diff --git a/huia-compiler/src/context.rs b/huia-compiler/src/context.rs
new file mode 100644
index 0000000..0164a51
--- /dev/null
+++ b/huia-compiler/src/context.rs
@@ -0,0 +1,130 @@
+use crate::error::CompileError;
+use crate::location::Location;
+use crate::stable::{StringIdx, StringTable};
+use crate::ty::{Ty, TyIdx};
+use huia_parser::input_location::InputLocation;
+
+#[derive(Debug)]
+pub struct Context {
+    errors: Vec<CompileError>,
+    strings: StringTable,
+    types: Vec<Ty>,
+    current_file: StringIdx,
+}
+
+impl Context {
+    pub fn new(path: &str) -> Context {
+        let errors = Vec::default();
+        let mut strings = StringTable::default();
+        let types = Vec::default();
+        let current_file = strings.intern(path);
+        Context {
+            errors,
+            strings,
+            types,
+            current_file,
+        }
+    }
+
+    #[cfg(test)]
+    pub fn test() -> Context {
+        Context::new("Test context")
+    }
+
+    pub fn constant_string(&mut self, value: &str) -> StringIdx {
+        self.strings.intern(value)
+    }
+
+    pub fn declare_type(
+        &mut self,
+        name: &StringIdx,
+        properties: Vec<(StringIdx, TyIdx)>,
+        location: Location,
+    ) -> TyIdx {
+        let idx = self.types.len();
+        let ty = Ty::new_type(name.clone(), location, properties);
+        self.types.push(ty);
+        idx.into()
+    }
+
+    pub fn declare_trait(
+        &mut self,
+        name: &StringIdx,
+        requirements: Vec<TyIdx>,
+        location: Location,
+    ) -> TyIdx {
+        let idx = self.types.len();
+        let ty = Ty::new_trait(Some(name.clone()), location, requirements);
+        self.types.push(ty);
+        idx.into()
+    }
+
+    pub fn anonymous_trait(&mut self, requirements: Vec<TyIdx>, location: Location) -> TyIdx {
+        let idx = self.types.len();
+        let ty = Ty::new_trait(None, location, requirements);
+        self.types.push(ty);
+        idx.into()
+    }
+
+    pub fn reference_type(&mut self, name: &StringIdx, location: Location) -> TyIdx {
+        // Try and eagerly deference types if we can.
+        // This can theoretically return another type reference, so we still
+        // have to do a full type-check.
+        for (i, ty) in self.types.iter().enumerate() {
+            if ty.name().is_some() && &ty.name().unwrap() == name {
+                return i.into();
+            }
+        }
+
+        // Otherwise create a new type reference.
+        let idx = self.types.len();
+        let ty = Ty::new_reference(name.clone(), location);
+        self.types.push(ty);
+        idx.into()
+    }
+
+    pub fn get_type(&self, idx: &TyIdx) -> Option<&Ty> {
+        self.types.get(usize::from(idx))
+    }
+
+    pub fn location(&self, location: &InputLocation) -> Location {
+        let path = self.strings.get(self.current_file.clone()).unwrap();
+        Location::new(location.clone(), path)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_types() {
+        let mut context = Context::test();
+        let s0 = context.constant_string("Marty McFly");
+        let s1 = context.constant_string("Doc Brown");
+
+        let t0 = context.declare_type(&s0, Vec::new(), Location::test());
+        let t1 = context.reference_type(&s0, Location::test());
+        let t2 = context.reference_type(&s1, Location::test());
+
+        assert_eq!(t0, t1);
+        assert_ne!(t0, t2);
+
+        let ty0 = context.get_type(&t0).unwrap();
+        let ty1 = context.get_type(&t1).unwrap();
+        let ty2 = context.get_type(&t2).unwrap();
+
+        assert_eq!(ty0, ty1);
+        assert_ne!(ty0, ty2);
+
+        assert!(ty0.is_type());
+        assert!(!ty0.is_trait());
+        assert!(!ty0.is_reference());
+        assert!(ty1.is_type());
+        assert!(!ty1.is_trait());
+        assert!(!ty1.is_reference());
+        assert!(!ty2.is_type());
+        assert!(!ty2.is_trait());
+        assert!(ty2.is_reference());
+    }
+}
diff --git a/huia-compiler/src/error.rs b/huia-compiler/src/error.rs
new file mode 100644
index 0000000..225ca4e
--- /dev/null
+++ b/huia-compiler/src/error.rs
@@ -0,0 +1,21 @@
+use crate::location::Location;
+use std::error::Error;
+use std::fmt;
+
+#[derive(Debug)]
+pub struct CompileError {
+    message: String,
+    location: Location,
+}
+
+impl fmt::Display for CompileError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Compile Error: {:?}", self)
+    }
+}
+
+impl Error for CompileError {
+    fn description(&self) -> &str {
+        &self.message
+    }
+}
diff --git a/huia-compiler/src/ir/bb.rs b/huia-compiler/src/ir/bb.rs
deleted file mode 100644
index 13c017b..0000000
--- a/huia-compiler/src/ir/bb.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-use crate::ir::Ir;
-
-#[derive(Debug, Clone)]
-pub struct BasicBlock {
-    statements: Vec<Ir>,
-    terminator: Terminator,
-}
-
-impl BasicBlock {
-    pub fn new() -> BasicBlock {
-        BasicBlock {
-            statements: Vec::default(),
-            terminator: Terminator::Invalid,
-        }
-    }
-}
-
-#[derive(Debug, Clone)]
-pub enum Terminator {
-    Invalid,
-}
diff --git a/huia-compiler/src/ir/builder.rs b/huia-compiler/src/ir/builder.rs
new file mode 100644
index 0000000..ef6baf8
--- /dev/null
+++ b/huia-compiler/src/ir/builder.rs
@@ -0,0 +1,359 @@
+use crate::context::Context;
+use crate::ir::{Val, IR};
+use huia_parser::ast::{Location, NodeType, Term, Value};
+
+/// The Builder is a simple stack machine for converting AST into IR.
+#[derive(Default)]
+struct Builder {
+    /// The IR stack - used to compose intermediate values.
+    stack: Vec<IR>,
+}
+
+impl Builder {
+    /// Consume an AST node and build IR.
+    ///
+    /// Any IR will be on the Builder's stack.
+    pub fn build(&mut self, node: Term, mut context: &mut Context) {
+        match node.node_type() {
+            NodeType::Atom => {
+                let ty_idx = context.constant_string("Huia.Native.Atom");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+                let idx = context.constant_string(node.atom().unwrap().value_ref().as_str());
+                self.stack.push(IR::Constant(ty, Val::Atom(idx)));
+            }
+            NodeType::Boolean => {
+                let ty_idx = context.constant_string("Huia.Native.Boolean");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+                let value = *node.boolean().unwrap().value_ref();
+                self.stack.push(IR::Constant(ty, Val::Boolean(value)));
+            }
+            NodeType::Float => {
+                let ty_idx = context.constant_string("Huia.Native.Float");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+                let value = *node.float().unwrap().value_ref();
+                self.stack.push(IR::Constant(ty, Val::Float(value)));
+            }
+            NodeType::Integer => {
+                let ty_idx = context.constant_string("Huia.Native.Integer");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+                let value = *node.integer().unwrap().value_ref();
+                self.stack.push(IR::Constant(ty, Val::Integer(value)));
+            }
+            NodeType::String => {
+                let ty_idx = context.constant_string("Huia.Native.String");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+                let idx = context.constant_string(node.string().unwrap().value_ref().as_str());
+                self.stack.push(IR::Constant(ty, Val::String(idx)));
+            }
+            NodeType::Ty => {
+                let ty_idx = context.constant_string(node.ty().unwrap().value_ref().as_str());
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+                self.stack.push(IR::TypeReference(ty));
+            }
+            NodeType::Array => {
+                let ty_idx = context.constant_string("Huia.Native.Array");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+
+                let elements = node
+                    .array()
+                    .unwrap()
+                    .iter()
+                    .map(|node| {
+                        self.build(node.clone(), &mut context);
+                        self.pop().unwrap()
+                    })
+                    .collect();
+                self.stack.push(IR::Constant(ty, Val::Array(elements)));
+            }
+            NodeType::Map => {
+                let ty_idx = context.constant_string("Huia.Native.Map");
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+
+                let elements = node
+                    .map()
+                    .unwrap()
+                    .iter()
+                    .map(|(key, value)| {
+                        self.build(key.clone(), &mut context);
+                        let key = self.pop().unwrap();
+                        self.build(value.clone(), &mut context);
+                        let value = self.pop().unwrap();
+                        (key, value)
+                    })
+                    .collect();
+                self.stack.push(IR::Constant(ty, Val::Map(elements)));
+            }
+            NodeType::Binary => {
+                let (op, lhs, rhs) = node.binary().unwrap();
+                self.build(lhs.clone(), &mut context);
+                self.build(rhs.clone(), &mut context);
+                let rhs = self.pop().unwrap();
+                let lhs = self.pop().unwrap();
+                self.stack
+                    .push(IR::Infix(op.value_ref().clone(), Box::new((lhs, rhs))));
+            }
+            NodeType::Constructor => {
+                let (ty, props) = node.constructor().unwrap();
+                let ty_idx = context.constant_string(ty.value_ref().as_str());
+                let location = context.location(&node.location());
+                let ty = context.reference_type(&ty_idx, location);
+
+                let elements = props
+                    .iter()
+                    .map(|(key, value)| {
+                        let key = context.constant_string(key.value_ref().as_str());
+                        self.build(value.clone(), &mut context);
+                        let value = self.stack.pop().unwrap();
+                        (key, value)
+                    })
+                    .collect();
+                self.stack.push(IR::Constructor(ty, elements));
+            }
+            NodeType::Unary => {
+                let (op, rhs) = node.unary().unwrap();
+                self.build(rhs.clone(), &mut context);
+                let rhs = self.pop().unwrap();
+                self.stack
+                    .push(IR::Unary(op.value_ref().clone(), Box::new(rhs)));
+            }
+            NodeType::Call => {
+                let (name, args) = node.call().unwrap();
+                let name = context.constant_string(name.value_ref().as_str());
+
+                let elements = args
+                    .iter()
+                    .map(|node| {
+                        self.build(node.clone(), &mut context);
+                        self.pop().unwrap()
+                    })
+                    .collect();
+
