code: private void addScopeVariables() {
      int num = 0;
      for (Var v : orderedVars) {
        scopeVariables.put(v.getName(), num);
        num++;
      }
    }
docs: Parameters belong to the function scope, but variables defined in the function body belong to
  the function body scope. Assign a unique index to each variable, regardless of which scope it's
  in.