diff --git a/trunk_lexer/src/token.rs b/trunk_lexer/src/token.rs
index 959857d..3dd3372 100644
--- a/trunk_lexer/src/token.rs
+++ b/trunk_lexer/src/token.rs
@@ -1,11 +1,11 @@
 pub type Span = (usize, usize);
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum OpenTagKind {
     Full,
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum TokenKind {
     Identifier(String),
     Variable(String),
diff --git a/trunk_parser/src/ast.rs b/trunk_parser/src/ast.rs
index 4dfd9f0..b4f88c9 100644
--- a/trunk_parser/src/ast.rs
+++ b/trunk_parser/src/ast.rs
@@ -1,3 +1,5 @@
+use trunk_lexer::TokenKind;
+
 pub type Block = Vec<Statement>;
 pub type Program = Block;
 
@@ -48,5 +50,27 @@ pub enum Statement {
 
 #[derive(Debug, PartialEq, Clone)]
 pub enum Expression {
+    Int(i64),
     Variable(String),
+    Infix(Box<Self>, InfixOp, Box<Self>),
+    Call(Box<Self>, Vec<Self>),
+    Identifier(String),
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum InfixOp {
+    Add,
+    Sub,
+    LessThan,
+}
+
+impl From<TokenKind> for InfixOp {
+    fn from(k: TokenKind) -> Self {
+        match k {
+            TokenKind::Plus => Self::Add,
+            TokenKind::Minus => Self::Sub,
+            TokenKind::LessThan => Self::LessThan,
+            _ => unreachable!()
+        }
+    }
 }
\ No newline at end of file
diff --git a/trunk_parser/src/parser.rs b/trunk_parser/src/parser.rs
index f6a9f88..f6f5a34 100644
--- a/trunk_parser/src/parser.rs
+++ b/trunk_parser/src/parser.rs
@@ -1,5 +1,7 @@
+use std::vec::IntoIter;
+use std::iter::Peekable;
 use trunk_lexer::{Token, TokenKind};
-use crate::{Program, Statement, Block};
+use crate::{Program, Statement, Block, Expression};
 
 macro_rules! expect {
     ($actual:expr, $expected:pat, $out:expr, $message:literal) => {
@@ -36,56 +38,190 @@ impl Parser {
         let mut iter = tokens.into_iter().peekable();
 
         while let Some(t) = iter.next() {
-            match t.kind {
-                TokenKind::OpenTag(_) => {},
-                TokenKind::InlineHtml(html) => {
-                    program.push(Statement::InlineHtml(html));
-                },
-                TokenKind::Function => {
-                    let name = expect!(iter.next(), TokenKind::Identifier(i), i, "expected identifier");
-
-                    expect!(iter.next(), TokenKind::LeftParen, "expected (");
-
-                    let mut params = Vec::new();
-
-                    while let Some(n) = iter.peek() && n.kind != TokenKind::RightParen {
-                        // TODO: Support variable types and default values.
-                        params.push(expect!(iter.next(), TokenKind::Variable(v), v, "expected variable").into());
-                        
-                        if let Some(Token { kind: TokenKind::Comma, .. }) = iter.peek() {
-                            iter.next();
-                        }
-                    }
-
-                    expect!(iter.next(), TokenKind::RightParen, "expected )");
-
-                    // TODO: Support return types here.
-
-                    expect!(iter.next(), TokenKind::LeftBrace, "expected {");
-
-                    // TODO: Parse body here.
-
-                    expect!(iter.next(), TokenKind::RightBrace, "expected }");
-
-                    program.push(Statement::Function { name: name.into(), params, body: Block::new() });
-                },
-                _ => todo!("unhandled token: {:?}", t)
+            if let TokenKind::OpenTag(_) = t.kind {
+                continue;
             }
+
+            program.push(self.statement(t, &mut iter)?);
         }
 
