Support singleton structs

158 files changed, 313 insertions, 129 deletions

diff --git a/examples/08-shared/hobgoblin.json5 b/examples/02-struct-singleton/hobgoblin.json5
index 19e0f93..19e0f93 100644
--- a/examples/08-shared/hobgoblin.json5
+++ b/examples/02-struct-singleton/hobgoblin.json5
diff --git a/examples/02-sum/output/java/.gitignore b/examples/02-struct-singleton/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/02-sum/output/java/.gitignore
+++ b/examples/02-struct-singleton/output/java/.gitignore
diff --git a/examples/02-sum/output/java/pom.xml b/examples/02-struct-singleton/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/02-sum/output/java/pom.xml
+++ b/examples/02-struct-singleton/output/java/pom.xml
diff --git a/examples/02-struct-singleton/output/java/src/test/java/org/zwobble/example/PointTests.java b/examples/02-struct-singleton/output/java/src/test/java/org/zwobble/example/PointTests.java
new file mode 100644
index 0000000..cec3047
--- /dev/null
+++ b/examples/02-struct-singleton/output/java/src/test/java/org/zwobble/example/PointTests.java
@@ -0,0 +1,12 @@
+package org.zwobble.example;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+import org.zwobble.example.types.point.Origin;
+
+public class PointTests {
+    @Test
+    public void origin() {
+        var origin = Origin.INSTANCE;
+    }
+}
diff --git a/examples/02-sum/output/rust/.gitignore b/examples/02-struct-singleton/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/02-sum/output/rust/.gitignore
+++ b/examples/02-struct-singleton/output/rust/.gitignore
diff --git a/examples/02-sum/output/rust/Cargo.lock b/examples/02-struct-singleton/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/02-sum/output/rust/Cargo.lock
+++ b/examples/02-struct-singleton/output/rust/Cargo.lock
diff --git a/examples/02-sum/output/rust/Cargo.toml b/examples/02-struct-singleton/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/02-sum/output/rust/Cargo.toml
+++ b/examples/02-struct-singleton/output/rust/Cargo.toml
diff --git a/examples/02-sum/output/rust/rust-toolchain.toml b/examples/02-struct-singleton/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/02-sum/output/rust/rust-toolchain.toml
+++ b/examples/02-struct-singleton/output/rust/rust-toolchain.toml
diff --git a/examples/02-struct-singleton/output/rust/src/lib.rs b/examples/02-struct-singleton/output/rust/src/lib.rs
new file mode 100644
index 0000000..7182bd8
--- /dev/null
+++ b/examples/02-struct-singleton/output/rust/src/lib.rs
@@ -0,0 +1,11 @@
+mod point;
+
+#[cfg(test)]
+mod test {
+    use super::point::Origin;
+
+    #[test]
+    fn origin() {
+        let origin = Origin {};
+    }
+}
diff --git a/examples/02-struct-singleton/output/rust/src/point.rs b/examples/02-struct-singleton/output/rust/src/point.rs
new file mode 100644
index 0000000..e2d608c
--- /dev/null
+++ b/examples/02-struct-singleton/output/rust/src/point.rs
@@ -0,0 +1,5 @@
+// Generated by hobgoblin.
+
+#[derive(Debug, Hash, PartialEq)]
+pub struct Origin {
+}
diff --git a/examples/02-struct-singleton/src/point.hob b/examples/02-struct-singleton/src/point.hob
new file mode 100644
index 0000000..930a1b5
--- /dev/null
+++ b/examples/02-struct-singleton/src/point.hob
@@ -0,0 +1,3 @@
+struct Origin {
+    singleton;
+}
diff --git a/examples/02-sum/hobgoblin.json5 b/examples/03-sum/hobgoblin.json5
index 12713d4..12713d4 100644
--- a/examples/02-sum/hobgoblin.json5
+++ b/examples/03-sum/hobgoblin.json5
diff --git a/examples/03-inductive-data-types/output/java/.gitignore b/examples/03-sum/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/03-inductive-data-types/output/java/.gitignore
+++ b/examples/03-sum/output/java/.gitignore
diff --git a/examples/03-inductive-data-types/output/java/pom.xml b/examples/03-sum/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/03-inductive-data-types/output/java/pom.xml
+++ b/examples/03-sum/output/java/pom.xml
diff --git a/examples/02-sum/output/java/src/main/java/org/zwobble/example/Shapes.java b/examples/03-sum/output/java/src/main/java/org/zwobble/example/Shapes.java
index a6a468f..a6a468f 100644
--- a/examples/02-sum/output/java/src/main/java/org/zwobble/example/Shapes.java
+++ b/examples/03-sum/output/java/src/main/java/org/zwobble/example/Shapes.java
diff --git a/examples/02-sum/output/java/src/test/java/org/zwobble/example/ShapesTests.java b/examples/03-sum/output/java/src/test/java/org/zwobble/example/ShapesTests.java
index 893a544..893a544 100644
--- a/examples/02-sum/output/java/src/test/java/org/zwobble/example/ShapesTests.java
+++ b/examples/03-sum/output/java/src/test/java/org/zwobble/example/ShapesTests.java
diff --git a/examples/03-inductive-data-types/output/rust/.gitignore b/examples/03-sum/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/03-inductive-data-types/output/rust/.gitignore
+++ b/examples/03-sum/output/rust/.gitignore
diff --git a/examples/03-inductive-data-types/output/rust/Cargo.lock b/examples/03-sum/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/03-inductive-data-types/output/rust/Cargo.lock
+++ b/examples/03-sum/output/rust/Cargo.lock
diff --git a/examples/03-inductive-data-types/output/rust/Cargo.toml b/examples/03-sum/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/03-inductive-data-types/output/rust/Cargo.toml
+++ b/examples/03-sum/output/rust/Cargo.toml
diff --git a/examples/03-inductive-data-types/output/rust/rust-toolchain.toml b/examples/03-sum/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/03-inductive-data-types/output/rust/rust-toolchain.toml
+++ b/examples/03-sum/output/rust/rust-toolchain.toml
diff --git a/examples/02-sum/output/rust/src/lib.rs b/examples/03-sum/output/rust/src/lib.rs
index f961002..f961002 100644
--- a/examples/02-sum/output/rust/src/lib.rs
+++ b/examples/03-sum/output/rust/src/lib.rs
diff --git a/examples/02-sum/output/rust/src/shapes.rs b/examples/03-sum/output/rust/src/shapes.rs
index a0a9b7f..a0a9b7f 100644
--- a/examples/02-sum/output/rust/src/shapes.rs
+++ b/examples/03-sum/output/rust/src/shapes.rs
diff --git a/examples/02-sum/src/shapes.hob b/examples/03-sum/src/shapes.hob
index 03a727a..03a727a 100644
--- a/examples/02-sum/src/shapes.hob
+++ b/examples/03-sum/src/shapes.hob
diff --git a/examples/03-inductive-data-types/hobgoblin.json5 b/examples/04-inductive-data-types/hobgoblin.json5
index 12713d4..12713d4 100644
--- a/examples/03-inductive-data-types/hobgoblin.json5
+++ b/examples/04-inductive-data-types/hobgoblin.json5
diff --git a/examples/04-enum/output/java/.gitignore b/examples/04-inductive-data-types/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/04-enum/output/java/.gitignore
+++ b/examples/04-inductive-data-types/output/java/.gitignore
diff --git a/examples/04-enum/output/java/pom.xml b/examples/04-inductive-data-types/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/04-enum/output/java/pom.xml
+++ b/examples/04-inductive-data-types/output/java/pom.xml
diff --git a/examples/03-inductive-data-types/output/java/src/main/java/org/zwobble/example/Arithmetic.java b/examples/04-inductive-data-types/output/java/src/main/java/org/zwobble/example/Arithmetic.java
index 08cb75c..08cb75c 100644
--- a/examples/03-inductive-data-types/output/java/src/main/java/org/zwobble/example/Arithmetic.java
+++ b/examples/04-inductive-data-types/output/java/src/main/java/org/zwobble/example/Arithmetic.java
diff --git a/examples/03-inductive-data-types/output/java/src/test/java/org/zwobble/example/ArithmeticTests.java b/examples/04-inductive-data-types/output/java/src/test/java/org/zwobble/example/ArithmeticTests.java
index cd4fdd0..cd4fdd0 100644
--- a/examples/03-inductive-data-types/output/java/src/test/java/org/zwobble/example/ArithmeticTests.java
+++ b/examples/04-inductive-data-types/output/java/src/test/java/org/zwobble/example/ArithmeticTests.java
diff --git a/examples/04-enum/output/rust/.gitignore b/examples/04-inductive-data-types/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/04-enum/output/rust/.gitignore
+++ b/examples/04-inductive-data-types/output/rust/.gitignore
diff --git a/examples/04-enum/output/rust/Cargo.lock b/examples/04-inductive-data-types/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/04-enum/output/rust/Cargo.lock
+++ b/examples/04-inductive-data-types/output/rust/Cargo.lock
diff --git a/examples/04-enum/output/rust/Cargo.toml b/examples/04-inductive-data-types/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/04-enum/output/rust/Cargo.toml
+++ b/examples/04-inductive-data-types/output/rust/Cargo.toml
diff --git a/examples/04-enum/output/rust/rust-toolchain.toml b/examples/04-inductive-data-types/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/04-enum/output/rust/rust-toolchain.toml
+++ b/examples/04-inductive-data-types/output/rust/rust-toolchain.toml
diff --git a/examples/03-inductive-data-types/output/rust/src/arithmetic.rs b/examples/04-inductive-data-types/output/rust/src/arithmetic.rs
index 121c355..121c355 100644
--- a/examples/03-inductive-data-types/output/rust/src/arithmetic.rs
+++ b/examples/04-inductive-data-types/output/rust/src/arithmetic.rs
diff --git a/examples/03-inductive-data-types/output/rust/src/lib.rs b/examples/04-inductive-data-types/output/rust/src/lib.rs
