{-# LANGUAGE DeriveDataTypeable #-}
# LANGUAGE FlexibleInstances #
# LANGUAGE MultiParamTypeClasses #
{-# LANGUAGE RankNTypes #-}
# LANGUAGE ScopedTypeVariables #
# LANGUAGE StandaloneDeriving #
# OPTIONS_GHC -Wall -fno - warn - orphans -fno - warn - unused - binds #

module Data.Logic.ATP.Lib
    ( Failing(Success, Failure)
    , failing
    , SetLike(slView, slMap, slUnion, slEmpty, slSingleton), slInsert, prettyFoldable

    , setAny
    , setAll
    , flatten
  , 
    -- , itlist  -- same as foldr with last arguments flipped
    , tryfind
    , runRS
    , evalRS
    , settryfind
  , end_itlist -- same as 
    , (|=>)
    , (|->)
    , fpf
    -- * Time and timeout
    , timeComputation
    , timeMessage
    , time
    , timeout
    , compete
    -- * Map aliases
    , defined
    , undefine
    , apply
    -- , exists
    , tryApplyD
    , allpairs
    , distrib
    , image
    , optimize
    , minimize
    , maximize
    , can
    , allsets
    , allsubsets
    , allnonemptysubsets
    , mapfilter
    , setmapfilter
    , (∅)
    , deepen, Depth(Depth)
    , testLib
    ) where

import Control.Applicative.Error (Failing(..))
import Control.Concurrent (forkIO, killThread, newEmptyMVar, putMVar, takeMVar, threadDelay)
import Control.Monad.RWS (evalRWS, runRWS, RWS)
import Data.Data (Data)
import Data.Foldable as Foldable (find, Foldable(foldr, foldr1), maximumBy)
import Data.Function (on)
import qualified Data.List as List (map)
import Data.Map.Strict as Map (delete, findMin, insert, lookup, Map, member, singleton)
import Data.Maybe (catMaybes, fromMaybe, isNothing)
import Data.Monoid ((<>))
import Data.Sequence as Seq ((><), Seq, singleton, viewl, ViewL(EmptyL, (:<)))
import Data.Set as Set (delete, empty, fold, fromList, insert, minView, Set, singleton, union)
import qualified Data.Set as Set (map)
import Data.Time.Clock (DiffTime, diffUTCTime, getCurrentTime, NominalDiffTime)
import Data.Typeable (Typeable)
import Debug.Trace (trace)
import Prelude (($), (++), (.), (<$>), all, any, Bool(..), const, Either(..), Enum(toEnum, succ, fromEnum), Eq((==)), flip, Fractional((/)), fst, Functor(fmap), Int, IO, mapM_, maybe, Maybe(..), Monad(..), Monoid(mempty), Num((-)), Ord((>), compare), Ordering, Rational, Read, realToFrac, Show(show), String, Traversable(mapM), unlines)
import Prelude hiding (map)
import System.IO (hPutStrLn, stderr)
import Test.HUnit (assertEqual, Test(TestCase, TestLabel, TestList))
import Text.PrettyPrint.HughesPJClass (comma, Doc, fsep, Pretty(pPrint), punctuate, space, text)

-- | An error idiom.  Rather like the error monad, but collect all
-- errors together
type ErrorMsg = String

failing :: ([String] -> b) -> (a -> b) -> Failing a -> b
failing f _ (Failure errs) = f errs
failing _ f (Success a)    = f a

  Declare a Monad instance for Failing so we can chain a series of
-- Failing actions with >> or >>=.  If any action fails the subsequent
-- actions in the chain will be aborted.
instance Monad Failing where
  return = Success
  m >>= f =
      case m of
        (Failure errs) -> (Failure errs)
        (Success a) -> f a
  fail errMsg = Failure [errMsg]

deriving instance Typeable Failing
deriving instance Data a => Data (Failing a)
deriving instance Read a => Read (Failing a)
deriving instance Eq a => Eq (Failing a)
deriving instance Ord a => Ord (Failing a)

instance Pretty a => Pretty (Failing a) where
    pPrint (Failure ss) = text (unlines ("Failures:" : List.map ("  " ++) ss))
    pPrint (Success a) = pPrint a

-- | A simple class, slightly more powerful than Foldable, so we can
-- write functions that operate on the elements of a set or a list.
class Foldable c => SetLike c where
    slView :: forall a. c a -> Maybe (a, c a)
    slMap :: forall a b. Ord b => (a -> b) -> c a -> c b
    slUnion :: Ord a => c a -> c a -> c a
    slEmpty :: c a
    slSingleton :: a -> c a

instance SetLike Set where
    slView = Set.minView
    slMap = Set.map
    slUnion = Set.union
    slEmpty = Set.empty
    slSingleton = Set.singleton

instance SetLike [] where
    slView [] = Nothing
    slView (h : t) = Just (h, t)
    slMap = List.map
    slUnion = (<>)
    slEmpty = mempty
    slSingleton = (: [])

instance SetLike Seq where
    slView s = case viewl s of
               EmptyL -> Nothing
               h :< t -> Just (h, t)
    slMap = fmap
    slUnion = (><)
    slEmpty = mempty
    slSingleton = Seq.singleton

slInsert :: (SetLike set, Ord a) => a -> set a -> set a
slInsert x s = slUnion (slSingleton x) s

prettyFoldable :: (Foldable t, Pretty a) => t a -> Doc
prettyFoldable s = fsep (punctuate (comma <> space) (List.map pPrint (Foldable.foldr (:) [] s)))

instance ( Pretty a , SetLike set ) = > Pretty ( set a ) where
--    pPrint = prettyFoldable

(∅) :: (Monoid (c a), SetLike c) => c a
(∅) = mempty

setAny :: Foldable t => (a -> Bool) -> t a -> Bool
setAny = any

setAll :: Foldable t => (a -> Bool) -> t a -> Bool
setAll = all

flatten :: Ord a => Set (Set a) -> Set a
flatten ss' = Set.fold Set.union Set.empty ss'


 ( * = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * ) 
 ( * Misc library functions to set up a nice environment .                       * ) 
 ( * = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * ) 

 let identity x = x ; ; 

 let ( * * ) = fun f g x - > f(g x ) ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * GCD and LCM on arbitrary - precision numbers .                                * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let  n1 n2 = 
   abs_num(num_of_big_int 
       ( Big_int.gcd_big_int ( big_int_of_num n1 ) ( big_int_of_num n2 ) ) ) ; ; 

 let lcm_num n1 n2 = abs_num(n1 * / n2 ) //  n1 n2 ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * A useful idiom for " non contradictory " etc .                                * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let non p x = not(p x ) ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Kind of assertion checking .                                                * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let check p x = if  ) then x else failwith " check " ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Repetition of a function .                                                  * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec funpow n f x = 
   if n < 1 then x else funpow ( n-1 ) f ( f x ) ; ; 

(* ========================================================================= *)
(* Misc library functions to set up a nice environment.                      *)
(* ========================================================================= *)

let identity x = x;;

let ( ** ) = fun f g x -> f(g x);;

(* ------------------------------------------------------------------------- *)
(* GCD and LCM on arbitrary-precision numbers.                               *)
(* ------------------------------------------------------------------------- *)

let gcd_num n1 n2 =
  abs_num(num_of_big_int
      (Big_int.gcd_big_int (big_int_of_num n1) (big_int_of_num n2)));;

let lcm_num n1 n2 = abs_num(n1 */ n2) // gcd_num n1 n2;;

(* ------------------------------------------------------------------------- *)
(* A useful idiom for "non contradictory" etc.                               *)
(* ------------------------------------------------------------------------- *)

let non p x = not(p x);;

(* ------------------------------------------------------------------------- *)
(* Kind of assertion checking.                                               *)
(* ------------------------------------------------------------------------- *)

let check p x = if p(x) then x else failwith "check";;

(* ------------------------------------------------------------------------- *)
(* Repetition of a function.                                                 *)
(* ------------------------------------------------------------------------- *)

let rec funpow n f x =
  if n < 1 then x else funpow (n-1) f (f x);;
-}
-- let can f x = try f x; true with Failure _ -> false;;
can :: (t -> Failing a) -> t -> Bool
can f x = failing (const True) (const False) (f x)


 let rec repeat f x = try repeat f ( f x ) with Failure _ - > x ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Handy list operations .                                                     * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec ( -- ) = fun m n - > if m > n then [ ] else m::((m + 1 ) -- n ) ; ; 

 let rec ( --- ) = fun m n - > if m > / n then [ ] else m::((m + / Int 1 ) --- n ) ; ; 

 let rec map2 f l1 l2 = 
   match ( l1,l2 ) with 
     [ ] , [ ] - > [ ] 
   | ( h1::t1),(h2::t2 ) - > let h = f h1 h2 in h::(map2 f t1 t2 ) 
   | _ - > failwith " map2 : length mismatch " ; ; 

 let rev = 
   let rec rev_append acc l = 
     match l with 
       [ ] - > acc 
     | h::t - > rev_append ( h::acc ) t in 
   fun l - > rev_append [ ] l ; ; 

 let hd l = 
   match l with 
    h::t - > h 
   | _ - > failwith " hd " ; ; 

 let tl l = 
   match l with 
    h::t - > t 
   | _ - > failwith " tl " ; ; 

let rec repeat f x = try repeat f (f x) with Failure _ -> x;;

(* ------------------------------------------------------------------------- *)
(* Handy list operations.                                                    *)
(* ------------------------------------------------------------------------- *)

let rec (--) = fun m n -> if m > n then [] else m::((m + 1) -- n);;

let rec (---) = fun m n -> if m >/ n then [] else m::((m +/ Int 1) --- n);;

let rec map2 f l1 l2 =
  match (l1,l2) with
    [],[] -> []
  | (h1::t1),(h2::t2) -> let h = f h1 h2 in h::(map2 f t1 t2)
  | _ -> failwith "map2: length mismatch";;

let rev =
  let rec rev_append acc l =
    match l with
      [] -> acc
    | h::t -> rev_append (h::acc) t in
  fun l -> rev_append [] l;;

let hd l =
  match l with
   h::t -> h
  | _ -> failwith "hd";;

let tl l =
  match l with
   h::t -> t
  | _ -> failwith "tl";;
-}

-- (^) = (++)

itlist :: Foldable t => (a -> b -> b) -> t a -> b -> b
itlist f xs z = Foldable.foldr f z xs

end_itlist :: Foldable t => (a -> a -> a) -> t a -> a
end_itlist = Foldable.foldr1

itlist2 :: (SetLike s, SetLike t) =>
           (a -> b -> Failing r -> Failing r) ->
           s a -> t b -> Failing r -> Failing r
itlist2 f s t r =
    case (slView s, slView t) of
      (Nothing, Nothing) -> r
      (Just (a, s'), Just (b, t')) ->
          f a b (itlist2 f s' t' r)
      _ -> Failure ["itlist2"]

