diff --git a/grammar.bnf b/grammar.bnf
index 86296ff..4a29053 100644
--- a/grammar.bnf
+++ b/grammar.bnf
@@ -10,11 +10,12 @@
 <ident> ::= <id-start>
         | <ident> <id-cont>
 
-<program> ::= <definition>
+<program> ::= <declaration>*
 
-<definition> ::= <var-decl> | <fn-decl>
+<declaration> ::= <fn-decl> | <global-decl>
 
-<fn-decl> ::= fn <ident> '(' <parameter-list> ,? ')' (-> <type-name>)? <block>
+<fn-proto> ::= fn <ident> '(' <parameter-list> ,? ')' (-> <type-name>)?
+<fn-decl> ::= <fn-proto> <block>
 
 <parameter-list> ::= <parameter>
                  | <parameter-list> , <parameter>
@@ -29,7 +30,7 @@
             | <var-decl> ';'
 <return-statement> ::= return <expr>? ';'
 <expr-statement> ::= <expr> ';'
-<assignment-statement> ::= <ident> <assignment-op> <expr> ';'
+<assignment-statement> ::= <expr> <assignment-op> <expr> ';'
 <assignment-op> ::= |= | &= | ^= | /= | *= | %= | <<= | >>= | += | -= | =
 
 <expr> ::= <or-expr>
@@ -58,7 +59,15 @@
 <prefix-expr> ::= <prefix-op> <as-expr>
 <prefix-op> ::= ! - + & *
 
-<as-expr> ::= <primary-expr> as <type-name>
+<as-expr> ::= <postfix-expr> as <type-name>
+
+<postfix-expr> ::= <primary-expr>
+               | <postfix-expr> '(' (<argument-list>,?)? ')'
+
+<argument-list> ::= <argument>
+                 | <parameter-list> , <argument>
+<argument> ::= <expr>
+           | <ident>: <expr>
 
 <primary-expr> ::= <constant>
                | <literal>
@@ -66,6 +75,7 @@
                | '(' <expr> ')'
 
 <var-decl> ::= (let | var) <ident> (':' <type-name>)? ( = <expr> )?
+<global-decl> ::= <var-decl> ';'
 
 <type-name> ::= <ident>
             | <primitive-type>
@@ -78,7 +88,6 @@
 
 <integral-type> ::= ('u' | 'i') <digits>+
 <floating-type> ::= 'f'('32' | '64')
-                
 
