[tlox] Add 'Nil'

jlox/tlox/src/main/java/xyz/ctsk/lox/nodes/expr/LoxNilLiteralNode.java

@@ -0,0 +1,11 @@
+package xyz.ctsk.lox.nodes.expr;
+
+import com.oracle.truffle.api.frame.VirtualFrame;
+import xyz.ctsk.lox.nodes.LoxExpressionNode;
+
+public class LoxNilLiteralNode extends LoxExpressionNode {
+    @Override
+    public Object executeGeneric(VirtualFrame frame) {
+        return null;
+    }
+}

jlox/tlox/src/main/java/xyz/ctsk/lox/parser/LoxNodeFactory.java

@@ -2,7 +2,6 @@ package xyz.ctsk.lox.parser;
 
 import com.oracle.truffle.api.strings.TruffleString;
 import org.antlr.v4.runtime.Token;
-import xyz.ctsk.lox.LoxException;
 import xyz.ctsk.lox.nodes.LoxExpressionNode;
 import xyz.ctsk.lox.nodes.expr.*;
 
@@ -22,6 +21,10 @@ public class LoxNodeFactory {
         return new LoxBooleanLiteralNode(value);
     }
 
+    public static LoxNilLiteralNode createNilLiteral() {
+        return new LoxNilLiteralNode();
+    }
+
     public static LoxExpressionNode createUnary(Token op, LoxExpressionNode value) {
         return switch (op.getText()) {
             case "-" -> LoxNegNodeGen.create(value);

jlox/tlox/src/main/resources/xyz/ctsk/lox/parser/Lox.g4

@@ -48,6 +48,7 @@ literal returns [LoxExpressionNode result]
     | STRING { $result = factory.createStringLiteral($STRING); }
     | TRUE   { $result = factory.createBooleanLiteral($TRUE); }
     | FALSE  { $result = factory.createBooleanLiteral($FALSE); }
+    | NIL    { $result = factory.createNilLiteral(); }
     ;
 
 AND: 'and' ;