{-
let rec zip l1 l2 =
  match (l1,l2) with
        ([],[]) -> []
      | (h1::t1,h2::t2) -> (h1,h2)::(zip t1 t2)
      | _ -> failwith "zip";;

let rec forall p l =
  match l with
    [] -> true
  | h::t -> p(h) & forall p t;;
-}
exists :: Foldable t => (a -> Bool) -> t a -> Bool
exists = any

 let partition p l = 
     itlist ( fun a ( yes , no ) - > if p a then a::yes , no else yes , a::no ) l ( [ ] , [ ] ) ; ; 

 let filter p l = fst(partition p l ) ; ; 

 let length = 
   let rec len k l = 
     if l = [ ] then k else len ( k + 1 ) ( tl l ) in 
   fun l - > len 0 l ; ; 

 let rec last l = 
   match l with 
     [ x ] - > x 
   | ( h::t ) - > last t 
   | [ ] - > failwith " last " ; ; 

 let rec butlast l = 
   match l with 
     [ _ ] - > [ ] 
   | ( h::t ) - > h::(butlast t ) 
   | [ ] - > failwith " butlast " ; ; 

 let rec find p l = 
   match l with 
       [ ] - > failwith " find " 
     | ( h::t ) - > if p(h ) then h else find p t ; ; 

 let rec el n l = 
   if n = 0 then hd l else  ( n - 1 ) ( tl l ) ; ; 

 let map f = 
   let rec  l = 
     match l with 
       [ ] - > [ ] 
     | ( x::t ) - > let y = f x in y::(mapf t ) in 
   mapf ; ; 

let partition p l =
    itlist (fun a (yes,no) -> if p a then a::yes,no else yes,a::no) l ([],[]);;

let filter p l = fst(partition p l);;

let length =
  let rec len k l =
    if l = [] then k else len (k + 1) (tl l) in
  fun l -> len 0 l;;

let rec last l =
  match l with
    [x] -> x
  | (h::t) -> last t
  | [] -> failwith "last";;

let rec butlast l =
  match l with
    [_] -> []
  | (h::t) -> h::(butlast t)
  | [] -> failwith "butlast";;

let rec find p l =
  match l with
      [] -> failwith "find"
    | (h::t) -> if p(h) then h else find p t;;

let rec el n l =
  if n = 0 then hd l else el (n - 1) (tl l);;

let map f =
  let rec mapf l =
    match l with
      [] -> []
    | (x::t) -> let y = f x in y::(mapf t) in
  mapf;;
-}

-- allpairs :: forall a b c. (Ord c) => (a -> b -> c) -> Set a -> Set b -> Set c
-- allpairs f xs ys = Set.fold (\ x zs -> Set.fold (\ y zs' -> Set.insert (f x y) zs') zs ys) Set.empty xs

allpairs :: forall a b c set. (SetLike set, Ord c) => (a -> b -> c) -> set a -> set b -> set c
allpairs f xs ys = Foldable.foldr (\ x zs -> Foldable.foldr (g x) zs ys) slEmpty xs
    where g :: a -> b -> set c -> set c
          g x y zs' = slInsert (f x y) zs'

distrib :: Ord a => Set (Set a) -> Set (Set a) -> Set (Set a)
distrib s1 s2 = allpairs (Set.union) s1 s2

test01 :: Test
test01 = TestCase $ assertEqual "allpairs" expected input
    where input = allpairs (,) (Set.fromList [1,2,3]) (Set.fromList [4,5,6])
          expected = Set.fromList [(1,4),(1,5),(1,6),(2,4),(2,5),(2,6),(3,4),(3,5),(3,6)] :: Set (Int, Int)


 let rec distinctpairs l = 
   match l with 
    x::t - > itlist ( fun y a - > ( x , y ) : : a ) t ( distinctpairs t ) 
   | [ ] - > [ ] ; ; 

 let rec chop_list n l = 
   if n = 0 then [ ] , l else 
   try let m , l ' = chop_list ( n-1 ) ( tl l ) in (   , l ' 
   with Failure _ - > failwith " chop_list " ; ; 

 let replicate n a = map ( fun x - > a ) ( 1 - -n ) ; ; 

 let rec insertat i x l = 
   if i = 0 then x::l else 
   match l with 
     [ ] - > failwith " insertat : list too short for position to exist " 
   | h::t - > h::(insertat ( i-1 ) x t ) ; ; 

 let rec forall2 p l1 l2 = 
   match ( l1,l2 ) with 
     [ ] , [ ] - > true 
   | ( h1::t1,h2::t2 ) - > p h1 h2 & forall2 p t1 t2 
   | _ - > false ; ; 

 let index x = 
   let rec ind n l = 
     match l with 
       [ ] - > failwith " index " 
     | ( h::t ) - > if Pervasives.compare x h = 0 then n else ind ( n + 1 ) t in 
   ind 0 ; ; 

 let rec unzip l = 
   match l with 
     [ ] - > [ ] , [ ] 
   | ( x , y)::t - > 
       let xs , ys = unzip t in x::xs ,   ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Whether the first of two items comes earlier in the list .                  * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec earlier l x y = 
   match l with 
     h::t - > ( Pervasives.compare h y < > 0 ) & 
             ( Pervasives.compare h x = 0 or earlier t x y ) 
   | [ ] - > false ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Application of ( presumably imperative ) function over a list .               * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec do_list f l = 
   match l with 
     [ ] - > ( ) 
   | h::t - > f(h ) ; do_list f t ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Association lists .                                                         * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec assoc a l = 
   match l with 
     ( x , y)::t - > if Pervasives.compare x a = 0 then y else assoc a t 
   | [ ] - > failwith " find " ; ; 

 let rec rev_assoc a l = 
   match l with 
     ( x , y)::t - > if Pervasives.compare y a = 0 then x else rev_assoc a t 
   | [ ] - > failwith " find " ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Merging of sorted lists ( maintaining repetitions ) .                         * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec merge  l1 l2 = 
   match l1 with 
     [ ] - > l2 
   | h1::t1 - > match l2 with 
                 [ ] - > l1 
               | h2::t2 - > if ord h1 h2 then h1::(merge ord t1 l2 ) 
                           else h2::(merge ord l1 t2 ) ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Bottom - up mergesort .                                                       * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let sort ord = 
   let rec  l1 l2 = 
     match ( l1,l2 ) with 
         ( [ s ] , [ ] ) - > s 
       | ( l , [ ] ) - >  [ ] l 
       | ( l,[s1 ] ) - >  ( s1::l ) [ ] 
       | ( l,(s1::s2::ss ) ) - >  ( ( merge ord s1 s2)::l ) ss in 
   fun l - > if l = [ ] then [ ] else  [ ] ( map ( fun x - > [ x ] ) l ) ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Common measure predicates to use with " sort " .                              * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let increasing f x y = Pervasives.compare ( f x ) ( f y ) < 0 ; ; 

 let decreasing f x y = Pervasives.compare ( f x ) ( f y ) > 0 ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Eliminate repetitions of adjacent elements , with and without counting .     * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec uniq l = 
   match l with 
     x::(y : : _ as t ) - > let t ' = uniq t in 
                       if Pervasives.compare x y = 0 then t ' else 
                       if t'==t then l else x::t ' 
  | _ - > l ; ; 

 let repetitions = 
   let rec repcount n l = 
     match l with 
       x::(y : : _ as ys ) - > if Pervasives.compare y x = 0 then repcount ( n + 1 ) ys 
                   else ( x , n)::(repcount 1 ys ) 
     | [ x ] - > [ x , n ] 
     | [ ] - > failwith " repcount " in 
   fun l - > if l = [ ] then [ ] else repcount 1 l ; ; 

let rec distinctpairs l =
  match l with
   x::t -> itlist (fun y a -> (x,y) :: a) t (distinctpairs t)
  | [] -> [];;

let rec chop_list n l =
  if n = 0 then [],l else
  try let m,l' = chop_list (n-1) (tl l) in (hd l)::m,l'
  with Failure _ -> failwith "chop_list";;

let replicate n a = map (fun x -> a) (1--n);;

let rec insertat i x l =
  if i = 0 then x::l else
  match l with
    [] -> failwith "insertat: list too short for position to exist"
  | h::t -> h::(insertat (i-1) x t);;

let rec forall2 p l1 l2 =
  match (l1,l2) with
    [],[] -> true
  | (h1::t1,h2::t2) -> p h1 h2 & forall2 p t1 t2
  | _ -> false;;

let index x =
  let rec ind n l =
    match l with
      [] -> failwith "index"
    | (h::t) -> if Pervasives.compare x h = 0 then n else ind (n + 1) t in
  ind 0;;

let rec unzip l =
  match l with
    [] -> [],[]
  | (x,y)::t ->
      let xs,ys = unzip t in x::xs,y::ys;;

(* ------------------------------------------------------------------------- *)
(* Whether the first of two items comes earlier in the list.                 *)
(* ------------------------------------------------------------------------- *)

let rec earlier l x y =
  match l with
    h::t -> (Pervasives.compare h y <> 0) &
            (Pervasives.compare h x = 0 or earlier t x y)
  | [] -> false;;

(* ------------------------------------------------------------------------- *)
(* Application of (presumably imperative) function over a list.              *)
(* ------------------------------------------------------------------------- *)

let rec do_list f l =
  match l with
    [] -> ()
  | h::t -> f(h); do_list f t;;

(* ------------------------------------------------------------------------- *)
(* Association lists.                                                        *)
(* ------------------------------------------------------------------------- *)

let rec assoc a l =
  match l with
    (x,y)::t -> if Pervasives.compare x a = 0 then y else assoc a t
  | [] -> failwith "find";;

let rec rev_assoc a l =
  match l with
    (x,y)::t -> if Pervasives.compare y a = 0 then x else rev_assoc a t
  | [] -> failwith "find";;

(* ------------------------------------------------------------------------- *)
(* Merging of sorted lists (maintaining repetitions).                        *)
(* ------------------------------------------------------------------------- *)

let rec merge ord l1 l2 =
  match l1 with
    [] -> l2
  | h1::t1 -> match l2 with
                [] -> l1
              | h2::t2 -> if ord h1 h2 then h1::(merge ord t1 l2)
                          else h2::(merge ord l1 t2);;

(* ------------------------------------------------------------------------- *)
(* Bottom-up mergesort.                                                      *)
(* ------------------------------------------------------------------------- *)

let sort ord =
  let rec mergepairs l1 l2 =
    match (l1,l2) with
        ([s],[]) -> s
      | (l,[]) -> mergepairs [] l
      | (l,[s1]) -> mergepairs (s1::l) []
      | (l,(s1::s2::ss)) -> mergepairs ((merge ord s1 s2)::l) ss in
  fun l -> if l = [] then [] else mergepairs [] (map (fun x -> [x]) l);;

(* ------------------------------------------------------------------------- *)
(* Common measure predicates to use with "sort".                             *)
(* ------------------------------------------------------------------------- *)

let increasing f x y = Pervasives.compare (f x) (f y) < 0;;

let decreasing f x y = Pervasives.compare (f x) (f y) > 0;;

