Support field accesses on constructed types

2 files changed, 29 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index fe8c7b9a..f42a4030 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -588,6 +588,18 @@ public class TypeChecker {
         TypeCheckerContext context
     ) {
         switch (receiverType) {
+            case ConstructedType<?> receiverTypeConstructed -> {
+                return fieldTypeOrEmpty(
+                    receiverTypeConstructed.genericType(),
+                    fieldName,
+                    source,
+                    context
+                ).map(genericFieldType -> TypeSubstitution.substitute(
+                    genericFieldType,
+                    receiverTypeConstructed.typeSubstitutionMap()
+                ));
+            }
+
             case StructType receiverTypeStruct -> {
                 var structTypeInfo = context.structTypeInfo(receiverTypeStruct, source);
                 return structTypeInfo.fieldType(fieldName);
diff --git a/src/main/java/org/shedlang/compiler/types/ConstructedType.java b/src/main/java/org/shedlang/compiler/types/ConstructedType.java
index 558b227b..09cfcc83 100644
--- a/src/main/java/org/shedlang/compiler/types/ConstructedType.java
+++ b/src/main/java/org/shedlang/compiler/types/ConstructedType.java
@@ -1,5 +1,6 @@
 package org.shedlang.compiler.types;
 
+import java.util.HashMap;
 import java.util.List;
 import java.util.stream.Collectors;
 
@@ -14,4 +15,20 @@ public record ConstructedType<T extends StructuredType>(
             .collect(Collectors.joining(", "));
         return constructor.describe() + "[" + argsString + "]";
     }
+
+    public T genericType() {
+        return constructor.genericType();
+    }
+
+    public TypeSubstitutionMap typeSubstitutionMap() {
+        var map = new HashMap<TypeParam, Type>();
+
+        for (var argIndex = 0; argIndex < args.size(); argIndex++) {
+            var param = constructor.params().get(argIndex);
+            var arg = args.get(argIndex);
+            map.put(param, arg);
+        }
+
+        return new TypeSubstitutionMap(map);
+    }
 }