 <constant> ::= <integral-constant>
            | <floating-constant>
diff --git a/src/ast.rs b/src/ast.rs
new file mode 100644
index 0000000..21838e1
--- /dev/null
+++ b/src/ast.rs
@@ -0,0 +1,217 @@
+use std::num::NonZero;
+
+pub type Node = NonZero<u32>;
+
+pub enum Tag {
+    Root,
+    FunctionProto {
+        /// Ident
+        name: Node,
+        /// ParameterList
+        parameters: Option<Node>,
+        return_type: Node,
+    },
+    ParameterList {
+        /// [Parameter]
+        parameters: Vec<Node>,
+    },
+    Parameter {
+        /// Ident
+        name: Node,
+        /// TypeName
+        ty: Node,
+    },
+    TypeName {
+        /// Ident | PrimitiveType | Pointer
+        inner: Node,
+    },
+    Pointer {
+        /// TypeName
+        pointee: Node,
+    },
+    PointerQualifier {
+        constness: bool,
+    },
+    IntegralType(IntegralType),
+    PrimitiveType(PrimitiveType),
+    Decl {
+        /// FunctionDecl | VarDecl
+        inner: Node,
+    },
+    FunctionDecl {
+        /// FunctionProto
+        proto: Node,
+        /// Block
+        body: Node,
+    },
+    Ident {
+        name: String,
+    },
+    IntegralConstant {
+        bits: u64,
+        ty: IntegralType,
+    },
+    FloatingConstant {
+        bits: u64,
+        ty: FloatingType,
+    },
+    Block {
+        /// ReturnStmt | ExprStmt | VarDecl
+        statements: Node,
+        trailing_expr: Option<Node>,
+    },
+    ReturnStmt {
+        expr: Option<Node>,
+    },
+    ExprStmt {
+        expr: Node,
+    },
+    VarDecl {
+        let_or_var: LetOrVar,
+        /// Ident
+        name: Node,
+        /// TypeName
+        explicit_type: Option<Node>,
+        expr: Option<Node>,
+    },
+    CallExpr {
+        /// Ident | Expr
+        lhs: Node,
+        /// ArgumentList
+        rhs: Option<Node>,
+    },
+    ArgumentList {
+        /// [Argument]
+        parameters: Vec<Node>,
+    },
+    Argument {
+        /// Ident
+        name: Option<Node>,
+        /// expr
+        expr: Node,
+    },
+    ExplicitCast {
+        lhs: Node,
+        /// TypeName
+        typename: Node,
+    },
+    Deref {
+        lhs: Node,
+    },
+    Ref {
+        lhs: Node,
+    },
+    Not {
+        lhs: Node,
+    },
+    Negate {
+        lhs: Node,
+    },
+    Or {
+        lhs: Node,
+        rhs: Node,
+    },
+    And {
+        lhs: Node,
+        rhs: Node,
+    },
+    BitOr {
+        lhs: Node,
+        rhs: Node,
+    },
+    BitAnd {
+        lhs: Node,
+        rhs: Node,
+    },
+    BitXOr {
+        lhs: Node,
+        rhs: Node,
+    },
+    Eq {
+        lhs: Node,
+        rhs: Node,
+    },
+    NEq {
+        lhs: Node,
+        rhs: Node,
+    },
+    Lt {
+        lhs: Node,
+        rhs: Node,
+    },
+    Gt {
+        lhs: Node,
+        rhs: Node,
+    },
+    Le {
+        lhs: Node,
+        rhs: Node,
+    },
+    Ge {
+        lhs: Node,
+        rhs: Node,
+    },
+    Shl {
+        lhs: Node,
+        rhs: Node,
+    },
+    Shr {
+        lhs: Node,
+        rhs: Node,
+    },
+    Add {
+        lhs: Node,
+        rhs: Node,
+    },
+    Sub {
+        lhs: Node,
+        rhs: Node,
+    },
+    Mul {
+        lhs: Node,
+        rhs: Node,
+    },
+    Rem {
+        lhs: Node,
+        rhs: Node,
+    },
+    Div {
+        lhs: Node,
+        rhs: Node,
+    },
+    Assign {
+        lhs: Node,
+        rhs: Node,
+    },
+}
+
+pub enum LetOrVar {
+    Let,
+    Var,
+}
+
+pub struct IntegralType {
+    pub signed: bool,
+    pub bits: u16,
+}
+
+pub enum FloatingType {
+    Binary32,
+    Binary64,
+}
+
+impl IntegralType {
+    pub fn u32() -> IntegralType {
+        Self {
+            signed: false,
+            bits: 32,
+        }
+    }
+}
+
+pub enum PrimitiveType {
+    FloatingType(FloatingType),
+    IntegralType(Node),
+    Bool,
+    Void,
+}
diff --git a/src/lexer.rs b/src/lexer.rs
index 0bfe059..a3053e3 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -6,7 +6,7 @@ use crate::common::FallibleParse;
 use crate::common::NextIf;
 
 #[derive(Debug, thiserror::Error)]
-pub enum LexerError {
+pub enum Error {
     #[error("{0}")]
     StringError(String),
     #[error("Exp part of floating constant had no digits.")]
@@ -25,7 +25,7 @@ pub enum LexerError {
     ExpectedIdStartForIdentifier,
 }
 
-pub type LexerResult<T> = core::result::Result<T, LexerError>;
+pub type Result<T> = core::result::Result<T, Error>;
 
 #[derive(Debug, Clone)]
 pub struct Chars<'a> {
@@ -52,6 +52,38 @@ impl<'a> Chars<'a> {
         self.offset
     }
 
+    pub fn get_source_span(
+        &self,
+        start: u32,
+        end: u32,
+    ) -> std::ops::RangeInclusive<SourceLocation> {
+        let (start_l, start_c) = {
+            let range = self.get_range(0, start);
+            range.chars().fold((1u32, 0u32), |(line, col), c| {
+                if c == '\n' {
+                    (line + 1, 0)
+                } else {
+                    (line, col + 1)
+                }
+            })
+        };
+        let (end_l, end_c) = {
+            let range = self.get_range(start, end);
+            range.chars().fold((start_l, start_c), |(line, col), c| {
+                if c == '\n' {
+                    (line + 1, 0)
+                } else {
+                    (line, col + 1)
+                }
+            })
+        };
+
+        core::ops::RangeInclusive::new(
+            SourceLocation::new(start_l, start_c),
+            SourceLocation::new(end_l, end_c),
+        )
+    }
+
     pub fn get_range(&self, start: u32, end: u32) -> &str {
         unsafe { core::str::from_utf8_unchecked(&self.bytes[start as usize..end as usize]) }
     }
@@ -77,6 +109,101 @@ pub struct Tokenizer<'a> {
     tokens: Vec<TokenPos>,
 }
 
