darcs patch: Add equating p x y = p x == p y

[kahl at cas.mcmaster.ca]

 > 
 > Control.Combinators? Such general beasts as mapFst, mapSnd
 > and >< from Data.Graph.Inductive.Query.Monad could go in
 > there, as could other pair handling combinators like (f <&>
 > g) x = (f x, g x)

Pair handling combinators could go into Data.Tuple.
I append what I currently have.
(This is a typical instance of the kind of module
 where the code is (at least an essential part of) the documentation.
 Can Haddock be told to include the code in the documentation?
)


Wolfram

---------------------------------------------------------------
\section{Tuple Utilities}

\begin{code}
module Data.Utils.Tuple where
\end{code}

\begin{code}
swap (x,y) = (y,x)
\end{code}

\begin{code}
pupd f g (x,y) = (f x, g y)
mapPair f (x,y) = (f x, f y)
mapTriple f (x,y,z) = (f x, f y, f z)

pupd1 f (x,y) = (f x, y)

pupd2 g (x,y) = (x, g y)

{-# INLINE pupd #-}
{-# INLINE pupd1 #-}
{-# INLINE pupd2 #-}
\end{code}

\begin{code}
keep1 f p@(x,y) = (x, f p)
keep2 f p@(x,y) = (f p, y)
\end{code}