index 3265e69..3265e69 100644
--- a/examples/03-inductive-data-types/output/rust/src/lib.rs
+++ b/examples/04-inductive-data-types/output/rust/src/lib.rs
diff --git a/examples/03-inductive-data-types/src/arithmetic.hob b/examples/04-inductive-data-types/src/arithmetic.hob
index b1ef6e5..b1ef6e5 100644
--- a/examples/03-inductive-data-types/src/arithmetic.hob
+++ b/examples/04-inductive-data-types/src/arithmetic.hob
diff --git a/examples/04-enum/hobgoblin.json5 b/examples/05-enum/hobgoblin.json5
index 12713d4..12713d4 100644
--- a/examples/04-enum/hobgoblin.json5
+++ b/examples/05-enum/hobgoblin.json5
diff --git a/examples/05-list/output/java/.gitignore b/examples/05-enum/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/05-list/output/java/.gitignore
+++ b/examples/05-enum/output/java/.gitignore
diff --git a/examples/05-list/output/java/pom.xml b/examples/05-enum/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/05-list/output/java/pom.xml
+++ b/examples/05-enum/output/java/pom.xml
diff --git a/examples/04-enum/output/java/src/main/java/org/zwobble/example/Numbers.java b/examples/05-enum/output/java/src/main/java/org/zwobble/example/Numbers.java
index fc17869..fc17869 100644
--- a/examples/04-enum/output/java/src/main/java/org/zwobble/example/Numbers.java
+++ b/examples/05-enum/output/java/src/main/java/org/zwobble/example/Numbers.java
diff --git a/examples/04-enum/output/java/src/test/java/org/zwobble/example/NumbersTests.java b/examples/05-enum/output/java/src/test/java/org/zwobble/example/NumbersTests.java
index 141d5d1..141d5d1 100644
--- a/examples/04-enum/output/java/src/test/java/org/zwobble/example/NumbersTests.java
+++ b/examples/05-enum/output/java/src/test/java/org/zwobble/example/NumbersTests.java
diff --git a/examples/05-list/output/rust/.gitignore b/examples/05-enum/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/05-list/output/rust/.gitignore
+++ b/examples/05-enum/output/rust/.gitignore
diff --git a/examples/05-list/output/rust/Cargo.lock b/examples/05-enum/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/05-list/output/rust/Cargo.lock
+++ b/examples/05-enum/output/rust/Cargo.lock
diff --git a/examples/05-list/output/rust/Cargo.toml b/examples/05-enum/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/05-list/output/rust/Cargo.toml
+++ b/examples/05-enum/output/rust/Cargo.toml
diff --git a/examples/05-list/output/rust/rust-toolchain.toml b/examples/05-enum/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/05-list/output/rust/rust-toolchain.toml
+++ b/examples/05-enum/output/rust/rust-toolchain.toml
diff --git a/examples/04-enum/output/rust/src/lib.rs b/examples/05-enum/output/rust/src/lib.rs
index ae0b67c..ae0b67c 100644
--- a/examples/04-enum/output/rust/src/lib.rs
+++ b/examples/05-enum/output/rust/src/lib.rs
diff --git a/examples/04-enum/output/rust/src/numbers.rs b/examples/05-enum/output/rust/src/numbers.rs
index 1c62012..1c62012 100644
--- a/examples/04-enum/output/rust/src/numbers.rs
+++ b/examples/05-enum/output/rust/src/numbers.rs
diff --git a/examples/04-enum/src/numbers.hob b/examples/05-enum/src/numbers.hob
index 125082d..125082d 100644
--- a/examples/04-enum/src/numbers.hob
+++ b/examples/05-enum/src/numbers.hob
diff --git a/examples/05-list/hobgoblin.json5 b/examples/06-list/hobgoblin.json5
index 12713d4..12713d4 100644
--- a/examples/05-list/hobgoblin.json5
+++ b/examples/06-list/hobgoblin.json5
diff --git a/examples/06-native-type/output/java/.gitignore b/examples/06-list/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/06-native-type/output/java/.gitignore
+++ b/examples/06-list/output/java/.gitignore
diff --git a/examples/06-native-type/output/java/pom.xml b/examples/06-list/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/06-native-type/output/java/pom.xml
+++ b/examples/06-list/output/java/pom.xml
diff --git a/examples/05-list/output/java/src/test/java/org/zwobble/example/PointTests.java b/examples/06-list/output/java/src/test/java/org/zwobble/example/PointTests.java
index e1528b5..e1528b5 100644
--- a/examples/05-list/output/java/src/test/java/org/zwobble/example/PointTests.java
+++ b/examples/06-list/output/java/src/test/java/org/zwobble/example/PointTests.java
diff --git a/examples/06-native-type/output/rust/.gitignore b/examples/06-list/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/06-native-type/output/rust/.gitignore
+++ b/examples/06-list/output/rust/.gitignore
diff --git a/examples/06-native-type/output/rust/Cargo.lock b/examples/06-list/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/06-native-type/output/rust/Cargo.lock
+++ b/examples/06-list/output/rust/Cargo.lock
diff --git a/examples/06-native-type/output/rust/Cargo.toml b/examples/06-list/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/06-native-type/output/rust/Cargo.toml
+++ b/examples/06-list/output/rust/Cargo.toml
diff --git a/examples/06-native-type/output/rust/rust-toolchain.toml b/examples/06-list/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/06-native-type/output/rust/rust-toolchain.toml
+++ b/examples/06-list/output/rust/rust-toolchain.toml
diff --git a/examples/05-list/output/rust/src/lib.rs b/examples/06-list/output/rust/src/lib.rs
index 907ab8b..907ab8b 100644
--- a/examples/05-list/output/rust/src/lib.rs
+++ b/examples/06-list/output/rust/src/lib.rs
diff --git a/examples/05-list/output/rust/src/point.rs b/examples/06-list/output/rust/src/point.rs
index 2625f9f..2625f9f 100644
--- a/examples/05-list/output/rust/src/point.rs
+++ b/examples/06-list/output/rust/src/point.rs
diff --git a/examples/05-list/src/point.hob b/examples/06-list/src/point.hob
index 8dd438c..8dd438c 100644
--- a/examples/05-list/src/point.hob
+++ b/examples/06-list/src/point.hob
diff --git a/examples/06-native-type/hobgoblin.json5 b/examples/07-native-type/hobgoblin.json5
index a0f60c3..a0f60c3 100644
--- a/examples/06-native-type/hobgoblin.json5
+++ b/examples/07-native-type/hobgoblin.json5
diff --git a/examples/07-native-type-custom-config/output/java/.gitignore b/examples/07-native-type/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/07-native-type-custom-config/output/java/.gitignore
+++ b/examples/07-native-type/output/java/.gitignore
diff --git a/examples/07-native-type-custom-config/output/java/pom.xml b/examples/07-native-type/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/07-native-type-custom-config/output/java/pom.xml
+++ b/examples/07-native-type/output/java/pom.xml
diff --git a/examples/06-native-type/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java b/examples/07-native-type/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java
index bdb5427..bdb5427 100644
--- a/examples/06-native-type/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java
+++ b/examples/07-native-type/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java
diff --git a/examples/06-native-type/output/java/src/main/java/org/zwobble/example/types/point/Point.java b/examples/07-native-type/output/java/src/main/java/org/zwobble/example/types/point/Point.java
index cd26290..cd26290 100644
--- a/examples/06-native-type/output/java/src/main/java/org/zwobble/example/types/point/Point.java
+++ b/examples/07-native-type/output/java/src/main/java/org/zwobble/example/types/point/Point.java
diff --git a/examples/06-native-type/output/java/src/test/java/org/zwobble/example/PointTests.java b/examples/07-native-type/output/java/src/test/java/org/zwobble/example/PointTests.java
index 8482673..8482673 100644
--- a/examples/06-native-type/output/java/src/test/java/org/zwobble/example/PointTests.java
+++ b/examples/07-native-type/output/java/src/test/java/org/zwobble/example/PointTests.java
diff --git a/examples/07-native-type-custom-config/output/rust/.gitignore b/examples/07-native-type/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/07-native-type-custom-config/output/rust/.gitignore
+++ b/examples/07-native-type/output/rust/.gitignore
diff --git a/examples/07-native-type-custom-config/output/rust/Cargo.lock b/examples/07-native-type/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/07-native-type-custom-config/output/rust/Cargo.lock
+++ b/examples/07-native-type/output/rust/Cargo.lock
diff --git a/examples/07-native-type-custom-config/output/rust/Cargo.toml b/examples/07-native-type/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/07-native-type-custom-config/output/rust/Cargo.toml
+++ b/examples/07-native-type/output/rust/Cargo.toml
diff --git a/examples/07-native-type-custom-config/output/rust/rust-toolchain.toml b/examples/07-native-type/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/07-native-type-custom-config/output/rust/rust-toolchain.toml
+++ b/examples/07-native-type/output/rust/rust-toolchain.toml
diff --git a/examples/06-native-type/output/rust/src/gen/point.rs b/examples/07-native-type/output/rust/src/gen/point.rs
index d383b15..d383b15 100644
--- a/examples/06-native-type/output/rust/src/gen/point.rs
+++ b/examples/07-native-type/output/rust/src/gen/point.rs
diff --git a/examples/06-native-type/output/rust/src/lib.rs b/examples/07-native-type/output/rust/src/lib.rs
index 1179cff..1179cff 100644
--- a/examples/06-native-type/output/rust/src/lib.rs
