我有很多用 OCaml 编写的程序,其中一些使用仿函数。现在,我正在考虑在 F# 中编写和重写部分代码(以利用 OCaml 没有的一些优势)。我害怕的一件事是在 F# 中为仿函数在 OCaml 中所做的事情编写代码。
例如,我们如何模拟 this example from OCaml manual在 F# 中?
type comparison = Less | Equal | Greater
module type ORDERED_TYPE = sig
type t
val compare: t -> t -> comparison
end
module Set =
functor (Elt: ORDERED_TYPE) -> struct
type element = Elt.t
type set = element list
let empty = []
let rec add x s =
match s with
[] -> [x]
| hd::tl ->
match Elt.compare x hd with
Equal -> s (* x is already in s *)
| Less -> x :: s (* x is smaller than all elements of s *)
| Greater -> hd :: add x tl
end
module OrderedString = struct
type t = string
let compare x y = if x = y then Equal else if x < y then Less else Greater
end
module OrderedInt = struct
type t = int
let compare x y = if x = y then Equal else if x < y then Less else Greater
end
module StringSet = Set(OrderedString)
module IntSet = Set(OrderedInt)
let try1 () = StringSet.add "foo" StringSet.empty
let try2 () = IntSet.add 2 IntSet.empty
最佳答案
这是一种有点不同的方法,它使用泛型类和每个类型一个对象来实现相同的结果。
type Comparison = Less | Equal | Greater
type Set<'a>(compare : 'a -> 'a -> Comparison) =
member this.Empty : 'a list = []
member this.Add x s =
match s with
| [] -> [x]
| hd::tl ->
match compare x hd with
| Equal -> s (* x is already in s *)
| Less -> x :: s (* x is smaller than all elements of s *)
| Greater -> hd :: this.Add x tl
let compare x y = if x = y then Equal else if x < y then Less else Greater
let compareFloats (x : float) (y : float) = if x = y then Equal else if x < y then Less else Greater
// Note that same generic compare function can be used for stringSet and intSet
// as long as the type parameter is explicitly given
let stringSet = Set<string>(compare)
let intSet = Set<int>(compare)
// Type parameter not needed, because compareFloats is not generic
let floatSet = Set(compareFloats)
let try1 () = stringSet.Add "foo" stringSet.Empty // -> ["foo"]
let try2 () = intSet.Add 2 intSet.Empty // -> [2]
let try3 () = floatSet.Add 3.0 floatSet.Empty // -> [3.0]
关于f# - 如何在 F# 中为 OCaml 中的仿函数编写代码?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36847449/