+                self.stack.push(IR::Call(name, elements));
+            }
+            NodeType::Declaration => {
+                let (name, node) = node.declaration().unwrap();
+                let name = context.constant_string(name.value_ref().as_str());
+                self.build(node.clone(), &mut context);
+                let node = self.pop().unwrap();
+                self.stack.push(IR::Declaration(name, Box::new(node)));
+            }
+            NodeType::TypeDef => {
+                let (ty, properties, body) = node.typedef().unwrap();
+                let ty_idx = context.constant_string(ty.value_ref().as_str());
+                let location = context.location(&node.location());
+
+                let properties = properties
+                    .iter()
+                    .map(|(key, value)| {
+                        let key = context.constant_string(key.value_ref().as_str());
+                        let location = context.location(&value.location());
+                        let types = value
+                            .value_ref()
+                            .iter()
+                            .map(|node| {
+                                let name = context.constant_string(node.value_ref().as_str());
+                                let location = context.location(&node.location());
+                                context.reference_type(&name, location)
+                            })
+                            .collect();
+                        let ty = context.anonymous_trait(types, location);
+                        (key, ty)
+                    })
+                    .collect();
+
+                for node in body {
+                    self.build(node.clone(), &mut context);
+                }
+
+                let ty = context.declare_type(&ty_idx, properties, location);
+                self.stack.push(IR::TypeDefinition(ty));
+            }
+            NodeType::TraitDef => {
+                let (ty, typespec, body) = node.traitdef().unwrap();
+                let ty_idx = context.constant_string(ty.value_ref().as_str());
+                let location = context.location(&node.location());
+
+                let types = if typespec.is_some() {
+                    typespec
+                        .unwrap()
+                        .value_ref()
+                        .iter()
+                        .map(|node| {
+                            let name = context.constant_string(node.value_ref().as_str());
+                            let location = context.location(&node.location());
+                            context.reference_type(&name, location)
+                        })
+                        .collect()
+                } else {
+                    Vec::new()
+                };
+
+                for node in body {
+                    self.build(node.clone(), &mut context);
+                }
+
+                let ty = context.declare_trait(&ty_idx, types, location);
+                self.stack.push(IR::TraitDefinition(ty));
+            }
+            _ => (),
+        }
+    }
+
+    pub fn pop(&mut self) -> Option<IR> {
+        self.stack.pop()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_atom() {
+        let term = Term::input(":marty").unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constant());
+    }
+
+    #[test]
+    fn test_boolean() {
+        let term = Term::input("true").unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constant());
+    }
+
+    #[test]
+    fn test_float() {
+        let term = Term::input("1.23").unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constant());
+    }
+
+    #[test]
+    fn test_string() {
+        let term = Term::input(r#" "Marty McFly"  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constant());
+    }
+
+    #[test]
+    fn test_type_reference() {
+        let term = Term::input(r#" MartyMcFly  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_type_reference());
+    }
+
+    #[test]
+    fn test_array() {
+        let term = Term::input(r#" [1, 2, 3]  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constant());
+    }
+
+    #[test]
+    fn test_map() {
+        let term = Term::input(r#" { a: 2, :b => 3 }  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constant());
+    }
+
+    #[test]
+    fn test_infix() {
+        let term = Term::input(r#" 1 + 2  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_infix());
+    }
+
+    #[test]
+    fn test_constructor() {
+        let term = Term::input(r#" Delorean { speed: 88 }  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_constuctor());
+    }
+
+    #[test]
+    fn test_unary() {
+        let term = Term::input(r#" +88  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_unary());
+    }
+
+    #[test]
+    fn test_call() {
+        let term = Term::input(r#" x(123)  "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_call());
+    }
+
+    #[test]
+    fn test_declaration() {
+        let term = Term::input(r#" let x = 123 "#).unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_declaration());
+    }
+
+    #[test]
+    fn test_type_definition() {
+        let term = Term::file("type Delorean(speed: Integer)").unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_type_definition());
+    }
+
+    #[test]
+    fn test_trait_definition() {
+        let term = Term::file("trait TimeMachine").unwrap()[0].clone();
+        let mut builder = Builder::default();
+        let mut context = Context::test();
+        builder.build(term, &mut context);
+        let ir = builder.pop().unwrap();
+        assert!(ir.is_trait_definition());
+    }
+
+}
diff --git a/huia-compiler/src/ir/constants.rs b/huia-compiler/src/ir/constants.rs
deleted file mode 100644
index 37df139..0000000
--- a/huia-compiler/src/ir/constants.rs
+++ /dev/null
@@ -1,53 +0,0 @@
-use string_interner::{StringInterner, Sym};
-
-/// Constant values specified in the code.
-#[derive(Debug, Clone, Default)]
-pub struct Constants {
-    strings: StringInterner<Sym>,
-    integers: Vec<i64>,
-    floats: Vec<f64>,
-    booleans: Vec<bool>,
-}
-
-/// An index into our constants for reference.
-#[derive(Debug, Clone, PartialEq)]
-pub enum ConstantIdx {
-    String(Sym),
-    Integer(usize),
-    Floats(usize),
-    Boolean(usize),
-}
-
-impl Constants {
-    /// Do we have any constants stored?
-    pub fn is_empty(&self) -> bool {
-        self.strings.is_empty() && self.integers.is_empty() && self.floats.is_empty()
-    }
-
-    /// Add a constant string.
-    pub fn push_string(&mut self, s: &str) -> ConstantIdx {
-        let sym = self.strings.get_or_intern(s);
-        ConstantIdx::String(sym)
-    }
-
-    /// Add a constant integer.
-    pub fn push_integer(&mut self, i: i64) -> ConstantIdx {
-        let idx = self.integers.len();
-        self.integers.push(i);
-        ConstantIdx::Integer(idx)
-    }
-
-    /// Add a constant float.
-    pub fn push_float(&mut self, f: f64) -> ConstantIdx {
-        let idx = self.floats.len();
-        self.floats.push(f);
-        ConstantIdx::Floats(idx)
-    }
-
-    /// Add a constant boolean.
-    pub fn push_boolean(&mut self, b: bool) -> ConstantIdx {
-        let idx = self.booleans.len();
-        self.booleans.push(b);
-        ConstantIdx::Boolean(idx)
-    }
-}
diff --git a/huia-compiler/src/ir/context.rs b/huia-compiler/src/ir/context.rs
deleted file mode 100644
index bdee649..0000000
--- a/huia-compiler/src/ir/context.rs
+++ /dev/null
@@ -1,408 +0,0 @@
-use huia_parser::ast::{unary, Location, NodeType, Term, Value};
-use huia_parser::input_location::InputLocation;
-
-use crate::ir::constants::{ConstantIdx, Constants};
-use crate::ir::modules::{Module, ModuleIdx, Modules};
-use crate::ir::ty::{Ty, TyIdx, TyKind, Types};
-use crate::ir::{Ir, IrKind};
-
-#[derive(Debug, Clone, Default)]
-pub struct Context {
-    pub constants: Constants,
-    pub types: Types,
-    // it should be an error to try and consume any terms unless there is a
-    // current module.
-    modules: Modules,
-}
-
-impl Context {
-    pub fn bootstrap() -> Context {
-        let mut context = Context::default();
-
-        // It's very important that the basic types are inserted such that their
-        // indexes are the same as those in the `TyKind` enum.  If I could
-        // iterate them then I would.
-        context.types.declare(
-            TyKind::Atom,
-            context.constants.push_string("Huia.Native.Atom"),
-        );
-        context.types.declare(
-            TyKind::Boolean,
-            context.constants.push_string("Huia.Native.Boolean"),
-        );
-        context.types.declare(
-            TyKind::Float,
-            context.constants.push_string("Huia.Native.Float"),
-        );
-        context.types.declare(
-            TyKind::Integer,
-            context.constants.push_string("Huia.Native.Integer"),
-        );
-        context.types.declare(
-            TyKind::String,
-            context.constants.push_string("Huia.Native.String"),
-        );
-
-        context.types.declare(
-            TyKind::Array,
-            context.constants.push_string("Huia.Native.Array"),
-        );
-        context.types.declare(
-            TyKind::Map,
-            context.constants.push_string("Huia.Native.Map"),
-        );
-
-        context
-    }
-
-    pub fn push_module(&mut self, name: &str) -> ModuleIdx {
-        let cidx = self.constants.push_string(name);
-        self.modules.push(cidx)
-    }
-
-    pub fn consume(&mut self, term: &Term) -> Ir {
-        assert!(
-            !self.modules.is_empty(),
-            "Cannot consume the AST without an active module."
-        );
-
-        match term.node_type() {
-            // Basic types.
-            NodeType::Atom => {
-                let idx = self
-                    .constants
-                    .push_string(term.atom().unwrap().value_ref().as_str());
-                Ir::new_constant(idx, TyKind::Atom, term.location().clone())
-            }
-            NodeType::Boolean => {
-                let idx = self
-                    .constants
-                    .push_boolean(*term.boolean().unwrap().value_ref());
-                Ir::new_constant(idx, TyKind::Boolean, term.location().clone())
-            }
-            NodeType::Float => {
-                let idx = self
-                    .constants
-                    .push_float(*term.float().unwrap().value_ref());
-                Ir::new_constant(idx, TyKind::Float, term.location().clone())
-            }
-            NodeType::Integer => {
-                let idx = self
-                    .constants
-                    .push_integer(*term.integer().unwrap().value_ref());
-                Ir::new_constant(idx, TyKind::Integer, term.location().clone())
-            }
-            NodeType::String => {
-                let idx = self
-                    .constants
-                    .push_string(term.string().unwrap().value_ref().as_str());
-                Ir::new_constant(idx, TyKind::String, term.location().clone())
-            }
-            NodeType::Ty => {