+#[derive(Debug, Clone)]
+pub struct TokenIterator<'a> {
+    tokenizer: &'a Tokenizer<'a>,
+    offset: usize,
+}
+
+impl<'a> TokenIterator<'a> {
+    pub fn expect_token(&mut self, token: Token) -> crate::parser::Result<TokenItem<'a>> {
+        self.next_if(|item| item.token() == token)
+            .ok_or(crate::parser::Error::ExpectedTokenNotFound(token))
+    }
+
+    pub fn eat_token(&mut self, token: Token) -> Option<TokenItem<'a>> {
+        self.next_if(|item| item.token() == token)
+    }
+    pub fn peek_token(&mut self) -> Option<TokenItem<'a>> {
+        self.clone().next()
+    }
+    pub fn peek_token_or_err(&mut self) -> crate::parser::Result<TokenItem<'a>> {
+        self.clone()
+            .next()
+            .ok_or(crate::parser::Error::UnexpectedEndOfTokens)
+    }
+
+    pub fn peek_expect_token(&mut self, token: Token) -> crate::parser::Result<TokenItem<'a>> {
+        self.clone()
+            .next()
+            .ok_or(crate::parser::Error::ExpectedTokenNotFound(token))
+    }
+
+    pub fn is_next_token(&mut self, token: Token) -> bool {
+        self.clone().next_if(|item| item.token() == token).is_some()
+    }
+}
+
+pub struct TokenItem<'a> {
+    tokenizer: &'a Tokenizer<'a>,
+    inner: TokenPos,
+}
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Hash)]
+pub struct SourceLocation {
+    pub line: u32,
+    pub column: u32,
+}
+
+impl SourceLocation {
+    pub fn new(line: u32, column: u32) -> Self {
+        Self { line, column }
+    }
+}
+
+impl<'a> TokenItem<'a> {
+    pub fn token(&self) -> Token {
+        self.inner.token
+    }
+
+    pub fn lexeme(&self) -> &str {
+        self.tokenizer
+            .source
+            .get_range(self.inner.start, self.inner.end)
+    }
+
+    pub fn source_location(&self) -> std::ops::RangeInclusive<SourceLocation> {
+        self.tokenizer
+            .source
+            .get_source_span(self.inner.start, self.inner.end)
+    }
+}
+
+impl<'a> Iterator for TokenIterator<'a> {
+    type Item = TokenItem<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.tokenizer.tokens.len() >= self.offset {
+            None
+        } else {
+            let index = self.offset;
+            self.offset += 1;
+            match self.tokenizer.tokens[index].token {
+                Token::SlashSlash
+                | Token::SlashSlashSlash
+                | Token::SlashStar
+                | Token::SlashStarStar
+                | Token::Comment
+                | Token::DocComment => self.next(),
+                _ => Some(Self::Item {
+                    tokenizer: self.tokenizer,
+                    inner: self.tokenizer.tokens[index],
+                }),
+            }
+        }
+    }
+}
+
 macro_rules! next_or_eof {
     ($expr:expr) => {
         match $expr.next() {
@@ -141,13 +268,20 @@ macro_rules! residual {
 }
 
 impl<'a> Tokenizer<'a> {
-    fn push_token(&mut self, token: Token, start: u32, end: u32) -> LexerResult<()> {
+    pub fn iter(&self) -> TokenIterator {
+        TokenIterator {
+            tokenizer: self,
+            offset: 0,
+        }
+    }
+
+    fn push_token(&mut self, token: Token, start: u32, end: u32) -> Result<()> {
         self.tokens.push(TokenPos::new(token, start, end));
 
         Ok(())
     }
 
-    pub fn next_token(&mut self) -> LexerResult<()> {
+    pub fn next_token(&mut self) -> Result<()> {
         self.source
             .take_while_ref(|&c| crate::common::is_whitespace(c))
             .count();
@@ -256,7 +390,7 @@ impl<'a> Tokenizer<'a> {
 
         self.source
             .next_if(|&c| crate::common::is_id_start(c))
-            .ok_or(LexerError::ExpectedIdStartForIdentifier)?;
+            .ok_or(Error::ExpectedIdStartForIdentifier)?;
         self.source
             .take_while_ref(|&c| crate::common::is_id_continue(c))
             .count();
@@ -267,7 +401,7 @@ impl<'a> Tokenizer<'a> {
 
