
+        )
+    }
+
+    fn step(&mut self) {
+        self.current = self.lexer.next();
+    }
+
+    fn curr_is(&self, kind: TokenKind) -> bool {
+        self.curr_kind() == Some(kind)
+    }
+
+    fn curr_kind(&self) -> Option<TokenKind> {
+        self.current.as_ref().map(|t| t.kind.clone())
+    }
+}
+
+#[test]
+fn test_parser() {
+    use crate::hash::hash;
+    use Node::*;
+
+    let parse = |text| Parser::new(text).parse();
+
+    #[allow(non_snake_case)]
+    fn B<T>(v: T) -> Box<T> {
+        Box::new(v)
+    }
+
+    assert_eq!(Parser::new("abc;").parse(), vec![Id(hash("abc"))]);
+    assert_eq!(Parser::new("123;").parse(), vec![Int(123)]);
+    assert_eq!(
+        Parser::new("\"hello\";").parse(),
+        vec![String("hello".to_string())]
+    );
+    assert_eq!(Parser::new("0;").parse(), vec![Int(0)]);
+    assert_eq!(Parser::new("0;abc;").parse(), vec![Int(0), Id(hash("abc"))]);
+    assert_eq!(
+        parse("add(mul(12, 34), 56);"),
+        vec![Call {
+            subject: B(Id(hash("add"))),
+            args: vec![
+                Call {
+                    subject: B(Id(hash("mul"))),
+                    args: vec![Int(12), Int(34)]
+                },
+                Int(56)
+            ]
+        }]
+    );
+    assert_eq!(
+        parse("a = 123;"),
+        vec![Assign {
+            subject: B(Id(hash("a"))),
+            value: B(Int(123))
+        }]
+    );
+    assert_eq!(parse("break;"), vec![Break]);
+    assert_eq!(parse("return;"), vec![Return { value: None }]);
+    assert_eq!(
+        parse("return add(1, 2);"),
+        vec![Return {
+            value: Some(B(Call {
+                subject: B(Id(hash("add"))),
+                args: vec![Int(1), Int(2)]
+            }))
+        }]
+    );
+    assert_eq!(
+        parse("a = 5;"),
+        vec![Assign {
+            subject: B(Id(hash("a"))),
+            value: B(Int(5))
+        }]
+    );
+    assert_eq!(
+        parse("let a = 5;"),
+        vec![Let {
+            subject: B(Param {
+                subject: B(Id(hash("a"))),
+                typ: None
+            }),
+            value: B(Int(5))
+        }]
+    );
+    assert_eq!(
+        parse("fn test() -> i32 {}"),
+        vec![Fn {
+            subject: B(Id(hash("test"))),
+            params: vec![],
+            return_typ: B(Id(hash("i32"))),
+            body: B(Block(vec![]))
+        }]
+    );
+    assert_eq!(
+        parse("if 0 {}"),
+        vec![If {
+            cond: B(Int(0)),
+            truthy: B(Block(vec![])),
+            falsy: None
+        }]
+    );
+    assert_eq!(
+        parse("if 0 {} else {}"),
+        vec![If {
+            cond: B(Int(0)),
+            truthy: B(Block(vec![])),
+            falsy: Some(B(Block(vec![]))),
+        }]
+    );
+    assert_eq!(
+        parse("loop {}"),
+        vec![Loop {
+            body: B(Block(vec![])),
+        }]
+    );
+}
diff --git a/src/sym.rs b/src/sym.rs
new file mode 100644
index 0000000..5b73808
--- /dev/null
+++ b/src/sym.rs
@@ -0,0 +1,49 @@
+#![allow(unused_variables)]
+use std::collections::HashMap;
+
+use crate::checked::Type;
+
+#[derive(Clone, PartialEq, Debug)]
+pub struct Sym {
+    pub id: u64,
+    pub typ: Type,
+}
+
+pub struct Syms<'syms> {
+    parent: Option<&'syms Syms<'syms>>,
+    map: HashMap<u64, Sym>,
+}
+
+impl<'syms> Syms<'syms> {
+    pub fn new() -> Self {
+        Self {
+            parent: None,
+            map: HashMap::new(),
+        }
+    }
+
+    pub fn child(&'syms self) -> Self {
+        Self {
+            parent: Some(self),
+            map: HashMap::new(),
+        }
+    }
+
+    pub fn get(&self, id: u64) -> Option<Sym> {
+        if let Some(sym) = self.map.get(&id) {
+            return Some(sym.clone());
+        }
+        if let Some(parent) = self.parent {
+            return parent.get(id);
+        }
+        None
+    }
+
+    pub fn defined_locally(&self, id: u64) -> bool {
+        self.map.contains_key(&id)
+    }
+
+    pub fn define(&mut self, id: u64, typ: Type) {
+        self.map.insert(id, Sym { id, typ });
+    }
+}
diff --git a/src/token.rs b/src/token.rs
new file mode 100644
index 0000000..a84f7c2
--- /dev/null
+++ b/src/token.rs
@@ -0,0 +1,40 @@
+#[derive(Clone, PartialEq, Debug)]
+pub struct Token {
+    pub kind: TokenKind,
+    pub value: TokenValue,
+    pub index: usize,
+    pub line: i32,
+    pub col: i32,
+}
+
+#[derive(Clone, PartialEq, Debug)]
+pub enum TokenKind {
+    Error,
+    Id,
+    Int,
+    String,
+    If,
+    Else,
+    Loop,
+    Break,
+    Let,
+    Fn,
+    Return,
+    LParen,
+    RParen,
+    LBrace,
+    RBrace,
+    Colon,
+    Comma,
+    Semicolon,
+    Equal,
+    MinusLt,
+}
+
+#[derive(Clone, PartialEq, Debug)]
+pub enum TokenValue {
+    None,
+    Id(u64),
+    Int(i64),
+    String(String),
+}