如何在没有给定类型声明的情况下测试 F# 中的原始类型和类型转换

Question

这是我认为通过模式匹配对任何类型进行类型检查的更好方法，而不是我见过的所有其他方法。

Answer 1

If you need a way to easily check for primitive types

I came up with it in my work making a Lexer and parser generator in F# without code generation and with DFA performance, and instant type checking.

Assume that we have some syntaks tree where you don't know how it looks or even which types it contains, but you need to construct it at some point in time, and before that might need to have a collection of different types.

That is against F#'s general type system.

I use obj which can be anything.

type Type = Type of obj

we define a function type that simply delay the work

Type delay = Delay of (unit -> Type)

let inline AnyType t = Type (t :> obj)

We define a function that delays the work.

let Delay f input = 
    fun _ ->
       f input |> AnyType
    |> Delay

and a function invoking the work

let Do (Delay f) = f()

now assume that we have some lexeme (string conforming to a pattern) and the type

type TYPE = INT of int | FLOAT of float | Error

with the function

let GetValue (Type t) =
    match (Type t) with
    | :? int as t -> INT t
    | :? float as t -> FLOAT t
    | _ -> ERROR

then we can do something like this

 let Float (str: string) = System.Double.Parse str
 let Int (str: string) = System.Int32.Parse str



let d = Delay Float "0.123" |> Do |> GetValue
let i = Delay Int "123" |> Do |> GetValue

without getting a compiletime type error. This will of course lead to the programmer checking for type correctness in the program, but that would be needed anyway