From ff49a4cd2231787867b4aafc95bd5705057bfcc3 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 2 Aug 2026 14:19:23 +0100
Subject: Introduce NativeTypeConstructor for greater safety

---
 .../hobgoblin/compiler/builtins/NativeTypes.java       |  8 ++++----
 .../hobgoblin/compiler/typechecker/TypeChecker.java    |  9 +++------
 .../compiler/types/NativeTypeConstructor.java          |  9 +++++++++
 .../hobgoblin/compiler/types/TypeConstructor.java      | 13 ++++++-------
 .../org/zwobble/hobgoblin/compiler/types/Types.java    | 18 ++++++++++++++++++
 5 files changed, 40 insertions(+), 17 deletions(-)
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/types/NativeTypeConstructor.java
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/types/Types.java

(limited to 'src/main/java/org/zwobble')

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/builtins/NativeTypes.java b/src/main/java/org/zwobble/hobgoblin/compiler/builtins/NativeTypes.java
index 485df8c..f4e499e 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/builtins/NativeTypes.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/builtins/NativeTypes.java
@@ -13,7 +13,7 @@ public class NativeTypes {
 
     public static final SimpleNativeType BOX_INNER = SimpleNativeType.builtin("Box");
 
-    public static TypeConstructor<SimpleNativeType> BOX = new TypeConstructor<>(
+    public static TypeConstructor<SimpleNativeType> BOX = Types.constructor(
         List.of(new TypeParam("T")),
         BOX_INNER
     );
@@ -24,7 +24,7 @@ public class NativeTypes {
 
     public static final SimpleNativeType LIST_INNER = SimpleNativeType.builtin("List");
 
-    public static TypeConstructor<SimpleNativeType> LIST = new TypeConstructor<>(
+    public static TypeConstructor<SimpleNativeType> LIST = Types.constructor(
         List.of(new TypeParam("T")),
         LIST_INNER
     );
@@ -35,7 +35,7 @@ public class NativeTypes {
 
     public static final SimpleNativeType OPTION_INNER = SimpleNativeType.builtin("Option");
 
-    public static TypeConstructor<SimpleNativeType> OPTION = new TypeConstructor<>(
+    public static TypeConstructor<SimpleNativeType> OPTION = Types.constructor(
         List.of(new TypeParam("T")),
         OPTION_INNER
     );
@@ -46,7 +46,7 @@ public class NativeTypes {
 
     public static final SimpleNativeType SHARED_INNER = SimpleNativeType.builtin("Shared");
 
-    public static TypeConstructor<SimpleNativeType> SHARED = new TypeConstructor<>(
+    public static TypeConstructor<SimpleNativeType> SHARED = Types.constructor(
         List.of(new TypeParam("T")),
         SHARED_INNER
     );
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 4b02f60..9429313 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -408,12 +408,9 @@ public class TypeChecker {
             .map(untypedArg -> typeCheckMetaType(untypedArg, context).value())
             .toList();
 
-        var constructedType = switch (receiver.genericType()) {
-            case SimpleNativeType _ -> {
-                @SuppressWarnings("unchecked")
-                var narrowReceiver = (TypeConstructor<SimpleNativeType>) receiver;
-                yield new ConstructedNativeType(narrowReceiver, args);
-            }
+        var constructedType = switch (receiver) {
+            case NativeTypeConstructor nativeTypeConstructor ->
+                new ConstructedNativeType(nativeTypeConstructor, args);
         };
 
         return new TypedConstructedTypeNode(
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/types/NativeTypeConstructor.java b/src/main/java/org/zwobble/hobgoblin/compiler/types/NativeTypeConstructor.java
new file mode 100644
index 0000000..43e0cfc
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/types/NativeTypeConstructor.java
@@ -0,0 +1,9 @@
+package org.zwobble.hobgoblin.compiler.types;
+
+import java.util.List;
+
+public record NativeTypeConstructor(
+    List<TypeParam> params,
+    SimpleNativeType genericType
+) implements TypeConstructor<SimpleNativeType> {
+}
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/types/TypeConstructor.java b/src/main/java/org/zwobble/hobgoblin/compiler/types/TypeConstructor.java
index 1e412d7..e2726fb 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/types/TypeConstructor.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/types/TypeConstructor.java
@@ -2,12 +2,11 @@ package org.zwobble.hobgoblin.compiler.types;
 
 import java.util.List;
 
-public record TypeConstructor<T extends ConstructibleType>(
-    List<TypeParam> params,
-    T genericType
-) implements TypeLevelValue {
-    @Override
-    public String describe() {
-        return genericType.describe();
+public sealed interface TypeConstructor<T extends ConstructibleType> extends TypeLevelValue permits NativeTypeConstructor {
+    List<TypeParam> params();
+    T genericType();
+
+    default String describe() {
+        return genericType().describe();
     }
 }
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/types/Types.java b/src/main/java/org/zwobble/hobgoblin/compiler/types/Types.java
new file mode 100644
index 0000000..6d8fcbb
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/types/Types.java
@@ -0,0 +1,18 @@
+package org.zwobble.hobgoblin.compiler.types;
+
+import java.util.List;
+
+public class Types {
+    private Types() {}
+
+    @SuppressWarnings("unchecked")
+    public static <T extends ConstructibleType> TypeConstructor<T> constructor(
+        List<TypeParam> params,
+        T genericType
+    ) {
+        return (TypeConstructor<T>) switch (genericType) {
+            case SimpleNativeType simpleNativeType ->
+                new NativeTypeConstructor(params, simpleNativeType);
+        };
+    }
+}
-- 
cgit v1.2.3