 /// IntegralType <-
 ///     ( 'u' | 'i' ) DIGITS+
-fn try_parse_integral_type(source: &mut Chars) -> LexerResult<Option<()>> {
+fn try_parse_integral_type(source: &mut Chars) -> Result<Option<()>> {
     if !source.next_if(|&c| c == 'u' || c == 'i').is_some() {
         return Ok(None);
     }
@@ -277,14 +411,14 @@ fn try_parse_integral_type(source: &mut Chars) -> LexerResult<Option<()>> {
         .count()
         <= 0
     {
-        return Err(LexerError::IntegralTypeExpectedDigit);
+        return Err(Error::IntegralTypeExpectedDigit);
     };
 
     Ok(Some(()))
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-enum Radix {
+pub enum Radix {
     Hex,
     Bin,
     Dec,
@@ -296,21 +430,29 @@ impl Radix {
     unsafe fn from_char_unchecked(c: char) -> Self {
         match c.to_ascii_lowercase() {
             'o' => Self::Oct,
-            'b' => Self::Oct,
-            'x' => Self::Oct,
-            'd' => Self::Oct,
+            'b' => Self::Bin,
+            'x' => Self::Hex,
+            'd' => Self::Dec,
             _ => unreachable!(),
         }
     }
     fn from_char(c: char) -> Option<Self> {
         match c.to_ascii_lowercase() {
             'o' => Some(Self::Oct),
-            'b' => Some(Self::Oct),
-            'x' => Some(Self::Oct),
-            'd' => Some(Self::Oct),
+            'b' => Some(Self::Bin),
+            'x' => Some(Self::Hex),
+            'd' => Some(Self::Dec),
             _ => None,
         }
     }
+    fn radix(self) -> u8 {
+        match self {
+            Radix::Hex => 16,
+            Radix::Bin => 2,
+            Radix::Oct => 8,
+            Radix::Dec => 10,
+        }
+    }
     fn to_token(self) -> Token {
         match self {
             Radix::Hex => Token::IntegerHexConstant,
@@ -319,7 +461,62 @@ impl Radix {
             Radix::Dec => Token::IntegerConstant,
         }
     }
-    fn is_digit(self) -> fn(char) -> bool {
+    pub fn from_token(token: Token) -> Option<Self> {
+        match token {
+            Token::IntegerHexConstant => Some(Radix::Hex),
+            Token::IntegerBinConstant => Some(Radix::Bin),
+            Token::IntegerOctConstant => Some(Radix::Oct),
+            Token::IntegerConstant => Some(Radix::Dec),
+            _ => None,
+        }
+    }
+    pub fn folding_method(self) -> fn(u64, char) -> u64 {
+        match self {
+            Radix::Hex => {
+                fn fold(acc: u64, c: char) -> u64 {
+                    let digit = match c {
+                        '0'..='9' => c as u8 - b'0',
+                        'a'..='f' => c as u8 - b'a',
+                        'A'..='F' => c as u8 - b'A',
+                        _ => unreachable!(),
+                    };
+                    acc + digit as u64 * 16
+                }
+                fold
+            }
+            Radix::Bin => {
+                fn fold(acc: u64, c: char) -> u64 {
+                    let digit = match c {
+                        '0'..='1' => c as u8 - b'0',
+                        _ => unreachable!(),
+                    };
+                    acc + digit as u64 * 2
+                }
+                fold
+            }
+            Radix::Dec => {
+                fn fold(acc: u64, c: char) -> u64 {
+                    let digit = match c {
+                        '0'..='9' => c as u8 - b'0',
+                        _ => unreachable!(),
+                    };
+                    acc + digit as u64 * 10
+                }
+                fold
+            }
+            Radix::Oct => {
+                fn fold(acc: u64, c: char) -> u64 {
+                    let digit = match c {
+                        '0'..='7' => c as u8 - b'0',
+                        _ => unreachable!(),
+                    };
+                    acc + digit as u64 * 8
+                }
+                fold
+            }
+        }
+    }
+    pub fn is_digit(self) -> fn(char) -> bool {
         match self {
             Radix::Hex => crate::common::is_hex_digit,
             Radix::Bin => crate::common::is_bin_digit,
@@ -337,7 +534,7 @@ fn parse_digit_part(
     source: &mut Chars,
     allow_leading_underscore: bool,
     radix: Radix,
-) -> LexerResult<()> {
+) -> Result<()> {
     let radix = radix.is_digit();
 
