diff --git a/demo.lang b/demo.lang
index 74c6b0e..45a1565 100644
--- a/demo.lang
+++ b/demo.lang
@@ -1,6 +1,9 @@
-i := 0;
+i := 0x0;
 
-while i < 10 {
-  i = i + 1;
-  print i;
+if i > 10 {
+  print "a";
+} else if i > 5 {
+  print "b";
+} else {
+  print "c";
 }
diff --git a/src/err.rs b/src/err.rs
index d447bb7..cbf2bd9 100644
--- a/src/err.rs
+++ b/src/err.rs
@@ -8,9 +8,9 @@ pub fn error<T>() -> Result<T> {
 
 #[derive(Clone)]
 pub struct Diagnostic {
-  reason: String,
-  span: Option<Span>,
-  backtrace: Vec<String>,
+  pub reason: String,
+  pub span: Option<Span>,
+  pub backtrace: Vec<String>,
 }
 
 impl Diagnostic {
@@ -30,8 +30,8 @@ impl std::fmt::Display for Diagnostic {
     } else {
       write!(f, "(E) {}\n", self.reason)?;
     }
-    for b in self.backtrace.iter().rev() {
-      write!(f, "--> {}\n", b)?;
+    for (_i, b) in self.backtrace.iter().enumerate() {
+      write!(f, "> {}\n", b)?;
     }
     Ok(())
   }
@@ -75,11 +75,11 @@ impl From<std::num::ParseFloatError> for Diagnostic {
 pub trait IntoDiagnostic<T, S: Into<String>> {
   fn reason(self, s: S) -> Result<T>;
   fn trace(self, s: S) -> Result<T>;
+  fn trace_span(self, span: Span, s: S) -> Result<T>;
 }
 
 pub trait WithSpan<T> {
   fn span(self, span: &Span) -> Result<T>;
-  fn no_span(self) -> Result<T>;
 }
 
 impl<T> WithSpan<T> for Result<T> {
@@ -89,17 +89,6 @@ impl<T> WithSpan<T> for Result<T> {
       e
     })
   }
-
-  fn no_span(self) -> Result<T> {
-    self.map_err(|mut e| {
-      e.span = None;
-      e
-    })
-  }
-}
-
-pub trait CoerceDiagnostic<T> {
-  fn coerce(self) -> Result<T>;
 }
 
 impl<T, S: Into<String>> IntoDiagnostic<T, S> for Option<T> {
@@ -124,6 +113,10 @@ impl<T, S: Into<String>> IntoDiagnostic<T, S> for Option<T> {
       }),
     }
   }
+
+  fn trace_span(self, span: Span, s: S) -> Result<T> {
+    self.trace(format!("{} {}", span, s.into()))
+  }
 }
 
 impl<T, E: Into<Diagnostic>, S: Into<String>> IntoDiagnostic<T, S>
@@ -131,7 +124,9 @@ impl<T, E: Into<Diagnostic>, S: Into<String>> IntoDiagnostic<T, S>
 {
   fn reason(self, s: S) -> Result<T> {
     self.map_err(|e| e.into()).map_err(|mut e| {
-      e.reason = s.into();
+      if e.reason == "" {
+        e.reason = s.into();
+      }
       e
     })
   }
@@ -142,10 +137,8 @@ impl<T, E: Into<Diagnostic>, S: Into<String>> IntoDiagnostic<T, S>
       e
     })
   }
-}
 
-impl<T, E: Into<Diagnostic>> CoerceDiagnostic<T> for std::result::Result<T, E> {
-  fn coerce(self) -> Result<T> {
-    self.map_err(|e| e.into())
+  fn trace_span(self, span: Span, s: S) -> Result<T> {
+    self.trace(format!("{} {}", span, s.into())).span(&span)
   }
 }
diff --git a/src/frontend.rs b/src/frontend.rs
new file mode 100644
index 0000000..09962a4
--- /dev/null
+++ b/src/frontend.rs
@@ -0,0 +1,67 @@
+use std::path::Path;
+
+use crate::{
+  err::*, treewalk::Interpreter, Parser, Statement, StatementKind, Token,
+  Tokenizer,
+};
+
+#[derive(Debug, Clone)]
+pub struct Module {
+  file_name: String,
+  source: String,
+  ast: Vec<Statement>,
+  errors: Vec<Diagnostic>,
+}
+
+impl Module {
+  pub fn from_file(path: impl AsRef<Path>) -> Result<Self> {
+    let file = std::fs::read(&path).trace(format!(
+      "while attempting to open file '{}'",
+      &path.as_ref().display()
+    ))?;
+    let source = String::from_utf8_lossy(&file);
+    Ok(Self::from_string(
+      format!("{}", path.as_ref().display()),
+      source.into(),
+    ))
+  }
+
+  pub fn from_string(file_name: String, source: String) -> Self {
+    let tokens = Tokenizer::new(source.chars()).filter(|t| t.0.is_meaningful());
+    let mut ast = vec![];
+    let mut errors = vec![];
+    for statement in Parser::new(tokens) {
+      use StatementKind as s;
+      match statement.kind {
+        s::Error(e) => errors.push(e),
+        _ => ast.push(statement),
+      }
+    }
+    Self {
+      file_name,
+      source: source.into(),
+      ast,
+      errors,
+    }
+  }
+
+  pub fn errors(&self) -> &[Diagnostic] {
+    &self.errors
+  }
+
+  pub fn ok(&self) -> bool {
+    self.errors.len() == 0
+  }
+
+  pub fn execute(&self) {
+    if !self.ok() {
+      for e in self.errors() {
+        eprintln!("{e}");
+      }
+      return;
+    }
+    Interpreter::new(self.ast.clone().into_iter())
+      .run()
+      .unwrap();
+  }
+}
diff --git a/src/lookahead.rs b/src/lookahead.rs
index 82dc6f9..848030b 100644
--- a/src/lookahead.rs
+++ b/src/lookahead.rs
@@ -34,10 +34,6 @@ where
     s
   }
 
-  pub fn inner(&self) -> &I {
-    &self.iterator
-  }
-
   fn normalize(&mut self) {
     for item in &mut self.buffer {
       if self.exhausted {
diff --git a/src/main.rs b/src/main.rs
index c9b3857..cb66d12 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,14 +1,16 @@
 mod err;
+mod frontend;
 mod lookahead;
 mod parse;
 mod token;
 mod treewalk;
+mod types;
 use std::ops::Add;
 
+use err::*;
 use lookahead::*;
 use parse::*;
 use token::*;
-use treewalk::Interpreter;
 
