diff --git a/fine/src/compiler.rs b/fine/src/compiler.rs
index 512919cd..fc817c65 100644
--- a/fine/src/compiler.rs
+++ b/fine/src/compiler.rs
@@ -658,7 +658,8 @@ fn compile_new_object_expression(c: &mut Compiler, t: TreeRef, tree: &Tree) -> C
     }
 
     // Fetch the correct constructor.
-    let type_reference = tree.child_tree_of_kind(c.syntax, TreeKind::TypeExpression)?;
+    // TODO: Binding this type should be done by semantics, and we should borrow it.
+    let type_reference = tree.child_tree_of_kind(c.syntax, TreeKind::TypeIdentifier)?;
     let identifier = type_reference.nth_token(0)?;
     let environment = c.semantics.environment_of(t);
     match environment.bind(identifier)? {
diff --git a/fine/src/parser.rs b/fine/src/parser.rs
index b2f5e460..8a906de0 100644
--- a/fine/src/parser.rs
+++ b/fine/src/parser.rs
@@ -120,6 +120,7 @@ impl<'a> std::ops::IndexMut<TreeRef> for SyntaxTree<'a> {
 pub enum TreeKind {
     Error,
 
+    AlternateType,
     Argument,
     ArgumentList,
     BinaryExpression,
@@ -150,6 +151,7 @@ pub enum TreeKind {
     SelfParameter,
     SelfReference,
     TypeExpression,
+    TypeIdentifier,
     TypeParameter,
     TypeParameterList,
     UnaryExpression,
@@ -688,14 +690,27 @@ fn return_type(p: &mut CParser) {
 fn type_expr(p: &mut CParser) {
     let m = p.start();
 
-    // TODO: Other kinds of type expressions probably!
-    p.expect(TokenKind::Identifier, "expected the identifier of a type");
+    alternate_type(p);
 
+    p.end(m, TreeKind::TypeExpression);
+}
+
+fn alternate_type(p: &mut CParser) {
+    let mut result = type_identifier(p);
+    while p.eat(TokenKind::Or) {
+        let m = p.start_before(result);
+        type_identifier(p);
+        result = p.end(m, TreeKind::AlternateType);
+    }
+}
+
+fn type_identifier(p: &mut CParser) -> MarkClosed {
+    let m = p.start();
+    p.expect(TokenKind::Identifier, "expected the identifier of a type");
     if p.at(TokenKind::Less) {
         type_parameter_list(p);
     }
-
-    p.end(m, TreeKind::TypeExpression);
+    p.end(m, TreeKind::TypeIdentifier)
 }
 
 fn type_parameter_list(p: &mut CParser) {
@@ -1095,7 +1110,7 @@ fn object_constructor(p: &mut CParser) -> MarkClosed {
     let m = p.start();
 
     p.expect_start(TokenKind::New);
-    type_expr(p);
+    type_identifier(p);
     if p.at(TokenKind::LeftBrace) {
         field_list(p);
     } else {
diff --git a/fine/src/semantics.rs b/fine/src/semantics.rs
index c447ec57..f09d1521 100644
--- a/fine/src/semantics.rs
+++ b/fine/src/semantics.rs
@@ -143,6 +143,9 @@ pub enum Type {
     // class need to be fetched explicitly from the semantics via the
     // TreeRef and `Semantics::class_of`; they are computed lazily.
     Object(TreeRef, Rc<str>),
+
+    // An alternate is one or another type.
+    Alternate(Box<Type>, Box<Type>),
 }
 
 impl Type {
@@ -204,6 +207,7 @@ impl fmt::Display for Type {
             List(t) => write!(f, "list<{t}>"),
             Object(_, name) => write!(f, "{} instance", name),
             Class(_, name) => write!(f, "class {}", name),
+            Alternate(l, r) => write!(f, "{l} or {r}"),
         }
     }
 }
@@ -592,7 +596,7 @@ impl<'a> Semantics<'a> {
         }
 
         let tree = &self.syntax_tree[t];
-        eprintln!(">>> environment_of => {tree:?}");
+        // eprintln!(">>> environment_of => {tree:?}");
 
         let parent = match self.logical_parents[t.index()] {
             Some(t) => self.environment_of(t),
@@ -613,7 +617,7 @@ impl<'a> Semantics<'a> {
         };
 
         self.environments.borrow_mut()[t.index()] = Incremental::Complete(result.clone());
-        eprintln!("<<< environment_of => {tree:?}");
+        // eprintln!("<<< environment_of => {tree:?}");
         result
     }
 
