anchor.diff:        test("eval values", testEvalValues);
         test("eval if", testEvalIf);
         test("eval defn", testEvalDefn);
  +      test("eval make update", testEvalMakeUpdate);
  +      test("eval make deref", testEvalMakeDeref);
  +      test("eval make deref var", testEvalMakeDerefVariant);
         test("eval defn concat", testEvalConcat);
         test("eval op", testEvalOp);
         test("eval first butfirst", testEvalFirstButFirst);
  
positive.code: 
  import "dart:math" as math;
  
  import "package:arrowlogo/interpreter.dart";
  import "package:arrowlogo/nodes.dart";
  import "package:arrowlogo/parser.dart";
  import "package:arrowlogo/scope.dart";
  
  class MockConsole {
    void receive(dynamic raw) {}
  }
  
  class InterpreterTest {
  
    Scope globalScope;
    var turtle = new Object();
    var console = new MockConsole();
    var parent = new Object();
    InterpreterImpl interpreter;
  
    InterpreterImpl makeInterpreter() {
      globalScope = new Scope(new Map());
      interpreter = new InterpreterImpl.internal(
          globalScope, parent, turtle, console);
      return interpreter;
    }
    
    InterpreterTest() {
    }
  
  
negative.code:         ListNode.makeList([Primitive.LPUT, Primitive.QUOTE, foo, barlist])),
          equals(ListNode.makeList([bar, foo])));                               
    }
  
    void testEvalOp() {
      makeInterpreter();
  
  