记录(Records)类似于元组,但是它包含命名字段。例如,
type website = { title : string; url : string }
定义记录
使用 type 关键字将记录定义为类型,并将记录的字段定义为以分号分隔的列表。
定义记录的语法是-
type recordName = { [ fieldName : dataType ] + }
创建记录
您可以通过指定记录的字段来创建记录,例如,让无涯教程创建一个名为 homepage 的网站记录-
let homepage={ Title="LearnFk"; Url="www.learnfk.com" }
例子1
该程序定义了一个名为网站的记录类型。然后,它创建一些类型为website的记录并打印记录。
(* defining a record type named website *) type website = { Title : string; Url : string } (* creating some records *) let homepage = { Title = "LearnFk"; Url = "www.learnfk.com" } let cpage = { Title = "Learn C"; Url = "www.learnfk.com/cprogramming/index.htm" } let fsharppage = { Title = "Learn F#"; Url = "www.learnfk.com/fsharp/index.htm" } let csharppage = { Title = "Learn C#"; Url = "www.learnfk.com/csharp/index.htm" } (*printing records *) (printfn "Home Page: Title: %A\n\t URL: %A") homepage.Title homepage.Url (printfn "C Page: Title: %A\n\t URL: %A") cpage.Title cpage.Url (printfn "F# Page: Title: %A\n\t URL: %A") fsharppage.Title fsharppage.Url (printfn "C# Page: Title: %A\n\t URL: %A") csharppage.Title csharppage.Url
编译并执行程序时,将产生以下输出-
Home Page: Title: "LearnFk" URL: "www.learnfk.com" C Page: Title: "Learn C" URL: "www.learnfk.com/cprogramming/index.htm" F# Page: Title: "Learn F#" URL: "www.learnfk.com/fsharp/index.htm" C# Page: Title: "Learn C#" URL: "www.learnfk.com/csharp/index.htm"
例子2
type student = { Name : string; ID : int; RegistrationText : string; IsRegistered : bool } let getStudent name id = { Name = name; ID = id; RegistrationText = null; IsRegistered = false } let registerStudent st = { st with RegistrationText = "Registered"; IsRegistered = true } let printStudent msg st = printfn "%s: %A" msg st let main() = let preRegisteredStudent = getStudent "Zara" 10 let postRegisteredStudent = registerStudent preRegisteredStudent printStudent "Before Registration: " preRegisteredStudent printStudent "After Registration: " postRegisteredStudent main()
编译并执行程序时,将产生以下输出-
Before Registration: : {Name="Zara"; ID=10; RegistrationText=null; IsRegistered=false;} After Registration: : {Name="Zara"; ID=10; RegistrationText="Registered"; IsRegistered=true;}