+++ b/examples/07-native-type/output/rust/src/lib.rs
diff --git a/examples/06-native-type/output/rust/src/point.rs b/examples/07-native-type/output/rust/src/point.rs
index c5b73d7..c5b73d7 100644
--- a/examples/06-native-type/output/rust/src/point.rs
+++ b/examples/07-native-type/output/rust/src/point.rs
diff --git a/examples/06-native-type/src/point.hob b/examples/07-native-type/src/point.hob
index 7178dcb..7178dcb 100644
--- a/examples/06-native-type/src/point.hob
+++ b/examples/07-native-type/src/point.hob
diff --git a/examples/07-native-type-custom-config/hobgoblin.json5 b/examples/08-native-type-custom-config/hobgoblin.json5
index f925903..f925903 100644
--- a/examples/07-native-type-custom-config/hobgoblin.json5
+++ b/examples/08-native-type-custom-config/hobgoblin.json5
diff --git a/examples/08-shared/output/java/.gitignore b/examples/08-native-type-custom-config/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/08-shared/output/java/.gitignore
+++ b/examples/08-native-type-custom-config/output/java/.gitignore
diff --git a/examples/08-shared/output/java/pom.xml b/examples/08-native-type-custom-config/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/08-shared/output/java/pom.xml
+++ b/examples/08-native-type-custom-config/output/java/pom.xml
diff --git a/examples/07-native-type-custom-config/output/java/src/main/java/org/zwobble/example/Point.java b/examples/08-native-type-custom-config/output/java/src/main/java/org/zwobble/example/Point.java
index 8862a62..8862a62 100644
--- a/examples/07-native-type-custom-config/output/java/src/main/java/org/zwobble/example/Point.java
+++ b/examples/08-native-type-custom-config/output/java/src/main/java/org/zwobble/example/Point.java
diff --git a/examples/07-native-type-custom-config/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java b/examples/08-native-type-custom-config/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java
index 74ac856..74ac856 100644
--- a/examples/07-native-type-custom-config/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java
+++ b/examples/08-native-type-custom-config/output/java/src/main/java/org/zwobble/example/types/point/HobgoblinNativePoint.java
diff --git a/examples/07-native-type-custom-config/output/java/src/test/java/org/zwobble/example/PointTests.java b/examples/08-native-type-custom-config/output/java/src/test/java/org/zwobble/example/PointTests.java
index ea635ca..ea635ca 100644
--- a/examples/07-native-type-custom-config/output/java/src/test/java/org/zwobble/example/PointTests.java
+++ b/examples/08-native-type-custom-config/output/java/src/test/java/org/zwobble/example/PointTests.java
diff --git a/examples/08-shared/output/rust/.gitignore b/examples/08-native-type-custom-config/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/08-shared/output/rust/.gitignore
+++ b/examples/08-native-type-custom-config/output/rust/.gitignore
diff --git a/examples/08-shared/output/rust/Cargo.lock b/examples/08-native-type-custom-config/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/08-shared/output/rust/Cargo.lock
+++ b/examples/08-native-type-custom-config/output/rust/Cargo.lock
diff --git a/examples/08-shared/output/rust/Cargo.toml b/examples/08-native-type-custom-config/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/08-shared/output/rust/Cargo.toml
+++ b/examples/08-native-type-custom-config/output/rust/Cargo.toml
diff --git a/examples/08-shared/output/rust/rust-toolchain.toml b/examples/08-native-type-custom-config/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/08-shared/output/rust/rust-toolchain.toml
+++ b/examples/08-native-type-custom-config/output/rust/rust-toolchain.toml
diff --git a/examples/07-native-type-custom-config/output/rust/src/main.rs b/examples/08-native-type-custom-config/output/rust/src/main.rs
index 10dc437..10dc437 100644
--- a/examples/07-native-type-custom-config/output/rust/src/main.rs
+++ b/examples/08-native-type-custom-config/output/rust/src/main.rs
diff --git a/examples/07-native-type-custom-config/output/rust/src/point.rs b/examples/08-native-type-custom-config/output/rust/src/point.rs
index 6ab4330..6ab4330 100644
--- a/examples/07-native-type-custom-config/output/rust/src/point.rs
+++ b/examples/08-native-type-custom-config/output/rust/src/point.rs
diff --git a/examples/07-native-type-custom-config/src/point.hob b/examples/08-native-type-custom-config/src/point.hob
index 7178dcb..7178dcb 100644
--- a/examples/07-native-type-custom-config/src/point.hob
+++ b/examples/08-native-type-custom-config/src/point.hob
diff --git a/examples/09-shared/hobgoblin.json5 b/examples/09-shared/hobgoblin.json5
new file mode 100644
index 0000000..19e0f93
--- /dev/null
+++ b/examples/09-shared/hobgoblin.json5
@@ -0,0 +1,23 @@
+{
+  outputs: {
+    langs: {
+      java: {
+        packageName: "org.zwobble.example.types",
+      },
+    },
+    generators: [
+      {
+        generator: "java-types",
+        path: "output/java/src/gen/java",
+      },
+      {
+        generator: "java-precisely-matchers",
+        path: "output/java/src/gen/java",
+      },
+      {
+        generator: "rust-types",
+        path: "output/rust/src",
+      },
+    ],
+  }
+}
diff --git a/examples/09-custom-code/output/java/.gitignore b/examples/09-shared/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/09-custom-code/output/java/.gitignore
+++ b/examples/09-shared/output/java/.gitignore
diff --git a/examples/09-custom-code/output/java/pom.xml b/examples/09-shared/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/09-custom-code/output/java/pom.xml
+++ b/examples/09-shared/output/java/pom.xml
diff --git a/examples/08-shared/output/java/src/test/java/org/zwobble/example/PointTests.java b/examples/09-shared/output/java/src/test/java/org/zwobble/example/PointTests.java
index b4c140d..b4c140d 100644
--- a/examples/08-shared/output/java/src/test/java/org/zwobble/example/PointTests.java
+++ b/examples/09-shared/output/java/src/test/java/org/zwobble/example/PointTests.java
diff --git a/examples/09-custom-code/output/rust/.gitignore b/examples/09-shared/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/09-custom-code/output/rust/.gitignore
+++ b/examples/09-shared/output/rust/.gitignore
diff --git a/examples/09-custom-code/output/rust/Cargo.lock b/examples/09-shared/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/09-custom-code/output/rust/Cargo.lock
+++ b/examples/09-shared/output/rust/Cargo.lock
diff --git a/examples/09-custom-code/output/rust/Cargo.toml b/examples/09-shared/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/09-custom-code/output/rust/Cargo.toml
+++ b/examples/09-shared/output/rust/Cargo.toml
diff --git a/examples/09-custom-code/output/rust/rust-toolchain.toml b/examples/09-shared/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/09-custom-code/output/rust/rust-toolchain.toml
+++ b/examples/09-shared/output/rust/rust-toolchain.toml
diff --git a/examples/08-shared/output/rust/src/lib.rs b/examples/09-shared/output/rust/src/lib.rs
index af2c87f..af2c87f 100644
--- a/examples/08-shared/output/rust/src/lib.rs
+++ b/examples/09-shared/output/rust/src/lib.rs
diff --git a/examples/08-shared/output/rust/src/point.rs b/examples/09-shared/output/rust/src/point.rs
index dea7678..dea7678 100644
--- a/examples/08-shared/output/rust/src/point.rs
+++ b/examples/09-shared/output/rust/src/point.rs
diff --git a/examples/08-shared/src/point.hob b/examples/09-shared/src/point.hob
index 7b9a8e6..7b9a8e6 100644
--- a/examples/08-shared/src/point.hob
+++ b/examples/09-shared/src/point.hob
diff --git a/examples/09-custom-code/hobgoblin.json5 b/examples/10-custom-code/hobgoblin.json5
index 1d08a40..1d08a40 100644
--- a/examples/09-custom-code/hobgoblin.json5
+++ b/examples/10-custom-code/hobgoblin.json5
diff --git a/examples/10-imports/output/java/.gitignore b/examples/10-custom-code/output/java/.gitignore
index ff511d4..ff511d4 100644
--- a/examples/10-imports/output/java/.gitignore
+++ b/examples/10-custom-code/output/java/.gitignore
diff --git a/examples/10-imports/output/java/pom.xml b/examples/10-custom-code/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/10-imports/output/java/pom.xml
+++ b/examples/10-custom-code/output/java/pom.xml
diff --git a/examples/09-custom-code/output/java/src/main/java/org/zwobble/example/types/shapes/Square.java b/examples/10-custom-code/output/java/src/main/java/org/zwobble/example/types/shapes/Square.java
index 69a1ab1..69a1ab1 100644
--- a/examples/09-custom-code/output/java/src/main/java/org/zwobble/example/types/shapes/Square.java
+++ b/examples/10-custom-code/output/java/src/main/java/org/zwobble/example/types/shapes/Square.java
diff --git a/examples/09-custom-code/output/java/src/test/java/org/zwobble/example/ShapesTests.java b/examples/10-custom-code/output/java/src/test/java/org/zwobble/example/ShapesTests.java
index fba8e6c..fba8e6c 100644
--- a/examples/09-custom-code/output/java/src/test/java/org/zwobble/example/ShapesTests.java
+++ b/examples/10-custom-code/output/java/src/test/java/org/zwobble/example/ShapesTests.java
diff --git a/examples/10-imports/output/rust/.gitignore b/examples/10-custom-code/output/rust/.gitignore
index ea8c4bf..ea8c4bf 100644