-                let idx = self
-                    .constants
-                    .push_string(term.ty().unwrap().value_ref().as_str());
-                let ty = self.types.declare(TyKind::Variable, idx);
-                Ir::new_type_ref(ty, term.location().clone())
-            }
-
-            // Compound types
-            NodeType::Array => {
-                let elements = term
-                    .array()
-                    .unwrap()
-                    .iter()
-                    .map(|t| self.consume(t))
-                    .collect();
-                Ir::new_constant_array(TyKind::Array, elements, term.location().clone())
-            }
-            NodeType::Map => {
-                let elements = term
-                    .map()
-                    .unwrap()
-                    .iter()
-                    .map(|(k, v)| (self.consume(k), self.consume(v)))
-                    .collect();
-                Ir::new_constant_map(TyKind::Map, elements, term.location().clone())
-            }
-
-            // Expressions.
-            NodeType::Binary => {
-                let (op, lhs, rhs) = term.binary().unwrap();
-                let lhs = self.consume(lhs);
-                let rhs = self.consume(rhs);
-                Ir::new_binary(op.value_ref().clone(), lhs, rhs, term.location().clone())
-            }
-            NodeType::Constructor => {
-                let (ty, properties) = term.constructor().unwrap();
-
-                let idx = self.constants.push_string(ty.value_ref().as_str());
-                let ty = self.types.declare(TyKind::Variable, idx);
-
-                let props = properties
-                    .iter()
-                    .map(|(key, value)| {
-                        let key = self.constants.push_string(key.value_ref().as_str());
-                        let value = self.consume(value);
-                        (key, value)
-                    })
-                    .collect();
-                Ir::new_instance(ty, props, term.location().clone())
-            }
-            NodeType::Unary => {
-                let (op, rhs) = term.unary().unwrap();
-                let rhs = self.consume(rhs);
-                Ir::new_unary(op.value_ref().clone(), rhs, term.location().clone())
-            }
-
-            NodeType::TypeDef => {
-                let (ty, props, body) = term.typedef().unwrap();
-                let idx = self.constants.push_string(ty.value_ref().as_str());
-                let tyidx = self.types.declare(TyKind::UserType, idx);
-
-                let props: Vec<(ConstantIdx, TyIdx)> = props
-                    .iter()
-                    .map(|(key, typespec)| {
-                        let keyidx = self.constants.push_string(key.value_ref().as_str());
-                        let tyidxs: Vec<TyIdx> = typespec
-                            .value_ref()
-                            .iter()
-                            .map(|ty| {
-                                let idx = self.constants.push_string(ty.value_ref().as_str());
-                                self.types.declare(TyKind::Variable, idx)
-                            })
-                            .collect();
-                        let tyidx = self.types.spec(tyidxs);
-                        (keyidx, tyidx)
-                    })
-                    .collect();
-
-                let ty = self.types.get_mut(tyidx).unwrap();
-                for (keyidx, tyidx) in props {
-                    ty.set_property(keyidx, tyidx);
-                }
-
-                println!("ty = {:?}", ty);
-
-                panic!("wat");
-            }
-
-            // // Type and variable declarations.
-            // NodeType::Definition => {
-            //     let (ident, term, props, body, reqs) = term.definition().unwrap();
-
-            //     println!("body = {:?}", body);
-
-            //     let deftype = ident.value_ref().as_str();
-            //     match deftype {
-            //         "type" => {
-            //             let type_name = term.ty().unwrap().value_ref().as_str();
-            //             let cidx = self.constants.push_string(type_name);
-            //             let tidx = self.types.declare(TyKind::UserType, cidx);
-
-            //             if !props.is_empty() {
-            //                 let props: Vec<(ConstantIdx, TyIdx)> = props
-            //                     .iter()
-            //                     .map(|(ident, tyref)| {
-            //                         let cidx0 =
-            //                             self.constants.push_string(ident.value_ref().as_str());
-            //                         let cidx1 = self
-            //                             .constants
-            //                             .push_string(tyref.ty().unwrap().value_ref().as_str());
-            //                         let tidx = self.types.declare(TyKind::Variable, cidx1);
-            //                         (cidx0, tidx)
-            //                     })
-            //                     .collect();
-
-            //                 let ty = self.types.get_mut(tidx.clone()).unwrap();
-            //                 for (cidx, tidx) in props {
-            //                     ty.set_property(cidx, tidx);
-            //                 }
-            //             }
-
-            //             if !body.is_empty() {
-            //                 let body: Vec<(ConstantIdx, Vec<Ir>)> = body
-            //                     .iter()
-            //                     .map(|(ident, block)| {
-            //                         let cidx =
-            //                             self.constants.push_string(ident.value_ref().as_str());
-            //                         let block =
-            //                             block.iter().map(|term| self.consume(term)).collect();
-            //                         (cidx, block)
-            //                     })
-            //                     .collect();
-
-            //                 let ty = self.types.get_mut(tidx.clone()).unwrap();
-            //             }
-
-            //             panic!("wat");
-            //         }
-            //         _ => panic!("Unexpected deftype {:?}", deftype),
-            //     }
-            // }
-            // NodeType::Declaration => {
-            //     let (identifier, term) = term.declaration().unwrap();
-            // }
-            _ => panic!("unexpected node type {:?}", term.node_type()),
-        }
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn atom_literal() {
-        let terms = Term::input(r#" :marty "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        assert_eq!(ir.ty(), TyIdx::from(TyKind::Atom));
-    }
-
-    #[test]
-    fn boolean_literals() {
-        {
-            let terms = Term::input(r#" true "#).unwrap();
-            let term = &terms[0];
-
-            let mut context = Context::bootstrap();
-            context.push_module("test environment");
-            let ir = context.consume(term);
-            assert!(ir.is_constant());
-            assert_eq!(ir.ty(), TyIdx::from(TyKind::Boolean));
-        }
-        {
-            let terms = Term::input(r#" false "#).unwrap();
-            let term = &terms[0];
-
-            let mut context = Context::bootstrap();
-            context.push_module("test environment");
-            let ir = context.consume(term);
-            assert!(ir.is_constant());
-            assert_eq!(ir.ty(), TyIdx::from(TyKind::Boolean));
-        }
-    }
-
-    #[test]
-    fn float_literal() {
-        let terms = Term::input(r#" 1.23 "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        assert_eq!(ir.ty(), TyIdx::from(TyKind::Float));
-    }
-
-    #[test]
-    fn integer_literal() {
-        let terms = Term::input(r#" 123 "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        assert_eq!(ir.ty(), TyIdx::from(TyKind::Integer));
-    }
-
-    #[test]
-    fn string_literal() {
-        let terms = Term::input(r#" "Marty McFly" "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        assert_eq!(ir.ty(), TyIdx::from(TyKind::String));
-    }
-
-    #[test]
-    fn type_literal() {
-        let terms = Term::input(r#" MartyMcFly "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        let ty = context.types.get(ir.ty()).unwrap();
-        assert_eq!(ty.kind(), TyKind::Variable);
-    }
-
-    #[test]
-    fn array_literal() {
-        let terms = Term::input(r#" [1, 2, 3] "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        assert!(ir.is_compound());
-        assert_eq!(ir.ty(), TyIdx::from(TyKind::Array));
-    }
-
-    #[test]
-    fn map_literal() {
-        let terms = Term::input(r#" { a: 1, b: 2 } "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_constant());
-        assert!(ir.is_compound());
-        assert_eq!(ir.ty(), TyIdx::from(TyKind::Map));
-    }
-
-    #[test]
-    fn unary() {
-        let terms = Term::input(r#" -(:a) "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_unary());
-    }
-
-    #[test]
-    fn binary() {
-        let terms = Term::input(r#" 1 + 2 "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_binary())
-    }
-
-    #[test]
-    fn constructor() {
-        let terms = Term::input(r#" Delorean { speed: 88, mr_fusion: 72.6 } "#).unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-        assert!(ir.is_instance())
-    }
-
-    #[test]
-    fn define_type() {
-        let terms = Term::file("type Delorean(speed: Integer) do  end").unwrap();
-        let term = &terms[0];
-
-        let mut context = Context::bootstrap();
-        context.push_module("test environment");
-        let ir = context.consume(term);
-    }
-}
diff --git a/huia-compiler/src/ir/functions.rs b/huia-compiler/src/ir/functions.rs
deleted file mode 100644
index e81c9cc..0000000
--- a/huia-compiler/src/ir/functions.rs
+++ /dev/null
@@ -1,41 +0,0 @@
-use crate::ir::constants::ConstantIdx;
-use crate::ir::context::Context;
-
-#[derive(Debug, Clone, Default)]
-pub struct Function {
-    function_name: Option<ConstantIdx>,
-}
-
-#[derive(Debug, Clone)]
-pub struct FunctionIdx(usize);
-
-impl From<usize> for FunctionIdx {
-    fn from(i: usize) -> FunctionIdx {
-        FunctionIdx(i)
-    }
-}
-
-impl From<FunctionIdx> for usize {
-    fn from(i: FunctionIdx) -> usize {
-        i.0
-    }
-}
-
-#[derive(Debug, Clone, Default)]
-pub struct Functions(Vec<Function>);
-
-impl Functions {
-    pub fn push(&mut self, function: Function) -> FunctionIdx {
-        let i = self.0.len();
-        self.0.push(function);
-        FunctionIdx::from(i)
-    }
-
-    pub fn get<T: Into<usize>>(&self, idx: T) -> Option<&Function> {
-        self.0.get(idx.into())
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-}
diff --git a/huia-compiler/src/ir/mod.rs b/huia-compiler/src/ir/mod.rs
index 0394ae7..b0134d6 100644
--- a/huia-compiler/src/ir/mod.rs
+++ b/huia-compiler/src/ir/mod.rs
@@ -1,158 +1,97 @@
-use huia_parser::ast::{binary, unary};
-use huia_parser::input_location::InputLocation;
+mod builder;
 