         Ok(program)
     }
+
+    #[allow(dead_code)]
+    fn statement(&self, t: Token, tokens: &mut Peekable<IntoIter<Token>>) -> Result<Statement, ParseError> {
+        Ok(match t.kind {
+            TokenKind::InlineHtml(html) => Statement::InlineHtml(html),
+            TokenKind::If => {
+                expect!(tokens.next(), TokenKind::LeftParen, "expected (");
+
+                let condition = self.expression(tokens, 0)?;
+
+                expect!(tokens.next(), TokenKind::RightParen, "expected )");
+
+                // TODO: Support one-liner if statements.
+                expect!(tokens.next(), TokenKind::LeftBrace, "expected {");
+
+                let mut then = Block::new();
+                while let Some(t) = tokens.peek() && t.kind != TokenKind::RightBrace {
+                    then.push(self.statement(tokens.next().unwrap(), tokens)?);
+                }
+
+                // TODO: Support one-liner if statements.
+                expect!(tokens.next(), TokenKind::RightBrace, "expected }");
+
+                Statement::If { condition, then }
+            },
+            TokenKind::Return => {
+                if let Some(Token { kind: TokenKind::SemiColon, .. }) = tokens.peek() {
+                    Statement::Return { value: None }
+                } else {
+                    let ret = Statement::Return { value: self.expression(tokens, 0).ok() };
+                    expect!(tokens.next(), TokenKind::SemiColon, "expected semi-colon");
+                    ret
+                }
+            },
+            TokenKind::Function => {
+                let name = expect!(tokens.next(), TokenKind::Identifier(i), i, "expected identifier");
+
+                expect!(tokens.next(), TokenKind::LeftParen, "expected (");
+
+                let mut params = Vec::new();
+
+                while let Some(n) = tokens.peek() && n.kind != TokenKind::RightParen {
+                    // TODO: Support variable types and default values.
+                    params.push(expect!(tokens.next(), TokenKind::Variable(v), v, "expected variable").into());
+                    
+                    if let Some(Token { kind: TokenKind::Comma, .. }) = tokens.peek() {
+                        tokens.next();
+                    }
+                }
+
+                expect!(tokens.next(), TokenKind::RightParen, "expected )");
+
+                // TODO: Support return types here.
+
+                expect!(tokens.next(), TokenKind::LeftBrace, "expected {");
+
+                let mut body = Block::new();
+
+                while let Some(n) = tokens.peek() && n.kind != TokenKind::RightBrace {
+                    body.push(self.statement(tokens.next().unwrap(), tokens)?);
+                }
+
+                expect!(tokens.next(), TokenKind::RightBrace, "expected }");
+
+                Statement::Function { name: name.into(), params, body }
+            },
+            _ => todo!("unhandled token: {:?}", t)
+        })
+    }
+
+    fn expression(&self, tokens: &mut Peekable<IntoIter<Token>>, bp: u8) -> Result<Expression, ParseError> {
+        if let None = tokens.peek() {
+            return Err(ParseError::UnexpectedEndOfFile);
+        }
+
+        let t = tokens.next().unwrap();
+
+        let mut lhs = match t.kind {
+            TokenKind::Variable(v) => Expression::Variable(v),
+            TokenKind::Int(i) => Expression::Int(i),
+            TokenKind::Identifier(i) => Expression::Identifier(i),
+            _ => todo!("lhs: {:?}", t.kind),
+        };
+
+        loop {
+            let t = tokens.peek();
+
+            let kind = match tokens.peek() {
+                Some(Token { kind: TokenKind::SemiColon, .. }) | None => break,
+                Some(Token { kind, .. }) => kind.clone(),
+            };
+
+            if let Some(lbp) = postfix_binding_power(&kind) {
+                if lbp < bp {
+                    break;
+                }
+
+                tokens.next();
+
+                let op = kind.clone();
+                lhs = self.postfix(tokens, lhs, &op)?;
+
+                continue;
+            }
+
+            if let Some((lbp, rbp)) = infix_binding_power(&kind) {
+                if lbp < bp {
+                    break;
+                }
+
+                tokens.next();
+
+                let op = kind.clone();
+                let rhs = self.expression(tokens, rbp)?;
+
+                lhs = infix(lhs, op, rhs);
+                continue;
+            }
+
+            break;
+        }
+
+        Ok(lhs)
+    }
+
+    fn postfix(&self, tokens: &mut Peekable<IntoIter<Token>>, lhs: Expression, op: &TokenKind) -> Result<Expression, ParseError> {
+        Ok(match op {
+            TokenKind::LeftParen => {
+                let mut args = Vec::new();
+                while let Some(t) = tokens.peek() && t.kind != TokenKind::RightParen {
+                    args.push(self.expression(tokens, 0)?);
+
+                    if let Some(Token { kind: TokenKind::Comma, .. }) = tokens.peek() {
+                        tokens.next();
+                    }
+                }
+
+                expect!(tokens.next(), TokenKind::RightParen, "expected )");
+    
+                Expression::Call(Box::new(lhs), args)
+            },
+            _ => todo!("postfix: {:?}", op),
+        })
+    }
+}
+
+fn infix(lhs: Expression, op: TokenKind, rhs: Expression) -> Expression {
+    Expression::Infix(Box::new(lhs), op.into(), Box::new(rhs))
+}
+
+fn infix_binding_power(t: &TokenKind) -> Option<(u8, u8)> {
+    Some(match t {
+        TokenKind::Plus | TokenKind::Minus => (11, 12),
+        TokenKind::LessThan => (9, 10),
+        _ => return None,
+    })
+}
+
+fn postfix_binding_power(t: &TokenKind) -> Option<u8> {
+    Some(match t {
+        TokenKind::LeftParen => 19,
+        _ => return None
+    })
 }
 
