text: exports.requires = ['helpers/$has']
  
  exports.definition = `
  const $len = (xs) => {
    if (xs && typeof xs.size === 'function') {
      return xs.size()
    } else if ($has(xs, 'length')) {
      return xs.length
    } else if (typeof xs === 'object') {
      return Object.keys(xs).length
    }
    throw new Error('Invalid argument supplied to len')
  }`
  