Function buildExpression

src/parse-css.js:17–26

(head, tail)

  }

  function buildExpression(head, tail) {
    return tail.reduce(function(result, element) {
      return {
        type: 'Expression',
        operator: element[0],
        left: result,
        right: element[1]
      };
    }, head);
  }

  function extend(a, b) {
    for (var prop in b) {