diff --git a/huia-compiler/src/clause.rs b/huia-compiler/src/clause.rs
index 9181465..83b6870 100644
--- a/huia-compiler/src/clause.rs
+++ b/huia-compiler/src/clause.rs
@@ -33,8 +33,8 @@ impl Clause {
 }
 
 impl ResultType for Clause {
-    fn result_type(&self) -> Option<&TyIdx> {
-        Some(&self.result_type)
+    fn result_type(&self) -> &TyIdx {
+        &self.result_type
     }
 }
 
diff --git a/huia-compiler/src/context/display.rs b/huia-compiler/src/context/display.rs
index bbf151a..3cced80 100644
--- a/huia-compiler/src/context/display.rs
+++ b/huia-compiler/src/context/display.rs
@@ -159,7 +159,11 @@ fn fmt_types(buffer: &mut String, context: &Context) {
         } else if ty.is_unresolved() {
             buffer.push_str("unknown type");
         }
-        buffer.push_str("\n")
+        if let Some(location) = ty.get_location() {
+            buffer.push_str(&format!(" defined at {}\n", location));
+        } else {
+            buffer.push_str("\n");
+        }
     }
 }
 
@@ -195,7 +199,7 @@ fn fmt_functions(mut buffer: &mut String, context: &Context) {
             }
             buffer.push_str(&format!(
                 " -> {}\n",
-                fmt_ty_name(clause.result_type().unwrap(), &context)
+                fmt_ty_name(clause.result_type(), &context)
             ));
 
             let mut jumps = Vec::new();
@@ -530,7 +534,7 @@ fn fmt_methods(mut buffer: &mut String, context: &Context) {
             }
             buffer.push_str(&format!(
                 " -> {}\n",
-                fmt_ty_name(clause.result_type().unwrap(), &context)
+                fmt_ty_name(clause.result_type(), &context)
             ));
 
             let mut jumps = vec![clause.body().clone()];
diff --git a/huia-compiler/src/function.rs b/huia-compiler/src/function.rs
index b2c481e..5e6765f 100644
--- a/huia-compiler/src/function.rs
+++ b/huia-compiler/src/function.rs
@@ -88,20 +88,20 @@ impl Locatable for &mut Function {
 }
 
 impl ResultType for Function {
-    fn result_type(&self) -> Option<&TyIdx> {
-        Some(&self.return_type)
+    fn result_type(&self) -> &TyIdx {
+        &self.return_type
     }
 }
 
 impl ResultType for &Function {
-    fn result_type(&self) -> Option<&TyIdx> {
-        Some(&self.return_type)
+    fn result_type(&self) -> &TyIdx {
+        &self.return_type
     }
 }
 
 impl ResultType for &mut Function {
-    fn result_type(&self) -> Option<&TyIdx> {
-        Some(&self.return_type)
+    fn result_type(&self) -> &TyIdx {
+        &self.return_type
     }
 }
 
diff --git a/huia-compiler/src/improvements/block_result_types.rs b/huia-compiler/src/improvements/block_result_types.rs
index fcfa834..fe1e53e 100644
--- a/huia-compiler/src/improvements/block_result_types.rs
+++ b/huia-compiler/src/improvements/block_result_types.rs
@@ -1,6 +1,7 @@
 use crate::block::BlockIdx;
 use crate::clause::Clauseable;
 use crate::context::Context;
+use crate::ty::ResultType;
 
 pub fn pass<T: Clauseable>(fun: &mut T, mut context: &mut Context) {
     for clause in fun.clauses() {
diff --git a/huia-compiler/src/improvements/clause_return_types.rs b/huia-compiler/src/improvements/clause_return_types.rs
index b564052..6568a6e 100644
--- a/huia-compiler/src/improvements/clause_return_types.rs
+++ b/huia-compiler/src/improvements/clause_return_types.rs
@@ -6,7 +6,7 @@ use crate::ty::ResultType;
 pub fn pass<T: Clauseable + Locatable + ResultType>(fun: &mut T, context: &mut Context) {
     for clause in fun.clauses() {
         let block_idx = clause.body();
-        let ty_idx = clause.result_type().unwrap();
+        let ty_idx = clause.result_type();
         let result_type = context.get_block(block_idx).unwrap().result_type().clone();
         let ty = context.get_type_mut(ty_idx).unwrap();
         ty.resolve(&result_type);
diff --git a/huia-compiler/src/improvements/desugar_infix.rs b/huia-compiler/src/improvements/desugar_infix.rs
index b1e682b..563396a 100644
--- a/huia-compiler/src/improvements/desugar_infix.rs
+++ b/huia-compiler/src/improvements/desugar_infix.rs
@@ -43,6 +43,7 @@ pub fn pass(ir: &mut IR, context: &mut Context) {
 mod test {
     use super::*;
     use crate::ir::builder::Builder;
+    use crate::location::Location;
     use huia_parser::ast::Term;
 
