diff --git a/huia-compiler/src/context.rs b/huia-compiler/src/context.rs
index 0164a51..258c72e 100644
--- a/huia-compiler/src/context.rs
+++ b/huia-compiler/src/context.rs
@@ -66,6 +66,13 @@ impl Context {
         idx.into()
     }
 
+    pub fn declare_impl(&mut self, tr: TyIdx, ty: TyIdx, location: Location) -> TyIdx {
+        let idx = self.types.len();
+        let ty = Ty::new_impl(ty, tr, location);
+        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
@@ -87,6 +94,12 @@ impl Context {
         self.types.get(usize::from(idx))
     }
 
+    #[cfg(test)]
+    pub fn find_type(&mut self, name: &str) -> Option<&Ty> {
+        let name = self.constant_string(name);
+        self.types.iter().find(|ty| ty.name() == Some(name.clone()))
+    }
+
     pub fn location(&self, location: &InputLocation) -> Location {
         let path = self.strings.get(self.current_file.clone()).unwrap();
         Location::new(location.clone(), path)
diff --git a/huia-compiler/src/ir/builder.rs b/huia-compiler/src/ir/builder.rs
index fb229ec..5c94c28 100644
--- a/huia-compiler/src/ir/builder.rs
+++ b/huia-compiler/src/ir/builder.rs
@@ -182,7 +182,6 @@ impl Builder {
                 }
 
                 self.pop_ty();
-                self.push_ir(IR::TypeDefinition(ty));
             }
             NodeType::TraitDef => {
                 let (ty, typespec, body) = node.traitdef().unwrap();
@@ -212,49 +211,48 @@ impl Builder {
                 }
 
                 self.pop_ty();
-                self.push_ir(IR::TraitDefinition(ty));
             }
             NodeType::ImplDef => {
                 let (ty, body) = node.impldef().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 tr = context.reference_type(&ty_idx, location.clone());
 
                 // the parser state should stop us from being in an
                 // implementation whilst not inside a type definition.
-                let current_type = self.peek_ty().unwrap().clone();
+                let ty = self.peek_ty().unwrap().clone();
+
+                let im = context.declare_impl(tr, ty, location);
+
+                self.push_ty(im.clone());
 
                 for node in body {
                     self.build(node.clone(), &mut context);
                 }
 
-                self.push_ir(IR::ImplementTrait(current_type, ty));
+                self.pop_ty();
             }
             _ => (),
         }
     }
 
-    pub fn pop(&mut self) -> Option<IR> {
-        self.pop_ir()
-    }
-
-    fn push_ir(&mut self, ir: IR) {
+    pub fn push_ir(&mut self, ir: IR) {
         self.ir_stack.push(ir);
     }
 
-    fn pop_ir(&mut self) -> Option<IR> {
+    pub fn pop_ir(&mut self) -> Option<IR> {
         self.ir_stack.pop()
     }
 
-    fn push_ty(&mut self, ty: TyIdx) {
+    pub fn push_ty(&mut self, ty: TyIdx) {
         self.ty_stack.push(ty);
     }
 
-    fn pop_ty(&mut self) -> Option<TyIdx> {
+    pub fn pop_ty(&mut self) -> Option<TyIdx> {
         self.ty_stack.pop()
     }
 
-    fn peek_ty(&self) -> Option<&TyIdx> {
+    pub fn peek_ty(&self) -> Option<&TyIdx> {
         let len = self.ty_stack.len();
         self.ty_stack.get(len - 1)
     }
@@ -270,8 +268,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
+        assert!(context.find_type("Huia.Native.Atom").is_some());
     }
 
     #[test]
@@ -280,8 +279,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
+        assert!(context.find_type("Huia.Native.Boolean").is_some());
     }
 
     #[test]
@@ -290,8 +290,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
+        assert!(context.find_type("Huia.Native.Float").is_some());
     }
 
     #[test]
@@ -300,8 +301,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
+        assert!(context.find_type("Huia.Native.String").is_some());
     }
 
     #[test]
@@ -310,8 +312,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_type_reference());
+        assert!(context.find_type("MartyMcFly").is_some());
     }
 