     if allow_leading_underscore {
@@ -345,9 +542,9 @@ fn parse_digit_part(
     }
     let _need_digit = source.next_if(|&c| radix(c)).ok_or_else(|| {
         if source.peek() == Some('_') {
-            LexerError::NumericalConstantDigitLeadingUnderscore
+            Error::NumericalConstantDigitLeadingUnderscore
         } else {
-            LexerError::NumericalConstantDigitNoDigit
+            Error::NumericalConstantDigitNoDigit
         }
     })?;
     let _rest = source.take_while_ref(|&c| radix(c) || c == '_').count();
@@ -361,7 +558,7 @@ fn parse_digit_part(
 ///
 /// EXP_PART <-
 ///     (`e`|`E`) (`-`|`+`)? DEC_DIGITS
-fn try_parse_exp_part(source: &mut Chars) -> LexerResult<Option<()>> {
+fn try_parse_exp_part(source: &mut Chars) -> Result<Option<()>> {
     if source.next_if(|&c| c.to_ascii_lowercase() == 'e').is_some() {
         let _sign = source.next_if(|&c| c == '-' || c == '+');
         if source
@@ -370,7 +567,7 @@ fn try_parse_exp_part(source: &mut Chars) -> LexerResult<Option<()>> {
             .lt(&1)
         {
             // need digits following exp notation
-            Err(LexerError::FloatingConstantExpPartNoDigit)
+            Err(Error::FloatingConstantExpPartNoDigit)
         } else {
             Ok(Some(()))
         }
@@ -387,7 +584,7 @@ fn try_parse_exp_part(source: &mut Chars) -> LexerResult<Option<()>> {
 ///    DEC_DIGITS FloatingType?
 ///    `.` DEC_DIGITS EXP_PART? FloatingType?
 ///    DEC_DIGITS `.` DEC_DIGITS? EXP_PART? FloatingType?
-fn parse_constant(source: &mut Chars) -> LexerResult<Token> {
+fn parse_constant(source: &mut Chars) -> Result<Token> {
     let zero = source.next_if(|&c| c == '0').is_some();
     let radix = zero
         .then(|| source.next_if_map(|c| Radix::from_char(c)))
@@ -423,7 +620,7 @@ fn parse_constant(source: &mut Chars) -> LexerResult<Token> {
         let digits = source.next_tuple::<(char, char)>();
         if !(digits == Some(('6', '4')) || digits == Some(('3', '2'))) {
             // need either f64 or f32 here!
-            return Err(LexerError::FloatingConstantInvalidTrailingType);
+            return Err(Error::FloatingConstantInvalidTrailingType);
         }
         true
     } else {
diff --git a/src/lib.rs b/src/lib.rs
index 1fdc1f2..500e683 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,8 @@
 #![feature(extract_if, iter_advance_by)]
+#![allow(dead_code, unused_macros)]
 