     #[test]
@@ -50,6 +51,7 @@ mod test {
         let terms = Term::input("3 * 2").unwrap();
         let mut context = Context::test();
         let mut builder = Builder::default();
+        builder.push_block(context.unknown_type(Location::test()));
 
         for term in terms {
             builder.build(term, &mut context);
diff --git a/huia-compiler/src/improvements/desugar_unary.rs b/huia-compiler/src/improvements/desugar_unary.rs
index 32286bb..8b14f85 100644
--- a/huia-compiler/src/improvements/desugar_unary.rs
+++ b/huia-compiler/src/improvements/desugar_unary.rs
@@ -27,6 +27,7 @@ pub fn pass(ir: &mut IR, context: &mut Context) {
 mod test {
     use super::*;
     use crate::ir::builder::Builder;
+    use crate::location::Location;
     use huia_parser::ast::Term;
 
     #[test]
@@ -34,6 +35,7 @@ mod test {
         let terms = Term::input("!3").unwrap();
         let mut context = Context::test();
         let mut builder = Builder::default();
+        builder.push_block(context.unknown_type(Location::test()));
 
         for term in terms {
             builder.build(term, &mut context);
diff --git a/huia-compiler/src/improvements/infix_folding.rs b/huia-compiler/src/improvements/infix_folding.rs
index a47af32..c5cf98e 100644
--- a/huia-compiler/src/improvements/infix_folding.rs
+++ b/huia-compiler/src/improvements/infix_folding.rs
@@ -71,6 +71,7 @@ fn perform_f64_infix_fold(op: &BinOp, lhs: f64, rhs: f64) -> Option<f64> {
 mod test {
     use super::*;
     use crate::ir::builder::Builder;
+    use crate::location::Location;
     use huia_parser::ast::Term;
 
     #[test]
@@ -78,6 +79,7 @@ mod test {
         let term = Term::input("3 * 2 + 13 / 2").unwrap()[0].clone();
         let mut context = Context::test();
         let mut builder = Builder::default();
+        builder.push_block(context.unknown_type(Location::test()));
 
         builder.build(term, &mut context);
         let mut ir = builder.pop_ir().unwrap();
@@ -92,6 +94,7 @@ mod test {
         let term = Term::input("1.5 * 2.0 / 3.0").unwrap()[0].clone();
         let mut context = Context::test();
         let mut builder = Builder::default();
+        builder.push_block(context.unknown_type(Location::test()));
 
         builder.build(term, &mut context);
         let mut ir = builder.pop_ir().unwrap();
diff --git a/huia-compiler/src/improvements/unary_folding.rs b/huia-compiler/src/improvements/unary_folding.rs
index ed58cbe..08ea83b 100644
--- a/huia-compiler/src/improvements/unary_folding.rs
+++ b/huia-compiler/src/improvements/unary_folding.rs
@@ -54,6 +54,8 @@ pub fn pass(ir: &mut IR, context: &mut Context) {
 mod test {
     use super::*;
     use crate::ir::builder::Builder;
+    use crate::location::Location;
+    use crate::ty::ResultType;
     use huia_parser::ast::Term;
 
     #[test]
@@ -61,6 +63,7 @@ mod test {
         let term = Term::input("!3").unwrap()[0].clone();
         let mut context = Context::test();
         let mut builder = Builder::default();
+        builder.push_block(context.unknown_type(Location::test()));
 
         builder.build(term, &mut context);
         let mut ir = builder.pop_ir().unwrap();
diff --git a/huia-compiler/src/ir/builder.rs b/huia-compiler/src/ir/builder.rs
index 95936aa..21925f7 100644
--- a/huia-compiler/src/ir/builder.rs
+++ b/huia-compiler/src/ir/builder.rs
@@ -9,7 +9,7 @@ use crate::location::Locatable;
 use crate::location::Location as Loc;
 use crate::method::{Method, MethodIdx, Modifier};
 use crate::stable::StringIdx;
-use crate::ty::TyIdx;
+use crate::ty::{ResultType, TyIdx};
 use huia_parser::ast::{Identifier, Location, NodeType, Term, TypeSpec, Value};
 