@@ -986,11 +990,12 @@ impl<'a> Semantics<'a> {
         }
 
         let tree = &self.syntax_tree[t];
-        eprintln!(">>> type_of => {tree:?}");
+        // eprintln!(">>> type_of => {tree:?}");
 
         let result = match tree.kind {
             TreeKind::Error => Some(Type::Error),
 
+            TreeKind::AlternateType => self.type_of_alternate_type(tree),
             TreeKind::Argument => self.type_of_argument(tree),
             TreeKind::BinaryExpression => self.type_of_binary(tree),
             TreeKind::Block => self.type_of_block(tree),
@@ -1016,7 +1021,8 @@ impl<'a> Semantics<'a> {
             TreeKind::ReturnType => self.type_of_return_type(tree),
             TreeKind::SelfParameter => self.type_of_self_parameter(tree),
             TreeKind::SelfReference => self.type_of_self_reference(t, tree),
-            TreeKind::TypeExpression => self.type_of_type_expr(t, tree),
+            TreeKind::TypeExpression => self.type_of_type_expr(tree),
+            TreeKind::TypeIdentifier => self.type_of_type_identifier(t, tree),
             TreeKind::TypeParameter => self.type_of_type_parameter(tree),
             TreeKind::UnaryExpression => self.type_of_unary(tree),
 
@@ -1026,7 +1032,7 @@ impl<'a> Semantics<'a> {
         // NOTE: These return `None` if they encounter some problem.
         let result = result.unwrap_or(Type::Error);
         self.types.borrow_mut()[t.index()] = Incremental::Complete(result.clone());
-        eprintln!("<<< type_of => {tree:?}");
+        // eprintln!("<<< type_of => {tree:?}");
 
         result
     }
@@ -1190,8 +1196,13 @@ impl<'a> Semantics<'a> {
         }
     }
 
-    fn type_of_type_expr(&self, t: TreeRef, tree: &Tree) -> Option<Type> {
+    fn type_of_type_expr(&self, tree: &Tree) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::TypeExpression);
+        Some(self.type_of(tree.nth_tree(0)?))
+    }
+
+    fn type_of_type_identifier(&self, t: TreeRef, tree: &Tree) -> Option<Type> {
+        assert_eq!(tree.kind, TreeKind::TypeIdentifier);
 
         // TODO: This will *clearly* need to get better.
         let token = tree.nth_token(0)?;
@@ -1711,6 +1722,13 @@ impl<'a> Semantics<'a> {
         Some(self.type_of(tree.nth_tree(0)?))
     }
 