(* ------------------------------------------------------------------------- *)
(* Eliminate repetitions of adjacent elements, with and without counting.    *)
(* ------------------------------------------------------------------------- *)

let rec uniq l =
  match l with
    x::(y::_ as t) -> let t' = uniq t in
                      if Pervasives.compare x y = 0 then t' else
                      if t'==t then l else x::t'
 | _ -> l;;

let repetitions =
  let rec repcount n l =
    match l with
      x::(y::_ as ys) -> if Pervasives.compare y x = 0 then repcount (n + 1) ys
                  else (x,n)::(repcount 1 ys)
    | [x] -> [x,n]
    | [] -> failwith "repcount" in
  fun l -> if l = [] then [] else repcount 1 l;;
-}

tryfind :: Foldable t => (a -> Failing r) -> t a -> Failing r
tryfind p s = maybe (Failure ["tryfind"]) p (find (failing (const False) (const True) . p) s)

evalRS :: RWS r () s a -> r -> s -> a
evalRS action r s = fst $ evalRWS action r s

runRS :: RWS r () s a -> r -> s -> (a, s)
runRS action r s = (\(a, s', _w) -> (a, s')) $ runRWS action r s

test02 :: Test
test02 =
    TestCase $
    assertEqual
      "tryfind on infinite list"
      (Success 3 :: Failing Int)
      (tryfind (\x -> if x == 3
                      then Success 3
                      else Failure ["test02"]) ([1..] :: [Int]))

settryfind :: (t -> Failing a) -> Set t -> Failing a
settryfind f l =
    case Set.minView l of
      Nothing -> Failure ["settryfind"]
      Just (h, t) -> failing (\ _ -> settryfind f t) Success (f h)

mapfilter :: (a -> Failing b) -> [a] -> [b]
mapfilter f l = catMaybes (List.map (failing (const Nothing) Just . f) l)
    -- filter (failing (const False) (const True)) (map f l)

setmapfilter :: Ord b => (a -> Failing b) -> Set a -> Set b
setmapfilter f s = Set.fold (\ a r -> failing (const r) (`Set.insert` r) (f a)) Set.empty s

-- -------------------------------------------------------------------------
-- Find list member that maximizes or minimizes a function.
-- -------------------------------------------------------------------------

optimize :: forall s a b. (SetLike s, Foldable s) => (b -> b -> Ordering) -> (a -> b) -> s a -> Maybe a
optimize _ _ l | isNothing (slView l) = Nothing
optimize ord f l = Just (Foldable.maximumBy (ord `on` f) l)

maximize :: (Ord b, SetLike s, Foldable s) => (a -> b) -> s a -> Maybe a
maximize = optimize compare

minimize :: (Ord b, SetLike s, Foldable s) => (a -> b) -> s a -> Maybe a
minimize = optimize (flip compare)

-- -------------------------------------------------------------------------
-- Set operations on ordered lists.
-- -------------------------------------------------------------------------

 let    let rec canonical lis = 
      match lis with 
        x::(y : : _ as rest ) - > Pervasives.compare x y < 0 & canonical rest 
      | _ - > true in 
   fun l - > if canonical l then l 
            else uniq ( sort ( fun x y - > Pervasives.compare x y < = 0 ) l ) ; ; 

 let union = 
   let rec union l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > l2 
       | ( l1 , [ ] ) - > l1 
       | ( ( h1::t1 as  as l2 ) ) - > 
           if h1 = h2 then h1::(union t1 t2 ) 
           else if h1 < h2 then h1::(union t1 l2 ) 
           else h2::(union l1 t2 ) in 
   fun s1 s2 - > union (   ) ( setify s2 ) ; ; 

 let intersect = 
   let rec intersect l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > [ ] 
       | ( l1 , [ ] ) - > [ ] 
       | ( ( h1::t1 as  as l2 ) ) - > 
           if h1 = h2 then h1::(intersect t1 t2 ) 
           else if h1 < h2 then intersect t1 l2 
           else intersect l1 t2 in 
   fun s1 s2 - > intersect (   ) ( setify s2 ) ; ; 

 let subtract = 
   let rec subtract l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > [ ] 
       | ( l1 , [ ] ) - > l1 
       | ( ( h1::t1 as  as l2 ) ) - > 
           if h1 = h2 then subtract t1 t2 
           else if h1 < h2 then h1::(subtract t1 l2 ) 
           else subtract l1 t2 in 
   fun s1 s2 - > subtract (   ) ( setify s2 ) ; ; 

 let subset , psubset = 
   let rec subset l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > true 
       | ( l1 , [ ] ) - > false 
       | ( h1::t1,h2::t2 ) - > 
           if h1 = h2 then subset t1 t2 
           else if h1 < h2 then false 
           else subset l1 t2 
   and psubset l1 l2 = 
     match ( l1,l2 ) with 
         ( l1 , [ ] ) - > false 
       | ( [ ] , l2 ) - > true 
       | ( h1::t1,h2::t2 ) - > 
           if h1 = h2 then psubset t1 t2 
           else if h1 < h2 then false 
           else subset l1 t2 in 
   ( fun s1 s2 - > subset (   ) ( setify s2 ) ) , 
   ( fun s1 s2 - > psubset (   ) ( setify s2 ) ) ; ; 

 let rec set_eq s1 s2 = (    setify s2 ) ; ; 

 let insert x s = union [ x ] s ; ; 

let setify =
  let rec canonical lis =
     match lis with
       x::(y::_ as rest) -> Pervasives.compare x y < 0 & canonical rest
     | _ -> true in
  fun l -> if canonical l then l
           else uniq (sort (fun x y -> Pervasives.compare x y <= 0) l);;

let union =
  let rec union l1 l2 =
    match (l1,l2) with
        ([],l2) -> l2
      | (l1,[]) -> l1
      | ((h1::t1 as l1),(h2::t2 as l2)) ->
          if h1 = h2 then h1::(union t1 t2)
          else if h1 < h2 then h1::(union t1 l2)
          else h2::(union l1 t2) in
  fun s1 s2 -> union (setify s1) (setify s2);;

let intersect =
  let rec intersect l1 l2 =
    match (l1,l2) with
        ([],l2) -> []
      | (l1,[]) -> []
      | ((h1::t1 as l1),(h2::t2 as l2)) ->
          if h1 = h2 then h1::(intersect t1 t2)
          else if h1 < h2 then intersect t1 l2
          else intersect l1 t2 in
  fun s1 s2 -> intersect (setify s1) (setify s2);;

let subtract =
  let rec subtract l1 l2 =
    match (l1,l2) with
        ([],l2) -> []
      | (l1,[]) -> l1
      | ((h1::t1 as l1),(h2::t2 as l2)) ->
          if h1 = h2 then subtract t1 t2
          else if h1 < h2 then h1::(subtract t1 l2)
          else subtract l1 t2 in
  fun s1 s2 -> subtract (setify s1) (setify s2);;

let subset,psubset =
  let rec subset l1 l2 =
    match (l1,l2) with
        ([],l2) -> true
      | (l1,[]) -> false
      | (h1::t1,h2::t2) ->
          if h1 = h2 then subset t1 t2
          else if h1 < h2 then false
          else subset l1 t2
  and psubset l1 l2 =
    match (l1,l2) with
        (l1,[]) -> false
      | ([],l2) -> true
      | (h1::t1,h2::t2) ->
          if h1 = h2 then psubset t1 t2
          else if h1 < h2 then false
          else subset l1 t2 in
  (fun s1 s2 -> subset (setify s1) (setify s2)),
  (fun s1 s2 -> psubset (setify s1) (setify s2));;

let rec set_eq s1 s2 = (setify s1 = setify s2);;

let insert x s = union [x] s;;
-}

image :: (Ord b, Ord a) => (a -> b) -> Set a -> Set b
image f s = Set.map f s


 ( * ------------------------------------------------------------------------- * ) 
 ( * Union of a family of sets .                                                 * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let unions s =  ( @ ) s [ ] ) ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * List membership . This does * not * assume the list is a set .                 * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec mem x lis = 
   match lis with 
     [ ] - > false 
   | ( h::t ) - > Pervasives.compare x h = 0 or mem x t ; ; 

(* ------------------------------------------------------------------------- *)
(* Union of a family of sets.                                                *)
(* ------------------------------------------------------------------------- *)

let unions s = setify(itlist (@) s []);;

(* ------------------------------------------------------------------------- *)
(* List membership. This does *not* assume the list is a set.                *)
(* ------------------------------------------------------------------------- *)

let rec mem x lis =
  match lis with
    [] -> false
  | (h::t) -> Pervasives.compare x h = 0 or mem x t;;
-}

-- -------------------------------------------------------------------------
-- Finding all subsets or all subsets of a given size.
-- -------------------------------------------------------------------------

  allsets : :  a = > Int - > Set a - > Set ( Set a )
allsets :: forall a b. (Num a, Eq a, Ord b) => a -> Set b -> Set (Set b)
allsets 0 _ = Set.singleton Set.empty
allsets m l =
    case Set.minView l of
      Nothing -> Set.empty
      Just (h, t) -> Set.union (Set.map (Set.insert h) (allsets (m - 1) t)) (allsets m t)

allsubsets :: forall a. Ord a => Set a -> Set (Set a)
allsubsets s =
    maybe (Set.singleton Set.empty)
          (\ (x, t) ->
               let res = allsubsets t in
               Set.union res (Set.map (Set.insert x) res))
          (Set.minView s)


allnonemptysubsets :: forall a. Ord a => Set a -> Set (Set a)
allnonemptysubsets s = Set.delete Set.empty (allsubsets s)


 ( * ------------------------------------------------------------------------- * ) 
 ( * Explosion and implosion of strings .                                        * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let explode s = 
   let rec exap n l = 
      if n < 0 then l else 
       exap ( n - 1 ) ( ( String.sub s n 1)::l ) in 
   exap ( String.length s - 1 ) [ ] ; ; 

 let implode l = itlist ( ^ ) l " " ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Timing ; useful for documentation but not logically necessary .              * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let time f x = 
   let start_time = Sys.time ( ) in 
   let result = f x in 
   let finish_time = Sys.time ( ) in 
   print_string 
     ( " CPU time ( user ): " ^(string_of_float(finish_time - . start_time ) ) ) ; 
   print_newline ( ) ; 
   result ; ; 

(* ------------------------------------------------------------------------- *)
(* Explosion and implosion of strings.                                       *)
(* ------------------------------------------------------------------------- *)

let explode s =
  let rec exap n l =
     if n < 0 then l else
      exap (n - 1) ((String.sub s n 1)::l) in
  exap (String.length s - 1) [];;

let implode l = itlist (^) l "";;