 #[derive(Clone, Copy, Debug)]
 pub struct Span {
@@ -16,13 +18,20 @@ pub struct Span {
   pub column: usize,
 }
 
+impl std::fmt::Display for Span {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "({}:{})", self.row, self.column)
+  }
+}
+
 impl Add<Span> for Span {
   type Output = Span;
 
   fn add(self, rhs: Span) -> Self::Output {
+    let max = (self.row, self.column).max((rhs.row, rhs.column));
     Span {
-      row: usize::min(self.row, rhs.row),
-      column: usize::max(self.column, rhs.column),
+      row: max.0,
+      column: max.1,
     }
   }
 }
@@ -45,13 +54,18 @@ fn test_tokenization() {
   }
 }
 
-fn main() {
-  let src = include_str!("../demo.lang");
-  println!("{src}");
-  let tokens: Vec<_> = Tokenizer::new(src.chars())
-    .filter(|t| t.0.is_meaningful())
-    .collect();
-  let parsed = Parser::new(tokens.into_iter()).file().unwrap();
-  let mut interp = Interpreter::new(parsed.into_iter());
-  interp.run().unwrap();
+fn test_expression(expr: &str) {
+  let source = expr.to_string();
+  let tokens = Tokenizer::new(source.chars()).filter(|t| t.0.is_meaningful());
+  let mut parser = Parser::new(tokens);
+  println!("{:?}", parser.expression(0).unwrap());
+}
+
+fn main() -> Result<()> {
+  /*
+  let module = frontend::Module::from_file("./demo.lang")?;
+  module.execute();
+  */
+  test_expression("(a: b) -> c {}");
+  Ok(())
 }
diff --git a/src/parse.rs b/src/parse.rs
deleted file mode 100644
index 1fa257f..0000000
--- a/src/parse.rs
+++ /dev/null
@@ -1,453 +0,0 @@
-use crate::err::*;
-use crate::{Span, Token, TokenKind};
-
-#[derive(Clone)]
-pub enum ExpressionKind {
-  Integer(i64),
-  Real(f64),
-  String(String),
-  Boolean(bool),
-  Identifier(String),
-  Binary {
-    token: TokenKind,
-    left: Box<Expression>,
-    right: Box<Expression>,
-  },
-  Unary {
-    token: TokenKind,
-    child: Box<Expression>,
-  },
-  Parenthesis(Box<Expression>),
-}
-
-#[derive(Clone)]
-pub struct Expression {
-  pub kind: ExpressionKind,
-  pub span: Span,
-}
-
-impl Expression {
-  pub fn new(kind: ExpressionKind, span: Span) -> Self {
-    Self { kind, span }
-  }
-}
-
-impl std::fmt::Debug for ExpressionKind {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-    use ExpressionKind as e;
-    match self {
-      e::Integer(i) => write!(f, "{i}"),
-      e::Binary { token, left, right } => {
-        write!(f, "({left:?} {token:?} {right:?})")
-      },
-      e::Parenthesis(inner) => write!(f, "{inner:?}"),
-      e::Unary { token, child } => {
-        write!(f, "({token:?} {child:?})")
-      },
-      e::Real(fp) => write!(f, "{fp}"),
-      e::String(s) => write!(f, r#""{s}""#),
-      e::Identifier(i) => write!(f, "{i}"),
-      e::Boolean(b) => write!(f, "{b}"),
-    }
-  }
-}
-
-impl std::fmt::Debug for Expression {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-    write!(f, "{:?}", self.kind)
-  }
-}
-
-#[derive(Debug, Clone)]
-pub enum StatementKind {
-  Mutable {
-    name: String,
-    type_: Option<String>,
-    value: Option<Expression>,
-  },
-  Immutable {
-    name: String,
-    type_: Option<String>,
-    value: Expression,
-  },
-  Assignment {
-    name: String,
-    value: Expression,
-  },
-  If {
-    predicate: Expression,
-    block: Vec<Statement>,
-    else_: Option<Box<Statement>>,
-  },
-  While {
-    predicate: Expression,
-    block: Vec<Statement>,
-  },
-  Print(Expression),
-  Expression(Expression),
-  Block(Vec<Statement>),
-}
-
-#[derive(Debug, Clone)]
-pub struct Statement {
-  pub kind: StatementKind,
-  pub span: Span,
-}
-
-pub type Precedence = usize;
-
-fn binary_prec(tok: &TokenKind) -> Result<(Precedence, bool)> {
-  use TokenKind::*;
-  Ok(match tok {
-    Star | Slash | Percent => (10, false),
-    Plus | Minus => (9, false),
-    And | Nand => (8, false),
-    Xor | Xnor => (7, false),
-    Or | Nor => (6, false),
-    DoubleEqual | BangEqual | Less | LessEqual | Greater | GreaterEqual => {
-      (5, false)
-    },
-    //Colon => Some((5, false)),
-    _ => {
-      return error()
-        .reason(format!("{:?} is not a valid binary operator", tok));
-    },
-  })
-}
-
-fn unary_prefix_prec(tok: &TokenKind) -> Result<Precedence> {
-  use TokenKind::*;
-  Ok(match tok {
-    Minus | Not => 11,
-    Break => 3,
-    _ => {
-      return error()
-        .reason(format!("{tok:?} is not a valid prefix unary operator"));
-    },
-  })
-}
-
-fn unary_postfix_prec(tok: &TokenKind) -> Result<Precedence> {
-  use TokenKind::*;
-  Ok(match tok {
-    Question => 12,
-    Bang => 12,
-    _ => {
-      return error()
-        .reason(format!("{tok:?} is not a valid postfix unary operator"));
-    },
-  })
-}
-
-const PARSER_LOOKAHEAD: usize = 3;
-
-type TokenIter<I> = crate::Window<PARSER_LOOKAHEAD, Token, I>;
-
-pub struct Parser<I: Iterator<Item = Token>> {
-  iter: TokenIter<I>,
-}
-
-impl<I: Iterator<Item = Token>> Parser<I> {
-  pub fn new(iter: I) -> Self {
-    Self {
-      iter: TokenIter::new(iter),
-    }
-  }
-
-  fn skip(&mut self, n: usize) {
-    for _ in 0..n {
-      let _ = self.next();
-    }
-  }
-
-  fn next(&mut self) -> Result<Token> {
-    self.iter.next().reason("Unexpected end of file")
-  }
-
-  fn peek(&self, n: usize) -> Result<Token> {
-    self.iter.peek(n).clone().reason("Unexpected end of file")
-  }
-
-  fn eat(&mut self, expect: TokenKind) -> Result<Token> {
-    match self.look(expect) {
-      Ok(t) => {
-        self.skip(1);
-        Ok(t)
-      },
-      Err(e) => Err(e),
-    }
-  }
-
-  fn look(&mut self, expect: TokenKind) -> Result<Token> {
-    let next = self.peek(0)?;
-    if next.0 == expect {
-      Ok(next)
-    } else {
-      error()
-        .reason(format!("Expected {expect:?}, found {:?}", next.0))
-        .span(&next.1)
-    }
-  }
-
-  pub fn file(&mut self) -> Result<Vec<Statement>> {
-    use TokenKind as t;
-    let mut statements = vec![];
-    loop {
-      // Trim extra ;
-      while self.eat(t::Semicolon).is_ok() {}
-      if self.eat(t::EOF).is_ok() {
-        return Ok(statements);
-      }
-      match self.statement() {
-        Ok(s) => statements.push(s),
-        Err(e) => {
-          return Err(e);
-        },
-      }
-    }
-  }
-
-  pub fn statement(&mut self) -> Result<Statement> {
-    use StatementKind as s;
-    use TokenKind as t;
-    let next = self.peek(0);
-    let next2 = self.peek(1);
-    let statement = match (next, next2) {
