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Chain of responsibility

The following sample wants to make sure the person’s age is between 18 and 65, weight is no more than 200 and tall enough (>120).

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type Record = {
    Name : string;
    Age : int;
    Weight: float;
    Height: float;
}

let ChainOfResponsibility() = 
    let validAge (record:Record) = 
        record.Age < 65 && record.Age > 18
    let validWeight (record:Record) = 
        record.Weight < 200.
    let validHeight (record:Record) = 
        record.Height > 120.

    let check (f:Record->bool) (record:Record, result:bool) = 
        if result=false then (record, false)
        else (record, f(record))

    let chainOfResponsibility = check(validAge) >> check(validWeight) >> check(validHeight)

    let john = { Name = "John"; Age = 80; Weight = 180.; Height=180. }
    let dan = { Name = "Dan"; Age = 20; Weight = 160.; Height=190. }

    printfn "john result = %b" ((chainOfResponsibility (john, true)) |> snd)
    printfn "dan result = %b" ((chainOfResponsibility (dan, true)) |> snd)

Record.Name: string

Multiple items
val string : value:'T -> string

Full name: Microsoft.FSharp.Core.Operators.string

--------------------
type string = System.String

Full name: Microsoft.FSharp.Core.string

Record.Age: int

Multiple items
val int : value:'T -> int (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.int

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>

Record.Weight: float

Multiple items
val float : value:'T -> float (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.float

--------------------
type float = System.Double

Full name: Microsoft.FSharp.Core.float

--------------------
type float<'Measure> = float

Full name: Microsoft.FSharp.Core.float<_>

Record.Height: float

val ChainOfResponsibility : unit -> unit

Full name: Script.ChainOfResponsibility

val validAge : (Record -> bool)

val record : Record

type Record =
  {Name: string;
   Age: int;
   Weight: float;
   Height: float;}

Full name: Script.Record

val validWeight : (Record -> bool)

val validHeight : (Record -> bool)

val check : ((Record -> bool) -> Record * bool -> Record * bool)

val f : (Record -> bool)

type bool = System.Boolean

Full name: Microsoft.FSharp.Core.bool

val result : bool

val chainOfResponsibility : (Record * bool -> Record * bool)

val john : Record

val dan : Record

val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

val snd : tuple:('T1 * 'T2) -> 'T2

Full name: Microsoft.FSharp.Core.Operators.snd

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More information

Link:	http://fssnip.net/7h
Posted:	13 years ago
Author:	Tao Liu
Tags:	design patterns