function usedSoFarInCurrentFunction(bindingName) {
    for (var i = _scopeStack.length - 1; i >= 0; i--) {
      var current = _scopeStack[i];
      if (current["(usages)"][bindingName]) {
        return current["(usages)"][bindingName];
      }
      if (current === _currentFunctBody) {
        break;
      }
    }
    return false;
  }
Determine if a given binding name has been referenced within the current
function or any function defined within.

@param {string} bindingName - the value of the identifier

@returns {boolean}