 /// The Builder is a simple stack machine for converting AST into IR.
@@ -69,7 +69,7 @@ impl Builder {
                     context.reference_type(&name, location.clone())
                 }
                 else if op.is_arithmetic() {
-                    lhs.result_type()
+                    lhs.result_type().clone()
                 }
                 else {
                     panic!("Operator {:?} is neither arithmetic nor logical", op);
@@ -123,7 +123,7 @@ impl Builder {
                 self.build(rhs.clone(), &mut context);
                 let rhs = self.pop_ir().unwrap();
                 self.env_set(&name, &rhs.result_type());
-                self.push_ir(IR::new_set_local(rhs.result_type(), location, name, rhs));
+                self.push_ir(IR::new_set_local(rhs.result_type().clone(), location, name, rhs));
             }
             NodeType::Float => {
                 let ty_idx = context.constant_string("Huia.Native.Float");
@@ -171,8 +171,8 @@ impl Builder {
                 if let Some(last_ir) = self.pop_ir() {
                     let rt = context.get_type_mut(&result_type).unwrap();
                     rt.resolve(&last_ir.result_type());
-                    self.push_ir(IR::new_set_local(last_ir.result_type(), location.clone(), value_var_name.clone(), last_ir.clone()));
-                    self.push_ir(IR::new_jump(last_ir.result_type(), location.clone(), following_block_idx.into()));
+                    self.push_ir(IR::new_set_local(last_ir.result_type().clone(), location.clone(), value_var_name.clone(), last_ir.clone()));
+                    self.push_ir(IR::new_jump(last_ir.result_type().clone(), location.clone(), following_block_idx.into()));
                 } else {
                     self.push_ir(IR::new_jump(result_type.clone(), location.clone(), following_block_idx.into()));
                 }
@@ -198,12 +198,12 @@ impl Builder {
 
                     if let Some(last_ir) = self.pop_ir() {
                         let rt = context.get_type(&result_type).unwrap();
-                        if rt.target().unwrap() != &last_ir.result_type() {
+                        if rt.target().unwrap() != last_ir.result_type() {
                             context.compile_error("Both branches of an if statement must result in the same type.", location.clone(), ErrorKind::InconsistentBranchTypes);
                         }
 
-                        self.push_ir(IR::new_set_local(last_ir.result_type(), location.clone(), value_var_name.clone(), last_ir.clone()));
-                        self.push_ir(IR::new_jump(last_ir.result_type(), location.clone(), following_block_idx.into()));
+                        self.push_ir(IR::new_set_local(last_ir.result_type().clone(), location.clone(), value_var_name.clone(), last_ir.clone()));
+                        self.push_ir(IR::new_jump(last_ir.result_type().clone(), location.clone(), following_block_idx.into()));
                     } else {
                         self.push_ir(IR::new_jump(result_type.clone(), location.clone(), following_block_idx.into()));
                     }
@@ -454,7 +454,7 @@ impl Builder {
                 let (op, rhs) = node.unary().unwrap();
                 self.build(rhs.clone(), &mut context);
                 let rhs = self.pop_ir().unwrap();
-                let result_type = rhs.result_type();
+                let result_type = rhs.result_type().clone();
                 self.push_ir(IR::new_unary(
                     result_type,
                     location,
@@ -524,7 +524,7 @@ impl Builder {
                 self.push_ir(last_ir);
             } else {
                 self.push_ir(IR::new_return(
-                    last_ir.result_type(),
+                    last_ir.result_type().clone(),
                     last_ir.get_location().clone(),
                     last_ir,
                 ));
@@ -668,7 +668,7 @@ impl Builder {
         None
     }
 
-    fn push_block(&mut self, result_type: TyIdx) {
+    pub fn push_block(&mut self, result_type: TyIdx) {
         match self.peek_block() {
             Some(ref block) => {
                 let env = block.env().clone();
@@ -707,6 +707,7 @@ mod test {
         let term = Term::input(":marty").unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
@@ -718,6 +719,7 @@ mod test {
         let term = Term::input("true").unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
@@ -729,6 +731,7 @@ mod test {
         let term = Term::input("1.23").unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
@@ -740,6 +743,7 @@ mod test {
         let term = Term::input(r#" "Marty McFly"  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
@@ -751,6 +755,7 @@ mod test {
         let term = Term::input(r#" MartyMcFly  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_type_reference());
@@ -762,6 +767,7 @@ mod test {
         let term = Term::input(r#" [1, 2, 3]  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
@@ -774,6 +780,7 @@ mod test {
         let term = Term::input(r#" { a: 2, :b => 3 }  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constant());
@@ -787,6 +794,7 @@ mod test {
         let term = Term::input(r#" if true do 123 end  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
 
