Add TypedValue.fieldValueAs

src/main/java/net/hydromatic/morel/compile/Resolver.java

@@ -507,13 +507,11 @@ Object valueOf(Core.Exp exp) {
         final Core.RecordSelector recordSelector =
             (Core.RecordSelector) apply.fn;
         final Object o = valueOf(apply.arg);
-        @SuppressWarnings("unchecked") List<Object> list =
-            o instanceof List
-                ? (List<Object>) o
-                : o instanceof Codes.TypedValue
-                    ? ((Codes.TypedValue) o).valueAs(List.class)
-                    : null;
-        if (list != null) {
+        if (o instanceof Codes.TypedValue) {
+          return ((Codes.TypedValue) o).fieldValueAs(recordSelector.slot,
+              Object.class);
+        } else if (o instanceof List) {
+          @SuppressWarnings("unchecked") List<Object> list = (List<Object>) o;
           return list.get(recordSelector.slot);
         }
       }

src/main/java/net/hydromatic/morel/compile/TypeResolver.java

@@ -190,10 +190,9 @@ private Resolved deduceType_(@Nullable Session session, Environment env,
           applies.add(apply);
         }
       });
-      final int originalExpandCount = typeSystem.expandCount.get();
       if (!applies.isEmpty()) {
         for (Ast.Apply apply : applies) {
-          expandField(session, env, typeMap, apply);
+          expandField(env, apply);
         }
       } else {
         checkNoUnresolvedFieldRefs(node2, typeMap);
@@ -210,27 +209,16 @@ private static boolean isProgressive(Type type) {
         .containsKey(ProgressiveRecordType.DUMMY);
   }
 
-  private Codes.@Nullable TypedValue expandField(@Nullable Session session,
-      Environment env, TypeMap typeMap, Ast.Exp exp) {
+  private Codes.@Nullable TypedValue expandField(Environment env, Ast.Exp exp) {
     switch (exp.op) {
     case APPLY:
       final Ast.Apply apply = (Ast.Apply) exp;
       if (apply.fn.op == Op.RECORD_SELECTOR) {
         final Ast.RecordSelector selector = (Ast.RecordSelector) apply.fn;
-        final Codes.TypedValue typedValue =
-            expandField(session, env, typeMap, apply.arg);
+        final Codes.TypedValue typedValue = expandField(env, apply.arg);
         if (typedValue != null) {
           typedValue.discoverField(typeSystem, selector.name);
-          final RecordLikeType type =
-              (RecordLikeType) typedValue.typeKey().toType(typeSystem);
-          int i =
-              ImmutableList.copyOf(type.argNameTypes().keySet())
-                  .indexOf(selector.name);
-          if (i >= 0) { // TODO: add a method TypedValue.fieldValue(name)
-            @SuppressWarnings("unchecked")
-            final List<Codes.TypedValue> list = typedValue.valueAs(List.class);
-            return list.get(i);
-          }
+          return typedValue.fieldValueAs(selector.name, Codes.TypedValue.class);
         }
       }
       return null;

src/main/java/net/hydromatic/morel/eval/Codes.java

@@ -3720,7 +3720,18 @@ public interface Positioned extends Applicable {
 
   /** A value that knows its own type. */
   public interface TypedValue {
+    /** Returns the value cast as a particular type. */
     <V> V valueAs(Class<V> clazz);
+
+    /** Returns the value of a field, cast as a particular type. */
+    default <V> V fieldValueAs(String fieldName, Class<V> clazz) {
+      throw new UnsupportedOperationException("not a record");
+    }
+
+    default <V> V fieldValueAs(int fieldIndex, Class<V> clazz) {
+      throw new UnsupportedOperationException("not a record");
+    }
+
     Type.Key typeKey();
 
     /** Tries to expand the type to include the given field name.

src/main/java/net/hydromatic/morel/eval/Files.java

@@ -215,8 +215,15 @@ private static class Directory extends AbstractList<File> implements File {
       }
       throw new IllegalArgumentException("not a " + clazz);
     }
-  }
 
+    @Override public <V> V fieldValueAs(String fieldName, Class<V> clazz) {
+      return clazz.cast(entries.get(fieldName));
+    }
+
+    @Override public <V> V fieldValueAs(int fieldIndex, Class<V> clazz) {
+      return clazz.cast(Iterables.get(entries.values(), fieldIndex));
+    }
+  }
 
   /** File that is not a directory, and can be parsed into a set of records. */
   private static class DataFile extends AbstractFile {