Implement support for variables and evaluation of logic expressions

pkg/kernel/bin/eval.dart

 #!/usr/bin/env dart
 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:kernel/kernel.dart';
 import 'package:kernel/interpreter/interpreter.dart';
 import 'dart:io';
 
 fail(String message) {
   stderr.writeln(message);
   exit(1);
 }
 
 main(List<String> args) {
   if (args.length == 1 && args[0].endsWith('.dill')) {
     var program = loadProgramFromBinary(args[0]);
-    new Interpreter(program).evalProgram();
+    new Interpreter(program).run();
   } else {
     return fail('One input binary file should be specified.');
   }
 }