--- a/examples/10-imports/output/rust/.gitignore
+++ b/examples/10-custom-code/output/rust/.gitignore
diff --git a/examples/10-imports/output/rust/Cargo.lock b/examples/10-custom-code/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/10-imports/output/rust/Cargo.lock
+++ b/examples/10-custom-code/output/rust/Cargo.lock
diff --git a/examples/10-imports/output/rust/Cargo.toml b/examples/10-custom-code/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/10-imports/output/rust/Cargo.toml
+++ b/examples/10-custom-code/output/rust/Cargo.toml
diff --git a/examples/10-imports/output/rust/rust-toolchain.toml b/examples/10-custom-code/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/10-imports/output/rust/rust-toolchain.toml
+++ b/examples/10-custom-code/output/rust/rust-toolchain.toml
diff --git a/examples/09-custom-code/output/rust/src/gen/shapes.rs b/examples/10-custom-code/output/rust/src/gen/shapes.rs
index 815db2a..815db2a 100644
--- a/examples/09-custom-code/output/rust/src/gen/shapes.rs
+++ b/examples/10-custom-code/output/rust/src/gen/shapes.rs
diff --git a/examples/09-custom-code/output/rust/src/lib.rs b/examples/10-custom-code/output/rust/src/lib.rs
index 1825d72..1825d72 100644
--- a/examples/09-custom-code/output/rust/src/lib.rs
+++ b/examples/10-custom-code/output/rust/src/lib.rs
diff --git a/examples/09-custom-code/output/rust/src/shapes.rs b/examples/10-custom-code/output/rust/src/shapes.rs
index f806bbb..f806bbb 100644
--- a/examples/09-custom-code/output/rust/src/shapes.rs
+++ b/examples/10-custom-code/output/rust/src/shapes.rs
diff --git a/examples/09-custom-code/src/shapes.hob b/examples/10-custom-code/src/shapes.hob
index 5dfe833..5dfe833 100644
--- a/examples/09-custom-code/src/shapes.hob
+++ b/examples/10-custom-code/src/shapes.hob
diff --git a/examples/10-imports/hobgoblin.json5 b/examples/11-imports/hobgoblin.json5
index 12713d4..12713d4 100644
--- a/examples/10-imports/hobgoblin.json5
+++ b/examples/11-imports/hobgoblin.json5
diff --git a/examples/11-imports/output/java/.gitignore b/examples/11-imports/output/java/.gitignore
new file mode 100644
index 0000000..ff511d4
--- /dev/null
+++ b/examples/11-imports/output/java/.gitignore
@@ -0,0 +1,2 @@
+/src/gen/
+/target/
diff --git a/examples/11-transient-0/output/java/pom.xml b/examples/11-imports/output/java/pom.xml
index 445fa65..445fa65 120000
--- a/examples/11-transient-0/output/java/pom.xml
+++ b/examples/11-imports/output/java/pom.xml
diff --git a/examples/10-imports/output/java/src/test/java/org/zwobble/example/LineTests.java b/examples/11-imports/output/java/src/test/java/org/zwobble/example/LineTests.java
index c376b19..c376b19 100644
--- a/examples/10-imports/output/java/src/test/java/org/zwobble/example/LineTests.java
+++ b/examples/11-imports/output/java/src/test/java/org/zwobble/example/LineTests.java
diff --git a/examples/11-imports/output/rust/.gitignore b/examples/11-imports/output/rust/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/examples/11-imports/output/rust/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/examples/11-transient-0/output/rust/Cargo.lock b/examples/11-imports/output/rust/Cargo.lock
index 9dc6e3e..9dc6e3e 100644
--- a/examples/11-transient-0/output/rust/Cargo.lock
+++ b/examples/11-imports/output/rust/Cargo.lock
diff --git a/examples/11-transient-0/output/rust/Cargo.toml b/examples/11-imports/output/rust/Cargo.toml
index 5d4c622..5d4c622 100644
--- a/examples/11-transient-0/output/rust/Cargo.toml
+++ b/examples/11-imports/output/rust/Cargo.toml
diff --git a/examples/11-transient-0/output/rust/rust-toolchain.toml b/examples/11-imports/output/rust/rust-toolchain.toml
index 4fedb95..4fedb95 100644
--- a/examples/11-transient-0/output/rust/rust-toolchain.toml
+++ b/examples/11-imports/output/rust/rust-toolchain.toml
diff --git a/examples/10-imports/output/rust/src/lib.rs b/examples/11-imports/output/rust/src/lib.rs
index ffbcbf4..ffbcbf4 100644
--- a/examples/10-imports/output/rust/src/lib.rs
+++ b/examples/11-imports/output/rust/src/lib.rs
diff --git a/examples/10-imports/output/rust/src/line.rs b/examples/11-imports/output/rust/src/line.rs
index d383b15..d383b15 100644
--- a/examples/10-imports/output/rust/src/line.rs
+++ b/examples/11-imports/output/rust/src/line.rs
diff --git a/examples/10-imports/output/rust/src/point.rs b/examples/11-imports/output/rust/src/point.rs
index 943331f..943331f 100644
--- a/examples/10-imports/output/rust/src/point.rs
+++ b/examples/11-imports/output/rust/src/point.rs
diff --git a/examples/10-imports/src/line.hob b/examples/11-imports/src/line.hob
index 562d77f..562d77f 100644
--- a/examples/10-imports/src/line.hob
+++ b/examples/11-imports/src/line.hob
diff --git a/examples/10-imports/src/point.hob b/examples/11-imports/src/point.hob
index 87f9953..87f9953 100644
--- a/examples/10-imports/src/point.hob
+++ b/examples/11-imports/src/point.hob
diff --git a/examples/11-transient-0/hobgoblin.json5 b/examples/12-transient-0/hobgoblin.json5
index 2160c60..2160c60 100644
--- a/examples/11-transient-0/hobgoblin.json5
+++ b/examples/12-transient-0/hobgoblin.json5
diff --git a/examples/11-transient-0/output/java/.gitignore b/examples/12-transient-0/output/java/.gitignore
index 2fcf0b8..2fcf0b8 100644
--- a/examples/11-transient-0/output/java/.gitignore
+++ b/examples/12-transient-0/output/java/.gitignore
diff --git a/examples/12-transient-0/output/java/pom.xml b/examples/12-transient-0/output/java/pom.xml
new file mode 120000
index 0000000..445fa65
--- /dev/null
+++ b/examples/12-transient-0/output/java/pom.xml
@@ -0,0 +1 @@
+../../../templates/java-junit/pom.xml
\ No newline at end of file
diff --git a/examples/11-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java b/examples/12-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java
index a924d1e..a924d1e 100644
--- a/examples/11-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java
+++ b/examples/12-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java
diff --git a/examples/11-transient-0/output/rust/.gitignore b/examples/12-transient-0/output/rust/.gitignore
index fc03479..fc03479 100644
--- a/examples/11-transient-0/output/rust/.gitignore
+++ b/examples/12-transient-0/output/rust/.gitignore
diff --git a/examples/12-transient-0/output/rust/Cargo.lock b/examples/12-transient-0/output/rust/Cargo.lock
new file mode 100644
index 0000000..9dc6e3e
--- /dev/null
+++ b/examples/12-transient-0/output/rust/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "example"
+version = "0.1.0"
diff --git a/examples/12-transient-0/output/rust/Cargo.toml b/examples/12-transient-0/output/rust/Cargo.toml
new file mode 100644
index 0000000..5d4c622
--- /dev/null
+++ b/examples/12-transient-0/output/rust/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "example"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/examples/12-transient-0/output/rust/rust-toolchain.toml b/examples/12-transient-0/output/rust/rust-toolchain.toml
new file mode 100644
index 0000000..4fedb95
--- /dev/null
+++ b/examples/12-transient-0/output/rust/rust-toolchain.toml
@@ -0,0 +1,2 @@
+[toolchain]
+channel = "1.96"
diff --git a/examples/11-transient-0/output/rust/src/data.rs b/examples/12-transient-0/output/rust/src/data.rs
index 7a0c4fa..7a0c4fa 100644
--- a/examples/11-transient-0/output/rust/src/data.rs
+++ b/examples/12-transient-0/output/rust/src/data.rs
diff --git a/examples/11-transient-0/output/rust/src/gen/data.rs b/examples/12-transient-0/output/rust/src/gen/data.rs
index 4ec0524..4ec0524 100644
--- a/examples/11-transient-0/output/rust/src/gen/data.rs
+++ b/examples/12-transient-0/output/rust/src/gen/data.rs
diff --git a/examples/11-transient-0/output/rust/src/gen/data/transient_0.rs b/examples/12-transient-0/output/rust/src/gen/data/transient_0.rs
index ea4a459..ea4a459 100644
--- a/examples/11-transient-0/output/rust/src/gen/data/transient_0.rs
+++ b/examples/12-transient-0/output/rust/src/gen/data/transient_0.rs
diff --git a/examples/11-transient-0/output/rust/src/gen/transient_0.rs b/examples/12-transient-0/output/rust/src/gen/transient_0.rs
index d88284e..d88284e 100644
--- a/examples/11-transient-0/output/rust/src/gen/transient_0.rs
+++ b/examples/12-transient-0/output/rust/src/gen/transient_0.rs
diff --git a/examples/11-transient-0/output/rust/src/lib.rs b/examples/12-transient-0/output/rust/src/lib.rs
index 3a02936..3a02936 100644
--- a/examples/11-transient-0/output/rust/src/lib.rs
+++ b/examples/12-transient-0/output/rust/src/lib.rs
diff --git a/examples/11-transient-0/output/rust/src/transient_0.rs b/examples/12-transient-0/output/rust/src/transient_0.rs
index 8b2b800..8b2b800 100644
--- a/examples/11-transient-0/output/rust/src/transient_0.rs
+++ b/examples/12-transient-0/output/rust/src/transient_0.rs
diff --git a/examples/11-transient-0/src/data.hob b/examples/12-transient-0/src/data.hob
index 9c715e9..9c715e9 100644
--- a/examples/11-transient-0/src/data.hob
+++ b/examples/12-transient-0/src/data.hob
diff --git a/hobgoblin/src/ast/untyped.hob b/hobgoblin/src/ast/untyped.hob
index 94f7c29..4c70d5e 100644
--- a/hobgoblin/src/ast/untyped.hob
+++ b/hobgoblin/src/ast/untyped.hob
@@ -46,7 +46,7 @@ struct UntypedNativeTypeDefinitionNode {
 