(* ------------------------------------------------------------------------- *)
(* Timing; useful for documentation but not logically necessary.             *)
(* ------------------------------------------------------------------------- *)

let time f x =
  let start_time = Sys.time() in
  let result = f x in
  let finish_time = Sys.time() in
  print_string
    ("CPU time (user): "^(string_of_float(finish_time -. start_time)));
  print_newline();
  result;;
-}

  | Perform an IO operation and return the elapsed time along with the result .
timeComputation :: IO r -> IO (r, NominalDiffTime)
timeComputation a = do
  start <- getCurrentTime
  r <- a
  end <- getCurrentTime
  return (r, diffUTCTime end start)

-- | Perform an IO operation and output a message about how long it took.
timeMessage :: (r -> NominalDiffTime -> String) -> IO r -> IO r
timeMessage pp a = do
  (r, e) <- timeComputation a
  hPutStrLn stderr (pp r e)
  return r

-- | Output elapsed time
time :: IO r -> IO r
time a = timeMessage (\_ e -> "Computation time: " ++ show e) a

-- | Allow a computation to proceed for a given amount of time.
timeout :: String -> DiffTime -> IO r -> IO (Either String r)
timeout message delay a = do
  compete [threadDelay (fromEnum (realToFrac (delay / 1e6) :: Rational)) >> return (Left message),
           Right <$> a]

  | Run several IO operations in parallel , return the result of the
-- first one that completes and kill the others.
compete :: [IO a] -> IO a
compete actions = do
  mvar <- newEmptyMVar
  tids <- mapM (\action -> forkIO $ action >>= putMVar mvar) actions
  result <- takeMVar mvar
  mapM_ killThread tids
  return result

  | Polymorphic finite partial functions via  trees .
--
-- The point of this strange representation is that it is canonical (equal
-- functions have the same encoding) yet reasonably efficient on average.
--
  Idea due to     ( OCaml list , 2003/11/10 ) .
data Func a b
    = Empty
    | Leaf Int [(a, b)]
    | Branch Int Int (Func a b) (Func a b)

-- | Undefined function.
undefinedFunction :: Func a b
undefinedFunction = Empty

-- -------------------------------------------------------------------------
-- In case of equality comparison worries, better use this.
-- -------------------------------------------------------------------------

isUndefined :: Func a b -> Bool
isUndefined Empty = True
isUndefined _ = False

-- -------------------------------------------------------------------------
-- Operation analogous to "map" for functions.
-- -------------------------------------------------------------------------

mapf :: (b -> c) -> Func a b -> Func a c
mapf f t =
    case t of
      Empty -> Empty
      Leaf h l -> Leaf h (map_list f l)
      Branch p b l r -> Branch p b (mapf f l) (mapf f r)
    where
      map_list f' l' =
          case l' of
            [] -> []
            (x,y) : t' -> (x, f' y) : map_list f' t'

-- -------------------------------------------------------------------------
  Operations analogous to " fold " for lists .
-- -------------------------------------------------------------------------

foldlFn :: (r -> a -> b -> r) -> r -> Func a b -> r
foldlFn f a t =
    case t of
      Empty -> a
      Leaf _h l -> foldl_list f a l
      Branch _p _b l r -> foldlFn f (foldlFn f a l) r
    where
      foldl_list _f a' l =
          case l of
            [] -> a'
            (x,y) : t' -> foldl_list f (f a' x y) t'

foldrFn :: (a -> b -> r -> r) -> Func a b -> r -> r
foldrFn f t a =
    case t of
      Empty -> a
      Leaf _h l -> foldr_list f l a
      Branch _p _b l r -> foldrFn f l (foldrFn f r a)
    where
      foldr_list f' l a' =
          case l of
            [] -> a'
            (x, y) : t' -> f' x y (foldr_list f' t' a')

-- -------------------------------------------------------------------------
-- Mapping to sorted-list representation of the graph, domain and range.
-- -------------------------------------------------------------------------

graph :: (Ord a, Ord b) => Func a b -> Set (a, b)
graph f = Set.fromList (foldlFn (\ a x y -> (x,y) : a) [] f)

dom :: Ord a => Func a b -> Set a
dom f = Set.fromList (foldlFn (\ a x _y -> x :a) [] f)

ran :: Ord b => Func a b -> Set b
ran f = Set.fromList (foldlFn (\ a _x y -> y : a) [] f)

-- -------------------------------------------------------------------------
-- Application.
-- -------------------------------------------------------------------------

applyD :: Ord k => Map k a -> k -> a -> Map k a
applyD m k a = Map.insert k a m

apply :: Ord k => Map k a -> k -> Maybe a
apply m k = Map.lookup k m

tryApplyD :: Ord k => Map k a -> k -> a -> a
tryApplyD m k d = fromMaybe d (Map.lookup k m)

tryApplyL :: Ord k => Map k [a] -> k -> [a]
tryApplyL m k = tryApplyD m k []
{-
applyD :: (t -> Maybe b) -> (t -> b) -> t -> b
applyD f d x = maybe (d x) id (f x)

apply :: (t -> Maybe b) -> t -> b
apply f = applyD f (\ _ -> error "apply")

tryApplyD :: (t -> Maybe b) -> t -> b -> b
tryApplyD f a d = maybe d id (f a)

tryApplyL :: (t -> Maybe [a]) -> t -> [a]
tryApplyL f x = tryApplyD f x []
-}

defined :: Ord t => Map t a -> t -> Bool
defined = flip Map.member

-- | Undefinition.
undefine :: forall k a. Ord k => k -> Map k a -> Map k a
undefine k mp = Map.delete k mp


 ( * ------------------------------------------------------------------------- * ) 
 ( * Redefinition and combination .                                              * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let ( |->),combine = 
   let newbranch p1 t1 p2 t2 = 
     let zp =   p2 in 
     let b = zp land ( -zp ) in 
     let p = p1 land ( b - 1 ) in 
     if p1 land b = 0 then Branch(p , b ,  ) 
     else Branch(p , b , t2,t1 ) in 
   let rec define_list ( x , y as xy ) l = 
     match l with 
       ( a , b as ab)::t - > 
           let c = Pervasives.compare x a in 
           if c = 0 then xy::t 
           else if c < 0 then xy::l 
           else ab::(define_list xy t ) 
     | [ ] - > [ xy ] 
   and combine_list op z l1 l2 = 
     match ( l1,l2 ) with 
       [ ] , _ - > l2 
     | _ , [ ] - > l1 
     | ( (  as xy1)::t1,(x2,y2 as  ) - > 
           let c = Pervasives.compare x1 x2 in 
           if c < 0 then xy1::(combine_list op z t1 l2 ) 
           else if c > 0 then xy2::(combine_list op z l1 t2 ) else 
           let y = op y1 y2 and l = combine_list op z t1 t2 in 
           if z(y ) then l else ( x1,y)::l in 
   let ( |- > ) x y = 
     let k = Hashtbl.hash x in 
     let rec upd t = 
       match t with 
         Empty - > Leaf ( k,[x , y ] ) 
         , l ) - > 
            if h = k then  , define_list ( x , y ) l ) 
            else newbranch h t k ( Leaf(k,[x , y ] ) ) 
       | Branch(p , b , l , r ) - > 
           if k land ( b - 1 ) < > p then newbranch p t k ( Leaf(k,[x , y ] ) ) 
           else if k land b = 0 then Branch(p , b , upd l , r ) 
           else Branch(p , b , l , upd r ) in 
     upd in 
   let rec combine op z t1 t2 = 
     match ( t1,t2 ) with 
       Empty , _ - > t2 
     | _ , Empty - > t1 
     | Leaf(h1,l1),Leaf(h2,l2 ) - > 
           if h1 = h2 then 
             let l = combine_list op z l1 l2 in 
             if l = [ ] then Empty else Leaf(h1,l ) 
           else newbranch h1 t1 h2 t2 
     | ( Leaf(k , lis ) as lf),(Branch(p , b , l , r ) as br ) - > 
           if k land ( b - 1 ) = p then 
             if k land b = 0 then 
               ( match combine op z lf l with 
                  Empty - > r | l ' - > Branch(p , b ,  ) ) 
             else 
               ( match combine op z lf r with 
                  Empty - > l | r ' - > Branch(p , b , l , r ' ) ) 
           else 
             newbranch k lf p br 
     | ( Branch(p , b , l , r ) as br),(Leaf(k , lis ) as lf ) - > 
           if k land ( b - 1 ) = p then 
             if k land b = 0 then 
               ( match combine op z l lf with 
                 Empty - > r | l ' - > Branch(p , b ,  ) ) 
             else 
               ( match combine op z r lf with 
                  Empty - > l | r ' - > Branch(p , b , l , r ' ) ) 
           else 
             newbranch        ) - > 
           if b1 < b2 then 
             if p2 land ( b1 - 1 ) < > p1 then newbranch p1 t1 p2 t2 
             else if p2 land b1 = 0 then 
               ( match combine op z l1 t2 with 
                  Empty - > r1 | l - > Branch(p1,b1,l , r1 ) ) 
             else 
               ( match combine op z r1 t2 with 
                  Empty - > l1 | r - > Branch(p1,b1,l1,r ) ) 
           else if b2 < b1 then 
             if p1 land ( b2 - 1 ) < > p2 then newbranch p1 t1 p2 t2 
             else if p1 land b2 = 0 then 
               ( match combine op z t1 l2 with 
                  Empty - > r2 | l - > Branch(p2,b2,l , r2 ) ) 
             else 
               ( match combine op z t1 r2 with 
                  Empty - > l2 | r - > Branch(p2,b2,l2,r ) ) 
           else if p1 = p2 then 
            ( match ( combine op z l1 l2,combine op z r1 r2 ) with 
               ( Empty , r ) - > r | ( l , Empty ) - > l | ( l , r ) - > Branch(p1,b1,l , r ) ) 
           else 
             newbranch p1 t1 p2 t2 in 
   ( |->),combine ; ; 

