From eb145887ab57b75299a55c85c753d3b4707105be Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 9 Aug 2026 22:16:47 +0100
Subject: Introduce variables for type params

---
 .../zwobble/hobgoblin/compiler/typechecker/TypeChecker.java | 11 ++++++++++-
 .../compiler/typechecker/TypeCheckerNamespaceContext.java   | 13 +++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

(limited to 'src/main')

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 97008b6..63fc357 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -239,8 +239,17 @@ public class TypeChecker {
                 throw new UnsupportedOperationException("TODO");
         };
 
+        var typeParams = switch (typeOrConstructor) {
+            case TypeOrConstructor.Type<SimpleStructType> _ ->
+                List.<TypeParam>of();
+
+            case TypeOrConstructor.Constructor<SimpleStructType> constructor ->
+                constructor.value().params();
+        };
+        var bodyContext = context.enter(typeParams);
+
         var typeCheckedFieldDefinitions = untyped.fields().isPresent()
-            ? Optional.of(typeCheckFieldDefinitions(untyped.fields().get(), context))
+            ? Optional.of(typeCheckFieldDefinitions(untyped.fields().get(), bodyContext))
             : Optional.<TypeCheckFieldDefinitionsResult>empty();
         var typedFields = typeCheckedFieldDefinitions.map(TypeCheckFieldDefinitionsResult::fields);
         var typedFieldNodes = typeCheckedFieldDefinitions.map(TypeCheckFieldDefinitionsResult::typedFieldNodes);
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 2c8ad67..ce7153f 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
@@ -89,4 +89,17 @@ public class TypeCheckerNamespaceContext {
     public List<Field> fieldsOf(SumType type) {
         return this.typesInfo.fieldsOf(type);
     }
+
+    public TypeCheckerNamespaceContext enter(List<TypeParam> typeParams) {
+        var newVariables = new HashMap<>(this.variables);
+        for (var typeParam : typeParams) {
+            newVariables.put(typeParam.name(), Types.metaType(typeParam));
+        }
+
+        return new TypeCheckerNamespaceContext(
+            this.namespaceName,
+            newVariables,
+            this.typesInfo
+        );
+    }
 }
-- 
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