From dc601f2d7cdec8cc9c366f70be59fc0666f132cb Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Thu, 14 Jul 2016 19:06:56 +0100
Subject: Make it easier to construct visitors that close over locals

---
 .../couscous/ast/visitors/DynamicNodeVisitor.java  | 14 +++++++++
 .../zwobble/couscous/interpreter/Evaluator.java    | 36 ++++++++++------------
 .../java/org/zwobble/couscous/util/ExtraSets.java  |  4 +++
 3 files changed, 35 insertions(+), 19 deletions(-)

diff --git a/src/main/java/org/zwobble/couscous/ast/visitors/DynamicNodeVisitor.java b/src/main/java/org/zwobble/couscous/ast/visitors/DynamicNodeVisitor.java
index a64b7bc..aed1253 100644
--- a/src/main/java/org/zwobble/couscous/ast/visitors/DynamicNodeVisitor.java
+++ b/src/main/java/org/zwobble/couscous/ast/visitors/DynamicNodeVisitor.java
@@ -19,6 +19,7 @@ import net.bytebuddy.matcher.ElementMatchers;
 import org.zwobble.couscous.ast.Node;
 import org.zwobble.couscous.ast.NodeTypes;
 import org.zwobble.couscous.util.ExtraIterables;
+import org.zwobble.couscous.util.ExtraSets;
 import org.zwobble.couscous.util.asm.Implementations;
 import org.zwobble.couscous.util.asm.StackManipulationSwitch;
 import org.zwobble.couscous.util.asm.TypeDescriptions;
@@ -26,10 +27,13 @@ import org.zwobble.couscous.util.asm.TypeDescriptions;
 import java.lang.reflect.Method;
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
+import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
 import static java.util.Arrays.asList;
+import static org.zwobble.couscous.util.ExtraIterables.lazyMap;
 import static org.zwobble.couscous.util.ExtraLists.eagerFilter;
 import static org.zwobble.couscous.util.ExtraLists.eagerMap;
 
@@ -84,6 +88,16 @@ public class DynamicNodeVisitor<T> {
         return new DynamicNodeVisitor<>(builder);
     }
 
+    public static <T> BiConsumer<Node, T> visitor(Class<T> clazz) {
+        Set<String> methodNames = ExtraSets.copyOf(lazyMap(asList(clazz.getDeclaredMethods()), Method::getName));
+        if (methodNames.size() != 1) {
+            throw new UnsupportedOperationException("Multiple method names");
+        }
+        String methodName = methodNames.iterator().next();
+        Function<T, Consumer> classSupplier = buildClassSupplier(clazz, Consumer.class, methodName, MethodReturn.VOID);
+        return (node, visitor) -> classSupplier.apply(visitor).accept(node);
+    }
+
     public static <T, F> Function<T, F> buildClassSupplier(Class<T> clazz, Class<F> function, String methodName, MethodReturn methodReturn) {
         Class<? extends F> visitorClass = buildClass(clazz, function, methodName, methodReturn);
 
diff --git a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
index afcea8b..75eeb76 100644
--- a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
+++ b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
@@ -12,6 +12,7 @@ import org.zwobble.couscous.types.Type;
 import org.zwobble.couscous.types.Types;
 
 import java.util.List;
+import java.util.function.BiConsumer;
 import java.util.stream.Collectors;
 
 import static org.zwobble.couscous.types.Types.erasure;
@@ -66,29 +67,26 @@ public class Evaluator implements ExpressionNodeMapper<InterpreterValue> {
     @Override
     public InterpreterValue visit(AssignmentNode assignment) {
         InterpreterValue value = eval(assignment.getValue());
-        assignVisitor.instantiate(new Assign(value)).accept(assignment.getTarget());
+        AssignableExpressionVisitor.visit.accept(assignment.getTarget(), new AssignableExpressionVisitor() {
+            @Override
+            public void visit(FieldAccessNode fieldAccess) {
+                ReceiverValue left = evalReceiver(fieldAccess.getLeft());
+                left.setField(fieldAccess.getFieldName(), value);
+            }
+
+            @Override
+            public void visit(VariableReferenceNode reference) {
+                environment.put(reference.getReferentId(), value);
+            }
+        });
         return value;
     }
 
-    private static final DynamicNodeVisitor<Assign> assignVisitor = DynamicNodeVisitor.build(
-        Assign.class, "visit"
-    );
+    public interface AssignableExpressionVisitor {
+        BiConsumer<Node, AssignableExpressionVisitor> visit = DynamicNodeVisitor.visitor(AssignableExpressionVisitor.class);
 
-    public class Assign {
-        private final InterpreterValue value;
-
-        private Assign(InterpreterValue value) {
-            this.value = value;
-        }
-
-        public void visit(FieldAccessNode fieldAccess) {
-            ReceiverValue left = evalReceiver(fieldAccess.getLeft());
-            left.setField(fieldAccess.getFieldName(), value);
-        }
-
-        public void visit(VariableReferenceNode reference) {
-            environment.put(reference.getReferentId(), value);
-        }
+        void visit(VariableReferenceNode node);
+        void visit(FieldAccessNode node);
     }
     
     @Override
diff --git a/src/main/java/org/zwobble/couscous/util/ExtraSets.java b/src/main/java/org/zwobble/couscous/util/ExtraSets.java
index 6e807c6..f1df962 100644
--- a/src/main/java/org/zwobble/couscous/util/ExtraSets.java
+++ b/src/main/java/org/zwobble/couscous/util/ExtraSets.java
@@ -18,4 +18,8 @@ public class ExtraSets {
     public static <T> Set<T> set(T... values) {
         return ImmutableSet.copyOf(values);
     }
+
+    public static <T> Set<T> copyOf(Iterable<T> iterable) {
+        return ImmutableSet.copyOf(iterable);
+    }
 }
-- 
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