+mod ast;
 mod common;
 mod lexer;
+mod parser;
 mod tokens;
diff --git a/src/parser.rs b/src/parser.rs
new file mode 100644
index 0000000..2b266f7
--- /dev/null
+++ b/src/parser.rs
@@ -0,0 +1,425 @@
+use std::collections::HashMap;
+
+use itertools::Itertools;
+
+use crate::{
+    ast::{FloatingType, IntegralType, LetOrVar, Node, PrimitiveType, Tag},
+    lexer::{Radix, TokenIterator},
+    tokens::Token,
+};
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("Unexpected end of token iter.")]
+    UnexpectedEndOfTokens,
+    #[error("Expected primitive type.")]
+    ExpectedPrimitiveType,
+    #[error("Expected token {0}.")]
+    ExpectedTokenNotFound(Token),
+    #[error("Dummy message.")]
+    ExpectedLetOrVar,
+}
+
+pub type Result<T> = core::result::Result<T, Error>;
+
+pub struct Tree {
+    nodes: Vec<Tag>,
+}
+
+impl Tree {
+    pub fn new() -> Tree {
+        Self {
+            nodes: vec![Tag::Root],
+        }
+    }
+
+    fn push_tag(&mut self, tag: Tag) -> Node {
+        let node = Node::new(self.nodes.len() as u32).unwrap();
+        self.nodes.push(tag);
+
+        node
+    }
+
+    /// returns (signed, bits)
+    fn parse_integral_type(lexeme: &str) -> IntegralType {
+        let mut iter = lexeme.chars();
+        let signed = match iter.next().unwrap() {
+            'u' => false,
+            'i' | 's' => true,
+            _ => unreachable!(),
+        };
+
+        let bits = iter.fold(0u16, |acc, c| {
+            let digit = c as u8 - b'0';
+            acc + digit as u16 * 10
+        });
+
+        IntegralType { signed, bits }
+    }
+
+    fn parse_integral_constant(token: Token, lexeme: &str) -> (u64, IntegralType) {
+        let radix = Radix::from_token(token).unwrap();
+
+        // TODO: figure out how to do this safely for bigger types, whether to
+        // wrap, saturate, or else.
+        let iter = &mut lexeme.char_indices();
+        let value = iter
+            .take_while_ref(|&(_, c)| radix.is_digit()(c) || c == '_')
+            .filter(|&(_, c)| c != '_')
+            .fold(0u64, |acc, (_, c)| radix.folding_method()(acc, c));
+
+        let ty = match iter.clone().next() {
+            Some((_, 'u')) | Some((_, 'i')) => {
+                Self::parse_integral_type(&lexeme[iter.next().unwrap().0..])
+            }
+            _ => IntegralType::u32(),
+        };
+
+        (value, ty)
+    }
+
+    fn parse_floating_constant(_token: Token, lexeme: &str) -> (u64, FloatingType) {
+        // let (dot, exp) = match token {
+        //     Token::DotFloatingExpConstant => (true, true),
+        //     Token::DotFloatingConstant => (true, false),
+        //     Token::FloatingExpConstant => (false, true),
+        //     Token::FloatingConstant => (false, false),
+        //     _ => unreachable!(),
+        // };
+
+        let lexeme = lexeme
+            .strip_suffix("f32")
+            .map(|l| (l, FloatingType::Binary32))
+            .unwrap_or(
+                lexeme
+                    .strip_suffix("f64")
+                    .map(|l| (l, FloatingType::Binary64))
+                    .unwrap_or((lexeme, FloatingType::Binary64)),
+            );
+
+        let bits = match lexeme.1 {
+            FloatingType::Binary32 => lexeme.0.parse::<f32>().unwrap().to_bits() as u64,
+            FloatingType::Binary64 => lexeme.0.parse::<f64>().unwrap().to_bits() as u64,
+        };
+
+        (bits, lexeme.1)
+    }
+
+    fn parse_ident(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let name = tokens.expect_token(Token::Ident)?.lexeme().to_owned();
+        Ok(self.push_tag(Tag::Ident { name }))
+    }
+
+    pub fn parse_primitive_type(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let token = tokens.next().ok_or(Error::UnexpectedEndOfTokens)?;
+        let prim = match token.token() {
+            Token::IntegralType => {
+                let int = Self::parse_integral_type(token.lexeme());
+                PrimitiveType::IntegralType(self.push_tag(Tag::IntegralType(int)))
+            }
+            Token::Void => PrimitiveType::Void,
+            Token::Bool => PrimitiveType::Bool,
+            Token::F32 => PrimitiveType::FloatingType(FloatingType::Binary32),
+            Token::F64 => PrimitiveType::FloatingType(FloatingType::Binary64),
+            _ => {
+                return Err(Error::ExpectedPrimitiveType);
+            }
+        };
+
+        Ok(self.push_tag(Tag::PrimitiveType(prim)))
+    }
+
+    pub fn parse_pointer(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        tokens.expect_token(Token::Star)?;
+        let _constness = tokens.eat_token(Token::Const);
+        let typename = self.parse_typename(tokens)?;
+
+        Ok(self.push_tag(Tag::Pointer { pointee: typename }))
