Last active
July 18, 2021 14:00
-
-
Save BashkaMen/8eeaf56db34c66b90eeaa7de16299081 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| module TypeClasses | |
| open System | |
| let inline (|HasId|) x = (^a : (member Id : 'Id)x) // define type class | |
| let inline getId (HasId x) = x // call type class instance | |
| let inline (|HasShow|) x = (^a : (static member Show : ^a -> string)x) // define type class | |
| let inline show (HasShow x) = x // call type class instance | |
| let inline (|HasMap|) f x = (^x : (static member Map : ('a -> 'b) * ^x -> ^z) f, x) // define type class | |
| let inline map f (HasMap f x) = x // call type class instance | |
| // ======================================================== | |
| type User = { Id: Guid; UserName: string; } // define type | |
| type Stack<'T> = Empty | Node of 'T * Stack<'T> // define type | |
| // ======================================================== | |
| type User with static member Show (x: User) = x.ToString() // implement type class | |
| type Stack<'a> with // implement type class | |
| static member Map (f, x) = | |
| match x with | |
| | Empty -> Empty | |
| | Node (x, xs) -> Node (f x, Stack.Map(f, xs)) | |
| // test usage | |
| let user = { Id = Guid.NewGuid(); UserName = "User"; } | |
| let userShow = show user // { Id = c3af72cf-d7fb-41fe-9e64-f4c15b316920 UserName = "User" } | |
| let userId = getId user // c3af72cf-d7fb-41fe-9e64-f4c15b316920 | |
| let stack = Node(9, Node(10, Empty)) // stack of int | |
| let mapStack = map (fun x -> x.ToString()) stack // stack of string | |
| let inline mapToStr x = map show x // combine type classes, require Map and Show members | |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment