F#
printf "Hello, world!"
System.Windows.Forms.MessageBox.Show "Hello World"
let results = [ for i in 0 .. 100 -> (i, i*i) ]
printfn "results = %A" results
let add a b =
a + b
let return10 _ =
add 5 5
// 12 is effectively ignored, and ten is set to the resulting
// value of add 5 5
let ten = return10 12
printf "ten = %d\n" ten
let add5 a =
add a 5
public class Adders {
public static int add(int a, int b) { return a + b; }
public static int add5(int a) { return add(a, 5); }
}
val ten : ('a -> int)
delegate int Transformer<T>(T ignored);
public class App
{
public static int return10(object ignored) { return 5 + 5; }
static void Main()
{
Transformer<object> ten = return10;
System.Console.WriteLine("ten = {0}", return10(0));
}
}
#light
let results = [ for i in 0 .. 100 -> (i, i*i) ]
printfn "results = %A" results
let compute2 x = (x, x*x)
let compute3 x = (x, x*x, x*x*x)
let results2 = [ for i in 0 .. 100 -> compute2 i ]
let results3 = [ for i in 0 .. 100 -> compute3 i ]
Figure 2 检索和分析 HTML/// Get the contents of the URL via a web request
let http(url: string) =
let req = System.Net.WebRequest.Create(url)
let resp = req.GetResponse()
let stream = resp.GetResponseStream()
let reader = new System.IO.StreamReader(stream)
let html = reader.ReadToEnd()
resp.Close()
html
let getWords s = String.split [ ' '; '\n'; '\t'; '<'; '>'; '=' ] s
let getStats site =
let url = "http://" + site
let html = http url
let words = html |> getWords
let hrefs = html |> getWords |> List.filter (fun s -> s = "href")
(site,html.Length, words.Length, hrefs.Length)
let words = getWords html
open System.Collections.Generic
let capitals = Dictionary<string, string>()
capitals.["Great Britain"] <- "London"
capitals.["France"] <- "Paris"
capitals.ContainsKey("France")
Figure 3 F# 和 C# 中的矢量变体 VECTOR2D IN F#
type Vector2D(dx:float,dy:float) =
let length = sqrt(dx*dx + dy*dy)
member obj.Length = length
member obj.DX = dx
member obj.DY = dy
member obj.Move(dx2,dy2) = Vector2D(dx+dx2,dy+dy2)
VECTOR2D IN C# (REFLECTOR>
[Serializable, CompilationMapping(SourceLevelConstruct.ObjectType)]
public class Vector2D
{
// Fields
internal double _dx@48;
internal double _dy@48;
internal double _length@49;
// Methods
public Vector2D(double dx, double dy)
{
Hello.Vector2D @this = this;
@this._dx@48 = dx;
@this._dy@48 = dy;
double d = (@this._dx@48 * @this._dx@48) +
(@this._dy@48 * @this._dy@48);
@this._length@49 = Math.Sqrt(d);
}
public Hello.Vector2D Move(double dx2, double dy2)
{
return new Hello.Vector2D(this._dx@48 + dx2, this._dy@48 + dy2);
}
// Properties
public double DX
{
get
{
return this._dx@48;
}
}
public double DY
{
get
{
return this._dy@48;
}
}
public double Length
{
get
{
return this._length@49;
}
}
}
Figure 4 使用 F# 编写 Windows 窗体#light
open System
open System.IO
open System.Windows.Forms
open Printf
let form = new Form(Text="My First F# Form", Visible=true)
let menu = form.Menu <- new MainMenu()
let mnuFile = form.Menu.MenuItems.Add("&File")
let filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*"
let mnuiOpen =
new MenuItem("&Open...",
new EventHandler(fun _ _ ->
let dialog =
new OpenFileDialog(InitialDirectory="c:\\",
Filter=filter;
FilterIndex=2,
RestoreDirectory=true)
if dialog.ShowDialog() = DialogResult.OK then
match dialog.OpenFile() with
| null -> printf "Could not read the file...\n"
| s ->
let r = new StreamReader(s)
printf "First line is: %s!\n" (r.ReadLine());
s.Close();
),
Shortcut.CtrlO)
mnuFile.MenuItems.Add(mnuiOpen)
[<STAThread>]
do Application.Run(form)
fun _ _ -> ...
if dialog.ShowDialog() = DialogResult.OK then
match dialog.OpenFile() with
| null -> printf "Could not read the file...\n"
| s ->
let r = new StreamReader(s) in
printf "First line is: %s!\n" (r.ReadLine());
s.Close();
// Declaration of the 'Expr' type
type Expr =
| Binary of string * Expr * Expr
| Variable of string
| Constant of int
// Create a value 'v' representing 'x + 10'
let v = Binary("+", Variable "x", Constant 10)
Figure 5 表达式执行let getVarValue v =
match v with
| "x" -> 25
| "y" -> 12
| _ -> 0
let rec eval x =
match x with
| Binary(op, l, r) ->
let (lv, rv) = (eval l, eval r) in
if (op = "+") then lv + rv
elif (op = "-") then lv - rv
else failwith "E_UNSUPPORTED"
| Variable(var) ->
getVarValue var
| Constant(n) ->
n
do printf "Results = %d\n" (eval v)
Figure 6 处理图像let TransformImage pixels i =
// Some kind of graphic manipulation of images
let ProcessImage(i) =
async { use inStream = File.OpenRead(sprintf "source%d.jpg" i)
let! pixels = inStream.ReadAsync(1024*1024)
let pixels' = TransformImage(pixels,i)
use outStream = File.OpenWrite(sprintf "result%d.jpg" i)
do! outStream.WriteAsync(pixels')
do Console.WriteLine "done!" }
let ProcessImages() =
Async.Run (Async.Parallel
[ for i in 1 .. numImages -> ProcessImage(i) ])
Figure 7 异步执行函数#light
open System.Threading
let printWithThread str =
printfn "[ThreadId = %d] %s" Thread.CurrentThread.ManagedThreadId str
let evals =
let z = 4.0
[ async { do printWithThread "Computing z*z\n"
return z * z };
async { do printWithThread "Computing sin(z)\n"
return (sin z) };
async { do printWithThread "Computing log(z)\n"
return (log z) } ]
let awr =
async { let! vs = Async.Parallel evals
do printWithThread "Computing v1+v2+v3\n"
return (Array.fold_left (fun a b -> a + b) 0.0 vs) }
let R = Async.Run awr
printf "Result = %f\n" R