 struct UntypedStructDefinitionNode {
     field name: String;
-    field fields: List[UntypedStructFieldDefinitionNode];
+    field fields: Option[List[UntypedStructFieldDefinitionNode]];
     field docComment: DocComment;
     field source: Source;
 }
diff --git a/makefile b/makefile
index 589f61d..df051f9 100644
--- a/makefile
+++ b/makefile
@@ -11,4 +11,4 @@ codegen: package
 .PHONY: codegen-only
 
 codegen-only:
-	java -jar target/hobgoblin-0.1.0.jar compile hobgoblin
+	hobgoblin compile hobgoblin
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedStructDefinitionNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedStructDefinitionNode.java
index dc9a8fe..f2e6b97 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedStructDefinitionNode.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedStructDefinitionNode.java
@@ -5,10 +5,11 @@ import org.zwobble.hobgoblin.compiler.sources.Source;
 import org.zwobble.hobgoblin.compiler.types.StructType;
 
 import java.util.List;
+import java.util.Optional;
 
 public record TypedStructDefinitionNode(
     StructType type,
-    List<TypedStructFieldDefinitionNode> fields,
+    Optional<List<TypedStructFieldDefinitionNode>> fields,
     DocComment docComment,
     Source source
 ) implements TypedNamespaceStatementNode {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNode.java
index 72f45eb..0239ff8 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNode.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNode.java
@@ -7,17 +7,17 @@ package org.zwobble.hobgoblin.compiler.ast.untyped;
 
 public record UntypedStructDefinitionNode(
     String name,
-    java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode> fields,
+    java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>> fields,
     org.zwobble.hobgoblin.compiler.ast.DocComment docComment,
     org.zwobble.hobgoblin.compiler.sources.Source source
 ) implements org.zwobble.hobgoblin.compiler.ast.untyped.UntypedNamespaceStatementNode {
     public static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder arbitrary() {
-        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder("", java.util.List.of(), org.zwobble.hobgoblin.compiler.ast.HobgoblinNativeAst.arbitraryDocComment(), org.zwobble.hobgoblin.compiler.sources.HobgoblinNativeSources.arbitrarySource());
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder("", java.util.Optional.empty(), org.zwobble.hobgoblin.compiler.ast.HobgoblinNativeAst.arbitraryDocComment(), org.zwobble.hobgoblin.compiler.sources.HobgoblinNativeSources.arbitrarySource());
     }
 
     public record Builder(
         String name,
-        java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode> fields,
+        java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>> fields,
         org.zwobble.hobgoblin.compiler.ast.DocComment docComment,
         org.zwobble.hobgoblin.compiler.sources.Source source
     ) implements org.zwobble.hobgoblin.compiler.ast.untyped.UntypedNamespaceStatementNode.Builder {
@@ -29,20 +29,12 @@ public record UntypedStructDefinitionNode(
             return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder(name, fields, docComment, source);
         }
 
-        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder withFields(java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode> fields) {
-            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder(name, fields, docComment, source);
-        }
-
-        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder addField(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode field) {
-            var fields = new java.util.ArrayList<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>(this.fields);
-            fields.add(field);
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder withFields(java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>> fields) {
             return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder(name, fields, docComment, source);
         }
 
-        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder addField(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode.Builder field) {
-            var fields = new java.util.ArrayList<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>(this.fields);
-            fields.add(field.build());
-            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder(name, fields, docComment, source);
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder withFields(java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode> fields) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder(name, java.util.Optional.of(fields), docComment, source);
         }
 
         public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode.Builder withDocComment(org.zwobble.hobgoblin.compiler.ast.DocComment docComment) {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java
index d7f4bb0..35bb931 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java
@@ -15,6 +15,8 @@ import java.util.Set;
 import java.util.stream.Collectors;
 
 public class JavaGenerator {
+    public static final JavaIdentifier INSTANCE_FIELD_NAME = JavaIdentifier.of("INSTANCE");
+
     private final JavaGeneratorConfig config;
 
     public JavaGenerator(JavaGeneratorConfig config) {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javapreciselymatchers/JavaPreciselyMatchersGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javapreciselymatchers/JavaPreciselyMatchersGenerator.java
index 72f6339..1069f4a 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javapreciselymatchers/JavaPreciselyMatchersGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javapreciselymatchers/JavaPreciselyMatchersGenerator.java
@@ -195,7 +195,7 @@ public class JavaPreciselyMatchersGenerator implements Generator {
             )
         ));
 
-        for (var field : structDefinition.fields()) {
+        for (var field : structDefinition.fields().orElse(List.of())) {
             var fieldType = field.type().value();
             var javaFieldTypeRef = this.javaGenerator.generateReferenceTypeRef(fieldType);
             var javaFieldName = this.javaGenerator.generateFieldName(field.name());
@@ -258,10 +258,6 @@ public class JavaPreciselyMatchersGenerator implements Generator {
             this.typesInfo = typesInfo;
         }
 