     #[test]
@@ -320,8 +323,10 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
+        assert!(context.find_type("Huia.Native.Array").is_some());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -330,8 +335,11 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
+        assert!(context.find_type("Huia.Native.Map").is_some());
+        assert!(context.find_type("Huia.Native.Atom").is_some());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -340,8 +348,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_infix());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -350,8 +359,10 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constuctor());
+        assert!(context.find_type("Delorean").is_some());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -360,8 +371,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_unary());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -370,8 +382,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_call());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -380,8 +393,9 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-        let ir = builder.pop().unwrap();
+        let ir = builder.pop_ir().unwrap();
         assert!(ir.is_declaration());
+        assert!(context.find_type("Huia.Native.Integer").is_some());
     }
 
     #[test]
@@ -390,8 +404,8 @@ mod test {
         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());
+        assert!(context.find_type("Delorean").is_some());
+        assert!(context.find_type("Integer").is_some());
     }
 
     #[test]
@@ -400,8 +414,7 @@ mod test {
         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());
+        assert!(context.find_type("TimeMachine").is_some());
     }
 
     #[test]
@@ -418,13 +431,8 @@ mod test {
         let mut builder = Builder::default();
         let mut context = Context::test();
         builder.build(term, &mut context);
-
-        // The type definition is pushed onto the stack last.
-        let ir = builder.pop().unwrap();
-        assert!(ir.is_type_definition());
-
-        let ir = builder.pop().unwrap();
-        assert!(ir.is_trait_implementation());
+        assert!(context.find_type("Delorean").is_some());
+        assert!(context.find_type("TimeMachine").is_some());
     }
 
 }
diff --git a/huia-compiler/src/ir/mod.rs b/huia-compiler/src/ir/mod.rs
index a8702c6..befb568 100644
--- a/huia-compiler/src/ir/mod.rs
+++ b/huia-compiler/src/ir/mod.rs
@@ -18,9 +18,6 @@ pub enum IR {
     Unary(UnOp, Box<IR>),
     Call(StringIdx, Vec<IR>),
     Declaration(StringIdx, Box<IR>),
-    TypeDefinition(TyIdx),
-    TraitDefinition(TyIdx),
-    ImplementTrait(TyIdx, TyIdx),
 }
 
 impl IR {
@@ -72,27 +69,6 @@ impl IR {
             _ => false,
         }
     }
-
-    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,
-        }
-    }
-
-    pub fn is_trait_implementation(&self) -> bool {
-        match self {
-            IR::ImplementTrait(..) => true,
-            _ => false,
-        }
-    }
 }
 
 /// A constant value.
diff --git a/huia-compiler/src/ty.rs b/huia-compiler/src/ty.rs
index bd18485..063d54c 100644
--- a/huia-compiler/src/ty.rs
+++ b/huia-compiler/src/ty.rs
@@ -47,6 +47,15 @@ impl Ty {
         }
     }
 
+    pub fn new_impl(ty: TyIdx, tr: TyIdx, location: Location) -> Ty {
+        Ty {
+            name: None,
+            location,
+            kind: TyKind::Impl,
+            inner: TyInner::Impl { ty, tr },
+        }
+    }
+
     pub fn name(&self) -> Option<StringIdx> {
         self.name.clone()
     }
@@ -72,6 +81,13 @@ impl Ty {
             _ => false,
         }
     }
+
+    pub fn is_impl(&self) -> bool {
+        match self.kind {
+            TyKind::Impl => true,
+            _ => false,
+        }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, PartialOrd, Ord, Eq)]
@@ -100,6 +116,7 @@ pub enum TyKind {
     Native,
     Type,
     Trait,
+    Impl,
     Unresolved,
 }
 
@@ -109,6 +126,7 @@ impl fmt::Display for TyKind {
             TyKind::Native => write!(f, "native type"),
             TyKind::Type => write!(f, "type"),
             TyKind::Trait => write!(f, "trait"),
+            TyKind::Impl => write!(f, "trait implementation"),
             TyKind::Unresolved => write!(f, "unresolved type"),
         }
     }
@@ -118,6 +136,7 @@ impl fmt::Display for TyKind {
 enum TyInner {
     Type { properties: Vec<(StringIdx, TyIdx)> },
     Trait { dependencies: Vec<TyIdx> },
+    Impl { tr: TyIdx, ty: TyIdx },
     NativeInteger,
     NativeFloat,
     NativeString,