 #[derive(Debug)]
 pub enum ParseError {
     ExpectedToken(String),
+    UnexpectedEndOfFile,
 }
 
 #[cfg(test)]
 mod tests {
     use trunk_lexer::Lexer;
-    use crate::{Statement, Block, Param};
+    use crate::{Statement, Block, Param, Expression, ast::InfixOp};
     use super::Parser;
 
     macro_rules! function {
@@ -116,6 +252,58 @@ mod tests {
         ]);
     }
 
+    #[test]
+    fn fib() {
+        assert_ast("\
+        <?php
+
+        function fib($n) {
+            if ($n < 2) {
+                return $n;
+            }
+
+            return fib($n - 1) + fib($n - 2);
+        }", &[
+            function!("fib", &["n"], &[
+                Statement::If {
+                    condition: Expression::Infix(
+                        Box::new(Expression::Variable("n".into())),
+                        InfixOp::LessThan,
+                        Box::new(Expression::Int(2)),
+                    ),
+                    then: vec![
+                        Statement::Return { value: Some(Expression::Variable("n".into())) }
+                    ],
+                },
+                Statement::Return {
+                    value: Some(Expression::Infix(
+                        Box::new(Expression::Call(
+                            Box::new(Expression::Identifier("fib".into())),
+                            vec![
+                                Expression::Infix(
+                                    Box::new(Expression::Variable("n".into())),
+                                    InfixOp::Sub,
+                                    Box::new(Expression::Int(1)),
+                                )
+                            ]
+                        )),
+                        InfixOp::Add,
+                        Box::new(Expression::Call(
+                            Box::new(Expression::Identifier("fib".into())),
+                            vec![
+                                Expression::Infix(
+                                    Box::new(Expression::Variable("n".into())),
+                                    InfixOp::Sub,
+                                    Box::new(Expression::Int(2)),
+                                )
+                            ]
+                        )),
+                    ))
+                }
+            ])
+        ]);
+    }
+
     fn assert_ast(source: &str, expected: &[Statement]) {
         let mut lexer = Lexer::new(None);
         let tokens = lexer.tokenize(source).unwrap();