-        public List<Field> fieldsOf(StructType type) {
-            return this.typesInfo.fieldsOf(type);
-        }
-
         public List<SumType> variantOf(StructType type) {
             return this.typesInfo.variantOf(type);
         }
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
index d8a0f5f..1c7c962 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
@@ -492,7 +492,7 @@ public class JavaTransient0Generator implements Generator {
         return generateEncodeMethod(
             structDefinition.type(),
             new JavaBlock(
-                structDefinition.fields().stream()
+                structDefinition.fields().orElse(List.of()).stream()
                     .flatMap(field -> generateEncode(
                         new JavaMethodCall(
                             new JavaRef(VALUE_NAME),
@@ -512,19 +512,23 @@ public class JavaTransient0Generator implements Generator {
         return generateDecodeMethod(
             structDefinition.type(),
             new JavaBlock(
-                Stream.concat(
-                    structDefinition.fields().stream()
-                        .flatMap(field -> generateDecode(
-                            this.javaGenerator.generateFieldName(field.name()),
-                            field.type().value()
-                        ).stream()),
-                    Stream.of(new JavaReturn(new JavaNewExpression(
-                        structJavaTypeRef,
-                        structDefinition.fields().stream()
-                            .<JavaExpression>map(field -> new JavaRef(this.javaGenerator.generateFieldName(field.name())))
-                            .toList()
-                    )))
-                ).toList()
+                structDefinition.fields().isEmpty()
+                    ? List.of(new JavaReturn(
+                        new JavaStaticFieldAccess(structJavaTypeRef, JavaGenerator.INSTANCE_FIELD_NAME)
+                    ))
+                    : Stream.concat(
+                        structDefinition.fields().get().stream()
+                            .flatMap(field -> generateDecode(
+                                this.javaGenerator.generateFieldName(field.name()),
+                                field.type().value()
+                            ).stream()),
+                        Stream.of(new JavaReturn(new JavaNewExpression(
+                            structJavaTypeRef,
+                            structDefinition.fields().get().stream()
+                                .<JavaExpression>map(field -> new JavaRef(this.javaGenerator.generateFieldName(field.name())))
+                                .toList()
+                        )))
+                    ).toList()
             )
         );
     }
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java
index 62c73ff..e8ecaa7 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java
@@ -122,7 +122,7 @@ public class JavaTypesGenerator implements Generator {
         TypedStructDefinitionNode structDefinition,
         Context context
     ) {
-        var components = structDefinition.fields().stream()
+        var components = structDefinition.fields().orElse(List.of()).stream()
             .map(field -> new JavaRecordComponent(
                 generateTypeRef(field.type(), context),
                 generateFieldName(field.name())
@@ -135,31 +135,51 @@ public class JavaTypesGenerator implements Generator {
 
         var builderJavaTypeRef = generateBuilderTypeRef(structDefinition.type());
 
-        var arbitraryComponentValues = structDefinition.fields().stream()
-            .map(field -> arbitraryValue(field.type(), context))
-            .toList();
+        var arbitraryValueExpression = new JavaNewExpression(
+            builderJavaTypeRef,
+            structDefinition.fields().orElse(List.of()).stream()
+                .map(field -> arbitraryValue(field.type(), context))
+                .toList()
+        );
+
+        var body = new ArrayList<JavaClassBodyDeclaration>();
+
+        if (structDefinition.fields().isEmpty()) {
+            body.add(new JavaFieldDeclaration(
+                JavaVisibility.PUBLIC,
+                JavaMemberKind.STATIC,
+                this.generateTypeRef(structDefinition.type(), context),
+                JavaGenerator.INSTANCE_FIELD_NAME,
+                Optional.of(new JavaNewExpression(
+                    generateTypeRef(structDefinition.type(), context),
+                    List.of()
+                ))
+            ));
+        }
+
+        body.add(new JavaMethodDeclaration(
+            ARBITRARY_METHOD_NAME,
+            JavaVisibility.PUBLIC,
+            JavaMemberKind.STATIC,
+            builderJavaTypeRef,
+            List.of(),
+            List.of(),
+            new JavaBlock(List.of(
+                new JavaReturn(arbitraryValueExpression)
+            ))
+        ));
+
+        body.add(generateStructDefinitionBuilder(
+            structDefinition,
+            components,
+            context
+        ));
 
         return new JavaRecordDeclaration(
             generateTypeRef(structDefinition.type(), context),
             components,
             implementsTypes,
-            List.of(
-                new JavaMethodDeclaration(
-                    ARBITRARY_METHOD_NAME,
-                    JavaVisibility.PUBLIC,
-                    JavaMemberKind.STATIC,
-                    builderJavaTypeRef,
-                    List.of(),
-                    List.of(),
-                    new JavaBlock(List.of(
-                        new JavaReturn(new JavaNewExpression(
-                            builderJavaTypeRef,
-                            arbitraryComponentValues
-                        ))
-                    ))
-                ),
-                generateStructDefinitionBuilder(structDefinition, components, context)
-            ),
+            body,
             structDefinition.docComment()
         );
     }
@@ -169,9 +189,11 @@ public class JavaTypesGenerator implements Generator {
         List<JavaRecordComponent> components,
         Context context
     ) {
-        var builderJavaTypeRef = generateBuilderTypeRef(structDefinition.type());
+        var structType = structDefinition.type();
 
-        var implementsTypes = context.variantOf(structDefinition.type()).stream()
+        var builderJavaTypeRef = generateBuilderTypeRef(structType);
+
+        var implementsTypes = context.variantOf(structType).stream()
             .map(sumType -> this.generateBuilderTypeRef(sumType))
             .toList();
 
@@ -180,18 +202,22 @@ public class JavaTypesGenerator implements Generator {
             BUILD_METHOD_NAME,
             JavaVisibility.PUBLIC,
             JavaMemberKind.INSTANCE,
-            generateTypeRef(structDefinition.type(), context),
+            generateTypeRef(structType, context),
             List.of(),
             List.of(),
             new JavaBlock(List.of(
-                new JavaReturn(new JavaNewExpression(
-                    generateTypeRef(structDefinition.type(), context),
-                    components.stream().<JavaExpression>map(component -> new JavaRef(component.name())).toList()
-                ))
+                new JavaReturn(
+                    structDefinition.fields().isPresent()
+                    ? new JavaNewExpression(
+                        generateTypeRef(structType, context),
+                        components.stream().<JavaExpression>map(component -> new JavaRef(component.name())).toList()
+                    )
+                    : new JavaStaticFieldAccess(this.generateTypeRef(structType, context), JavaGenerator.INSTANCE_FIELD_NAME)
+                )
             ))
         ));
 
-        for (var field : structDefinition.fields()) {
+        for (var field : structDefinition.fields().orElse(List.of())) {
             body.addAll(generateBuilderMethodsForField(field, components, builderJavaTypeRef, context));
         }
 
@@ -585,9 +611,9 @@ public class JavaTypesGenerator implements Generator {
             case StructType structType -> {
                 var newSeenTypes = new HashSet<>(seenTypes);
                 newSeenTypes.add(type);
-                var result =  context.fieldsOf(structType).stream()
+                var fields = context.fieldsOf(structType);
+                yield fields.orElse(List.of()).stream()
                     .allMatch(field -> isNonRecursivelyConstructable(field.type(), newSeenTypes, context));
-                yield result;
             }
 
             case SumType sumType -> {
@@ -633,7 +659,7 @@ public class JavaTypesGenerator implements Generator {
             return this.typesInfo.enumVariants(type);
         }
 
-        public List<Field> fieldsOf(StructType type) {
+        public Optional<List<Field>> fieldsOf(StructType type) {
             return this.typesInfo.fieldsOf(type);
         }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java
index 15e9e9d..1401b83 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java
@@ -386,7 +386,7 @@ public class RustTransient0Generator implements Generator {
     private RustItem generateEncodeStructFunction(TypedStructDefinitionNode structDefinition) {
         return generateEncodeFunction(
             structDefinition.type(),
-            structDefinition.fields().stream()
+            structDefinition.fields().orElse(List.of()).stream()
                 .map(field -> generateEncode(
                     new RustPrefixExpression(
                         RustPrefixOperator.BORROW,
@@ -406,24 +406,26 @@ public class RustTransient0Generator implements Generator {
 
         return generateDecodeFunction(
             structDefinition.type(),
-            new RustBlockExpression(
-                structDefinition.fields().stream()
-                    .<RustStatement>map(field -> new RustLetStatement(
-                        this.rustGenerator.generateFieldName(field.name()),
-                        false,
-                        generateDecode(field.type().value())
-                    ))
-                    .toList(),
-                Optional.of(new RustStructExpression(
-                    rustType,
-                    structDefinition.fields().stream()
-                        .map(field -> new RustStructExprField(
+            structDefinition.fields().isEmpty()
+                ? new RustBlockExpression(List.of(), Optional.of(rustType))
+                : new RustBlockExpression(
+                    structDefinition.fields().get().stream()
+                        .<RustStatement>map(field -> new RustLetStatement(
                             this.rustGenerator.generateFieldName(field.name()),
-                            RustPath.of(this.rustGenerator.generateFieldName(field.name()))
+                            false,
+                            generateDecode(field.type().value())
                         ))
-                        .toList()
-                ))
-            )
+                        .toList(),
+                    Optional.of(new RustStructExpression(
+                        rustType,
+                        structDefinition.fields().get().stream()
+                            .map(field -> new RustStructExprField(
+                                this.rustGenerator.generateFieldName(field.name()),
+                                RustPath.of(this.rustGenerator.generateFieldName(field.name()))
+                            ))
+                            .toList()
+                    ))
+                )
         );
     }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java
index 99b4208..8ed9d9e 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java
@@ -127,7 +127,7 @@ public class RustTypesGenerator implements Generator {
 
         var rustStructName = this.rustGenerator.generateTypeName(structDefinition.name());
 
