f# - 摆脱 F# 中的 "pyramid of doom"

Question

我有几个口头表达，我已经打包成一个函数:

open FsVerbalExpressions
open FsVerbalExpressions.VerbalExpression
open System.Text.RegularExpressions
open System

let createOrVerbExFromList (verbExList: VerbEx list) = 
    let orVerbEx = 
        verbExList
        |> List.reduce (fun acc thing -> verbExOrVerbEx RegexOptions.IgnoreCase acc thing) //simpleVerbEx

    orVerbEx 

let k12VerbEx =     
    let kTo12 =  ["SCHOOL"; "DIST"; "SD"; "HS"; "BD OF ED"]
    kTo12
    |> List.map (fun word -> VerbEx(word))
    |> createOrVerbExFromList

let twoYearCollegeVerbEx = 
    VerbEx("2 Year College")

let universityVerbEx = 
    VerbEx("UNIV")

let privateSchoolVerbEx = 
    VerbEx("ACAD")

//Here there be dragons:
let newInst (x: string) =
    match (isMatch x k12VerbEx) with 
    | true -> "K - 12"
    | _ -> match (isMatch x twoYearCollegeVerbEx) with
            | true -> "2 Year College"
            | _ -> match (isMatch x universityVerbEx) with
                    | true -> "University" 
                    | _ -> match (isMatch x privateSchoolVerbEx) with
                            | true -> "Private / Charter School"
                            | _ -> "Other"

我想重写 newInst功能，使其不再是“末日金字塔。我的问题是我怎样才能摆脱厄运金字塔？我可以摆脱它吗？我怀疑这将是某种 async 工作流程或其他计算表达式，但这些对我来说都很新。

Answer 1

如果你只匹配 bool 值，那么 if ... elif足够了:

let newInst (x: string) =
    if isMatch x k12VerbEx then
        "K - 12"
    elif isMatch x twoYearCollegeVerbEx then
        "2 Year College"
    elif isMatch x universityVerbEx then
        "University"
    elif isMatch x privateSchoolVerbEx then
        "Private / Charter School"
    else
        "Other"

更灵活的可能性是创建一个事件模式:

let (|IsMatch|_|) f x =
    if isMatch x f then Some () else None

let newInst (x: string) =
    match x with
    | IsMatch k12VerbEx -> "K - 12"
    | IsMatch twoYearCollegeVerbEx -> "2 Year College"
    | IsMatch universityVerbEx -> "University"
    | IsMatch privateSchoolVerbEx -> "Private / Charter School"
    | _ -> "Other"