Monad7.hs

{-@ LIQUID "--expect-any-error" @-}
module Monad7 () where

import Language.Haskell.Liquid.Prelude 

{-@ type OList a = [a]<{\fld v -> (v >= fld)}> @-}
{-@ gpp :: (Ord a, Monad m) => [a] -> m (OList a) @-}
gpp :: (Ord a, Monad m) => [a] -> m [a]
gpp ls = return $ reverse $ insertSort ls

{-@ insertSort :: (Ord a) => xs:[a] -> OList a @-}
insertSort            :: (Ord a) => [a] -> [a]
insertSort []         = []
insertSort (x:xs)     = insert x (insertSort xs) 

insert y []                   = [y]
insert y (x : xs) | y <= x    = y : x : xs 
                  | otherwise = x : insert y xs