-      // (im)mutable declaration
-      (Ok(Token(t::Identifier(name), span)), Ok(Token(t::Colon, _))) => {
-        self.skip(2);
-        let type_ = match self.eat(t::Identifier("".into())) {
-          Ok(Token(t::Identifier(s), _)) => Some(s),
-          _ => None,
-        };
-        match self.eat(t::Equal).or_else(|_| self.eat(t::Colon)) {
-          Ok(Token(t::Colon, _)) => Statement {
-            kind: s::Immutable {
-              name,
-              type_,
-              value: self
-                .expression(0)
-                .trace("while parsing immutable declaration")?,
-            },
-            span,
-          },
-          Ok(Token(t::Equal, _)) => Statement {
-            kind: s::Mutable {
-              name,
-              type_,
-              value: Some(
-                self
-                  .expression(0)
-                  .trace("while parsing mutable declaration")?,
-              ),
-            },
-            span,
-          },
-          _ => return error().reason("Expected expression here"),
-        }
-      },
-      (Ok(Token(t::Identifier(name), span)), Ok(Token(t::Equal, _))) => {
-        self.skip(2);
-        let value = self
-          .expression(0)
-          .trace("while parsing assignment expression")?;
-        Statement {
-          kind: s::Assignment { name, value },
-          span,
-        }
-      },
-      // If
-      (Ok(Token(t::If, span)), _) => {
-        self.skip(1);
-        let predicate = self
-          .expression(0)
-          .reason("Expected predicate after 'if' keyword")
-          .span(&span)?;
-        let block = self.block().trace("while parsing if statement")?;
-        return Ok(Statement {
-          span,
-          kind: s::If {
-            predicate,
-            block: block.0,
-            else_: None,
-          },
-        });
-      },
-      // While
-      (Ok(Token(t::While, span)), _) => {
-        self.skip(1);
-        let predicate = self
-          .expression(0)
-          .reason("Expected predicate after 'while' keyword")
-          .span(&span)?;
-        let block = self.block().trace("while parsing while statement")?;
-        return Ok(Statement {
-          span,
-          kind: s::While {
-            predicate,
-            block: block.0,
-          },
-        });
-      },
-      // (DEBUG) print
-      (Ok(Token(t::Print, span)), _) => {
-        self.skip(1);
-        let expr = self.expression(0).trace("while parsing print statement")?;
-        Statement {
-          span: span + expr.span,
-          kind: s::Print(expr),
-        }
-      },
-      // Block
-      (Ok(Token(t::LeftBrace, _)), _) => {
-        // Skip check for semicolon
-        let (block, span) =
-          self.block().trace("while parsing block statement")?;
-        return Ok(Statement {
-          kind: s::Block(block),
-          span,
-        });
-      },
-      // Expression
-      _ => {
-        let expr = self
-          .expression(0)
-          .trace("while parsing expression statement")?;
-        Statement {
-          span: expr.span,
-          kind: s::Expression(expr),
-        }
-      },
-    };
-    // Check for semicolon
-    if self.eat(t::Semicolon).is_ok() {
-      Ok(statement)
-    } else {
-      error().reason("Expected ;")
-    }
-  }
-
-  pub fn expression(
-    &mut self,
-    mut precedence: Precedence,
-  ) -> Result<Expression> {
-    use ExpressionKind as e;
-    use TokenKind as t;
-    let next = self.peek(0)?;
-    // Unary prefix expression
-    let mut current = if let Ok(p) = unary_prefix_prec(&next.0) {
-      let operator = self.next().expect("unreachable");
-      let child = self
-        .expression(p)
-        .trace(format!("while parsing unary {:?}", operator.0))
-        .span(&operator.1)?;
-      let span = child.span + operator.1;
-      Expression::new(
-        e::Unary {
-          token: operator.0,
-          child: child.into(),
-        },
-        span,
-      )
-    }
-    // Terminal or paren
-    else {
-      self.primary()?
-    };
-    // Precedence climbing loop
-    while let Ok(next) = self.peek(0) {
-      // Binary infix
-      if let Ok((new_precedence, left_assoc)) = binary_prec(&next.0) {
-        if (!left_assoc && new_precedence <= precedence)
-          || (new_precedence < precedence)
-        {
-          return Ok(current);
-        }
-        let operator = self.next().expect("unreachable");
-        let rhs = self
-          .expression(new_precedence)
-          .trace(format!("while parsing binary {:?}", operator.0))
-          .span(&operator.1)?;
-        let span = next.1 + rhs.span;
-        current = Expression::new(
-          e::Binary {
-            token: operator.0,
-            left: current.into(),
-            right: rhs.into(),
-          },
-          span,
-        );
-      }
-      // Unary postfix
-      else if let Ok(new_precedence) = unary_postfix_prec(&next.0) {
-        let operator = self.next().expect("unreachable");
-        let span = next.1 + operator.1;
-        precedence = new_precedence;
-        current = Expression::new(
-          e::Unary {
-            token: operator.0,
-            child: current.into(),
-          },
-          span,
-        );
-      } else {
-        break;
-      }
-    }
-    Ok(current)
-  }
-
-  fn primary(&mut self) -> Result<Expression> {
-    use ExpressionKind as e;
-    use TokenKind as t;
-    let next = self.peek(0)?;
-    let span = next.1;
-    let kind = match next.0 {
-      t::IntegerLiteral(i) => e::Integer(i),
-      t::FloatLiteral(f) => e::Real(f),
-      t::StringLiteral(s) => e::String(s),
-      t::True => e::Boolean(true),
-      t::Identifier(i) => e::Identifier(i),
-      t::LeftParen => {
-        self.eat(t::LeftParen).expect("unreachable");
-        let expr = self
-          .expression(0)
-          .trace("while parsing parenthesized expression")?;
-        self
-          .look(t::RightParen)
-          .reason("Unclosed '('")
-          .span(&expr.span)?;
-        e::Parenthesis(expr.into())
-      },
-      _ => {
-        return error()
-          .span(&span)
-          .reason(format!("Expected primary, found {:?}", next.0));
-      },
-    };
-    self.skip(1);
-    Ok(Expression { kind, span })
-  }
-
-  fn block(&mut self) -> Result<(Vec<Statement>, Span)> {