-        var rustFields = structDefinition.fields().stream()
+        var rustFields = structDefinition.fields().orElse(List.of()).stream()
             .map(field -> new RustStructField(
                 this.rustGenerator.generateFieldName(field.name()),
                 generateRustTypeExpression(field.type(), context)
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
index 47a8095..e312f30 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
@@ -210,11 +210,7 @@ public class Parser {
         var name = tokens.next(TokenType.IDENTIFIER);
         tokens.skip(TokenType.SYMBOL_BRACE_OPEN);
 
-        var fields = parseMany(
-            () -> tokens.isNext(TokenType.SYMBOL_BRACE_CLOSE),
-            () -> parseStructFieldDefinition(tokens),
-            () -> true
-        );
+        var fields = parseStructDefinitionFields(tokens);
 
         tokens.skip(TokenType.SYMBOL_BRACE_CLOSE);
 
@@ -229,6 +225,21 @@ public class Parser {
         );
     }
 
+    private static Optional<List<UntypedStructFieldDefinitionNode>> parseStructDefinitionFields(TokenIterator tokens) {
+        var isSingleton = tokens.trySkip(TokenType.IDENTIFIER, "singleton");
+        if (isSingleton) {
+            tokens.skip(TokenType.SYMBOL_SEMICOLON);
+            return Optional.empty();
+        } else {
+            var fields = parseMany(
+                () -> tokens.isNext(TokenType.SYMBOL_BRACE_CLOSE),
+                () -> parseStructFieldDefinition(tokens),
+                () -> true
+            );
+            return Optional.of(fields);
+        }
+    }
+
     private static UntypedStructFieldDefinitionNode parseStructFieldDefinition(
         TokenIterator tokens
     ) {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenIterator.java b/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenIterator.java
index 55edd97..43705a1 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenIterator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenIterator.java
@@ -54,6 +54,16 @@ class TokenIterator {
         }
     }
 
+    public boolean trySkip(TokenType tokenType, String value) {
+        var token = peek();
+        if (token.tokenType().equals(tokenType) && value.contentEquals(token.charSequence())) {
+            this.tokenIndex++;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
     private Token getAbsolute(int index) {
         if (index < this.tokens.size()) {
             return this.tokens.get(index);
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
index d55c490..f03f979 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -8,6 +8,7 @@ import org.zwobble.hobgoblin.compiler.types.*;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 
 import static org.zwobble.hobgoblin.compiler.typechecker.NamespaceNameResolution.resolveNamespaceName;
 import static org.zwobble.hobgoblin.compiler.typechecker.TypeCheckerSubtyping.isSubtype;
@@ -180,9 +181,13 @@ public class TypeChecker {
     ) {
         var structType = (StructType) lookupMetaType(untyped.name(), untyped.source(), context);
 
-        var typeCheckedFieldDefinitions = typeCheckFieldDefinitions(untyped.fields(), context);
+        var typeCheckedFieldDefinitions = untyped.fields().isPresent()
+            ? Optional.of(typeCheckFieldDefinitions(untyped.fields().get(), context))
+            : Optional.<TypeCheckFieldDefinitionsResult>empty();
+        var typedFields = typeCheckedFieldDefinitions.map(TypeCheckFieldDefinitionsResult::fields);
+        var typedFieldNodes = typeCheckedFieldDefinitions.map(TypeCheckFieldDefinitionsResult::typedFieldNodes);
 
-        context.defineStructType(structType, typeCheckedFieldDefinitions.fields());
+        context.defineStructType(structType, typedFields);
 
         for (var sumType : context.variantOf(structType)) {
             var sumTypeFields = context.fieldsOf(sumType);
@@ -190,14 +195,14 @@ public class TypeChecker {
                 sumType,
                 sumTypeFields,
                 structType,
-                typeCheckedFieldDefinitions.fields,
+                typedFields,
                 context.toTypesInfo()
             );
         }
 
         return new TypedStructDefinitionNode(
             structType,
-            typeCheckedFieldDefinitions.typedFieldNodes(),
+            typedFieldNodes,
             untyped.docComment(),
             untyped.source()
         );
@@ -303,13 +308,15 @@ public class TypeChecker {
         SumType sumType,
         List<Field> sumTypeFields,
         StructType variantType,
-        List<Field> variantTypeFields,
+        Optional<List<Field>> variantTypeFields,
         TypesInfo typesInfo
     ) {
         for (var sumTypeField : sumTypeFields) {
-            var variantTypeField = variantTypeFields.stream()
-                .filter(field -> field.name().equals(sumTypeField.name()))
-                .findFirst();
+            var variantTypeField = variantTypeFields.flatMap(
+                fields -> fields.stream()
+                    .filter(field -> field.name().equals(sumTypeField.name()))
+                    .findFirst()
+            );
 
             if (variantTypeField.isEmpty()) {
                 throw new SubtypeIsMissingFieldError(sumType, variantType, sumTypeField.name(), sumTypeField.source());
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
index 0a61de7..5484904 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
@@ -61,7 +61,7 @@ public class TypeCheckerNamespaceContext {
         this.typesInfo.defineEnumType(enumType, enumVariants);
     }
 
-    public void defineStructType(StructType structType, List<Field> fields) {
+    public void defineStructType(StructType structType, Optional<List<Field>> fields) {
         this.typesInfo.defineStructType(structType, fields);
     }
 
@@ -69,7 +69,7 @@ public class TypeCheckerNamespaceContext {
         return this.typesInfo.isDefined(type);
     }
 
-    public List<Field> fieldsOf(StructType type) {
+    public Optional<List<Field>> fieldsOf(StructType type) {
         return this.typesInfo.fieldsOf(type);
     }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfo.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfo.java
index 814466c..697be9b 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfo.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfo.java
@@ -3,12 +3,13 @@ package org.zwobble.hobgoblin.compiler.typechecker;
 import org.zwobble.hobgoblin.compiler.types.*;
 
 import java.util.List;
+import java.util.Optional;
 
 public interface TypesInfo {
     TypesInfo EMPTY = TypesInfoInMemory.empty();
 
     boolean isDefined(StructType type);
-    List<Field> fieldsOf(StructType structType);
+    Optional<List<Field>> fieldsOf(StructType structType);
 
     List<SumType> variantOf(StructType variantType);
     List<Type> sumVariants(SumType type);
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfoInMemory.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfoInMemory.java
index d9c0c85..821238b 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfoInMemory.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypesInfoInMemory.java
@@ -6,27 +6,32 @@ import org.zwobble.hobgoblin.compiler.util.ManyToMany;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 
 public class TypesInfoInMemory implements TypesInfo {
     public static TypesInfoInMemory empty() {
         return new TypesInfoInMemory(
             new HashMap<>(),
             new HashMap<>(),
+            new HashMap<>(),
             new ManyToMany<>()
         );
     }
 
     private final Map<EnumType, List<EnumVariant>> enumVariants;
-    private final Map<Type, List<Field>> fieldsOf;
+    private final Map<Type, Optional<List<Field>>> structFields;
+    private final Map<Type, List<Field>> sumFields;
     private final ManyToMany<SumType, Type> sumVariants;
 
     public TypesInfoInMemory(
         Map<EnumType, List<EnumVariant>> enumVariants,
-        Map<Type, List<Field>> fieldsOf,
+        Map<Type, Optional<List<Field>>> structFields,
+        Map<Type, List<Field>> sumFields,
         ManyToMany<SumType, Type> sumVariants
     ) {
         this.enumVariants = enumVariants;
-        this.fieldsOf = fieldsOf;
+        this.structFields = structFields;
+        this.sumFields = sumFields;
         this.sumVariants = sumVariants;
     }
 
@@ -38,19 +43,21 @@ public class TypesInfoInMemory implements TypesInfo {
         return this.enumVariants.get(enumType);
     }
 
-    public void defineStructType(StructType structType, List<Field> fields) {
-        this.fieldsOf.put(structType, fields);
+    public void defineStructType(StructType structType, Optional<List<Field>> fields) {
+        this.structFields.put(structType, fields);
     }
 
     @Override
     public boolean isDefined(StructType type) {
-        return this.fieldsOf.containsKey(type);
+        return this.structFields.containsKey(type);
     }
 
-    public List<Field> fieldsOf(StructType structType) {
-        var fields = this.fieldsOf.get(structType);
+    @Override
+    public Optional<List<Field>> fieldsOf(StructType structType) {
+        var fields = this.structFields.get(structType);
         if (fields == null) {
-            return List.of();
+            // TODO: better error
+            throw new RuntimeException("struct not defined");
         } else {
             return fields;
         }
@@ -64,7 +71,7 @@ public class TypesInfoInMemory implements TypesInfo {
         for (var variantType : variantTypes) {
             this.sumVariants.add(sumType, variantType);
         }
-        this.fieldsOf.put(sumType, fields);
+        this.sumFields.put(sumType, fields);
     }
 
     public List<SumType> variantOf(StructType variantType) {
@@ -76,7 +83,7 @@ public class TypesInfoInMemory implements TypesInfo {
     }
 
     public List<Field> fieldsOf(SumType sumType) {
-        var fields = this.fieldsOf.get(sumType);
+        var fields = this.sumFields.get(sumType);
         if (fields == null) {
             return List.of();
         } else {
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNodeMatcher.java b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNodeMatcher.java
index 429e438..dd66994 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNodeMatcher.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedStructDefinitionNodeMatcher.java
@@ -36,7 +36,7 @@ public class UntypedStructDefinitionNodeMatcher implements org.zwobble.precisely
         return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNodeMatcher(submatchers);
     }
 
