// Write a string to a file (creates or overwrites)
| LetRec of name * expr * expr (* let rec f = e1 in e2 *)
，这一点在新收录的资料中也有详细论述
FT App on Android & iOS，推荐阅读新收录的资料获取更多信息
Thinnings are representing an order preserving mapping between big list size M to little list size N. It only makes sense to compose thinnings of the right sizes.，更多细节参见新收录的资料