{

 Copyright (c) 20092010 Johnny Morrice

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}
  This module provides a nice syntax for defining a list of pairs.
{# OPTIONS XFlexibleInstances XRankNTypes #}
module Network.Shpider.Pairs
( PairsWriter
, (=:)
, pairs
) where
import Control.Monad.State
  The abstract type describing the monadic state of a list of pairs.
type PairsWriter a b =
State [ ( a , b ) ]
  Take a monadic PairsWriter and return a list of pairs.
pairs :: forall a b c. PairsWriter a b c > [ ( a , b ) ]
pairs =
reverse . snd . flip runState [ ]
  Make a list of pairs of pairs like

 @
 pairs $ do $ 3 =: ( \" is my favourite number or \" , 5 )
 10 =: ( \" pints have I drunk or was it \" , 11 )
 @
(=:) :: forall a b. a > b > PairsWriter a b ( )
(=:) k v = do
st < get
put $ ( k , v ) : st