(* ------------------------------------------------------------------------- *)
(* Redefinition and combination.                                             *)
(* ------------------------------------------------------------------------- *)

let (|->),combine =
  let newbranch p1 t1 p2 t2 =
    let zp = p1 lxor p2 in
    let b = zp land (-zp) in
    let p = p1 land (b - 1) in
    if p1 land b = 0 then Branch(p,b,t1,t2)
    else Branch(p,b,t2,t1) in
  let rec define_list (x,y as xy) l =
    match l with
      (a,b as ab)::t ->
          let c = Pervasives.compare x a in
          if c = 0 then xy::t
          else if c < 0 then xy::l
          else ab::(define_list xy t)
    | [] -> [xy]
  and combine_list op z l1 l2 =
    match (l1,l2) with
      [],_ -> l2
    | _,[] -> l1
    | ((x1,y1 as xy1)::t1,(x2,y2 as xy2)::t2) ->
          let c = Pervasives.compare x1 x2 in
          if c < 0 then xy1::(combine_list op z t1 l2)
          else if c > 0 then xy2::(combine_list op z l1 t2) else
          let y = op y1 y2 and l = combine_list op z t1 t2 in
          if z(y) then l else (x1,y)::l in
  let (|->) x y =
    let k = Hashtbl.hash x in
    let rec upd t =
      match t with
        Empty -> Leaf (k,[x,y])
      | Leaf(h,l) ->
           if h = k then Leaf(h,define_list (x,y) l)
           else newbranch h t k (Leaf(k,[x,y]))
      | Branch(p,b,l,r) ->
          if k land (b - 1) <> p then newbranch p t k (Leaf(k,[x,y]))
          else if k land b = 0 then Branch(p,b,upd l,r)
          else Branch(p,b,l,upd r) in
    upd in
  let rec combine op z t1 t2 =
    match (t1,t2) with
      Empty,_ -> t2
    | _,Empty -> t1
    | Leaf(h1,l1),Leaf(h2,l2) ->
          if h1 = h2 then
            let l = combine_list op z l1 l2 in
            if l = [] then Empty else Leaf(h1,l)
          else newbranch h1 t1 h2 t2
    | (Leaf(k,lis) as lf),(Branch(p,b,l,r) as br) ->
          if k land (b - 1) = p then
            if k land b = 0 then
              (match combine op z lf l with
                 Empty -> r | l' -> Branch(p,b,l',r))
            else
              (match combine op z lf r with
                 Empty -> l | r' -> Branch(p,b,l,r'))
          else
            newbranch k lf p br
    | (Branch(p,b,l,r) as br),(Leaf(k,lis) as lf) ->
          if k land (b - 1) = p then
            if k land b = 0 then
              (match combine op z l lf with
                Empty -> r | l' -> Branch(p,b,l',r))
            else
              (match combine op z r lf with
                 Empty -> l | r' -> Branch(p,b,l,r'))
          else
            newbranch p br k lf
    | Branch(p1,b1,l1,r1),Branch(p2,b2,l2,r2) ->
          if b1 < b2 then
            if p2 land (b1 - 1) <> p1 then newbranch p1 t1 p2 t2
            else if p2 land b1 = 0 then
              (match combine op z l1 t2 with
                 Empty -> r1 | l -> Branch(p1,b1,l,r1))
            else
              (match combine op z r1 t2 with
                 Empty -> l1 | r -> Branch(p1,b1,l1,r))
          else if b2 < b1 then
            if p1 land (b2 - 1) <> p2 then newbranch p1 t1 p2 t2
            else if p1 land b2 = 0 then
              (match combine op z t1 l2 with
                 Empty -> r2 | l -> Branch(p2,b2,l,r2))
            else
              (match combine op z t1 r2 with
                 Empty -> l2 | r -> Branch(p2,b2,l2,r))
          else if p1 = p2 then
           (match (combine op z l1 l2,combine op z r1 r2) with
              (Empty,r) -> r | (l,Empty) -> l | (l,r) -> Branch(p1,b1,l,r))
          else
            newbranch p1 t1 p2 t2 in
  (|->),combine;;
-}

-- -------------------------------------------------------------------------
-- Special case of point function.
-- -------------------------------------------------------------------------

(|=>) :: Ord k => k -> a -> Map k a
x |=> y = Map.singleton x y

-- -------------------------------------------------------------------------
-- Idiom for a mapping zipping domain and range lists.
-- -------------------------------------------------------------------------

(|->) :: Ord k => k -> a -> Map k a -> Map k a
(|->) = Map.insert

fpf :: Ord a => Map a b -> a -> Maybe b
fpf = flip Map.lookup

-- -------------------------------------------------------------------------
-- Grab an arbitrary element.
-- -------------------------------------------------------------------------

choose :: Map k a -> (k, a)
choose = Map.findMin


 ( * ------------------------------------------------------------------------- * ) 
 ( * Install a ( trivial ) printer for finite partial functions .                  * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let print_fpf ( f:('a,'b)func ) = print_string " < func > " ; ; 

 # install_printer print_fpf ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Related stuff for standard functions .                                      * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let  a y f x = if x = a then y else f(x ) ; ; 

 let undef x = failwith " undefined function " ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * Union - find algorithm .                                                      * ) 
 ( * ------------------------------------------------------------------------- * ) 

 type ( ' a)pnode = Nonterminal of ' a | Terminal of ' a * int ; ; 

 type ( ' a)partition = Partition of ( ' a,('a)pnode)func ; ; 

 let rec terminus ( Partition f as ptn ) a = 
   match ( apply f a ) with 
     Nonterminal(b ) - > terminus ptn b 
   | Terminal(p , q ) - > ( p , q ) ; ; 

 let tryterminus ptn a = 
   try terminus ptn a with Failure _ - > ( a,1 ) ; ; 

 let canonize ptn a = fst(tryterminus ptn a ) ; ; 

 let equivalent eqv a b = canonize eqv a = canonize eqv b ; ; 

 let equate ( a , b ) ( Partition f as ptn ) = 
   let ( a',na ) = tryterminus ptn a 
   and ( b',nb ) = tryterminus ptn b in 
   Partition 
    ( if a ' = b ' then f else 
     if na < = nb then 
        itlist identity [ a ' |- > Nonterminal b ' ; b ' |- > Terminal(b',na+nb ) ] f 
     else 
        itlist identity [ b ' |- > Nonterminal a ' ; a ' |- > Terminal(a',na+nb ) ] f ) ; ; 

 let unequal = Partition undefined ; ; 

 let equated ( Partition f ) = dom f ; ; 

 ( * ------------------------------------------------------------------------- * ) 
 ( * First number starting at n for which p succeeds .                           * ) 
 ( * ------------------------------------------------------------------------- * ) 

 let rec first n p = if p(n ) then n else first ( n + / Int 1 ) p ; ; 

(* ------------------------------------------------------------------------- *)
(* Install a (trivial) printer for finite partial functions.                 *)
(* ------------------------------------------------------------------------- *)

let print_fpf (f:('a,'b)func) = print_string "<func>";;

#install_printer print_fpf;;

(* ------------------------------------------------------------------------- *)
(* Related stuff for standard functions.                                     *)
(* ------------------------------------------------------------------------- *)

let valmod a y f x = if x = a then y else f(x);;

let undef x = failwith "undefined function";;

(* ------------------------------------------------------------------------- *)
(* Union-find algorithm.                                                     *)
(* ------------------------------------------------------------------------- *)

type ('a)pnode = Nonterminal of 'a | Terminal of 'a * int;;

type ('a)partition = Partition of ('a,('a)pnode)func;;

let rec terminus (Partition f as ptn) a =
  match (apply f a) with
    Nonterminal(b) -> terminus ptn b
  | Terminal(p,q) -> (p,q);;

let tryterminus ptn a =
  try terminus ptn a with Failure _ -> (a,1);;

let canonize ptn a = fst(tryterminus ptn a);;

let equivalent eqv a b = canonize eqv a = canonize eqv b;;

let equate (a,b) (Partition f as ptn) =
  let (a',na) = tryterminus ptn a
  and (b',nb) = tryterminus ptn b in
  Partition
   (if a' = b' then f else
    if na <= nb then
       itlist identity [a' |-> Nonterminal b'; b' |-> Terminal(b',na+nb)] f
    else
       itlist identity [b' |-> Nonterminal a'; a' |-> Terminal(a',na+nb)] f);;

let unequal = Partition undefined;;

let equated (Partition f) = dom f;;

(* ------------------------------------------------------------------------- *)
(* First number starting at n for which p succeeds.                          *)
(* ------------------------------------------------------------------------- *)

let rec first n p = if p(n) then n else first (n +/ Int 1) p;;
-}

-- | Try f with higher and higher values of n until it succeeds, or
-- optional maximum depth limit is exceeded.
{-
let rec deepen f n =
  try print_string "Searching with depth limit ";
      print_int n; print_newline(); f n
  with Failure _ -> deepen f (n + 1);;
-}
deepen :: (Depth -> Failing t) -> Depth -> Maybe Depth -> Failing (t, Depth)
deepen _ n (Just m) | n > m = Failure ["Exceeded maximum depth limit"]
deepen f n m =
    -- If no maximum depth limit is given print a trace of the
    -- levels tried.  The assumption is that we are running
    -- interactively.
    let n' = maybe (trace ("Searching with depth limit " ++ show n) n) (\_ -> n) m in
    case f n' of
      Failure _ -> deepen f (succ n) m
      Success x -> Success (x, n)

newtype Depth = Depth Int deriving (Eq, Ord, Show)

instance Enum Depth where
    toEnum = Depth
    fromEnum (Depth n) = n

instance Pretty Depth where
    pPrint = text . show

testLib :: Test
testLib = TestLabel "Lib" (TestList [test01])

# LANGUAGE DeriveDataTypeable #
# LANGUAGE RankNTypes #
 , itlist  -- same as foldr with last arguments flipped
 same as 
 * Time and timeout
 * Map aliases
 , exists
 | An error idiom.  Rather like the error monad, but collect all
 errors together
 Failing actions with >> or >>=.  If any action fails the subsequent
 actions in the chain will be aborted.
 | A simple class, slightly more powerful than Foldable, so we can
 write functions that operate on the elements of a set or a list.
    pPrint = prettyFoldable
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
 let can f x = try f x; true with Failure _ -> false;;
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
 ) = fun m n - > if m > n then [ ] else m::((m + 1 ) -- n ) ; ; 
- ) = fun m n - > if m > / n then [ ] else m::((m + / Int 1 ) --- n ) ; ; 
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
) = fun m n -> if m > n then [] else m::((m + 1) -- n);;
-) = fun m n -> if m >/ n then [] else m::((m +/ Int 1) --- n);;
 (^) = (++)

let rec zip l1 l2 =
  match (l1,l2) with
        ([],[]) -> []
      | (h1::t1,h2::t2) -> (h1,h2)::(zip t1 t2)
      | _ -> failwith "zip";;

let rec forall p l =
  match l with
    [] -> true
  | h::t -> p(h) & forall p t;;

 allpairs :: forall a b c. (Ord c) => (a -> b -> c) -> Set a -> Set b -> Set c
 allpairs f xs ys = Set.fold (\ x zs -> Set.fold (\ y zs' -> Set.insert (f x y) zs') zs ys) Set.empty xs
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
n);;
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
 filter (failing (const False) (const True)) (map f l)
 -------------------------------------------------------------------------
 Find list member that maximizes or minimizes a function.
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 Set operations on ordered lists.
 -------------------------------------------------------------------------
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
 -------------------------------------------------------------------------
 Finding all subsets or all subsets of a given size.
 -------------------------------------------------------------------------
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
 | Perform an IO operation and output a message about how long it took.
 | Output elapsed time
 | Allow a computation to proceed for a given amount of time.
 first one that completes and kill the others.

