{- |

Module : $Header$

Description : utils for singleton sets

Copyright : (c) C. Maeder, Uni Bremen 2002-2007

License : similar to LGPL, see HetCATS/LICENSE.txt or LIZENZ.txt

Maintainer : maeder@tzi.de

Stability : provisional

Portability : portable

utils for singleton sets that could also be part of "Data.Set". These

functions rely on 'Data.Set.size' being computable in constant time and

would need to be rewritten for set implementations with a size

function that is only linear.

-}

module Common.SetUtils where

import Data.Set

-- | /O(1)/ try to extract the element from a singleton set

lookupSingleton :: Set a -> Maybe a

lookupSingleton s = if size s == 1 then Just $ findMin s else Nothing

-- | /O(1)/ test if the set's size is one

isSingleton :: Set a -> Bool

isSingleton s = size s == 1

-- | /O(1)/ comparison of the number with the set's size

compareSize :: Int -> Set a -> Ordering

compareSize i = compare i . size

-- | /O(1)/ test if the set's size is greater one

hasMany :: Set a -> Bool

hasMany s = compareSize 1 s == LT