anchor.diff:  // Version of DartFuzz. Increase this each time changes are made
   // to preserve the property that a given version of DartFuzz yields
   // the same fuzzed program for a deterministic random seed.
  -const String version = '1.30';
  +const String version = '1.31';
   
   // Restriction on statements and expressions.
   const int stmtLength = 2;
  
positive.code:         if (tp == proto[i]) choices.add('$paramName$i');
        }
      }
      // Remove possible modification of the iteration variable from the loop
      // body.
      if (isLhs) {
        if (rand.nextInt(10) != 0) {
          Set<String> cleanChoices = choices.difference(Set.from(iterVars));
          if (cleanChoices.isNotEmpty) {
            choices = cleanChoices;
  
negative.code:     }
    }
  
    // Emit call to a specific method.
    void emitCall(int depth, String name, List<DartType> proto) {
      emit(name);
      emitExprList(depth + 1, proto);
    }
  
    // Helper for a method call.
    bool pickedCall(
        int depth, DartType tp, String name, List<List<DartType>> protos, int m) {
      for (int i = m - 1; i >= 0; i--) {
        if (tp == protos[i][0]) {
          emitCall(depth + 1, "$name$i", protos[i]);
          return true;
        }
      }
  