-mod bb;
-mod constants;
-mod context;
-mod functions;
-mod modules;
-mod ty;
+use crate::stable::StringIdx;
+use crate::ty::TyIdx;
+use huia_parser::ast::binary::Operator as BinOp;
+use huia_parser::ast::unary::Operator as UnOp;
 
-use constants::ConstantIdx;
-use ty::TyIdx;
-
-#[derive(Debug, Clone)]
-pub struct Ir {
-    pub kind: IrKind,
-    pub ty: TyIdx,
-    pub input_location: InputLocation,
+/// Describes the intermediate representation as converted from the Parser's AST.
+#[derive(Debug)]
+pub enum IR {
+    Constant(TyIdx, Val),
+    TypeReference(TyIdx),
+    Infix(BinOp, Box<(IR, IR)>),
+    Constructor(TyIdx, Vec<(StringIdx, IR)>),
+    Unary(UnOp, Box<IR>),
+    Call(StringIdx, Vec<IR>),
+    Declaration(StringIdx, Box<IR>),
+    TypeDefinition(TyIdx),
+    TraitDefinition(TyIdx),
 }
 
-impl Ir {
-    pub fn new_constant<T: Into<TyIdx>>(
-        idx: ConstantIdx,
-        ty: T,
-        input_location: InputLocation,
-    ) -> Ir {
-        Ir {
-            kind: IrKind::Constant(idx),
-            ty: ty.into(),
-            input_location,
-        }
-    }
-
-    pub fn new_constant_array<T: Into<TyIdx>>(
-        ty: T,
-        elements: Vec<Ir>,
-        input_location: InputLocation,
-    ) -> Ir {
-        Ir {
-            kind: IrKind::Array(elements),
-            ty: ty.into(),
-            input_location,
-        }
-    }
-
-    pub fn new_constant_map<T: Into<TyIdx>>(
-        ty: T,
-        elements: Vec<(Ir, Ir)>,
-        input_location: InputLocation,
-    ) -> Ir {
-        Ir {
-            kind: IrKind::Map(elements),
-            ty: ty.into(),
-            input_location,
-        }
-    }
-
-    pub fn new_unary(op: unary::Operator, rhs: Ir, input_location: InputLocation) -> Ir {
-        let ty = rhs.ty.clone();
-        Ir {
-            kind: IrKind::Unary(op, Box::new(rhs)),
-            ty,
-            input_location,
-        }
-    }
-
-    pub fn new_binary(op: binary::Operator, lhs: Ir, rhs: Ir, input_location: InputLocation) -> Ir {
-        // Massive assumption that the result of addition is the same type as
-        // the LHS value.
-        let ty = lhs.ty.clone();
-        Ir {
-            kind: IrKind::Binary(op, Box::new(lhs), Box::new(rhs)),
-            ty,
-            input_location,
-        }
-    }
-
-    pub fn new_type_ref(ty: TyIdx, input_location: InputLocation) -> Ir {
-        Ir {
-            kind: IrKind::TypeRef,
-            ty,
-            input_location,
-        }
-    }
-
-    pub fn new_instance(
-        ty: TyIdx,
-        properties: Vec<(ConstantIdx, Ir)>,
-        input_location: InputLocation,
-    ) -> Ir {
-        Ir {
-            kind: IrKind::Instance(properties),
-            ty,
-            input_location,
-        }
-    }
-
-    pub fn ty(&self) -> TyIdx {
-        self.ty.clone()
-    }
-
+impl IR {
     pub fn is_constant(&self) -> bool {
-        match self.kind {
-            IrKind::Constant(_) => true,
-            IrKind::Array(_) => true,
-            IrKind::Map(_) => true,
-            IrKind::TypeRef => true,
+        match self {
+            IR::Constant(..) => true,
             _ => false,
         }
     }
 
-    pub fn is_compound(&self) -> bool {
-        match self.kind {
-            IrKind::Array(_) => true,
-            IrKind::Map(_) => true,
+    pub fn is_type_reference(&self) -> bool {
+        match self {
+            IR::TypeReference(..) => true,
+            _ => false,
+        }
+    }
+
+    pub fn is_infix(&self) -> bool {
+        match self {
+            IR::Infix(..) => true,
+            _ => false,
+        }
+    }
+
+    pub fn is_constuctor(&self) -> bool {
+        match self {
+            IR::Constructor(..) => true,
             _ => false,
         }
     }
 
     pub fn is_unary(&self) -> bool {
-        match self.kind {
-            IrKind::Unary(_, _) => true,
+        match self {
+            IR::Unary(..) => true,
             _ => false,
         }
     }
 
-    pub fn is_binary(&self) -> bool {
-        match self.kind {
-            IrKind::Binary(_, _, _) => true,
+    pub fn is_call(&self) -> bool {
+        match self {
+            IR::Call(..) => true,
             _ => false,
         }
     }
 
