From 2053e1f02448c947200ac93d76ecc3aeb0775f0c Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Fri, 8 May 2026 09:51:17 +0100
Subject: Type check constructed types

---
 .../ast/typed/TypedConstructedTypeNode.java        | 10 +++++++
 .../ast/typed/TypedTypeLevelExpressionNode.java    |  2 +-
 .../compiler/typechecker/TypeChecker.java          | 21 ++++++++++++-
 .../compiler/ast/typed/TypedNodeMatchers.java      | 27 +++++++++++++++++
 .../hobgoblin/compiler/ast/untyped/UntypedArb.java | 13 ++++++++
 .../TypeCheckerConstructedTypeTests.java           | 35 ++++++++++++++++++++++
 6 files changed, 106 insertions(+), 2 deletions(-)
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedConstructedTypeNode.java
 create mode 100644 src/test/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedNodeMatchers.java
 create mode 100644 src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerConstructedTypeTests.java

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedConstructedTypeNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedConstructedTypeNode.java
new file mode 100644
index 0000000..5567516
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedConstructedTypeNode.java
@@ -0,0 +1,10 @@
+package org.zwobble.hobgoblin.compiler.ast.typed;
+
+import org.zwobble.hobgoblin.compiler.sources.Source;
+import org.zwobble.hobgoblin.compiler.types.ConstructedNativeType;
+
+public record TypedConstructedTypeNode(
+    ConstructedNativeType value,
+    Source source
+) implements TypedTypeLevelExpressionNode<ConstructedNativeType> {
+}
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedTypeLevelExpressionNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedTypeLevelExpressionNode.java
index c588f95..e80635d 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedTypeLevelExpressionNode.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedTypeLevelExpressionNode.java
@@ -2,6 +2,6 @@ package org.zwobble.hobgoblin.compiler.ast.typed;
 
 import org.zwobble.hobgoblin.compiler.types.TypeLevelValue;
 
-public sealed interface TypedTypeLevelExpressionNode<T extends TypeLevelValue> extends TypedNode permits TypedTypeLevelReferenceNode {
+public sealed interface TypedTypeLevelExpressionNode<T extends TypeLevelValue> extends TypedNode permits TypedConstructedTypeNode, TypedTypeLevelReferenceNode {
     T value();
 }
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 a535bc8..5219d4d 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -144,13 +144,32 @@ public class TypeChecker {
     ) {
         return switch (untyped) {
             case UntypedConstructedTypeNode untypedConstructedType ->
-                throw new UnsupportedOperationException("TODO");
+                typeCheckConstructedType(untypedConstructedType, context);
 
             case UntypedTypeLevelReferenceNode untypedTypeLevelReference ->
                 typeCheckTypeLevelReference(untypedTypeLevelReference, context);
         };
     }
 
+    private static TypedTypeLevelExpressionNode<? extends TypeLevelValue> typeCheckConstructedType(
+        UntypedConstructedTypeNode untyped,
+        TypeCheckerNamespaceContext context
+    ) {
+        var typedReceiver = typeCheckTypeLevelExpression(untyped.receiver(), context);
+        var receiver = (TypeConstructor<SimpleNativeType>) typedReceiver.value();
+
+        var args = untyped.args().stream()
+            .map(untypedArg -> typeCheckMetaType(untypedArg, context).value())
+            .toList();
+
+        var constructedType = new ConstructedNativeType(receiver, args);
+
+        return new TypedConstructedTypeNode(
+            constructedType,
+            untyped.source()
+        );
+    }
+
     private static TypedTypeLevelExpressionNode<? extends TypeLevelValue> typeCheckTypeLevelReference(
         UntypedTypeLevelReferenceNode untyped,
         TypeCheckerNamespaceContext context
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedNodeMatchers.java b/src/test/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedNodeMatchers.java
new file mode 100644
index 0000000..bbf6a84
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/ast/typed/TypedNodeMatchers.java
@@ -0,0 +1,27 @@
+package org.zwobble.hobgoblin.compiler.ast.typed;
+
+import org.zwobble.hobgoblin.compiler.types.ConstructedNativeType;
+import org.zwobble.precisely.Matcher;
+
+import static org.zwobble.precisely.Matchers.*;
+
+public class TypedNodeMatchers {
+    private TypedNodeMatchers() {
+    }
+
+    public static Matcher<TypedTypeLevelExpressionNode<?>> isTypedConstructedTypeNode(
+        Matcher<ConstructedNativeType> value
+    ) {
+        return instanceOf(
+            TypedConstructedTypeNode.class,
+            has("value", TypedConstructedTypeNode::value, value)
+        );
+    }
+
+    public static Matcher<TypedTypeLevelExpressionNode<?>> isTypedTypeLevelReferenceNode(String name) {
+        return instanceOf(
+            TypedTypeLevelReferenceNode.class,
+            has("name", TypedTypeLevelReferenceNode::name, equalTo(name))
+        );
+    }
+}
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedArb.java b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedArb.java
index 5a011d7..3943bc7 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedArb.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedArb.java
@@ -2,10 +2,23 @@ package org.zwobble.hobgoblin.compiler.ast.untyped;
 
 import org.zwobble.hobgoblin.compiler.sources.NullSource;
 
+import java.util.List;
+
 public class UntypedArb {
     private UntypedArb() {
     }
 
+    public static UntypedConstructedTypeNode constructedType(
+        UntypedTypeLevelExpressionNode receiver,
+        List<UntypedTypeLevelExpressionNode> args
+    ) {
+        return new UntypedConstructedTypeNode(
+            receiver,
+            args,
+            NullSource.INSTANCE
+        );
+    }
+
     public static UntypedTypeLevelReferenceNode typeLevelReference(String name) {
         return new UntypedTypeLevelReferenceNode(name, NullSource.INSTANCE);
     }
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerConstructedTypeTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerConstructedTypeTests.java
new file mode 100644
index 0000000..2fd1e91
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerConstructedTypeTests.java
@@ -0,0 +1,35 @@
+package org.zwobble.hobgoblin.compiler.typechecker;
+
+import org.junit.jupiter.api.Test;
+import org.zwobble.hobgoblin.compiler.ast.untyped.UntypedArb;
+import org.zwobble.hobgoblin.compiler.types.*;
+
+import java.util.List;
+
+import static org.zwobble.hobgoblin.compiler.ast.typed.TypedNodeMatchers.isTypedConstructedTypeNode;
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.equalTo;
+
+public class TypeCheckerConstructedTypeTests {
+    @Test
+    public void whenArgsMatchParamsThenCanConstructTypeFromTypeConstructor() {
+        var untyped = UntypedArb.constructedType(
+            UntypedArb.typeLevelReference("List"),
+            List.of(UntypedArb.typeLevelReference("Int32"))
+        );
+        var context = TypeCheckerContextArb.namespaceContext();
+        context.declare("List");
+        var listType = new SimpleNativeType("List");
+        var listTypeConstructor = new TypeConstructor<>(List.of(new TypeParam("T")), listType);
+        context.define("List", new TypeLevelValueType(listTypeConstructor));
+        context.declare("Int32");
+        var int32Type = new SimpleNativeType("Int32");
+        context.define("Int32", new TypeLevelValueType(int32Type));
+
+        var typed = TypeChecker.typeCheckTypeLevelExpression(untyped, context);
+
+        assertThat(typed, isTypedConstructedTypeNode(
+            equalTo(new ConstructedNativeType(listTypeConstructor, List.of(int32Type)))
+        ));
+    }
+}
-- 
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