+    }
+
+    pub fn parse_typename(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        match tokens.peek_token_or_err()?.token() {
+            Token::Star => self.parse_pointer(tokens),
+            Token::Ident => Ok(self.push_tag(Tag::Ident {
+                name: tokens.next().unwrap().lexeme().to_owned(),
+            })),
+            _ => self.parse_primitive_type(tokens),
+        }
+    }
+
+    pub fn parse_var_decl(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let let_or_var = match tokens
+            .eat_token(Token::Let)
+            .or_else(|| tokens.eat_token(Token::Var))
+            .map(|itm| itm.token())
+            .ok_or(Error::ExpectedLetOrVar)?
+        {
+            Token::Let => LetOrVar::Let,
+            Token::Var => LetOrVar::Var,
+            _ => unreachable!(),
+        };
+
+        let name = self.parse_ident(tokens)?;
+
+        let explicit_type = if tokens.eat_token(Token::Colon).is_some() {
+            Some(self.parse_typename(tokens)?)
+        } else {
+            None
+        };
+
+        let expr = if tokens.eat_token(Token::Equal).is_some() {
+            Some(self.parse_expr(tokens)?)
+        } else {
+            None
+        };
+
+        Ok(self.push_tag(Tag::VarDecl {
+            let_or_var,
+            name,
+            explicit_type,
+            expr,
+        }))
+    }
+
+    pub fn parse_global_decl(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let node = self.parse_var_decl(tokens)?;
+        tokens.expect_token(Token::Semi)?;
+
+        Ok(node)
+    }
+
+    pub fn parse_parameter(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let name = self.parse_ident(tokens)?;
+        tokens.expect_token(Token::Colon)?;
+        let ty = self.parse_typename(tokens)?;
+
+        Ok(self.push_tag(Tag::Parameter { name, ty }))
+    }
+
+    pub fn parse_parameter_list(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let mut parameters = Vec::new();
+
+        loop {
+            parameters.push(self.parse_parameter(tokens)?);
+            if !tokens.eat_token(Token::Comma).is_some() {
+                break;
+            }
+            if !tokens.is_next_token(Token::Ident) {
+                break;
+            }
+        }
+
+        todo!()
+    }
+
+    pub fn parse_fn_proto(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        tokens.expect_token(Token::Fn)?;
+        let name = self.parse_ident(tokens)?;
+        tokens.expect_token(Token::OpenParens)?;
+        let parameters = if !tokens.is_next_token(Token::CloseParens) {
+            Some(self.parse_parameter_list(tokens)?)
+        } else {
+            None
+        };
+        tokens.expect_token(Token::CloseParens)?;
+
+        let return_type = if tokens.eat_token(Token::MinusGreater).is_some() {
+            self.parse_typename(tokens)?
+        } else {
+            self.push_tag(Tag::PrimitiveType(PrimitiveType::Void))
+        };
+
+        Ok(self.push_tag(Tag::FunctionProto {
+            name,
+            parameters,
+            return_type,
+        }))
+    }
+
+    pub fn parse_fn_decl(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let proto = self.parse_fn_proto(tokens)?;
+
+        let body = self.parse_block(tokens)?;
+
+        Ok(self.push_tag(Tag::FunctionDecl { proto, body }))
+    }
+
+    pub fn parse_block(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        todo!()
+    }
+
+    pub fn parse_assignment(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        todo!()
+    }
+
+    pub fn parse_return_stmt(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        todo!()
+    }
+
+    pub fn parse_statement(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        todo!()
+    }
+
+    pub fn parse_binary_expr(
+        &mut self,
+        tokens: &mut TokenIterator,
+        precedence: u32,
+    ) -> Result<Node> {
+        let mut node = self.parse_prefix_expr(tokens)?;
+
+        loop {
+            let Some(tok) = tokens.peek_token() else {
+                break;
+            };
+            let Some(prec) = PRECEDENCE_MAP.get(&tok.token()).cloned() else {
+                break;
+            };
+
+            if prec < precedence {
+                break;
+            }
+
+            let tok = tokens.next().unwrap();
+
+            let lhs = node;
+            let rhs = self.parse_binary_expr(tokens, prec + 1)?;
+
+            let tag = match tok.token() {
+                Token::PipePipe => Tag::Or { lhs, rhs },
+                Token::AmpersandAmpersand => Tag::And { lhs, rhs },
+                Token::Pipe => Tag::BitOr { lhs, rhs },
+                Token::Caret => Tag::BitXOr { lhs, rhs },
+                Token::Ampersand => Tag::BitAnd { lhs, rhs },