-    pub fn is_type_ref(&self) -> bool {
-        match self.kind {
-            IrKind::TypeRef => true,
+    pub fn is_declaration(&self) -> bool {
+        match self {
+            IR::Declaration(..) => true,
             _ => false,
         }
     }
 
-    pub fn is_instance(&self) -> bool {
-        match self.kind {
-            IrKind::Instance(_) => true,
+    pub fn is_type_definition(&self) -> bool {
+        match self {
+            IR::TypeDefinition(..) => true,
+            _ => false,
+        }
+    }
+
+    pub fn is_trait_definition(&self) -> bool {
+        match self {
+            IR::TraitDefinition(..) => true,
             _ => false,
         }
     }
 }
 
-#[derive(Debug, Clone)]
-pub enum IrKind {
-    Constant(ConstantIdx),
-    Array(Vec<Ir>),
-    Map(Vec<(Ir, Ir)>),
-    Unary(unary::Operator, Box<Ir>),
-    Binary(binary::Operator, Box<Ir>, Box<Ir>),
-    TypeRef,
-    Instance(Vec<(ConstantIdx, Ir)>),
+/// A constant value.
+#[derive(Debug)]
+pub enum Val {
+    Atom(StringIdx),
+    Boolean(bool),
+    Float(f64),
+    Integer(i64),
+    String(StringIdx),
+    Array(Vec<IR>),
+    Map(Vec<(IR, IR)>),
 }
diff --git a/huia-compiler/src/ir/modules.rs b/huia-compiler/src/ir/modules.rs
deleted file mode 100644
index 7ce5db1..0000000
--- a/huia-compiler/src/ir/modules.rs
+++ /dev/null
@@ -1,42 +0,0 @@
-use crate::ir::constants::ConstantIdx;
-use crate::ir::context::Context;
-
-#[derive(Debug, Clone)]
-pub struct Module {
-    file_name: ConstantIdx,
-}
-
-#[derive(Debug, Clone)]
-pub struct ModuleIdx(usize);
-
-impl From<usize> for ModuleIdx {
-    fn from(i: usize) -> ModuleIdx {
-        ModuleIdx(i)
-    }
-}
-
-impl From<ModuleIdx> for usize {
-    fn from(i: ModuleIdx) -> usize {
-        i.0
-    }
-}
-
-#[derive(Debug, Clone, Default)]
-pub struct Modules(Vec<Module>);
-
-impl Modules {
-    pub fn push(&mut self, file_name: ConstantIdx) -> ModuleIdx {
-        let module = Module { file_name };
-        let i = self.0.len();
-        self.0.push(module);
-        ModuleIdx::from(i)
-    }
-
-    pub fn get<T: Into<usize>>(&self, idx: T) -> Option<&Module> {
-        self.0.get(idx.into())
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-}
diff --git a/huia-compiler/src/ir/ty.rs b/huia-compiler/src/ir/ty.rs
deleted file mode 100644
index fd8e6c4..0000000
--- a/huia-compiler/src/ir/ty.rs
+++ /dev/null
@@ -1,211 +0,0 @@
-use crate::ir::constants::ConstantIdx;
-use crate::ir::functions::Functions;
-
-#[derive(Debug, Clone)]
-pub struct Ty {
-    kind: TyKind,
-    data: TyData,
-}
-
-impl Ty {
-    pub fn kind(&self) -> TyKind {
-        self.kind.clone()
-    }
-
-    pub fn name(&self) -> Option<ConstantIdx> {
-        match self.data {
-            TyData::Type { ref name, .. } => Some(name.clone()),
-            TyData::Trait { ref name, .. } => Some(name.clone()),
-            _ => None,
-        }
-    }
-
-    pub fn set_property(&mut self, key: ConstantIdx, value: TyIdx) {
-        match &mut self.data {
-            TyData::Type { properties, .. } => properties.push((key, value)),
-            _ => panic!("Cannot add properties to {:?} types", self.data),
-        }
-    }
-}
-
-#[derive(Debug, Clone, PartialEq, PartialOrd)]
-pub enum TyKind {
-    // Basic Types
-    Atom = 0,
-    Boolean,
-    Float,
-    Integer,
-    String,
-
-    // Compound types,
-    Array,
-    Map,
-
-    // User defined types.
-    UserTrait,
-    UserType,
-
-    // Type variable for an unresolved type during compilation.
-    Variable,
-
-    // Compound type for typesoecs;
-    Compound,
-
-    // A type error.
-    Error,
-}
-
-#[derive(Debug, Clone)]
-pub enum TyData {
-    Type {
-        name: ConstantIdx,
-        properties: Vec<(ConstantIdx, TyIdx)>,
-    },
-    Trait {
-        name: ConstantIdx,
-        corequires: Vec<TyIdx>,
-    },
-    Native {
-        name: ConstantIdx,
-    },
-    Spec(Vec<TyIdx>),
-}
-
-#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord)]
-pub struct TyIdx(usize);
-
-impl From<usize> for TyIdx {
-    fn from(i: usize) -> TyIdx {
-        TyIdx(i)
-    }
-}
-
-impl From<TyKind> for TyIdx {
-    fn from(kind: TyKind) -> TyIdx {
-        assert!(kind < TyKind::UserTrait, "Cannot imply type for {:?}", kind);
-        TyIdx(kind as usize)
-    }
-}
-
-impl From<TyIdx> for usize {
-    fn from(i: TyIdx) -> usize {
-        i.0
-    }
-}
-
-#[derive(Debug, Clone, Default)]
-pub struct Types(Vec<Ty>);
-
-impl Types {
-    pub fn declare(&mut self, kind: TyKind, name: ConstantIdx) -> TyIdx {
-        // Look for an existing type with the same name.
-        for (i, ty) in self.0.iter().enumerate() {
-            match ty.data {
-                TyData::Native { name: ref n } => {
-                    if n == &name {
-                        return TyIdx::from(i);
-                    }
-                }
-                TyData::Type { name: ref n, .. } => {
-                    if n == &name {
-                        return TyIdx::from(i);
-                    }
-                }
-                TyData::Trait { name: ref n, .. } => {
-                    if n == &name {
-                        return TyIdx::from(i);
-                    }
-                }
-                _ => (),
-            }
-        }
-
-        // Otherwise add a new type.
-        let i = self.0.len();
-        let data = match kind {
-            TyKind::Atom => TyData::Native { name },
-            TyKind::Boolean => TyData::Native { name },
-            TyKind::Float => TyData::Native { name },
-            TyKind::Integer => TyData::Native { name },
-            TyKind::String => TyData::Native { name },
-            TyKind::Array => TyData::Native { name },
-            TyKind::Map => TyData::Native { name },
-            TyKind::UserTrait => TyData::Trait {
-                name,
-                corequires: Vec::new(),
-            },
-            TyKind::UserType => TyData::Type {
-                name,
-                properties: Vec::new(),
-            },
-            TyKind::Variable => TyData::Native { name },
-            _ => panic!("Cannot declare {:?} type", kind),
-        };
-        let ty = Ty { kind, data };
-        self.0.push(ty);
-        TyIdx::from(i)
-    }
-
-    pub fn spec(&mut self, mut idxs: Vec<TyIdx>) -> TyIdx {
-        idxs.sort();
-        // Look for an existing typespec with the same types.
-
-        for (i, ty) in self.0.iter().enumerate() {
-            match &ty.data {
-                TyData::Spec(tys) => {
-                    if tys == &idxs {
-                        return TyIdx::from(i);
-                    }
-                }
-                _ => (),
-            }
-        }
-
-        let i = self.0.len();
-        let data = TyData::Spec(idxs);
-        let kind = TyKind::Compound;
-        let ty = Ty { kind, data };
-        self.0.push(ty);
-        TyIdx::from(i)
-    }
-
-    pub fn get<T: Into<usize>>(&self, idx: T) -> Option<&Ty> {
-        self.0.get(idx.into())
-    }
-
-    pub fn get_mut<T: Into<usize>>(&mut self, idx: T) -> Option<&mut Ty> {
-        self.0.get_mut(idx.into())
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn declare_test() {
-        let name0 = ConstantIdx::Integer(0);
-        let name1 = ConstantIdx::Integer(1);
-
-        let mut types = Types::default();
-
-        let idx0 = types.declare(TyKind::Integer, name0.clone());
-        let idx1 = types.declare(TyKind::Integer, name1);
-        let idx2 = types.declare(TyKind::Integer, name0);
-
-        assert_eq!(idx0, idx2);
-        assert_ne!(idx0, idx1);
-    }
-
-    #[test]
-    fn spec_test() {
-        let mut types = Types::default();
-
-        let name0 = ConstantIdx::Integer(0);
-        let name1 = ConstantIdx::Integer(1);
-        let idx0 = types.declare(TyKind::Integer, name0);
-        let idx1 = types.declare(TyKind::Integer, name1);
-
-        types.spec(vec![idx0, idx1]);
-    }
-}
diff --git a/huia-compiler/src/lib.rs b/huia-compiler/src/lib.rs
index 5b6c825..fc53442 100644
--- a/huia-compiler/src/lib.rs
+++ b/huia-compiler/src/lib.rs
@@ -1 +1,6 @@
+mod context;
+mod error;
 mod ir;
+mod location;
+mod stable;
+mod ty;
diff --git a/huia-compiler/src/location.rs b/huia-compiler/src/location.rs
new file mode 100644
index 0000000..f1379c5
--- /dev/null
+++ b/huia-compiler/src/location.rs
@@ -0,0 +1,31 @@
+use huia_parser::input_location::InputLocation;
+use std::fmt;
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Location {
+    location: InputLocation,
+    source_path: String,
+}
+
+impl Location {
+    pub fn new(location: InputLocation, source_path: &str) -> Location {
+        Location {
+            location,
+            source_path: source_path.to_string(),
+        }
+    }
+
+    #[cfg(test)]
+    pub fn test() -> Location {
+        Location {
+            location: InputLocation::pos(0),
+            source_path: String::from("Test Example"),
+        }
+    }
+}
+
+impl fmt::Display for Location {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}:{}", self.source_path, self.location)
+    }
+}
diff --git a/huia-compiler/src/stable.rs b/huia-compiler/src/stable.rs
new file mode 100644
index 0000000..16b26fd
--- /dev/null
+++ b/huia-compiler/src/stable.rs
@@ -0,0 +1,61 @@
+use string_interner::{StringInterner, Sym};
+
+#[derive(Debug, Default)]
+pub struct StringTable(StringInterner<Sym>);
+
+impl StringTable {
+    pub fn intern(&mut self, value: &str) -> StringIdx {
+        self.0.get_or_intern(value).into()
+    }
+
+    pub fn get(&self, idx: StringIdx) -> Option<&str> {
+        self.0.resolve(idx.into())
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct StringIdx(Sym);
+
+impl From<Sym> for StringIdx {
+    fn from(s: Sym) -> StringIdx {
+        StringIdx(s)
+    }
+}
+
+impl From<StringIdx> for Sym {
+    fn from(s: StringIdx) -> Sym {
+        s.0
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_default() {
+        let stable = StringTable::default();
+        assert!(stable.is_empty());
+    }
+
+    #[test]
+    fn test_insert() {
+        let mut stable = StringTable::default();
+        assert!(stable.is_empty());
+
+        let idx0 = stable.intern("Marty McFly");
+        let idx1 = stable.intern("Marty McFly");
+        assert_eq!(idx0, idx1);
+    }
+
+    #[test]
+    fn test_get() {
+        let mut stable = StringTable::default();
+        let idx = stable.intern("Marty McFly");
+        assert_eq!(stable.get(idx).unwrap(), "Marty McFly");
+    }
+}
diff --git a/huia-compiler/src/ty.rs b/huia-compiler/src/ty.rs
new file mode 100644
index 0000000..99dc05e
--- /dev/null
+++ b/huia-compiler/src/ty.rs
@@ -0,0 +1,122 @@
+use crate::location::Location;
+use crate::stable::StringIdx;
+use std::fmt;
+
+#[derive(Debug, PartialEq)]
+pub struct Ty {
+    name: Option<StringIdx>,
+    location: Location,
+    kind: TyKind,
+    inner: TyInner,
+}
+
+impl Ty {
+    pub fn new_type(
+        name: StringIdx,
+        location: Location,
+        properties: Vec<(StringIdx, TyIdx)>,
+    ) -> Ty {
+        Ty {
+            name: Some(name),
+            location,
+            kind: TyKind::Type,
+            inner: TyInner::Type { properties },
+        }
+    }
+
+    pub fn new_trait(name: Option<StringIdx>, location: Location, dependencies: Vec<TyIdx>) -> Ty {
+        Ty {
+            name,
+            location,
+            kind: TyKind::Trait,
+            inner: TyInner::Trait { dependencies },
+        }
+    }
+
+    pub fn new_reference(name: StringIdx, location: Location) -> Ty {
+        Ty {
+            name: Some(name),
+            location,
+            kind: TyKind::Unresolved,
+            inner: TyInner::Empty,
+        }
+    }
+
+    pub fn name(&self) -> Option<StringIdx> {
+        self.name.clone()
+    }
+
+    pub fn is_type(&self) -> bool {
+        match self.kind {
+            TyKind::Native => true,
+            TyKind::Type => true,
+            _ => false,
+        }
+    }
+
+    pub fn is_trait(&self) -> bool {
+        match self.kind {
+            TyKind::Trait => true,
+            _ => false,
+        }
+    }
+
+    pub fn is_reference(&self) -> bool {
+        match self.kind {
+            TyKind::Unresolved => true,
+            _ => false,
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, PartialOrd, Ord, Eq)]
+pub struct TyIdx(usize);
+
+impl From<usize> for TyIdx {
+    fn from(i: usize) -> TyIdx {
+        TyIdx(i)
+    }
+}
+
+impl From<TyIdx> for usize {
+    fn from(i: TyIdx) -> usize {
+        i.0
+    }
+}
+
+impl From<&TyIdx> for usize {
+    fn from(i: &TyIdx) -> usize {
+        i.0
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum TyKind {
+    Native,
+    Type,
+    Trait,
+    Unresolved,
+}
+
+impl fmt::Display for TyKind {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TyKind::Native => write!(f, "native type"),
+            TyKind::Type => write!(f, "type"),
+            TyKind::Trait => write!(f, "trait"),
+            TyKind::Unresolved => write!(f, "unresolved type"),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+enum TyInner {
+    Type { properties: Vec<(StringIdx, TyIdx)> },
+    Trait { dependencies: Vec<TyIdx> },
+    NativeInteger,
+    NativeFloat,
+    NativeString,
+    NativeArray,
+    NativeMap,
+    Empty,
+}
diff --git a/huia-parser/src/ast/atom.rs b/huia-parser/src/ast/atom.rs
index f8ecaef..0404b57 100644
--- a/huia-parser/src/ast/atom.rs
+++ b/huia-parser/src/ast/atom.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Atom {
     value: String,
     location: InputLocation,
diff --git a/huia-parser/src/ast/binary.rs b/huia-parser/src/ast/binary.rs
index 019fa10..bcc096f 100644
--- a/huia-parser/src/ast/binary.rs
+++ b/huia-parser/src/ast/binary.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Binary {
     value: Operator,
     location: InputLocation,
@@ -11,7 +11,6 @@ pub struct Binary {
 
