OCaml入门

Posted 2022-03-11 mutourend

1. 引言

OCaml为函数式编程语言。

相关入门资料有：

• o1-labs的 OCaml By Examples（具体见https://github.com/o1-labs/ocamlbyexample）
• OCaml官方教程

OCaml变量与Rust类似，默认是not mutable的。如下例，是对变量$b$的重定义。若需对同一变量值进行修改，可加“mutable”关键字，或使用引用（关键字为“ref”，引用值修改用操作符":="），访问引用值 使用 解引用操作符"!"。而“ref”的底层本质就是a record with a mutable filed + some re-define operators to facilitate manipulation of the mutable field。

utop # let a =
    let b = 5 in 
    let b = 5 + b in 
    b;;
val a : int = 10

utop # type bus =  mutable passengers : int ;;
type bus =  mutable passengers : int; 

utop # let shuttle =  passengers = 0 ;;
val shuttle : bus = passengers = 0

utop # shuttle.passengers <- 3;;
- : unit = ()

utop # shuttle;;
- : bus = passengers = 3

utop # let counter = ref 0;;
val counter : int ref = contents = 0

utop # counter := 3;;
- : unit = ()

utop # counter;;
- : int ref = contents = 3

utop # !counter + 4;;
- : int = 7

utop # type 'a ref =  mutable contents : 'a 
let (:=) r v = r.contents <- v
let (!) r = r.contents;;
type 'a ref =  mutable contents : 'a; 
val ( := ) : 'a ref -> 'a -> unit = <fun>
val ( ! ) : 'a ref -> 'a = <fun>