-    use TokenKind as t;
-    let mut span = self.eat(t::LeftBrace).reason("Expected block")?.1;
-    let mut statements = vec![];
-    loop {
-      let next = self.peek(0)?;
-      span = span + next.1;
-      match self.eat(t::RightBrace) {
-        Ok(t) => {
-          span = span + t.1;
-          break;
-        },
-        _ => {
-          let statement = self.statement()?;
-          span = span + statement.span;
-          statements.push(statement);
-        },
-      };
-    }
-    Ok((statements, span))
-  }
-}
diff --git a/src/parse/expression.rs b/src/parse/expression.rs
new file mode 100644
index 0000000..c9f6e24
--- /dev/null
+++ b/src/parse/expression.rs
@@ -0,0 +1,304 @@
+use super::*;
+
+#[derive(Clone)]
+pub struct Parameter {
+  name: String,
+  type_: String,
+}
+
+impl std::fmt::Debug for Parameter {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "{}: {}", self.name, self.type_)
+  }
+}
+
+#[derive(Clone)]
+pub enum ExpressionKind {
+  Integer(i64),
+  Real(f64),
+  String(String),
+  Boolean(bool),
+  Identifier(String),
+  Binary {
+    token: TokenKind,
+    left: Box<Expression>,
+    right: Box<Expression>,
+  },
+  Unary {
+    token: TokenKind,
+    child: Box<Expression>,
+  },
+  Parenthesis(Box<Expression>),
+  Function {
+    params: Vec<Parameter>,
+    returns: Option<String>,
+    body: Vec<Statement>,
+  },
+  Call {
+    callee: Box<Expression>,
+    args: Vec<Expression>,
+  },
+  Field {
+    namespace: Box<Expression>,
+    field: Box<Expression>,
+  },
+}
+
+#[derive(Clone)]
+pub struct Expression {
+  pub kind: ExpressionKind,
+  pub span: Span,
+}
+
+impl Expression {
+  pub fn new(kind: ExpressionKind, span: Span) -> Self {
+    Self { kind, span }
+  }
+}
+
+impl std::fmt::Debug for ExpressionKind {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    use ExpressionKind as e;
+    match self {
+      e::Integer(i) => write!(f, "{i}"),
+      e::Binary { token, left, right } => {
+        write!(f, "({left:?} {token:?} {right:?})")
+      },
+      e::Parenthesis(inner) => write!(f, "{inner:?}"),
+      e::Unary { token, child } => {
+        write!(f, "({token:?} {child:?})")
+      },
+      e::Real(fp) => write!(f, "{fp}"),
+      e::String(s) => write!(f, r#""{s}""#),
+      e::Identifier(i) => write!(f, "{i}"),
+      e::Boolean(b) => write!(f, "{b}"),
+      e::Call { callee, args } => write!(f, "({callee:?} call {args:?})"),
+      e::Field { namespace, field } => {
+        write!(f, "({namespace:?} . {field:?})")
+      },
+      e::Function {
+        params, returns, ..
+      } => {
+        write!(f, "(fn({params:?}) -> {returns:?})")
+      },
+    }
+  }
+}
+
+impl std::fmt::Debug for Expression {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "{:?}", self.kind)
+  }
+}
+
+impl<I: Iterator<Item = Token>> Parser<I> {
+  pub fn expression(&mut self, precedence: Precedence) -> Result<Expression> {
+    use ExpressionKind as e;
+    use TokenKind as t;
+    let next = self.peek(0)?;
+    // Unary prefix expression
+    let mut current = if let Ok(p) = unary_prefix_prec(&next.0) {
+      let operator = self.next_tok().expect("unreachable");
+      let child = self
+        .expression(p)
+        .trace(format!("while parsing unary {}", operator.0))
+        .span(&operator.1)?;
+      let span = child.span + operator.1;
+      Expression::new(
+        e::Unary {
+          token: operator.0,
+          child: child.into(),
+        },
+        span,
+      )
+    }
+    // Terminal or paren
+    else {
+      self.primary().reason("Expected expression")?
+    };
+
+    // Precedence climbing loop
+    while let Ok(next) = self.peek(0) {
+      // Binary infix
+      if let Ok((new_precedence, left_assoc)) = binary_prec(&next.0) {
+        if (!left_assoc && new_precedence <= precedence)
+          || (new_precedence < precedence)
+        {
+          return Ok(current);
+        }
+        let operator = self.next_tok().expect("unreachable");
+        let rhs = self
+          .expression(new_precedence)
+          .trace(format!("while parsing binary {}", operator.0))
+          .span(&operator.1)?;
+        let span = next.1 + rhs.span;
+        current = Expression::new(
+          e::Binary {
+            token: operator.0,
+            left: current.into(),
+            right: rhs.into(),
+          },
+          span,
+        );
+      }
+      // Field
+      else if let Token(t::Dot, span) = next {
+        if FIELD_PREC <= precedence {
+          return Ok(current);
+        }
+        self.skip(1);
+        let field = self
+          .expression(FIELD_PREC)
+          .trace_span(span, "in field expression")?;
+        current = Expression::new(
+          e::Field {
+            namespace: current.into(),
+            field: field.into(),
+          },
+          span,
+        )
+      }
+      // Function call
+      else if let Token(t::LeftParen, mut span) = next {
+        if CALL_PREC <= precedence {
+          return Ok(current);
+        }
+        self.skip(1);
+        let mut args = vec![];
+        loop {
+          match self.expression(0) {
+            Ok(a) => {
+              span = span + a.span;
+              args.push(a)
+            },
+            Err(_) => break,
+          };
+          if !self.eat(t::Comma).is_ok() {
+            break;
+          }
+        }
+        let Token(_, span2) = self.eat(t::RightParen).span(&span)?;
+        current = Expression::new(
+          e::Call {
+            callee: current.into(),
+            args,
+          },
+          span + span2,
+        );
+      }
+      // Unary postfix
+      else if let Ok(_) = unary_postfix_prec(&next.0) {
+        let operator = self.next_tok().expect("unreachable");
+        let span = next.1 + operator.1;
+        current = Expression::new(
+          e::Unary {
+            token: operator.0,
+            child: current.into(),
+          },
+          span,
+        );
+      } else {
+        break;
+      }
+    }
+    Ok(current)
+  }
+
+  fn primary(&mut self) -> Result<Expression> {
+    use ExpressionKind as e;
+    use TokenKind as t;
+    let next = self.peek(0)?;
+    let mut span = next.1;
+    let kind = match next.0 {
+      t::IntegerLiteral(i) => e::Integer(i),
+      t::FloatLiteral(f) => e::Real(f),
+      t::StringLiteral(s) => e::String(s),
+      t::True => e::Boolean(true),