 #[derive(Debug, Clone, PartialEq)]
 pub enum Operator {
-    Assign,
     BitwiseAnd,
     BitwiseOr,
     BitwiseXor,
@@ -55,10 +54,6 @@ impl Location for Binary {
 impl<'a> From<Pair<'a, Rule>> for Binary {
     fn from(pair: Pair<'a, Rule>) -> Self {
         match pair.as_rule() {
-            Rule::assign => Binary {
-                value: Operator::Assign,
-                location: InputLocation::from(pair.into_span()),
-            },
             Rule::bitwise_and => Binary {
                 value: Operator::BitwiseAnd,
                 location: InputLocation::from(pair.into_span()),
diff --git a/huia-parser/src/ast/boolean.rs b/huia-parser/src/ast/boolean.rs
index 3ce9552..159ddaf 100644
--- a/huia-parser/src/ast/boolean.rs
+++ b/huia-parser/src/ast/boolean.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Boolean {
     value: bool,
     location: InputLocation,
diff --git a/huia-parser/src/ast/float.rs b/huia-parser/src/ast/float.rs
index bf22087..06d4de7 100644
--- a/huia-parser/src/ast/float.rs
+++ b/huia-parser/src/ast/float.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Float {
     value: f64,
     location: InputLocation,
diff --git a/huia-parser/src/ast/identifier.rs b/huia-parser/src/ast/identifier.rs
index 5b1ea17..77f1deb 100644
--- a/huia-parser/src/ast/identifier.rs
+++ b/huia-parser/src/ast/identifier.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Identifier {
     value: String,
     location: InputLocation,
@@ -52,7 +52,10 @@ impl<'a> From<Pair<'a, Rule>> for Identifier {
                     location: InputLocation::from(pair.into_span()),
                 }
             }
-            _ => unreachable!("Expected pair to be an Identifier (received {:?})", pair.as_rule()),
+            _ => unreachable!(
+                "Expected pair to be an Identifier (received {:?})",
+                pair.as_rule()
+            ),
         }
     }
 }
diff --git a/huia-parser/src/ast/integer.rs b/huia-parser/src/ast/integer.rs
index cc2fe72..864ba2c 100644
--- a/huia-parser/src/ast/integer.rs
+++ b/huia-parser/src/ast/integer.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Integer {
     value: i64,
     radix: usize,
diff --git a/huia-parser/src/ast/local.rs b/huia-parser/src/ast/local.rs
index 912cb0a..697eebb 100644
--- a/huia-parser/src/ast/local.rs
+++ b/huia-parser/src/ast/local.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Local {
     value: String,
     location: InputLocation,
diff --git a/huia-parser/src/ast/string.rs b/huia-parser/src/ast/string.rs
index bb2ee4a..5e32f96 100644
--- a/huia-parser/src/ast/string.rs
+++ b/huia-parser/src/ast/string.rs
@@ -4,7 +4,7 @@ use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 use std::string;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct String {
     value: string::String,
     location: InputLocation,
diff --git a/huia-parser/src/ast/term.rs b/huia-parser/src/ast/term.rs
index 4e880fb..64c539e 100644
--- a/huia-parser/src/ast/term.rs
+++ b/huia-parser/src/ast/term.rs
@@ -10,7 +10,7 @@ use pest::Parser;
 // terminals and the term enum handles mashing them together with their children
 // for compound nodes.
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Term {
     location: InputLocation,
     inner: Inner,
@@ -37,7 +37,6 @@ pub enum NodeType {
 