-    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNodeMatcher withFields(org.zwobble.precisely.Matcher<? super java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>> fields) {
+    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNodeMatcher withFields(org.zwobble.precisely.Matcher<? super java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructFieldDefinitionNode>>> fields) {
         var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode>>(this.submatchers);
         submatchers.add(org.zwobble.precisely.Matchers.has("fields", org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNode::fields, fields));
         return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedStructDefinitionNodeMatcher(submatchers);
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java
index 6c90356..0b8ba5e 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java
@@ -24,7 +24,8 @@ public class ParserStructDefinitionTests {
 
         assertThat(node, instanceOf(
             UntypedStructDefinitionNode.class,
-            has("name", UntypedStructDefinitionNode::name, equalTo("Point"))
+            has("name", UntypedStructDefinitionNode::name, equalTo("Point")),
+            has("fields", UntypedStructDefinitionNode::fields, isOptionalOf(isSequence()))
         ));
     }
 
@@ -43,7 +44,7 @@ public class ParserStructDefinitionTests {
 
         assertThat(node, instanceOf(
             UntypedStructDefinitionNode.class,
-            has("fields", UntypedStructDefinitionNode::fields, isSequence(
+            has("fields", UntypedStructDefinitionNode::fields, isOptionalOf(isSequence(
                 instanceOf(
                     UntypedStructFieldDefinitionNode.class,
                     has("name", UntypedStructFieldDefinitionNode::name, equalTo("x")),
@@ -68,7 +69,25 @@ public class ParserStructDefinitionTests {
                         )
                     )
                 )
-            ))
+            )))
+        ));
+    }
+
+    @Test
+    public void singletonStruct() {
+        var source = """
+            struct Point {
+                singleton;
+            }""";
+
+        var node = parseString(
+            source,
+            Parser::parseNamespaceStatement
+        );
+
+        assertThat(node, instanceOf(
+            UntypedStructDefinitionNode.class,
+            has("fields", UntypedStructDefinitionNode::fields, isOptionalEmpty())
         ));
     }
 
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceTests.java
index 2f7cc6b..b5814a8 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceTests.java
@@ -100,9 +100,9 @@ public class TypeCheckerNamespaceTests {
         ));
         assertThat(
             context.toTypesInfo().fieldsOf(new StructType(NamespaceName.of("a", "b"), "X")),
-            isSequence(
+            isOptionalOf(isSequence(
                 isField("y", new SimpleNativeType(NamespaceName.of("a", "c"), "Y"))
-            )
+            ))
         );
     }
 
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerStructDefinitionTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerStructDefinitionTests.java
index 0efe3b4..d86fd59 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerStructDefinitionTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerStructDefinitionTests.java
@@ -14,6 +14,7 @@ import org.zwobble.hobgoblin.compiler.types.SimpleNativeType;
 import org.zwobble.hobgoblin.compiler.types.StructType;
 
 import java.util.List;
+import java.util.Optional;
 
 import static org.zwobble.hobgoblin.compiler.typechecker.TypeCheckerTesting.typeCheckNamespaceStatement;
 import static org.zwobble.hobgoblin.compiler.types.TypeMatchers.isField;
@@ -64,7 +65,7 @@ public class TypeCheckerStructDefinitionTests {
             has(
                 "fields",
                 TypedStructDefinitionNode::fields,
-                isSequence(
+                isOptionalOf(isSequence(
                     allOf(
                         has("name", TypedStructFieldDefinitionNode::name, equalTo("a")),
                         has("type", TypedStructFieldDefinitionNode::type, has(
@@ -81,16 +82,47 @@ public class TypeCheckerStructDefinitionTests {
                             equalTo(int64Type)
                         ))
                     )
-                )
+                ))
             )
         ));
         var typesInfo = globalContext.toTypesInfo();
         assertThat(
             typesInfo.fieldsOf(new StructType(namespaceName, "X")),
-            isSequence(
+            isOptionalOf(isSequence(
                 isField("a", int32Type),
                 isField("b", int64Type)
+            ))
+        );
+    }
+
+    @Test
+    public void singletonStructHasNoFields() {
+        var int32Type = SimpleNativeType.builtin("Int32");
+        var int64Type = SimpleNativeType.builtin("Int64");
+        var untyped = UntypedStructDefinitionNode.arbitrary()
+            .withName("X")
+            .withFields(Optional.empty())
+            .build();
+        var globalContext = TypeCheckerGlobalContext.initial();
+        globalContext.addNativeType(int32Type);
+        globalContext.addNativeType(int64Type);
+        var namespaceName = NamespaceName.of("a", "b");
+        var namespaceContext = globalContext.enterNamespace(namespaceName);
+
+        var typed = typeCheckNamespaceStatement(untyped, namespaceContext);
+
+        assertThat(typed, instanceOf(
+            TypedStructDefinitionNode.class,
+            has(
+                "fields",
+                TypedStructDefinitionNode::fields,
+                isOptionalEmpty()
             )
+        ));
+        var typesInfo = globalContext.toTypesInfo();
+        assertThat(
+            typesInfo.fieldsOf(new StructType(namespaceName, "X")),
+            isOptionalEmpty()
         );
     }
 
@@ -130,7 +162,7 @@ public class TypeCheckerStructDefinitionTests {
                     has(
                         "fields",
                         TypedStructDefinitionNode::fields,
-                        isSequence(
+                        isOptionalOf(isSequence(
                             allOf(
                                 has("name", TypedStructFieldDefinitionNode::name, equalTo("value")),
                                 has("type", TypedStructFieldDefinitionNode::type, has(
@@ -139,7 +171,7 @@ public class TypeCheckerStructDefinitionTests {
                                     equalTo(new StructType(namespaceName, "Y"))
                                 ))
                             )
-                        )
+                        ))
                     )
                 ),
                 instanceOf(
@@ -148,7 +180,7 @@ public class TypeCheckerStructDefinitionTests {
                     has(
                         "fields",
                         TypedStructDefinitionNode::fields,
-                        isSequence(
+                        isOptionalOf(isSequence(
                             allOf(
                                 has("name", TypedStructFieldDefinitionNode::name, equalTo("value")),
                                 has("type", TypedStructFieldDefinitionNode::type, has(
@@ -157,7 +189,7 @@ public class TypeCheckerStructDefinitionTests {
                                     equalTo(int32Type)
                                 ))
                             )
-                        )
+                        ))
                     )
                 )
             )
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerSumDefinitionTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerSumDefinitionTests.java
index bfc9280..68b1b06 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerSumDefinitionTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerSumDefinitionTests.java
@@ -12,6 +12,7 @@ import org.zwobble.hobgoblin.compiler.typechecker.errors.UnexpectedTypeError;
 import org.zwobble.hobgoblin.compiler.types.*;
 
 import java.util.List;
+import java.util.Optional;
 
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.zwobble.hobgoblin.compiler.typechecker.TypeCheckerTesting.typeCheckNamespaceStatement;
@@ -159,7 +160,7 @@ public class TypeCheckerSumDefinitionTests {
             .enterNamespace(namespaceName);
         var variantType = new StructType(namespaceName, "Square");
         namespaceContext.declare("Square", new TypeLevelValueType(variantType), NullSource.INSTANCE);
-        namespaceContext.defineStructType(variantType, List.of());
+        namespaceContext.defineStructType(variantType, Optional.of(List.of()));
 
         var error = assertThrows(
             SubtypeIsMissingFieldError.class,
@@ -196,7 +197,7 @@ public class TypeCheckerSumDefinitionTests {
             .enterNamespace(namespaceName);
         var variantType = new StructType(namespaceName, "Square");
         namespaceContext.declare("Square", new TypeLevelValueType(variantType), NullSource.INSTANCE);
-        namespaceContext.defineStructType(variantType, List.of(new Field("area", int64Type, NullSource.INSTANCE)));
+        namespaceContext.defineStructType(variantType, Optional.of(List.of(new Field("area", int64Type, NullSource.INSTANCE))));
 
         // TODO: more specific error
         var error = assertThrows(
@@ -232,7 +233,7 @@ public class TypeCheckerSumDefinitionTests {
             .enterNamespace(namespaceName);
         var variantType = new StructType(namespaceName, "Square");
         namespaceContext.declare("Square", new TypeLevelValueType(variantType), NullSource.INSTANCE);
-        namespaceContext.defineStructType(variantType, List.of());
+        namespaceContext.defineStructType(variantType, Optional.of(List.of()));
 
         assertThrows(
             SubtypeIsMissingFieldError.class,