mapSnd :: ( t1 -> t2 ) -> [ ( t, t1 ) ] -> [ ( t , t2 ) ] 
mapSnd fun = map ( second fun )
mapSnd :: ( t1 -> t2 ) -> [ ( t, t1 ) ] -> [ ( t , t2 ) ]
mapSnd fun = map ( second fun )
mapSnd fun = map ( second fun )