lucienne-0.0.1: Lucienne/Fetch/Util.hs

module Lucienne.Fetch.Util 
       (partitionM)
where
  
import Control.Monad (foldM)
  
-- Note: order of elements is reversed in result
partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a],[a])
partitionM p = foldM (selectM p) ([],[])

selectM :: Monad m => (a -> m Bool) -> ([a], [a]) -> a -> m ([a], [a])
selectM p (ts,fs) x = do 
  true <- p x       
  return $ if true then (x:ts, fs) else (ts, x:fs)