using SCG = System.Collections.Generic;
using SRCS = System.Runtime.CompilerServices;
using SAT = System.AttributeTargets;

namespace System
{
 namespace Runtime.CompilerServices
 {
  [System.AttributeUsage (SAT.Class | SAT.Method)]
  public class ExtensionAttribute : Attribute
  {}
 }
 public delegate Func[T, TResult] (arg : T) : TResult;
 namespace Linq
 {
  [SRCS.ExtensionAttribute]
  public module Enumerable
  {
    [SRCS.ExtensionAttribute]
    public Where[TSource] (
      source : SCG.IEnumerable[TSource],
      predicate : Func[TSource, bool]
    ) : SCG.IEnumerable[TSource]
    {
      foreach (x in source)
      when (predicate(x))
        yield x;
    }
  }
 }
}

[Nemerle.Internal.ExtensionAttribute]
public module Test2
{
  [Nemerle.Internal.ExtensionAttribute]
  public Where2[T] (
    source : SCG.IEnumerable[T],
    pred : T->bool
  ) : SCG.IEnumerable[T]
  {
    foreach (x in source)
    when (pred(x))
      yield x;
  }
}

public module Test3
{
  public Where3[T] (
    this source : SCG.IEnumerable[T],
    pred : T->bool
  ) : SCG.IEnumerable[T]
  {
    foreach (x in source)
    when (pred(x))
      yield x;
  }
}