 The point of this strange representation is that it is canonical (equal
 functions have the same encoding) yet reasonably efficient on average.

 | Undefined function.
 -------------------------------------------------------------------------
 In case of equality comparison worries, better use this.
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 Operation analogous to "map" for functions.
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 Mapping to sorted-list representation of the graph, domain and range.
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 Application.
 -------------------------------------------------------------------------

applyD :: (t -> Maybe b) -> (t -> b) -> t -> b
applyD f d x = maybe (d x) id (f x)

apply :: (t -> Maybe b) -> t -> b
apply f = applyD f (\ _ -> error "apply")

tryApplyD :: (t -> Maybe b) -> t -> b -> b
tryApplyD f a d = maybe d id (f a)

tryApplyL :: (t -> Maybe [a]) -> t -> [a]
tryApplyL f x = tryApplyD f x []

 | Undefinition.
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
 -------------------------------------------------------------------------
 Special case of point function.
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 Idiom for a mapping zipping domain and range lists.
 -------------------------------------------------------------------------
 -------------------------------------------------------------------------
 Grab an arbitrary element.
 -------------------------------------------------------------------------
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- * ) 
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
----------------------------------------------------------------------- *)
 | Try f with higher and higher values of n until it succeeds, or
 optional maximum depth limit is exceeded.

let rec deepen f n =
  try print_string "Searching with depth limit ";
      print_int n; print_newline(); f n
  with Failure _ -> deepen f (n + 1);;

 If no maximum depth limit is given print a trace of the
 levels tried.  The assumption is that we are running
 interactively.
# LANGUAGE FlexibleInstances #
# LANGUAGE MultiParamTypeClasses #
# LANGUAGE ScopedTypeVariables #
# LANGUAGE StandaloneDeriving #
# OPTIONS_GHC -Wall -fno - warn - orphans -fno - warn - unused - binds #

module Data.Logic.ATP.Lib
    ( Failing(Success, Failure)
    , failing
    , SetLike(slView, slMap, slUnion, slEmpty, slSingleton), slInsert, prettyFoldable

    , setAny
    , setAll
    , flatten
  , 
    , tryfind
    , runRS
    , evalRS
    , settryfind
    , (|=>)
    , (|->)
    , fpf
    , timeComputation
    , timeMessage
    , time
    , timeout
    , compete
    , defined
    , undefine
    , apply
    , tryApplyD
    , allpairs
    , distrib
    , image
    , optimize
    , minimize
    , maximize
    , can
    , allsets
    , allsubsets
    , allnonemptysubsets
    , mapfilter
    , setmapfilter
    , (∅)
    , deepen, Depth(Depth)
    , testLib
    ) where

import Control.Applicative.Error (Failing(..))
import Control.Concurrent (forkIO, killThread, newEmptyMVar, putMVar, takeMVar, threadDelay)
import Control.Monad.RWS (evalRWS, runRWS, RWS)
import Data.Data (Data)
import Data.Foldable as Foldable (find, Foldable(foldr, foldr1), maximumBy)
import Data.Function (on)
import qualified Data.List as List (map)
import Data.Map.Strict as Map (delete, findMin, insert, lookup, Map, member, singleton)
import Data.Maybe (catMaybes, fromMaybe, isNothing)
import Data.Monoid ((<>))
import Data.Sequence as Seq ((><), Seq, singleton, viewl, ViewL(EmptyL, (:<)))
import Data.Set as Set (delete, empty, fold, fromList, insert, minView, Set, singleton, union)
import qualified Data.Set as Set (map)
import Data.Time.Clock (DiffTime, diffUTCTime, getCurrentTime, NominalDiffTime)
import Data.Typeable (Typeable)
import Debug.Trace (trace)
import Prelude (($), (++), (.), (<$>), all, any, Bool(..), const, Either(..), Enum(toEnum, succ, fromEnum), Eq((==)), flip, Fractional((/)), fst, Functor(fmap), Int, IO, mapM_, maybe, Maybe(..), Monad(..), Monoid(mempty), Num((-)), Ord((>), compare), Ordering, Rational, Read, realToFrac, Show(show), String, Traversable(mapM), unlines)
import Prelude hiding (map)
import System.IO (hPutStrLn, stderr)
import Test.HUnit (assertEqual, Test(TestCase, TestLabel, TestList))
import Text.PrettyPrint.HughesPJClass (comma, Doc, fsep, Pretty(pPrint), punctuate, space, text)

type ErrorMsg = String

failing :: ([String] -> b) -> (a -> b) -> Failing a -> b
failing f _ (Failure errs) = f errs
failing _ f (Success a)    = f a

  Declare a Monad instance for Failing so we can chain a series of
instance Monad Failing where
  return = Success
  m >>= f =
      case m of
        (Failure errs) -> (Failure errs)
        (Success a) -> f a
  fail errMsg = Failure [errMsg]

deriving instance Typeable Failing
deriving instance Data a => Data (Failing a)
deriving instance Read a => Read (Failing a)
deriving instance Eq a => Eq (Failing a)
deriving instance Ord a => Ord (Failing a)

instance Pretty a => Pretty (Failing a) where
    pPrint (Failure ss) = text (unlines ("Failures:" : List.map ("  " ++) ss))
    pPrint (Success a) = pPrint a

class Foldable c => SetLike c where
    slView :: forall a. c a -> Maybe (a, c a)
    slMap :: forall a b. Ord b => (a -> b) -> c a -> c b
    slUnion :: Ord a => c a -> c a -> c a
    slEmpty :: c a
    slSingleton :: a -> c a

instance SetLike Set where
    slView = Set.minView
    slMap = Set.map
    slUnion = Set.union
    slEmpty = Set.empty
    slSingleton = Set.singleton

instance SetLike [] where
    slView [] = Nothing
    slView (h : t) = Just (h, t)
    slMap = List.map
    slUnion = (<>)
    slEmpty = mempty
    slSingleton = (: [])

instance SetLike Seq where
    slView s = case viewl s of
               EmptyL -> Nothing
               h :< t -> Just (h, t)
    slMap = fmap
    slUnion = (><)
    slEmpty = mempty
    slSingleton = Seq.singleton

slInsert :: (SetLike set, Ord a) => a -> set a -> set a
slInsert x s = slUnion (slSingleton x) s

prettyFoldable :: (Foldable t, Pretty a) => t a -> Doc
prettyFoldable s = fsep (punctuate (comma <> space) (List.map pPrint (Foldable.foldr (:) [] s)))

instance ( Pretty a , SetLike set ) = > Pretty ( set a ) where

(∅) :: (Monoid (c a), SetLike c) => c a
(∅) = mempty

setAny :: Foldable t => (a -> Bool) -> t a -> Bool
setAny = any

setAll :: Foldable t => (a -> Bool) -> t a -> Bool
setAll = all

flatten :: Ord a => Set (Set a) -> Set a
flatten ss' = Set.fold Set.union Set.empty ss'


 ( * = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * ) 
 ( * Misc library functions to set up a nice environment .                       * ) 
 ( * = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * ) 

 let identity x = x ; ; 

 let ( * * ) = fun f g x - > f(g x ) ; ; 

 ( * GCD and LCM on arbitrary - precision numbers .                                * ) 

 let  n1 n2 = 
   abs_num(num_of_big_int 
       ( Big_int.gcd_big_int ( big_int_of_num n1 ) ( big_int_of_num n2 ) ) ) ; ; 

 let lcm_num n1 n2 = abs_num(n1 * / n2 ) //  n1 n2 ; ; 

 ( * A useful idiom for " non contradictory " etc .                                * ) 

 let non p x = not(p x ) ; ; 

 ( * Kind of assertion checking .                                                * ) 

 let check p x = if  ) then x else failwith " check " ; ; 

 ( * Repetition of a function .                                                  * ) 

 let rec funpow n f x = 
   if n < 1 then x else funpow ( n-1 ) f ( f x ) ; ; 

(* ========================================================================= *)
(* Misc library functions to set up a nice environment.                      *)
(* ========================================================================= *)

let identity x = x;;

let ( ** ) = fun f g x -> f(g x);;

(* GCD and LCM on arbitrary-precision numbers.                               *)

let gcd_num n1 n2 =
  abs_num(num_of_big_int
      (Big_int.gcd_big_int (big_int_of_num n1) (big_int_of_num n2)));;

let lcm_num n1 n2 = abs_num(n1 */ n2) // gcd_num n1 n2;;

(* A useful idiom for "non contradictory" etc.                               *)

let non p x = not(p x);;

(* Kind of assertion checking.                                               *)

let check p x = if p(x) then x else failwith "check";;

(* Repetition of a function.                                                 *)

let rec funpow n f x =
  if n < 1 then x else funpow (n-1) f (f x);;
-}
can :: (t -> Failing a) -> t -> Bool
can f x = failing (const True) (const False) (f x)


 let rec repeat f x = try repeat f ( f x ) with Failure _ - > x ; ; 

 ( * Handy list operations .                                                     * ) 



 let rec map2 f l1 l2 = 
   match ( l1,l2 ) with 
     [ ] , [ ] - > [ ] 
   | ( h1::t1),(h2::t2 ) - > let h = f h1 h2 in h::(map2 f t1 t2 ) 
   | _ - > failwith " map2 : length mismatch " ; ; 

 let rev = 
   let rec rev_append acc l = 
     match l with 
       [ ] - > acc 
     | h::t - > rev_append ( h::acc ) t in 
   fun l - > rev_append [ ] l ; ; 

 let hd l = 
   match l with 
    h::t - > h 
   | _ - > failwith " hd " ; ; 

 let tl l = 
   match l with 
    h::t - > t 
   | _ - > failwith " tl " ; ; 

let rec repeat f x = try repeat f (f x) with Failure _ -> x;;