+      t::Identifier(i) => e::Identifier(i),
+      // function
+      t::LeftParen
+        if (self.look(1, t::Identifier("".into())).is_ok()
+          && self.look(2, t::Colon).is_ok())
+          || self.look(1, t::RightParen).is_ok() =>
+      {
+        self.skip(1);
+        let mut params = vec![];
+        loop {
+          let (name, span2) = match self.identifier() {
+            Ok((name, span)) => (name, span),
+            Err(_) => break,
+          };
+          span = span + span2;
+          self
+            .eat(t::Colon)
+            .trace_span(span, "while parsing function parameter type")?;
+          let (type_, span2) = self
+            .identifier()
+            .trace_span(span, "while parsing function parameter type")?;
+          span = span + span2;
+          params.push(Parameter { name, type_ });
+          if !self.eat(t::Comma).is_ok() {
+            break;
+          }
+        }
+        let Token(_, span2) = self
+          .eat(t::RightParen)
+          .span(&span)
+          .trace_span(span, "while parsing function definition")?;
+        let returns = if let Ok(Token(_, span2)) = self.eat(t::Arrow) {
+          span = span + span2;
+          let (identifier, span2) = self
+            .identifier()
+            .trace_span(span, "while parsing function return type")?;
+          span = span + span2;
+          Some(identifier)
+        } else {
+          None
+        };
+        span = span + span2;
+        let (body, span2) = self
+          .block()
+          .trace_span(span, "while parsing function body")?;
+        span = span + span2;
+        e::Function {
+          params,
+          returns,
+          body,
+        }
+      },
+      // parenthetical
+      t::LeftParen => {
+        self.skip(1);
+        let expr = self
+          .expression(0)
+          .trace("while parsing parenthesized expression")?;
+        self
+          .look(0, t::RightParen)
+          .reason("Unclosed '('")
+          .span(&expr.span)?;
+        e::Parenthesis(expr.into())
+      },
+      _ => {
+        return error()
+          .span(&span)
+          .reason(format!("Expected expression, found {}", next.0));
+      },
+    };
+    self.skip(1);
+    Ok(Expression { kind, span })
+  }
+
+  fn identifier(&mut self) -> Result<(String, Span)> {
+    use TokenKind as t;
+    match self.peek(0) {
+      Ok(Token(t::Identifier(i), span)) => {
+        self.skip(1);
+        Ok((i, span))
+      },
+      Ok(t) => error()
+        .reason(format!("Expected identifier, found {}", t.0))
+        .span(&t.1),
+      Err(e) => Err(e),
+    }
+  }
+}
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
new file mode 100644
index 0000000..e425b5b
--- /dev/null
+++ b/src/parse/mod.rs
@@ -0,0 +1,165 @@
+mod expression;
+mod statement;
+pub use expression::*;
+pub use statement::*;
+
+use crate::err::*;
+use crate::{Span, Token, TokenKind};
+
+pub type Precedence = usize;
+
+const FIELD_PREC: Precedence = 13;
+const CALL_PREC: Precedence = 12;
+
+fn binary_prec(tok: &TokenKind) -> Result<(Precedence, bool)> {
+  use TokenKind::*;
+  Ok(match tok {
+    Star | Slash | Percent => (10, false),
+    Plus | Minus => (9, false),
+    And | Nand => (8, false),
+    Xor | Xnor => (7, false),
+    Or | Nor => (6, false),
+    DoubleEqual | BangEqual | Less | LessEqual | Greater | GreaterEqual => {
+      (5, false)
+    },
+    //Colon => Some((5, false)),
+    _ => {
+      return error().reason(format!("{} is not a valid binary operator", tok));
+    },
+  })
+}
+
+fn unary_prefix_prec(tok: &TokenKind) -> Result<Precedence> {
+  use TokenKind::*;
+  Ok(match tok {
+    Minus | Not => 11,
+    Break => 3,
+    _ => {
+      return error()
+        .reason(format!("{tok} is not a valid prefix unary operator"));
+    },
+  })
+}
+
+fn unary_postfix_prec(tok: &TokenKind) -> Result<Precedence> {
+  use TokenKind::*;
+  Ok(match tok {
+    Question => 12,
+    Bang => 12,
+    _ => {
+      return error()
+        .reason(format!("{tok} is not a valid postfix unary operator"));
+    },
+  })
+}
+
+const PARSER_LOOKAHEAD: usize = 3;
+
+type TokenIter<I> = crate::Window<PARSER_LOOKAHEAD, Token, I>;
+
+pub struct Parser<I: Iterator<Item = Token>> {
+  iter: TokenIter<I>,
+}
+
+impl<I: Iterator<Item = Token>> Iterator for Parser<I> {
+  type Item = Statement;
+
+  fn next(&mut self) -> Option<Self::Item> {
+    use StatementKind as s;
+    use TokenKind as t;
+    // Trim extra ;
+    while self.eat(t::Semicolon).is_ok() {}
+    loop {
+      if self.eat(t::EOF).is_ok() || self.iter.finished {
+        return None;
+      }
+      match self.statement() {
+        Ok(s) => return Some(s),
+        Err(e) => {
+          loop {
+            let next = self.next_tok();
+            match next {
+              Ok(Token(t::Semicolon | t::RightBrace | t::EOF, _)) => break,
+              _ => {},
+            }
+          }
+          return Some(Statement {
+            span: e.span.unwrap_or(Span { row: 0, column: 0 }),
+            kind: s::Error(e),
+          });
+        },
+      }
+    }
+  }
+}
+
+impl<I: Iterator<Item = Token>> Parser<I> {
+  pub fn new(iter: I) -> Self {
+    Self {
+      iter: TokenIter::new(iter),
+    }
+  }
+
+  fn skip(&mut self, n: usize) {
+    for _ in 0..n {
+      let _ = self.next_tok();
+    }
+  }
+
+  fn next_tok(&mut self) -> Result<Token> {
+    match self.iter.next() {
+      Some(Token(TokenKind::Error(e), span)) => Err(e).span(&span),
+      r => r.reason("Unexpected end of file"),
+    }
+  }
+
+  fn peek(&self, n: usize) -> Result<Token> {
+    match self.iter.peek(n).clone() {
+      Some(Token(TokenKind::Error(e), span)) => Err(e).span(&span),
+      r => r.reason("Unexpected end of file"),
+    }
+  }
+
+  fn eat(&mut self, expect: TokenKind) -> Result<Token> {
+    match self.look(0, expect) {
+      Ok(t) => {
+        self.skip(1);
+        Ok(t)
+      },
+      Err(e) => Err(e),
+    }
+  }
+
+  fn look(&mut self, n: usize, expect: TokenKind) -> Result<Token> {
+    let next = self.peek(n)?;
+    if next.0 == expect {
+      Ok(next)
+    } else {
+      error()
+        .reason(format!("Expected {expect}, found {}", next.0))
+        .span(&next.1)
+    }
+  }
+
+  fn block(&mut self) -> Result<(Vec<Statement>, Span)> {
+    use TokenKind as t;
+    let mut span = self.eat(t::LeftBrace).reason("Expected block")?.1;
