From 6d9a2f0b07204debf78f70e3d1ed5078ee4e54c0 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Thu, 28 Sep 2023 11:38:44 +0100
Subject: Basic type checking for field access

---
 .../shedlang/compiler/typechecker/TypeChecker.java | 27 ++++++++++++++++++++--
 .../compiler/typechecker/TypeCheckerContext.java   |  5 ++++
 .../shedlang/compiler/types/StructTypeInfo.java    |  5 ++++
 src/main/java/org/shedlang/compiler/util/P.java    |  9 ++++++++
 4 files changed, 44 insertions(+), 2 deletions(-)

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 042fb614..f11b0e1e 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -361,8 +361,8 @@ public class TypeChecker {
             case UntypedCallNode untypedCall ->
                 typeCheckCall(untypedCall, context);
 
-            case UntypedFieldAccessNode untypedFieldAccessNode ->
-                throw new UnsupportedOperationException("TODO");
+            case UntypedFieldAccessNode untypedFieldAccess ->
+                typeCheckFieldAccess(untypedFieldAccess, context);
 
             case UntypedIfNode untypedIf ->
                 typeCheckIf(untypedIf, context);
@@ -393,6 +393,29 @@ public class TypeChecker {
         });
     }
 
+    private static TypeCheckerResult<TypedFieldAccessNode> typeCheckFieldAccess(
+        UntypedFieldAccessNode untyped,
+        TypeCheckerContext context
+    ) {
+        var typedReceiverResult = typeCheckExpression(untyped.receiver(), context);
+        var typedReceiver = typedReceiverResult.value();
+        context = typedReceiverResult.context();
+
+        var structTypeInfo = context.structTypeInfo(
+            (StructType) typedReceiver.type(),
+            untyped.fieldName()
+        );
+
+        var fieldType = structTypeInfo.orElseThrow().fieldType(untyped.fieldName()).orElseThrow();
+
+        return context.toResult(new TypedFieldAccessNode(
+            typedReceiver,
+            untyped.fieldName(),
+            fieldType,
+            untyped.source()
+        ));
+    }
+
     private static TypeCheckSteps<TypedFunctionDefinitionNode> typeCheckStepsFunctionDefinition(
         UntypedFunctionDefinitionNode untyped
     ) {
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
index 06b237e1..18b030f8 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
@@ -361,6 +361,11 @@ public class TypeCheckerContext {
         );
     }
 
+    public Optional<StructTypeInfo> structTypeInfo(StructType type, String fieldName) {
+        return Optional.ofNullable(this.structTypeInfo.get(type));
+    }
+
+
     public PMap<StructType, StructTypeInfo> structTypeInfo() {
         return structTypeInfo;
     }
diff --git a/src/main/java/org/shedlang/compiler/types/StructTypeInfo.java b/src/main/java/org/shedlang/compiler/types/StructTypeInfo.java
index fb776091..f0c3eff7 100644
--- a/src/main/java/org/shedlang/compiler/types/StructTypeInfo.java
+++ b/src/main/java/org/shedlang/compiler/types/StructTypeInfo.java
@@ -2,5 +2,10 @@ package org.shedlang.compiler.types;
 
 import org.pcollections.OrderedPMap;
 
+import java.util.Optional;
+
 public record StructTypeInfo(OrderedPMap<String, Type> fields) {
+    public Optional<Type> fieldType(String fieldName) {
+        return Optional.ofNullable(this.fields.get(fieldName));
+    }
 }
diff --git a/src/main/java/org/shedlang/compiler/util/P.java b/src/main/java/org/shedlang/compiler/util/P.java
index fc822614..5d40d596 100644
--- a/src/main/java/org/shedlang/compiler/util/P.java
+++ b/src/main/java/org/shedlang/compiler/util/P.java
@@ -28,6 +28,15 @@ public class P {
         return map;
     }
 
+    @SafeVarargs
+    public static <K, V> OrderedPMap<K, V> orderedPMap(Map.Entry<K, V>... entries) {
+        var map = OrderedPMap.<K, V>empty();
+        for (var entry : entries) {
+            map = map.plus(entry.getKey(), entry.getValue());
+        }
+        return map;
+    }
+
     @SafeVarargs
     public static <T> OrderedPSet<T> orderedSet(T... values) {
         return OrderedPSet.from(Arrays.asList(values));
-- 
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