+                Token::BangEqual => Tag::NEq { lhs, rhs },
+                Token::EqualEqual => Tag::Eq { lhs, rhs },
+                Token::LessEqual => Tag::Le { lhs, rhs },
+                Token::GreaterEqual => Tag::Ge { lhs, rhs },
+                Token::Less => Tag::Lt { lhs, rhs },
+                Token::Greater => Tag::Gt { lhs, rhs },
+                Token::GreaterGreater => Tag::Shr { lhs, rhs },
+                Token::LessLess => Tag::Shl { lhs, rhs },
+                Token::Plus => Tag::Add { lhs, rhs },
+                Token::Minus => Tag::Sub { lhs, rhs },
+                Token::Percent => Tag::Rem { lhs, rhs },
+                Token::Star => Tag::Mul { lhs, rhs },
+                Token::Slash => Tag::Div { lhs, rhs },
+                _ => unreachable!(),
+            };
+
+            node = self.push_tag(tag);
+        }
+
+        Ok(node)
+    }
+
+    pub fn parse_prefix_expr(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        match tokens.peek_token_or_err()?.token() {
+            Token::Bang => {
+                _ = tokens.next();
+                let lhs = self.parse_as_expr(tokens)?;
+                Ok(self.push_tag(Tag::Not { lhs }))
+            }
+            Token::Minus => {
+                _ = tokens.next();
+                let lhs = self.parse_as_expr(tokens)?;
+                Ok(self.push_tag(Tag::Negate { lhs }))
+            }
+            Token::Plus => {
+                _ = tokens.next();
+                self.parse_as_expr(tokens)
+            }
+            Token::Ampersand => {
+                _ = tokens.next();
+                let lhs = self.parse_as_expr(tokens)?;
+                Ok(self.push_tag(Tag::Ref { lhs }))
+            }
+            Token::Star => {
+                _ = tokens.next();
+                let lhs = self.parse_as_expr(tokens)?;
+                Ok(self.push_tag(Tag::Deref { lhs }))
+            }
+            _ => self.parse_as_expr(tokens),
+        }
+    }
+
+    pub fn parse_as_expr(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let expr = self.parse_primary_expr(tokens)?;
+
+        if tokens.eat_token(Token::As).is_some() {
+            let typename = self.parse_typename(tokens)?;
+            Ok(self.push_tag(Tag::ExplicitCast {
+                lhs: expr,
+                typename,
+            }))
+        } else {
+            Ok(expr)
+        }
+    }
+
+    pub fn parse_postfix_expr(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        // TODO
+        self.parse_primary_expr(tokens)
+    }
+
+    pub fn parse_primary_expr(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        let token = tokens.peek_token_or_err()?;
+        match token.token() {
+            Token::Ident => Ok(self.parse_ident(tokens)?),
+            Token::IntegerBinConstant
+            | Token::IntegerHexConstant
+            | Token::IntegerOctConstant
+            | Token::IntegerConstant => {
+                let (bits, ty) = Self::parse_integral_constant(token.token(), token.lexeme());
+                Ok(self.push_tag(Tag::IntegralConstant { bits, ty }))
+            }
+            Token::FloatingConstant
+            | Token::FloatingExpConstant
+            | Token::DotFloatingConstant
+            | Token::DotFloatingExpConstant => {
+                let (bits, ty) = Self::parse_floating_constant(token.token(), token.lexeme());
+
+                Ok(self.push_tag(Tag::FloatingConstant { bits, ty }))
+            }
+            Token::OpenParens => {
+                _ = tokens.next();
+                let node = self.parse_expr(tokens)?;
+                tokens.expect_token(Token::CloseParens)?;
+                Ok(node)
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    pub fn parse_expr(&mut self, tokens: &mut TokenIterator) -> Result<Node> {
+        todo!()
+    }
+
+    pub fn parse_program(&mut self, tokens: &mut TokenIterator) -> Result<Vec<Node>> {
+        todo!()
+    }
+
+    pub fn parse(&mut self, tokens: TokenIterator) {}
+}
+
+static PRECEDENCE_MAP: std::sync::LazyLock<HashMap<Token, u32>> = std::sync::LazyLock::new(|| {
+    HashMap::from([
+        (Token::PipePipe, 10),
+        (Token::AmpersandAmpersand, 20),
+        (Token::Pipe, 30),
+        (Token::Caret, 40),
+        (Token::Ampersand, 50),
+        (Token::BangEqual, 60),
+        (Token::EqualEqual, 60),
+        (Token::LessEqual, 70),
+        (Token::GreaterEqual, 70),
+        (Token::Less, 70),
+        (Token::Greater, 70),
+        (Token::GreaterGreater, 80),
+        (Token::LessLess, 80),
+        (Token::Plus, 90),
+        (Token::Minus, 90),
+        (Token::Percent, 100),
+        (Token::Star, 100),
+        (Token::Slash, 100),
+    ])
+});