+    let mut statements = vec![];
+    loop {
+      let next = self.peek(0)?;
+      span = span + next.1;
+      match self.eat(t::RightBrace) {
+        Ok(t) => {
+          span = span + t.1;
+          break;
+        },
+        _ => {
+          let statement = self.statement()?;
+          span = span + statement.span;
+          statements.push(statement);
+        },
+      };
+    }
+    Ok((statements, span))
+  }
+}
diff --git a/src/parse/statement.rs b/src/parse/statement.rs
new file mode 100644
index 0000000..c990185
--- /dev/null
+++ b/src/parse/statement.rs
@@ -0,0 +1,207 @@
+use super::*;
+
+#[derive(Debug, Clone)]
+pub enum StatementKind {
+  Mutable {
+    name: String,
+    type_: Option<String>,
+    value: Option<Expression>,
+  },
+  Immutable {
+    name: String,
+    type_: Option<String>,
+    value: Expression,
+  },
+  Assignment {
+    name: String,
+    value: Expression,
+  },
+  If {
+    predicate: Expression,
+    block: Vec<Statement>,
+    else_: Option<Box<Statement>>,
+  },
+  While {
+    predicate: Expression,
+    block: Vec<Statement>,
+  },
+  Print(Expression),
+  Expression(Expression),
+  Block(Vec<Statement>),
+  Error(Diagnostic),
+}
+
+#[derive(Debug, Clone)]
+pub struct Statement {
+  pub kind: StatementKind,
+  pub span: Span,
+}
+
+impl<I: Iterator<Item = Token>> Parser<I> {
+  pub fn statement(&mut self) -> Result<Statement> {
+    use StatementKind as s;
+    use TokenKind as t;
+    let next = self.peek(0)?;
+    let next2 = self.peek(1);
+    let mut span = next.1;
+    let statement = match (next, next2) {
+      // (im)mutable declaration
+      (Token(t::Identifier(name), span2), Ok(Token(t::Colon, span3))) => {
+        self.skip(2);
+        span = span + span2 + span3;
+        // type
+        let type_ = match self.eat(t::Identifier("".into())) {
+          Ok(Token(t::Identifier(s), span2)) => {
+            span = span + span2;
+            Some(s)
+          },
+          _ => None,
+        };
+        // value
+        match self.eat(t::Equal).or_else(|_| self.eat(t::Colon)) {
+          Ok(Token(t::Colon, span2)) => {
+            span = span + span2;
+            let value = self
+              .expression(0)
+              .trace_span(span, "while parsing mutable declaration")?;
+            span = span + value.span;
+            Statement {
+              kind: s::Immutable { name, type_, value },
+              span,
+            }
+          },
+          Ok(Token(t::Equal, span2)) => {
+            span = span + span2;
+            let value = self
+              .expression(0)
+              .trace_span(span, "while parsing mutable declaration")?;
+            span = span + value.span;
+            Statement {
+              kind: s::Mutable {
+                name,
+                type_,
+                value: Some(value),
+              },
+              span,
+            }
+          },
+          _ => return error().reason("Expected expression").span(&span),
+        }
+      },
+      // Assignment
+      (Token(t::Identifier(name), span2), Ok(Token(t::Equal, span3))) => {
+        self.skip(2);
+        span = span + span2 + span3;
+        let value = self
+          .expression(0)
+          .trace_span(span, "while parsing assignment")?;
+        Statement {
+          span,
+          kind: s::Assignment { name, value },
+        }
+      },
+      // If
+      (Token(t::If, _), _) => {
+        return self.if_else();
+      },
+      // While
+      (Token(t::While, span2), _) => {
+        self.skip(1);
+        span = span + span2;
+        let predicate = self
+          .expression(0)
+          .reason("Expected predicate after 'while' keyword")
+          .span(&span)?;
+        span = span + predicate.span;
+        let block = self
+          .block()
+          .trace_span(span, "while parsing while statement")?;
+        span = span + block.1;
+        return Ok(Statement {
+          span,
+          kind: s::While {
+            predicate,
+            block: block.0,
+          },
+        });
+      },
+      // (DEBUG) print
+      (Token(t::Print, span2), _) => {
+        self.skip(1);
+        span = span + span2;
+        let expr = self
+          .expression(0)
+          .trace_span(span, "while parsing print statement")?;
+        span = span + expr.span;
+        Statement {
+          span,
+          kind: s::Print(expr),
+        }
+      },
+      // Block
+      (Token(t::LeftBrace, span2), _) => {
+        // Skip check for semicolon
+        span = span + span2;
+        let (block, span2) = self
+          .block()
+          .trace_span(span, "while parsing block statement")?;
+        span = span + span2;
+        return Ok(Statement {
+          kind: s::Block(block),
+          span,
+        });
+      },
+      // Expression
+      (Token(_, span2), _) => {
+        span = span + span2;
+        let expr = self
+          .expression(0)
+          .trace_span(span, "while parsing expression statement")?;
+        span = span + expr.span;
+        Statement {
+          span,
+          kind: s::Expression(expr),
+        }
+      },
+    };
+    // Check for semicolon
+    if self.eat(t::Semicolon).is_ok() {
+      Ok(statement)
+    } else {
+      error().reason("Expected ;").span(&span)
+    }
+  }
+
+  fn if_else(&mut self) -> Result<Statement> {
+    use TokenKind as t;
+    if let Ok(Token(_, span)) = self.eat(t::If) {
+      let predicate = self
+        .expression(0)
+        .trace_span(span, "in predicate of 'if' statement")?;
+      let span = span + predicate.span;
+      let block = self
+        .block()
+        .trace_span(span, "in block of 'if' statement")?;
+      let (block, span) = (block.0, span + block.1);
+      let else_ = if self.eat(t::Else).is_ok() {
+        Some(Box::new(self.if_else()?))
+      } else {
+        None
+      };
+      Ok(Statement {
+        kind: StatementKind::If {
+          predicate,
+          block,
+          else_,
+        },
+        span,
+      })
+    } else {
+      let (block, span) = self.block()?;
+      Ok(Statement {
+        kind: StatementKind::Block(block),
+        span,
+      })
+    }
+  }
+}
diff --git a/src/token.rs b/src/token.rs
index 2ebc6b9..3bbb0a7 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -49,7 +49,7 @@ pub enum TokenKind {
 