     Call,
     Declaration,
-    Definition,
     Local,
 
     TypeDef,
@@ -48,7 +47,7 @@ pub enum NodeType {
     StaticMethod,
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 enum Inner {
     Array(Vec<Term>),
     Atom(Atom),
@@ -66,9 +65,24 @@ enum Inner {
     TypeDef(Ty, Vec<(Identifier, TypeSpec)>, Vec<Term>),
     TraitDef(Ty, Option<TypeSpec>, Vec<Term>),
     ImplDef(Ty, Vec<Term>),
-    PublicMethod(Identifier, Vec<(Identifier, TypeSpec)>, Option<TypeSpec>, Vec<Term>),
-    PrivateMethod(Identifier, Vec<(Identifier, TypeSpec)>, Option<TypeSpec>, Vec<Term>),
-    StaticMethod(Identifier, Vec<(Identifier, TypeSpec)>, Option<TypeSpec>, Vec<Term>),
+    PublicMethod(
+        Identifier,
+        Vec<(Identifier, TypeSpec)>,
+        Option<TypeSpec>,
+        Vec<Term>,
+    ),
+    PrivateMethod(
+        Identifier,
+        Vec<(Identifier, TypeSpec)>,
+        Option<TypeSpec>,
+        Vec<Term>,
+    ),
+    StaticMethod(
+        Identifier,
+        Vec<(Identifier, TypeSpec)>,
+        Option<TypeSpec>,
+        Vec<Term>,
+    ),
     Unary(Unary, Box<Term>),
 }
 
@@ -185,42 +199,69 @@ impl Term {
     pub fn traitdef(&self) -> Option<(&Ty, Option<&TypeSpec>, &Vec<Term>)> {
         match self.inner {
             Inner::TraitDef(ref ty, ref reqs, ref body) => Some((ty, reqs.as_ref(), body)),
-            _ => None
+            _ => None,
         }
     }
 
     pub fn typedef(&self) -> Option<(&Ty, &Vec<(Identifier, TypeSpec)>, &Vec<Term>)> {
         match self.inner {
             Inner::TypeDef(ref ty, ref props, ref body) => Some((ty, props, body)),
-            _ => None
+            _ => None,
         }
     }
 
     pub fn impldef(&self) -> Option<(&Ty, &Vec<Term>)> {
         match self.inner {
             Inner::ImplDef(ref ty, ref body) => Some((ty, body)),
-            _ => None
+            _ => None,
         }
     }
 
-    pub fn public_method(&self) -> Option<(&Identifier, &Vec<(Identifier, TypeSpec)>, Option<&TypeSpec>, &Vec<Term>)> {
+    pub fn public_method(
+        &self,
+    ) -> Option<(
+        &Identifier,
+        &Vec<(Identifier, TypeSpec)>,
+        Option<&TypeSpec>,
+        &Vec<Term>,
+    )> {
         match self.inner {
-            Inner::PublicMethod(ref name, ref args, ref rval, ref body) => Some((name, args, rval.as_ref(), body)),
-            _ => None
+            Inner::PublicMethod(ref name, ref args, ref rval, ref body) => {
+                Some((name, args, rval.as_ref(), body))
+            }
+            _ => None,
         }
     }
 
-    pub fn private_method(&self) -> Option<(&Identifier, &Vec<(Identifier, TypeSpec)>, Option<&TypeSpec>, &Vec<Term>)> {
+    pub fn private_method(
+        &self,
+    ) -> Option<(
+        &Identifier,
+        &Vec<(Identifier, TypeSpec)>,
+        Option<&TypeSpec>,
+        &Vec<Term>,
+    )> {
         match self.inner {
-            Inner::PrivateMethod(ref name, ref args, ref rval, ref body) => Some((name, args, rval.as_ref(), body)),
-            _ => None
+            Inner::PrivateMethod(ref name, ref args, ref rval, ref body) => {
+                Some((name, args, rval.as_ref(), body))
+            }
+            _ => None,
         }
     }
 
-    pub fn static_method(&self) -> Option<(&Identifier, &Vec<(Identifier, TypeSpec)>, Option<&TypeSpec>, &Vec<Term>)> {
+    pub fn static_method(
+        &self,
+    ) -> Option<(
+        &Identifier,
+        &Vec<(Identifier, TypeSpec)>,
+        Option<&TypeSpec>,
+        &Vec<Term>,
+    )> {
         match self.inner {
-            Inner::StaticMethod(ref name, ref args, ref rval, ref body) => Some((name, args, rval.as_ref(), body)),
-            _ => None
+            Inner::StaticMethod(ref name, ref args, ref rval, ref body) => {
+                Some((name, args, rval.as_ref(), body))
+            }
+            _ => None,
         }
     }
 
@@ -404,105 +445,125 @@ impl<'a> From<Pair<'a, Rule>> for Term {
                     location: InputLocation::from(pair),
                     inner: Inner::Unary(operator, Box::new(rhs)),
                 }
-            },
+            }
 
             Rule::traitdef => {
                 let mut inner = pair.clone().into_inner();
                 let ty = Ty::from(inner.next().unwrap());
                 let reqs = match inner.next().unwrap().into_inner().next() {
                     Some(p) => Some(TypeSpec::from(p)),
-                    None => None
+                    None => None,
                 };
-                let block = inner.next().unwrap().into_inner().map(|p| Term::from(p)).collect();
+                let block = inner.next().unwrap().into_inner().map(Term::from).collect();
                 Term {
                     location: InputLocation::from(pair),
-                    inner: Inner::TraitDef(ty, reqs, block)
+                    inner: Inner::TraitDef(ty, reqs, block),
                 }
-            },
+            }
 
             Rule::typedef => {
                 let mut inner = pair.clone().into_inner();
                 let ty = Ty::from(inner.next().unwrap());
-                let props = inner.next().unwrap().into_inner().map(|p| {
-                    let mut inner = p.into_inner();
-                    let keyword = Identifier::from(inner.next().unwrap());
-                    let typespec = TypeSpec::from(inner.next().unwrap());
-                    (keyword, typespec)
-                }).collect();
-                let block = inner.next().unwrap().into_inner().map(|p| Term::from(p)).collect();
-                Term{
+                let props = inner
+                    .next()
+                    .unwrap()
+                    .into_inner()
+                    .map(|p| {
+                        let mut inner = p.into_inner();
+                        let keyword = Identifier::from(inner.next().unwrap());
+                        let typespec = TypeSpec::from(inner.next().unwrap());
+                        (keyword, typespec)
+                    })
+                    .collect();
+                let block = inner.next().unwrap().into_inner().map(Term::from).collect();
+                Term {
                     location: InputLocation::from(pair),
-                    inner: Inner::TypeDef(ty, props, block)
+                    inner: Inner::TypeDef(ty, props, block),
                 }
             }
 
             Rule::impldef => {
                 let mut inner = pair.clone().into_inner();
                 let ty = Ty::from(inner.next().unwrap());
-                let block = inner.next().unwrap().into_inner().map(|p| Term::from(p)).collect();
+                let block = inner.next().unwrap().into_inner().map(Term::from).collect();
                 Term {
                     location: InputLocation::from(pair),
-                    inner: Inner::ImplDef(ty, block)
+                    inner: Inner::ImplDef(ty, block),
                 }
             }
 
