    {-# LANGUAGE GADTs #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Profunctor.Trace
    -- Copyright   :  (C) 2011-2012 Edward Kmett
    -- License     :  BSD-style (see the file LICENSE)
    --
    -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
    -- Stability   :  provisional
    -- Portability :  GADTs
    --
    ----------------------------------------------------------------------------
    module Data.Profunctor.Trace
      ( Trace(..)
      ) where

    -- | Coend of 'Data.Profunctor.Profunctor' from @Hask -> Hask@.
    data Trace f where
      Trace :: f a a -> Trace f