F# dynamic

dynamic.fs

//         dynamic x = "Foo";
//         Console.WriteLine(x.ToString());

open System
open System.Runtime.CompilerServices
open Microsoft.CSharp.RuntimeBinder

let mutable toStringSite: CallSite<Func<CallSite, obj, obj>> option = None
let mutable writelineSite: CallSite<Action<CallSite, Type, obj>> option = None

type Marker() = class end

let x = "Foo" :> obj

if writelineSite = None then
    let typeFromHandle = typeof<Marker>
    let args = Array.zeroCreate<CSharpArgumentInfo> 2
    args.[0] <- CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.UseCompileTimeType ||| CSharpArgumentInfoFlags.IsStaticType, null)
    args.[1] <- CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null)
    writelineSite <- Some (CallSite<Action<CallSite, Type, obj>>.Create(Binder.InvokeMember(CSharpBinderFlags.ResultDiscarded, "WriteLine", null, typeFromHandle, args)))
    
if toStringSite = None then
    let typeFromHandle = typeof<Marker>
    let args = Array.zeroCreate<CSharpArgumentInfo> 1
    args.[0] <- CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null)
    toStringSite <- Some (CallSite<Func<CallSite, obj, obj>>.Create(Binder.InvokeMember(CSharpBinderFlags.None, "ToString", null, typeFromHandle, args)))
    
let target = writelineSite.Value.Target
target.Invoke(writelineSite.Value, typeof<Console>, toStringSite.Value.Target.Invoke(toStringSite.Value, x))