   Identifier(String),
   StringLiteral(String),
-  CharLiteral(char),
+  GlyphLiteral(char),
   IntegerLiteral(i64),
   FloatLiteral(f64),
 
@@ -78,6 +78,7 @@ pub enum TokenKind {
   SmallComment(String),
   BigComment(String),
 
+  Error(Diagnostic),
   Idk,
   EOF,
 }
@@ -103,6 +104,87 @@ impl PartialEq for TokenKind {
 impl Eq for TokenKind {
 }
 
+impl std::fmt::Display for TokenKind {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    use TokenKind::*;
+    write!(
+      f,
+      "'{}'",
+      match self {
+        LeftParen => "(",
+        RightParen => ")",
+        LeftBrace => "{",
+        RightBrace => "}",
+        LeftSquare => "[",
+        RightSquare => "]",
+        Comma => ",",
+        Colon => ":",
+        Semicolon => ";",
+        Dot => ".",
+        DotDot => "..",
+        Plus => "+",
+        Minus => "-",
+        Slash => "/",
+        Star => "*",
+        Percent => "%",
+        Arrow => "->",
+        FatArrow => "=>",
+        PlusEqual => "+=",
+        MinusEqual => "-=",
+        SlashEqual => "/=",
+        StarEqual => "*=",
+        PercentEqual => "%=",
+        Bang => "!",
+        BangEqual => "!=",
+        Question => "?",
+        QuestionEqual => "?=",
+        Equal => "=",
+        DoubleEqual => "==",
+        Greater => ">",
+        GreaterEqual => ">=",
+        Less => "<",
+        LessEqual => "<=",
+        Pipe => "|",
+        Ampersand => "&",
+        Carrot => "^",
+        Hash => "#",
+        DotDotEqual => "..=",
+        Identifier(i) => i,
+        StringLiteral(s) => s.as_str(),
+        GlyphLiteral(_) => "<glyph>",
+        IntegerLiteral(_) => "<integer>",
+        FloatLiteral(_) => "<real>",
+        If => "if",
+        Else => "else",
+        And => "and",
+        Or => "or",
+        Xor => "xor",
+        Not => "not",
+        Nand => "nand",
+        Nor => "nor",
+        Xnor => "xnor",
+        Print => "print",
+        Break => "break",
+        Return => "return",
+        Continue => "continue",
+        For => "for",
+        While => "while",
+        True => "true",
+        False => "false",
+        Struct => "struct",
+        Enum => "enum",
+        Union => "union",
+        Whitespace(_) => "<whitespace>",
+        SmallComment(_) => "<comment>",
+        BigComment(_) => "<comment>",
+        Error(_) => "<error>",
+        Idk => unreachable!(),
+        EOF => "<end of file>",
+      }
+    )
+  }
+}
+
 #[derive(Clone, Debug)]
 pub struct Token(pub TokenKind, pub Span);
 
@@ -118,7 +200,6 @@ pub struct Tokenizer<I: Iterator<Item = char>> {
   iter: CharIter<I>,
   column: usize,
   row: usize,
-  finished: bool,
 }
 
 impl<I: Iterator<Item = char>> Tokenizer<I> {
@@ -127,14 +208,6 @@ impl<I: Iterator<Item = char>> Tokenizer<I> {
       iter: CharIter::new(iter),
       column: 1,
       row: 1,
-      finished: false,
-    }
-  }
-
-  pub fn span(&self) -> Span {
-    Span {
-      column: self.column,
-      row: self.row,
     }
   }
 
@@ -187,6 +260,16 @@ impl<I: Iterator<Item = char>> Tokenizer<I> {
       column: self.column,
     };
     let current = match self.next_char() {
+      Some(std::char::REPLACEMENT_CHARACTER) => {
+        return t(
+          Error(Diagnostic {
+            reason: "Non-UTF8 encoded glyph".into(),
+            span: Some(position),
+            backtrace: vec![],
+          }),
+          position,
+        );
+      },
       Some(c) => c,
       None => return t(EOF, position),
     };
@@ -327,7 +410,7 @@ impl<I: Iterator<Item = char>> Tokenizer<I> {
           .reason("Single quote (') contains more than one character")
           .span(&position);
       }
-      let kind = CharLiteral(
+      let kind = GlyphLiteral(
         baked
           .chars()
           .next()
@@ -351,8 +434,12 @@ impl<I: Iterator<Item = char>> Tokenizer<I> {
       // Only one dot per number
       let mut encountered_dot = false;
       while let Some(c) = self.peek(0) {
-        if c == '.' && !encountered_dot {
-          if let Some('.') = self.peek(1) {
+        if c == '.' {
+          if encountered_dot {
+            break;
+          }
+          let Some(next) = self.peek(1) else { break };
+          if !next.is_ascii_digit() {
             break;
           }
           encountered_dot = true;
@@ -407,19 +494,12 @@ impl<I: Iterator<Item = char>> Iterator for Tokenizer<I> {
   type Item = Token;
 