             Rule::defpublic => {
                 let mut inner = pair.clone().into_inner();
                 let name = Identifier::from(inner.next().unwrap());
-                let args = inner.next().unwrap().into_inner().map(|p| {
-                    let mut inner = p.into_inner();
-                    let keyword = Identifier::from(inner.next().unwrap());
-                    let typespec = TypeSpec::from(inner.next().unwrap());
-                    (keyword, typespec)
-                }).collect();
+                let args = inner
+                    .next()
+                    .unwrap()
+                    .into_inner()
+                    .map(|p| {
+                        let mut inner = p.into_inner();
+                        let keyword = Identifier::from(inner.next().unwrap());
+                        let typespec = TypeSpec::from(inner.next().unwrap());
+                        (keyword, typespec)
+                    })
+                    .collect();
                 let rval = match inner.next().unwrap().into_inner().next() {
                     Some(value) => Some(TypeSpec::from(value)),
-                    _ => None
+                    _ => None,
                 };
-                let block = inner.next().unwrap().into_inner().map(|p| Term::from(p)).collect();
-                Term{
+                let block = inner.next().unwrap().into_inner().map(Term::from).collect();
+                Term {
                     location: InputLocation::from(pair),
-                    inner: Inner::PublicMethod(name, args, rval, block)
+                    inner: Inner::PublicMethod(name, args, rval, block),
                 }
-            },
+            }
             Rule::defprivate => {
                 let mut inner = pair.clone().into_inner();
                 let name = Identifier::from(inner.next().unwrap());
-                let args = inner.next().unwrap().into_inner().map(|p| {
-                    let mut inner = p.into_inner();
-                    let keyword = Identifier::from(inner.next().unwrap());
-                    let typespec = TypeSpec::from(inner.next().unwrap());
-                    (keyword, typespec)
-                }).collect();
+                let args = inner
+                    .next()
+                    .unwrap()
+                    .into_inner()
+                    .map(|p| {
+                        let mut inner = p.into_inner();
+                        let keyword = Identifier::from(inner.next().unwrap());
+                        let typespec = TypeSpec::from(inner.next().unwrap());
+                        (keyword, typespec)
+                    })
+                    .collect();
                 let rval = match inner.next().unwrap().into_inner().next() {
                     Some(value) => Some(TypeSpec::from(value)),
-                    _ => None
+                    _ => None,
                 };
-                let block = inner.next().unwrap().into_inner().map(|p| Term::from(p)).collect();
-                Term{
+                let block = inner.next().unwrap().into_inner().map(Term::from).collect();
+                Term {
                     location: InputLocation::from(pair),
-                    inner: Inner::PrivateMethod(name, args, rval, block)
+                    inner: Inner::PrivateMethod(name, args, rval, block),
                 }
-            },
+            }
             Rule::defstatic => {
                 let mut inner = pair.clone().into_inner();
                 let name = Identifier::from(inner.next().unwrap());
-                let args = inner.next().unwrap().into_inner().map(|p| {
-                    let mut inner = p.into_inner();
-                    let keyword = Identifier::from(inner.next().unwrap());
-                    let typespec = TypeSpec::from(inner.next().unwrap());
-                    (keyword, typespec)
-                }).collect();
+                let args = inner
+                    .next()
+                    .unwrap()
+                    .into_inner()
+                    .map(|p| {
+                        let mut inner = p.into_inner();
+                        let keyword = Identifier::from(inner.next().unwrap());
+                        let typespec = TypeSpec::from(inner.next().unwrap());
+                        (keyword, typespec)
+                    })
+                    .collect();
                 let rval = match inner.next().unwrap().into_inner().next() {
                     Some(value) => Some(TypeSpec::from(value)),
-                    _ => None
+                    _ => None,
                 };
-                let block = inner.next().unwrap().into_inner().map(|p| Term::from(p)).collect();
-                Term{
+                let block = inner.next().unwrap().into_inner().map(Term::from).collect();
+                Term {
                     location: InputLocation::from(pair),
-                    inner: Inner::StaticMethod(name, args, rval, block)
+                    inner: Inner::StaticMethod(name, args, rval, block),
                 }
-            },
+            }
 
             _ => panic!("Unexpected pair {:?}", pair),
         }
@@ -650,11 +711,14 @@ mod test {
 
     #[test]
     fn test_typedef_with_impl() {
-        let terms = Term::file(r#"
+        let terms = Term::file(
+            r#"
                 type Delorean(speed: Integer) do
                     impl TimeMachine
                 end
-            "#).unwrap();
+            "#,
+        )
+        .unwrap();
         let (ty, props, body) = terms[0].typedef().unwrap();
         assert_eq!(ty.value_ref(), "Delorean");
         assert_eq!(props.len(), 1);
@@ -671,13 +735,16 @@ mod test {
 
     #[test]
     fn test_typdef_with_methods() {
-        let terms = Term::file(r#"
+        let terms = Term::file(
+            r#"
                 type Delorean(speed: Integer) do
                     defs new() do
                         Delorean { speed: 0 }
                     end
                 end
-        "#).unwrap();
+        "#,
+        )
+        .unwrap();
         let (ty, props, body) = terms[0].typedef().unwrap();
         assert_eq!(ty.value_ref(), "Delorean");
         assert_eq!(props.len(), 1);
@@ -687,7 +754,6 @@ mod test {
         assert_eq!(key.value_ref(), "speed");
         assert_eq!(value.value_ref()[0].value_ref(), "Integer");
 
-
         let (name, args, rval, block) = &body[0].static_method().unwrap();
         assert_eq!(name.value_ref(), "new");
         assert!(args.is_empty());
@@ -695,7 +761,6 @@ mod test {
         assert_eq!(block.len(), 1);
     }
 
-
     #[test]
     fn test_declaration() {
         let terms = Term::input("let speed = 88").unwrap();
diff --git a/huia-parser/src/ast/ty.rs b/huia-parser/src/ast/ty.rs
index 49d1d99..da7a7d7 100644
--- a/huia-parser/src/ast/ty.rs
+++ b/huia-parser/src/ast/ty.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Ty {
     value: String,
     location: InputLocation,
diff --git a/huia-parser/src/ast/typespec.rs b/huia-parser/src/ast/typespec.rs
index c206f66..112831a 100644
--- a/huia-parser/src/ast/typespec.rs
+++ b/huia-parser/src/ast/typespec.rs
@@ -1,9 +1,9 @@
-use crate::ast::{Location, Value, Ty};
+use crate::ast::{Location, Ty, Value};
 use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct TypeSpec {
     value: Vec<Ty>,
     location: InputLocation,
@@ -31,14 +31,13 @@ impl<'a> From<Pair<'a, Rule>> for TypeSpec {
     fn from(pair: Pair<'a, Rule>) -> Self {
         match pair.as_rule() {
             Rule::typespec => {
-                let value = pair.clone().into_inner().map(|p| Ty::from(p)).collect();
+                let value = pair.clone().into_inner().map(Ty::from).collect();
                 TypeSpec {
                     value,
                     location: InputLocation::from(pair.into_span()),
                 }
-
-            },
-                _ => unreachable!("Expected pair to be an TypeSpec"),
+            }
+            _ => unreachable!("Expected pair to be an TypeSpec"),
         }
     }
 }
diff --git a/huia-parser/src/ast/unary.rs b/huia-parser/src/ast/unary.rs
index 5cbc73b..3a5c0ce 100644
--- a/huia-parser/src/ast/unary.rs
+++ b/huia-parser/src/ast/unary.rs
@@ -3,7 +3,7 @@ use crate::grammar::Rule;
 use crate::input_location::InputLocation;
 use pest::iterators::Pair;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Unary {
     value: Operator,
     location: InputLocation,
diff --git a/huia-parser/src/input_location.rs b/huia-parser/src/input_location.rs
index 52305d4..184be0a 100644
--- a/huia-parser/src/input_location.rs
+++ b/huia-parser/src/input_location.rs
@@ -1,7 +1,8 @@
 use crate::grammar::Rule;
 use pest;
+use std::fmt;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum InputLocation {
     Pos(usize),
     Span(usize, usize),
@@ -43,3 +44,12 @@ impl<'a> From<pest::iterators::Pair<'a, Rule>> for InputLocation {
         InputLocation::from(pair.into_span())
     }
 }
+
+impl fmt::Display for InputLocation {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            InputLocation::Pos(pos) => write!(f, "{}", pos),
+            InputLocation::Span(start, end) => write!(f, "{}:{}", start, end),
+        }
+    }
+}