         // Pop the follower block off the block stack.
@@ -803,6 +811,7 @@ mod test {
         let term = Term::input(r#" if true do 123 else 456 end  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
 
         // Pop the follower block off the block stack.
@@ -820,6 +829,7 @@ mod test {
         let term = Term::input(r#" 1 + 2  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_infix());
@@ -831,6 +841,7 @@ mod test {
         let term = Term::input(r#" Delorean { speed: 88 }  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_constructor());
@@ -843,6 +854,7 @@ mod test {
         let term = Term::input(r#" +88  "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_unary());
@@ -854,6 +866,7 @@ mod test {
         let terms = Term::input(" let x = 1\n x(123)  ").unwrap();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         for term in terms {
             builder.build(term, &mut context);
         }
@@ -867,6 +880,7 @@ mod test {
         let term = Term::input(r#" let x = 123 "#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_set_local());
@@ -878,6 +892,7 @@ mod test {
         let term = Term::file("type Delorean(speed: Integer)").unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         assert!(context.find_type("Delorean").is_some());
         assert!(context.find_type("Integer").is_some());
@@ -888,6 +903,7 @@ mod test {
         let term = Term::file("trait TimeMachine").unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         assert!(context.find_type("TimeMachine").is_some());
     }
@@ -905,6 +921,7 @@ mod test {
             .clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         assert!(context.find_type("Delorean").is_some());
         assert!(context.find_type("TimeMachine").is_some());
@@ -915,6 +932,7 @@ mod test {
         let term = Term::input(r#"fn (speed: Integer) do "WAT" end"#).unwrap()[0].clone();
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
         let ir = builder.pop_ir().unwrap();
         assert!(ir.is_function());
@@ -964,9 +982,7 @@ mod test {
 
         let mut builder = Builder::default();
         let mut context = Context::test();
+        builder.push_block(context.unknown_type(Loc::test()));
         builder.build(term, &mut context);
-
-        // println!("context: {:#?}", context);
-        // assert!(false);
     }
 }
diff --git a/huia-compiler/src/ir/mod.rs b/huia-compiler/src/ir/mod.rs
index 98c32f5..f450bcc 100644
--- a/huia-compiler/src/ir/mod.rs
+++ b/huia-compiler/src/ir/mod.rs
@@ -5,7 +5,7 @@ use crate::context::Context;
 use crate::function::FunctionIdx;
 use crate::location::Location;
 use crate::stable::StringIdx;
-use crate::ty::TyIdx;
+use crate::ty::{ResultType, TyIdx};
 use huia_parser::ast::binary::Operator as BinOp;
 use huia_parser::ast::unary::Operator as UnOp;
 
@@ -526,10 +526,6 @@ impl IR {
         }
     }
 
-    pub fn result_type(&self) -> TyIdx {
-        self.result_type.clone()
-    }
-
     pub fn set_kind(&mut self, kind: IRKind) {
         self.kind = kind;
     }
@@ -539,6 +535,12 @@ impl IR {
     }
 }
 
+impl ResultType for IR {
+    fn result_type(&self) -> &TyIdx {
+        &self.result_type
+    }
+}
+
 #[derive(Debug, PartialEq, Clone)]
 pub enum IRKind {
     /// Call the provided callee with arguments.
diff --git a/huia-compiler/src/method.rs b/huia-compiler/src/method.rs
index 9b7a026..b9b79cc 100644
--- a/huia-compiler/src/method.rs
+++ b/huia-compiler/src/method.rs
@@ -159,8 +159,8 @@ impl Locatable for &mut Method {
 }
 
 impl ResultType for &mut Method {
-    fn result_type(&self) -> Option<&TyIdx> {
-        Some(&self.return_type)
+    fn result_type(&self) -> &TyIdx {
+        &self.return_type
     }
 }
 
diff --git a/huia-compiler/src/ty.rs b/huia-compiler/src/ty.rs
index d706140..2241447 100644
--- a/huia-compiler/src/ty.rs
+++ b/huia-compiler/src/ty.rs
@@ -23,6 +23,10 @@ impl Ty {
         }
     }
 
+    pub fn get_location(&self) -> Option<&Location> {
+        self.location.as_ref()
+    }
+
     pub fn get_prop_type(&self, name: &StringIdx) -> Option<&TyIdx> {
         match self.inner {
             TyInner::Type { ref properties } => properties.get(name),
@@ -369,5 +373,5 @@ enum TyInner {
 }
 
 pub trait ResultType {
-    fn result_type(&self) -> Option<&TyIdx>;
+    fn result_type(&self) -> &TyIdx;
 }