(* Handy list operations.                                                    *)



let rec map2 f l1 l2 =
  match (l1,l2) with
    [],[] -> []
  | (h1::t1),(h2::t2) -> let h = f h1 h2 in h::(map2 f t1 t2)
  | _ -> failwith "map2: length mismatch";;

let rev =
  let rec rev_append acc l =
    match l with
      [] -> acc
    | h::t -> rev_append (h::acc) t in
  fun l -> rev_append [] l;;

let hd l =
  match l with
   h::t -> h
  | _ -> failwith "hd";;

let tl l =
  match l with
   h::t -> t
  | _ -> failwith "tl";;
-}


itlist :: Foldable t => (a -> b -> b) -> t a -> b -> b
itlist f xs z = Foldable.foldr f z xs

end_itlist :: Foldable t => (a -> a -> a) -> t a -> a
end_itlist = Foldable.foldr1

itlist2 :: (SetLike s, SetLike t) =>
           (a -> b -> Failing r -> Failing r) ->
           s a -> t b -> Failing r -> Failing r
itlist2 f s t r =
    case (slView s, slView t) of
      (Nothing, Nothing) -> r
      (Just (a, s'), Just (b, t')) ->
          f a b (itlist2 f s' t' r)
      _ -> Failure ["itlist2"]

exists :: Foldable t => (a -> Bool) -> t a -> Bool
exists = any

 let partition p l = 
     itlist ( fun a ( yes , no ) - > if p a then a::yes , no else yes , a::no ) l ( [ ] , [ ] ) ; ; 

 let filter p l = fst(partition p l ) ; ; 

 let length = 
   let rec len k l = 
     if l = [ ] then k else len ( k + 1 ) ( tl l ) in 
   fun l - > len 0 l ; ; 

 let rec last l = 
   match l with 
     [ x ] - > x 
   | ( h::t ) - > last t 
   | [ ] - > failwith " last " ; ; 

 let rec butlast l = 
   match l with 
     [ _ ] - > [ ] 
   | ( h::t ) - > h::(butlast t ) 
   | [ ] - > failwith " butlast " ; ; 

 let rec find p l = 
   match l with 
       [ ] - > failwith " find " 
     | ( h::t ) - > if p(h ) then h else find p t ; ; 

 let rec el n l = 
   if n = 0 then hd l else  ( n - 1 ) ( tl l ) ; ; 

 let map f = 
   let rec  l = 
     match l with 
       [ ] - > [ ] 
     | ( x::t ) - > let y = f x in y::(mapf t ) in 
   mapf ; ; 

let partition p l =
    itlist (fun a (yes,no) -> if p a then a::yes,no else yes,a::no) l ([],[]);;

let filter p l = fst(partition p l);;

let length =
  let rec len k l =
    if l = [] then k else len (k + 1) (tl l) in
  fun l -> len 0 l;;

let rec last l =
  match l with
    [x] -> x
  | (h::t) -> last t
  | [] -> failwith "last";;

let rec butlast l =
  match l with
    [_] -> []
  | (h::t) -> h::(butlast t)
  | [] -> failwith "butlast";;

let rec find p l =
  match l with
      [] -> failwith "find"
    | (h::t) -> if p(h) then h else find p t;;

let rec el n l =
  if n = 0 then hd l else el (n - 1) (tl l);;

let map f =
  let rec mapf l =
    match l with
      [] -> []
    | (x::t) -> let y = f x in y::(mapf t) in
  mapf;;
-}


allpairs :: forall a b c set. (SetLike set, Ord c) => (a -> b -> c) -> set a -> set b -> set c
allpairs f xs ys = Foldable.foldr (\ x zs -> Foldable.foldr (g x) zs ys) slEmpty xs
    where g :: a -> b -> set c -> set c
          g x y zs' = slInsert (f x y) zs'

distrib :: Ord a => Set (Set a) -> Set (Set a) -> Set (Set a)
distrib s1 s2 = allpairs (Set.union) s1 s2

test01 :: Test
test01 = TestCase $ assertEqual "allpairs" expected input
    where input = allpairs (,) (Set.fromList [1,2,3]) (Set.fromList [4,5,6])
          expected = Set.fromList [(1,4),(1,5),(1,6),(2,4),(2,5),(2,6),(3,4),(3,5),(3,6)] :: Set (Int, Int)


 let rec distinctpairs l = 
   match l with 
    x::t - > itlist ( fun y a - > ( x , y ) : : a ) t ( distinctpairs t ) 
   | [ ] - > [ ] ; ; 

 let rec chop_list n l = 
   if n = 0 then [ ] , l else 
   try let m , l ' = chop_list ( n-1 ) ( tl l ) in (   , l ' 
   with Failure _ - > failwith " chop_list " ; ; 

 let replicate n a = map ( fun x - > a ) ( 1 - -n ) ; ; 

 let rec insertat i x l = 
   if i = 0 then x::l else 
   match l with 
     [ ] - > failwith " insertat : list too short for position to exist " 
   | h::t - > h::(insertat ( i-1 ) x t ) ; ; 

 let rec forall2 p l1 l2 = 
   match ( l1,l2 ) with 
     [ ] , [ ] - > true 
   | ( h1::t1,h2::t2 ) - > p h1 h2 & forall2 p t1 t2 
   | _ - > false ; ; 

 let index x = 
   let rec ind n l = 
     match l with 
       [ ] - > failwith " index " 
     | ( h::t ) - > if Pervasives.compare x h = 0 then n else ind ( n + 1 ) t in 
   ind 0 ; ; 

 let rec unzip l = 
   match l with 
     [ ] - > [ ] , [ ] 
   | ( x , y)::t - > 
       let xs , ys = unzip t in x::xs ,   ; 

 ( * Whether the first of two items comes earlier in the list .                  * ) 

 let rec earlier l x y = 
   match l with 
     h::t - > ( Pervasives.compare h y < > 0 ) & 
             ( Pervasives.compare h x = 0 or earlier t x y ) 
   | [ ] - > false ; ; 

 ( * Application of ( presumably imperative ) function over a list .               * ) 

 let rec do_list f l = 
   match l with 
     [ ] - > ( ) 
   | h::t - > f(h ) ; do_list f t ; ; 

 ( * Association lists .                                                         * ) 

 let rec assoc a l = 
   match l with 
     ( x , y)::t - > if Pervasives.compare x a = 0 then y else assoc a t 
   | [ ] - > failwith " find " ; ; 

 let rec rev_assoc a l = 
   match l with 
     ( x , y)::t - > if Pervasives.compare y a = 0 then x else rev_assoc a t 
   | [ ] - > failwith " find " ; ; 

 ( * Merging of sorted lists ( maintaining repetitions ) .                         * ) 

 let rec merge  l1 l2 = 
   match l1 with 
     [ ] - > l2 
   | h1::t1 - > match l2 with 
                 [ ] - > l1 
               | h2::t2 - > if ord h1 h2 then h1::(merge ord t1 l2 ) 
                           else h2::(merge ord l1 t2 ) ; ; 

 ( * Bottom - up mergesort .                                                       * ) 

 let sort ord = 
   let rec  l1 l2 = 
     match ( l1,l2 ) with 
         ( [ s ] , [ ] ) - > s 
       | ( l , [ ] ) - >  [ ] l 
       | ( l,[s1 ] ) - >  ( s1::l ) [ ] 
       | ( l,(s1::s2::ss ) ) - >  ( ( merge ord s1 s2)::l ) ss in 
   fun l - > if l = [ ] then [ ] else  [ ] ( map ( fun x - > [ x ] ) l ) ; ; 

 ( * Common measure predicates to use with " sort " .                              * ) 

 let increasing f x y = Pervasives.compare ( f x ) ( f y ) < 0 ; ; 

 let decreasing f x y = Pervasives.compare ( f x ) ( f y ) > 0 ; ; 

 ( * Eliminate repetitions of adjacent elements , with and without counting .     * ) 

 let rec uniq l = 
   match l with 
     x::(y : : _ as t ) - > let t ' = uniq t in 
                       if Pervasives.compare x y = 0 then t ' else 
                       if t'==t then l else x::t ' 
  | _ - > l ; ; 

 let repetitions = 
   let rec repcount n l = 
     match l with 
       x::(y : : _ as ys ) - > if Pervasives.compare y x = 0 then repcount ( n + 1 ) ys 
                   else ( x , n)::(repcount 1 ys ) 
     | [ x ] - > [ x , n ] 
     | [ ] - > failwith " repcount " in 
   fun l - > if l = [ ] then [ ] else repcount 1 l ; ; 

let rec distinctpairs l =
  match l with
   x::t -> itlist (fun y a -> (x,y) :: a) t (distinctpairs t)
  | [] -> [];;

let rec chop_list n l =
  if n = 0 then [],l else
  try let m,l' = chop_list (n-1) (tl l) in (hd l)::m,l'
  with Failure _ -> failwith "chop_list";;


let rec insertat i x l =
  if i = 0 then x::l else
  match l with
    [] -> failwith "insertat: list too short for position to exist"
  | h::t -> h::(insertat (i-1) x t);;

let rec forall2 p l1 l2 =
  match (l1,l2) with
    [],[] -> true
  | (h1::t1,h2::t2) -> p h1 h2 & forall2 p t1 t2
  | _ -> false;;

let index x =
  let rec ind n l =
    match l with
      [] -> failwith "index"
    | (h::t) -> if Pervasives.compare x h = 0 then n else ind (n + 1) t in
  ind 0;;

let rec unzip l =
  match l with
    [] -> [],[]
  | (x,y)::t ->
      let xs,ys = unzip t in x::xs,y::ys;;

(* Whether the first of two items comes earlier in the list.                 *)

let rec earlier l x y =
  match l with
    h::t -> (Pervasives.compare h y <> 0) &
            (Pervasives.compare h x = 0 or earlier t x y)
  | [] -> false;;

(* Application of (presumably imperative) function over a list.              *)

let rec do_list f l =
  match l with
    [] -> ()
  | h::t -> f(h); do_list f t;;

(* Association lists.                                                        *)

let rec assoc a l =
  match l with
    (x,y)::t -> if Pervasives.compare x a = 0 then y else assoc a t
  | [] -> failwith "find";;

let rec rev_assoc a l =
  match l with
    (x,y)::t -> if Pervasives.compare y a = 0 then x else rev_assoc a t
  | [] -> failwith "find";;

(* Merging of sorted lists (maintaining repetitions).                        *)

let rec merge ord l1 l2 =
  match l1 with
    [] -> l2
  | h1::t1 -> match l2 with
                [] -> l1
              | h2::t2 -> if ord h1 h2 then h1::(merge ord t1 l2)
                          else h2::(merge ord l1 t2);;

(* Bottom-up mergesort.                                                      *)

let sort ord =
  let rec mergepairs l1 l2 =
    match (l1,l2) with
        ([s],[]) -> s
      | (l,[]) -> mergepairs [] l
      | (l,[s1]) -> mergepairs (s1::l) []
      | (l,(s1::s2::ss)) -> mergepairs ((merge ord s1 s2)::l) ss in
  fun l -> if l = [] then [] else mergepairs [] (map (fun x -> [x]) l);;

(* Common measure predicates to use with "sort".                             *)

let increasing f x y = Pervasives.compare (f x) (f y) < 0;;

let decreasing f x y = Pervasives.compare (f x) (f y) > 0;;

