From 72c84ea17a7e4b27cf9428ef23f713e32f5339d3 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 25 Apr 2026 10:56:55 +0100
Subject: Type check struct fields

---
 .../hobgoblin/compiler/HobgoblinCompiler.java      |  3 +++
 .../compiler/typechecker/TypeChecker.java          | 31 +++++++++++++++++-----
 .../typechecker/TypeCheckerGlobalContext.java      | 14 +++++++++-
 .../typechecker/TypeCheckerNamespaceContext.java   | 15 ++++++++---
 .../hobgoblin/compiler/typechecker/Variable.java   |  4 +++
 5 files changed, 57 insertions(+), 10 deletions(-)

(limited to 'src/main')

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java b/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java
index 4f56fb1..d9f7d21 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java
@@ -4,6 +4,7 @@ import org.zwobble.hobgoblin.compiler.parser.Parser;
 import org.zwobble.hobgoblin.compiler.typechecker.TypeChecker;
 import org.zwobble.hobgoblin.compiler.typechecker.TypeCheckerGlobalContext;
 import org.zwobble.hobgoblin.compiler.types.NamespaceName;
+import org.zwobble.hobgoblin.compiler.types.ScalarType;
 import org.zwobble.sourcetext.SourceText;
 
 import java.io.IOException;
@@ -29,6 +30,8 @@ public class HobgoblinCompiler {
             var untypedNamespaceNode = Parser.parseNamespace(sourceText, namespaceName);
 
             var typeCheckerContext = TypeCheckerGlobalContext.initial();
+            typeCheckerContext.addBuiltinScalarType(new ScalarType("Int32"));
+
             var typedNamespaceNode = TypeChecker.typeCheckNamespace(untypedNamespaceNode, typeCheckerContext);
         }
     }
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 b8bdd7f..d9a37e2 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -2,13 +2,9 @@ package org.zwobble.hobgoblin.compiler.typechecker;
 
 import org.zwobble.hobgoblin.compiler.ast.typed.*;
 import org.zwobble.hobgoblin.compiler.ast.untyped.*;
-import org.zwobble.hobgoblin.compiler.types.StructType;
-import org.zwobble.hobgoblin.compiler.types.TypeLevelValue;
-import org.zwobble.hobgoblin.compiler.types.TypeLevelValueType;
-import org.zwobble.hobgoblin.compiler.types.TypeSet;
+import org.zwobble.hobgoblin.compiler.types.*;
 
 import java.util.ArrayList;
-import java.util.List;
 
 public class TypeChecker {
     private TypeChecker() {
@@ -49,13 +45,36 @@ public class TypeChecker {
     ) {
         var structType = new StructType(context.namespaceName(), untyped.name());
 
+        var typedFields = new ArrayList<TypedStructFieldDefinitionNode>();
+        for (var untypedField : untyped.fields()) {
+            var typedField = new TypedStructFieldDefinitionNode(
+                untypedField.name(),
+                typeCheckMetaType(untypedField.type(), context),
+                untyped.source()
+            );
+            typedFields.add(typedField);
+        }
+
         return new TypedStructDefinitionNode(
             structType,
-            List.of(),
+            typedFields,
             untyped.source()
         );
     }
 
+    private static TypedTypeLevelExpressionNode<Type> typeCheckMetaType(
+        UntypedTypeLevelExpressionNode untyped,
+        TypeCheckerNamespaceContext context
+    ) {
+        var typed = typeCheckTypeLevelExpression(untyped, context);
+        if (typed.value() instanceof Type) {
+            return (TypedTypeLevelExpressionNode<Type>) typed;
+        } else {
+            // TODO: better error
+            throw new RuntimeException("not a metatype");
+        }
+    }
+
     static TypedTypeLevelExpressionNode<? extends TypeLevelValue> typeCheckTypeLevelExpression(
         UntypedTypeLevelExpressionNode untyped,
         TypeCheckerNamespaceContext context
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerGlobalContext.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerGlobalContext.java
index 3915767..849da2f 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerGlobalContext.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerGlobalContext.java
@@ -1,8 +1,16 @@
 package org.zwobble.hobgoblin.compiler.typechecker;
 
 import org.zwobble.hobgoblin.compiler.types.NamespaceName;
+import org.zwobble.hobgoblin.compiler.types.ScalarType;
+import org.zwobble.hobgoblin.compiler.types.Type;
+import org.zwobble.hobgoblin.compiler.types.TypeLevelValueType;
+
+import java.util.HashMap;
+import java.util.Map;
 
 public class TypeCheckerGlobalContext {
+    private final Map<String, Type> builtins = new HashMap<>();
+
     public static TypeCheckerGlobalContext initial() {
         return new TypeCheckerGlobalContext();
     }
@@ -10,7 +18,11 @@ public class TypeCheckerGlobalContext {
     private TypeCheckerGlobalContext() {
     }
 
+    public void addBuiltinScalarType(ScalarType type) {
+        this.builtins.put(type.name(), new TypeLevelValueType(type));
+    }
+
     public TypeCheckerNamespaceContext enterNamespace(NamespaceName namespaceName) {
-        return TypeCheckerNamespaceContext.initial(namespaceName);
+        return TypeCheckerNamespaceContext.initial(namespaceName, this.builtins);
     }
 }
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 c1a23fd..353209b 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerNamespaceContext.java
@@ -3,13 +3,22 @@ package org.zwobble.hobgoblin.compiler.typechecker;
 import org.zwobble.hobgoblin.compiler.types.NamespaceName;
 import org.zwobble.hobgoblin.compiler.types.Type;
 
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
+import java.util.stream.Collectors;
 
 public class TypeCheckerNamespaceContext {
-    public static TypeCheckerNamespaceContext initial(NamespaceName namespaceName) {
-        return new TypeCheckerNamespaceContext(namespaceName, new HashMap<>());
+    public static TypeCheckerNamespaceContext initial(
+        NamespaceName namespaceName,
+        Map<String, Type> builtins
+    ) {
+        var variables = builtins.entrySet().stream()
+            .collect(Collectors.toMap(
+                entry -> entry.getKey(),
+                entry -> Variable.defined(entry.getValue())
+            ));
+
+        return new TypeCheckerNamespaceContext(namespaceName, variables);
     }
 
     private final NamespaceName namespaceName;
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/Variable.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/Variable.java
index 1d3a4b6..e80283f 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/Variable.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/Variable.java
@@ -3,6 +3,10 @@ package org.zwobble.hobgoblin.compiler.typechecker;
 import org.zwobble.hobgoblin.compiler.types.Type;
 
 public sealed interface Variable {
+    public static Variable defined(Type type) {
+        return new Defined(type);
+    }
+
     record Declared() implements Variable {
     }
 
-- 
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