   fn next(&mut self) -> Option<Self::Item> {
-    loop {
-      match self._next() {
-        Ok(Token(TokenKind::EOF, span)) => {
-          if self.finished {
-            return None;
-          } else {
-            self.finished = true;
-            return Some(Token(TokenKind::EOF, span));
-          }
-        },
-        Ok(r) => return Some(r),
-        _ => {},
-      };
+    match self._next() {
+      Ok(s) => Some(s),
+      Err(e) => Some(Token(
+        TokenKind::Error(e.clone()),
+        e.span.expect("error without span in tokenizer"),
+      )),
     }
   }
 }
@@ -429,29 +509,35 @@ fn parse_number(num: &str) -> Result<TokenKind> {
   let num = num.replace('_', "");
   // Floating point (only decimal)
   if num.contains('.') {
-    num.parse::<f64>().map(|f| FloatLiteral(f)).coerce()
+    num
+      .parse::<f64>()
+      .map(|f| FloatLiteral(f))
+      .reason("Could not parse real number")
   }
   // Hex integer
   else if let Some(hex) = num.strip_prefix("0x") {
     i64::from_str_radix(hex, 16)
       .map(|i| IntegerLiteral(i))
-      .coerce()
+      .reason("Could not parse hex integer number")
   }
   // Octal integer
   else if let Some(oct) = num.strip_prefix("0o") {
     i64::from_str_radix(oct, 8)
       .map(|i| IntegerLiteral(i))
-      .coerce()
+      .reason("Could not parse octal integer number")
   }
   // Binary integer
   else if let Some(bin) = num.strip_prefix("0b") {
     i64::from_str_radix(bin, 2)
       .map(|i| IntegerLiteral(i))
-      .coerce()
+      .reason("Could not parse binary integer number")
   }
   // Decimal integer
   else {
-    num.parse::<i64>().map(|i| IntegerLiteral(i)).coerce()
+    num
+      .parse::<i64>()
+      .map(|i| IntegerLiteral(i))
+      .reason("Could not parse integer number")
   }
 }
 
diff --git a/src/treewalk.rs b/src/treewalk.rs
index a074f5b..0b07252 100644
--- a/src/treewalk.rs
+++ b/src/treewalk.rs
@@ -14,6 +14,19 @@ enum Value {
   Undefined,
 }
 
+impl std::fmt::Display for Value {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    use Value::*;
+    match self {
+      Integer(i) => write!(f, "{i}"),
+      Real(r) => write!(f, "{r}"),
+      String(s) => write!(f, "{s}"),
+      Boolean(b) => write!(f, "{b}"),
+      Undefined => write!(f, "undefined"),
+    }
+  }
+}
+
 #[derive(Debug, Clone)]
 struct Scope {
   outer: Option<Box<Scope>>,
@@ -189,6 +202,13 @@ impl<I: Iterator<Item = Statement>> Interpreter<I> {
       },
       e::Unary { token, child } => self.evaluate_unary(token, *child),
       e::Parenthesis(e) => self.evaluate(*e),
+      e::Call { callee, args } => todo!(),
+      e::Field { namespace, field } => todo!(),
+      e::Function {
+        params,
+        returns,
+        body,
+      } => todo!(),
     }
     .span(&expr.span)
   }
@@ -215,7 +235,7 @@ impl<I: Iterator<Item = Statement>> Interpreter<I> {
       },
       s::Print(e) => {
         let e = self.evaluate(e)?;
-        println!("{e:?}");
+        println!("{e}");
       },
       s::Expression(e) => {
         self.evaluate(e)?;
@@ -231,6 +251,8 @@ impl<I: Iterator<Item = Statement>> Interpreter<I> {
         if let Value::Boolean(b) = value {
           if b {
             self.block(block)?;
+          } else if let Some(else_) = else_ {
+            self.execute(*else_)?;
           }
         } else {
           return error()
@@ -252,6 +274,10 @@ impl<I: Iterator<Item = Statement>> Interpreter<I> {
           }
         }
       },
+      s::Error(e) => {
+        eprintln!("{e}");
+        panic!();
+      },
     }
     Ok(())
   }
diff --git a/src/types.rs b/src/types.rs
new file mode 100644
index 0000000..4dc3a00
--- /dev/null
+++ b/src/types.rs
@@ -0,0 +1,91 @@
+use super::err::*;
+
+macro_rules! primitives {
+  ( $($i:ident),* ) => {
+    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+    #[allow(non_camel_case_types, dead_code)]
+    pub enum Primitive {
+      whole_ambiguous,
+      integer_ambiguous,
+      real_ambiguous,
+      $($i,)*
+    }
+
+    impl Primitive {
+      pub fn from_string(string: &'static str) -> Option<Self> {
+        match string {
+          $(stringify!{$i} => Some(Self::$i),)*
+          _ => None,
+        }
+      }
+    }
+    impl std::fmt::Display for Primitive {
+      fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+          Primitive::whole_ambiguous => write!(f, "<ambiguous whole>"),
+          Primitive::integer_ambiguous => write!(f, "<ambiguous integer>"),
+          Primitive::real_ambiguous => write!(f, "<ambiguous real>"),
+          $(Primitive::$i => write!(f, stringify!{$i}),)*
+        }
+      }
+    }
+  };
+}
+
+primitives! {
+  w8, w16, w32, w64, whole,
+  i8, i16, i32, i64, integer,
+  r32, r64, real,
+  boolean,
+  string, glyph
+}
+
+impl Primitive {
+  pub fn coerce(a: Self, b: Self) -> Result<Self> {
+    use Primitive::*;
+    match (a, b) {
+      // Whole? coerces to any whole or integer
+      (whole_ambiguous, w @ (w8 | w16 | w32 | w64 | i8 | i16 | i32 | i64))
+      | (w @ (w8 | w16 | w32 | w64 | i8 | i16 | i32 | i64), whole_ambiguous) => {
+        w
+      },
+      // Integer? coerces to any integer
+      (integer_ambiguous, i @ (i8 | i16 | i32 | i64))
+      | (i @ (i8 | i16 | i32 | i64), integer_ambiguous) => i,
+      _ => whole_ambiguous,
+    };
+    todo!()
+  }
+}
+
+use Primitive as p;
+
+// Implement math operations for regular types
+macro_rules! selfsame_op {
+  ($trait:ident, $fn:ident, $($i:ident),* ) => {
+    impl std::ops::$trait for Primitive {
+      type Output = Result<Primitive>;
+      fn $fn(self, rhs: Self) -> Self::Output {
+        match (self, rhs) {
+          $((p::$i, p::$i) => Ok(p::$i),)*
+          _ => error()
+          .reason(format!("Operation not defined for primitives {} and {}", self, rhs))
+        }
+      }
+    }
+  };
+}
+
+// Implement all regular math
+macro_rules! all_selfsame {
+  ($($i:ident),*) => {
+    selfsame_op!(Add, add, $($i),*);
+    selfsame_op!(Sub, sub, $($i),*);
+    selfsame_op!(Mul, mul, $($i),*);
+    selfsame_op!(Div, div, $($i),*);
+  };
+}
+
+all_selfsame!(
+  w8, w16, w32, w64, whole, i8, i16, i32, i64, integer, r32, r64, real, string
+);