+    fn type_of_alternate_type(&self, tree: &Tree) -> Option<Type> {
+        // TODO: IDEA: nth_tree returns a bogus tree if not a tree, stop returning Option?
+        let left = self.type_of(tree.nth_tree(0)?);
+        let right = self.type_of(tree.nth_tree(2)?);
+        Some(Type::Alternate(Box::new(left), Box::new(right)))
+    }
+
     pub fn dump_compiler_state(&self, tr: Option<TreeRef>) {
         eprintln!("Parsed the tree as:");
         eprintln!("\n{}", self.syntax_tree.dump(true));
@@ -1789,7 +1807,7 @@ pub fn check(s: &Semantics) {
             TreeKind::Parameter => {
                 let _ = s.type_of(t);
             }
-            TreeKind::TypeExpression => {
+            TreeKind::TypeExpression | TreeKind::AlternateType | TreeKind::TypeIdentifier => {
                 let _ = s.type_of(t);
             }
             TreeKind::Block => {
diff --git a/fine/tests/errors/resilience/function_extra_comma.fine b/fine/tests/errors/resilience/function_extra_comma.fine
index a8d571b9..2be131ee 100644
--- a/fine/tests/errors/resilience/function_extra_comma.fine
+++ b/fine/tests/errors/resilience/function_extra_comma.fine
@@ -15,7 +15,8 @@ fun f3() {}
 // |         Identifier:'"x"'
 // |         Colon:'":"'
 // |         TypeExpression
-// |           Identifier:'"f64"'
+// |           TypeIdentifier
+// |             Identifier:'"f64"'
 // |         Comma:'","'
 // |       Error:'"Error at 'fun': expect ')' to end a parameter list"'
 // |   FunctionDecl
@@ -27,7 +28,8 @@ fun f3() {}
 // |         Identifier:'"x"'
 // |         Colon:'":"'
 // |         TypeExpression
-// |           Identifier:'"f64"'
+// |           TypeIdentifier
+// |             Identifier:'"f64"'
 // |         Comma:'","'
 // |       Error
 // |         Error:'"Error at ',': expected parameter"'
@@ -36,7 +38,8 @@ fun f3() {}
 // |         Identifier:'"z"'
 // |         Colon:'":"'
 // |         TypeExpression
-// |           Identifier:'"f64"'
+// |           TypeIdentifier
+// |             Identifier:'"f64"'
 // |       RightParen:'")"'
 // |     Block
 // |       LeftBrace:'"{"'
diff --git a/fine/tests/errors/resilience/incomplete_function.fine b/fine/tests/errors/resilience/incomplete_function.fine
index 2a627c13..20531986 100644
--- a/fine/tests/errors/resilience/incomplete_function.fine
+++ b/fine/tests/errors/resilience/incomplete_function.fine
@@ -15,7 +15,8 @@ fun fib(n: f64) -> f64 {
 // |         Identifier:'"f1"'
 // |         Colon:'":"'
 // |         TypeExpression
-// |           Identifier:'"f64"'
+// |           TypeIdentifier
+// |             Identifier:'"f64"'
 // |         Comma:'","'
 // |       Error:'"Error at 'fun': expect ')' to end a parameter list"'
 // |   FunctionDecl
@@ -27,12 +28,14 @@ fun fib(n: f64) -> f64 {
 // |         Identifier:'"n"'
 // |         Colon:'":"'
 // |         TypeExpression
-// |           Identifier:'"f64"'
+// |           TypeIdentifier
+// |             Identifier:'"f64"'
 // |       RightParen:'")"'
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"f64"'
+// |         TypeIdentifier
+// |           Identifier:'"f64"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       ExpressionStatement
diff --git a/fine/tests/expression/argument.fine b/fine/tests/expression/argument.fine
index 2c8164a6..a432d24e 100644
--- a/fine/tests/expression/argument.fine
+++ b/fine/tests/expression/argument.fine
@@ -20,12 +20,14 @@ fun test() -> f64 {
 // |         Identifier:'"x"'
 // |         Colon:'":"'
 // |         TypeExpression
-// |           Identifier:'"f64"'
+// |           TypeIdentifier
+// |             Identifier:'"f64"'
 // |       RightParen:'")"'
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"f64"'
+// |         TypeIdentifier
+// |           Identifier:'"f64"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       ExpressionStatement
@@ -45,7 +47,8 @@ fun test() -> f64 {
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"f64"'
+// |         TypeIdentifier
+// |           Identifier:'"f64"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       ExpressionStatement
diff --git a/fine/tests/expression/arithmetic.fine b/fine/tests/expression/arithmetic.fine
index 395ba11b..03639511 100644
--- a/fine/tests/expression/arithmetic.fine
+++ b/fine/tests/expression/arithmetic.fine
@@ -16,7 +16,8 @@ fun test() -> f64 {
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"f64"'
+// |         TypeIdentifier
+// |           Identifier:'"f64"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       ExpressionStatement
diff --git a/fine/tests/expression/boolean.fine b/fine/tests/expression/boolean.fine
index 5ed756f0..98a991a1 100644
--- a/fine/tests/expression/boolean.fine
+++ b/fine/tests/expression/boolean.fine
@@ -41,7 +41,8 @@ fun test() -> bool {
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"bool"'
+// |         TypeIdentifier
+// |           Identifier:'"bool"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       ExpressionStatement
diff --git a/fine/tests/expression/conditional.fine b/fine/tests/expression/conditional.fine
index 425f6684..cad9fa10 100644
--- a/fine/tests/expression/conditional.fine
+++ b/fine/tests/expression/conditional.fine
@@ -29,7 +29,8 @@ fun test() -> f64 {
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"f64"'
+// |         TypeIdentifier
+// |           Identifier:'"f64"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       IfStatement
diff --git a/fine/tests/expression/variable.fine b/fine/tests/expression/variable.fine
index 6c3ee1c8..e7335ac8 100644
--- a/fine/tests/expression/variable.fine
+++ b/fine/tests/expression/variable.fine
@@ -50,7 +50,8 @@ fun test() -> f64 {
 // |     ReturnType
 // |       Arrow:'"->"'
 // |       TypeExpression
-// |         Identifier:'"f64"'
+// |         TypeIdentifier
+// |           Identifier:'"f64"'
 // |     Block
 // |       LeftBrace:'"{"'
 // |       ExpressionStatement