Convert C# delegate to f#

Question

how do I convert delegate to F#?

the delegate:

delegate IntPtr HookProc(int code, IntPtr wParam, IntPtr lParam);

Edited

What I'm doing is to do Low Level Keyboard Hook using managed API from c# in F#

Code:

[<DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)>]
extern bool UnhookWindowsHookEx(System.IntPtr hhk);

[<DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)>]
extern System.IntPtr CallNextHookEx(System.IntPtr hhk, int nCode,System.IntPtr wParam, System.IntPtr lParam);

[<DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)>]
extern System.IntPtr GetModuleHandle(string lpModuleName);

[<DllImport("user32.dll")>]
extern System.IntPtr SetWindowsHookEx(int code, HookProc func, System.IntPtr hInstance, int threadID);

Delegate:

type HookProc = delegate of (int * nativeint * nativeint) -> nativeint

Functions

let HookCallback(nCode:int,wParam:System.IntPtr,lParam:System.IntPtr) = 
                    let t = (int)wParam
                    if  t = WM_KEYUP then 
                         let vkCode:int = Marshal.ReadInt32(lParam)
                         printfn "%A The Pressed key code is : "  vkCode
                    CallNextHookEx(_hookID, nCode, wParam, lParam)



let HookProcF = new HookProc(HookCallback)
let SetHook() = 
                let curProcess = Process.GetCurrentProcess()
                let curModule = curProcess.MainModule
                let t =0
                let h =  GetModuleHandle(curModule.ModuleName)
                SetWindowsHookEx(WH_KEYBOARD_LL, HookProcF, h, t);



let HookMoniter() = 
        let _hookID = SetHook()
        UnhookWindowsHookEx(_hookID);

Answer 1

Try the following

type HookProc = delegate of int * nativeint * nativeint -> nativeint

Note that nativeint is just F# name for IntPtr

Answer 2

Do you mean call a C# function by delegate with F#?

See the following:

Using c# delegates with f# functions

http://msdn.microsoft.com/en-us/library/dd233206.aspx