(* Eliminate repetitions of adjacent elements, with and without counting.    *)

let rec uniq l =
  match l with
    x::(y::_ as t) -> let t' = uniq t in
                      if Pervasives.compare x y = 0 then t' else
                      if t'==t then l else x::t'
 | _ -> l;;

let repetitions =
  let rec repcount n l =
    match l with
      x::(y::_ as ys) -> if Pervasives.compare y x = 0 then repcount (n + 1) ys
                  else (x,n)::(repcount 1 ys)
    | [x] -> [x,n]
    | [] -> failwith "repcount" in
  fun l -> if l = [] then [] else repcount 1 l;;
-}

tryfind :: Foldable t => (a -> Failing r) -> t a -> Failing r
tryfind p s = maybe (Failure ["tryfind"]) p (find (failing (const False) (const True) . p) s)

evalRS :: RWS r () s a -> r -> s -> a
evalRS action r s = fst $ evalRWS action r s

runRS :: RWS r () s a -> r -> s -> (a, s)
runRS action r s = (\(a, s', _w) -> (a, s')) $ runRWS action r s

test02 :: Test
test02 =
    TestCase $
    assertEqual
      "tryfind on infinite list"
      (Success 3 :: Failing Int)
      (tryfind (\x -> if x == 3
                      then Success 3
                      else Failure ["test02"]) ([1..] :: [Int]))

settryfind :: (t -> Failing a) -> Set t -> Failing a
settryfind f l =
    case Set.minView l of
      Nothing -> Failure ["settryfind"]
      Just (h, t) -> failing (\ _ -> settryfind f t) Success (f h)

mapfilter :: (a -> Failing b) -> [a] -> [b]
mapfilter f l = catMaybes (List.map (failing (const Nothing) Just . f) l)

setmapfilter :: Ord b => (a -> Failing b) -> Set a -> Set b
setmapfilter f s = Set.fold (\ a r -> failing (const r) (`Set.insert` r) (f a)) Set.empty s


optimize :: forall s a b. (SetLike s, Foldable s) => (b -> b -> Ordering) -> (a -> b) -> s a -> Maybe a
optimize _ _ l | isNothing (slView l) = Nothing
optimize ord f l = Just (Foldable.maximumBy (ord `on` f) l)

maximize :: (Ord b, SetLike s, Foldable s) => (a -> b) -> s a -> Maybe a
maximize = optimize compare

minimize :: (Ord b, SetLike s, Foldable s) => (a -> b) -> s a -> Maybe a
minimize = optimize (flip compare)


 let    let rec canonical lis = 
      match lis with 
        x::(y : : _ as rest ) - > Pervasives.compare x y < 0 & canonical rest 
      | _ - > true in 
   fun l - > if canonical l then l 
            else uniq ( sort ( fun x y - > Pervasives.compare x y < = 0 ) l ) ; ; 

 let union = 
   let rec union l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > l2 
       | ( l1 , [ ] ) - > l1 
       | ( ( h1::t1 as  as l2 ) ) - > 
           if h1 = h2 then h1::(union t1 t2 ) 
           else if h1 < h2 then h1::(union t1 l2 ) 
           else h2::(union l1 t2 ) in 
   fun s1 s2 - > union (   ) ( setify s2 ) ; ; 

 let intersect = 
   let rec intersect l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > [ ] 
       | ( l1 , [ ] ) - > [ ] 
       | ( ( h1::t1 as  as l2 ) ) - > 
           if h1 = h2 then h1::(intersect t1 t2 ) 
           else if h1 < h2 then intersect t1 l2 
           else intersect l1 t2 in 
   fun s1 s2 - > intersect (   ) ( setify s2 ) ; ; 

 let subtract = 
   let rec subtract l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > [ ] 
       | ( l1 , [ ] ) - > l1 
       | ( ( h1::t1 as  as l2 ) ) - > 
           if h1 = h2 then subtract t1 t2 
           else if h1 < h2 then h1::(subtract t1 l2 ) 
           else subtract l1 t2 in 
   fun s1 s2 - > subtract (   ) ( setify s2 ) ; ; 

 let subset , psubset = 
   let rec subset l1 l2 = 
     match ( l1,l2 ) with 
         ( [ ] , l2 ) - > true 
       | ( l1 , [ ] ) - > false 
       | ( h1::t1,h2::t2 ) - > 
           if h1 = h2 then subset t1 t2 
           else if h1 < h2 then false 
           else subset l1 t2 
   and psubset l1 l2 = 
     match ( l1,l2 ) with 
         ( l1 , [ ] ) - > false 
       | ( [ ] , l2 ) - > true 
       | ( h1::t1,h2::t2 ) - > 
           if h1 = h2 then psubset t1 t2 
           else if h1 < h2 then false 
           else subset l1 t2 in 
   ( fun s1 s2 - > subset (   ) ( setify s2 ) ) , 
   ( fun s1 s2 - > psubset (   ) ( setify s2 ) ) ; ; 

 let rec set_eq s1 s2 = (    setify s2 ) ; ; 

 let insert x s = union [ x ] s ; ; 

let setify =
  let rec canonical lis =
     match lis with
       x::(y::_ as rest) -> Pervasives.compare x y < 0 & canonical rest
     | _ -> true in
  fun l -> if canonical l then l
           else uniq (sort (fun x y -> Pervasives.compare x y <= 0) l);;

let union =
  let rec union l1 l2 =
    match (l1,l2) with
        ([],l2) -> l2
      | (l1,[]) -> l1
      | ((h1::t1 as l1),(h2::t2 as l2)) ->
          if h1 = h2 then h1::(union t1 t2)
          else if h1 < h2 then h1::(union t1 l2)
          else h2::(union l1 t2) in
  fun s1 s2 -> union (setify s1) (setify s2);;

let intersect =
  let rec intersect l1 l2 =
    match (l1,l2) with
        ([],l2) -> []
      | (l1,[]) -> []
      | ((h1::t1 as l1),(h2::t2 as l2)) ->
          if h1 = h2 then h1::(intersect t1 t2)
          else if h1 < h2 then intersect t1 l2
          else intersect l1 t2 in
  fun s1 s2 -> intersect (setify s1) (setify s2);;

let subtract =
  let rec subtract l1 l2 =
    match (l1,l2) with
        ([],l2) -> []
      | (l1,[]) -> l1
      | ((h1::t1 as l1),(h2::t2 as l2)) ->
          if h1 = h2 then subtract t1 t2
          else if h1 < h2 then h1::(subtract t1 l2)
          else subtract l1 t2 in
  fun s1 s2 -> subtract (setify s1) (setify s2);;

let subset,psubset =
  let rec subset l1 l2 =
    match (l1,l2) with
        ([],l2) -> true
      | (l1,[]) -> false
      | (h1::t1,h2::t2) ->
          if h1 = h2 then subset t1 t2
          else if h1 < h2 then false
          else subset l1 t2
  and psubset l1 l2 =
    match (l1,l2) with
        (l1,[]) -> false
      | ([],l2) -> true
      | (h1::t1,h2::t2) ->
          if h1 = h2 then psubset t1 t2
          else if h1 < h2 then false
          else subset l1 t2 in
  (fun s1 s2 -> subset (setify s1) (setify s2)),
  (fun s1 s2 -> psubset (setify s1) (setify s2));;

let rec set_eq s1 s2 = (setify s1 = setify s2);;

let insert x s = union [x] s;;
-}

image :: (Ord b, Ord a) => (a -> b) -> Set a -> Set b
image f s = Set.map f s


 ( * Union of a family of sets .                                                 * ) 

 let unions s =  ( @ ) s [ ] ) ; ; 

 ( * List membership . This does * not * assume the list is a set .                 * ) 

 let rec mem x lis = 
   match lis with 
     [ ] - > false 
   | ( h::t ) - > Pervasives.compare x h = 0 or mem x t ; ; 

(* Union of a family of sets.                                                *)

let unions s = setify(itlist (@) s []);;

(* List membership. This does *not* assume the list is a set.                *)

let rec mem x lis =
  match lis with
    [] -> false
  | (h::t) -> Pervasives.compare x h = 0 or mem x t;;
-}


  allsets : :  a = > Int - > Set a - > Set ( Set a )
allsets :: forall a b. (Num a, Eq a, Ord b) => a -> Set b -> Set (Set b)
allsets 0 _ = Set.singleton Set.empty
allsets m l =
    case Set.minView l of
      Nothing -> Set.empty
      Just (h, t) -> Set.union (Set.map (Set.insert h) (allsets (m - 1) t)) (allsets m t)

allsubsets :: forall a. Ord a => Set a -> Set (Set a)
allsubsets s =
    maybe (Set.singleton Set.empty)
          (\ (x, t) ->
               let res = allsubsets t in
               Set.union res (Set.map (Set.insert x) res))
          (Set.minView s)


allnonemptysubsets :: forall a. Ord a => Set a -> Set (Set a)
allnonemptysubsets s = Set.delete Set.empty (allsubsets s)


 ( * Explosion and implosion of strings .                                        * ) 

 let explode s = 
   let rec exap n l = 
      if n < 0 then l else 
       exap ( n - 1 ) ( ( String.sub s n 1)::l ) in 
   exap ( String.length s - 1 ) [ ] ; ; 

 let implode l = itlist ( ^ ) l " " ; ; 

 ( * Timing ; useful for documentation but not logically necessary .              * ) 

 let time f x = 
   let start_time = Sys.time ( ) in 
   let result = f x in 
   let finish_time = Sys.time ( ) in 
   print_string 
     ( " CPU time ( user ): " ^(string_of_float(finish_time - . start_time ) ) ) ; 
   print_newline ( ) ; 
   result ; ; 

(* Explosion and implosion of strings.                                       *)

let explode s =
  let rec exap n l =
     if n < 0 then l else
      exap (n - 1) ((String.sub s n 1)::l) in
  exap (String.length s - 1) [];;

let implode l = itlist (^) l "";;

(* Timing; useful for documentation but not logically necessary.             *)

let time f x =
  let start_time = Sys.time() in
  let result = f x in
  let finish_time = Sys.time() in
  print_string
    ("CPU time (user): "^(string_of_float(finish_time -. start_time)));
  print_newline();
  result;;
-}

  | Perform an IO operation and return the elapsed time along with the result .
timeComputation :: IO r -> IO (r, NominalDiffTime)
timeComputation a = do
  start <- getCurrentTime
  r <- a
  end <- getCurrentTime
  return (r, diffUTCTime end start)

timeMessage :: (r -> NominalDiffTime -> String) -> IO r -> IO r
timeMessage pp a = do
  (r, e) <- timeComputation a
  hPutStrLn stderr (pp r e)
  return r

time :: IO r -> IO r
time a = timeMessage (\_ e -> "Computation time: " ++ show e) a

timeout :: String -> DiffTime -> IO r -> IO (Either String r)
timeout message delay a = do
  compete [threadDelay (fromEnum (realToFrac (delay / 1e6) :: Rational)) >> return (Left message),
           Right <$> a]

  | Run several IO operations in parallel , return the result of the
compete :: [IO a] -> IO a
compete actions = do
  mvar <- newEmptyMVar
  tids <- mapM (\action -> forkIO $ action >>= putMVar mvar) actions
  result <- takeMVar mvar
  mapM_ killThread tids
  return result

  | Polymorphic finite partial functions via  trees .
  Idea due to     ( OCaml list , 2003/11/10 ) .
data Func a b
    = Empty
    | Leaf Int [(a, b)]
    | Branch Int Int (Func a b) (Func a b)

undefinedFunction :: Func a b
undefinedFunction = Empty


isUndefined :: Func a b -> Bool
isUndefined Empty = True
isUndefined _ = False


mapf :: (b -> c) -> Func a b -> Func a c
mapf f t =
    case t of
      Empty -> Empty
      Leaf h l -> Leaf h (map_list f l)
      Branch p b l r -> Branch p b (mapf f l) (mapf f r)
    where
      map_list f' l' =
          case l' of
            [] -> []
            (x,y) : t' -> (x, f' y) : map_list f' t'

  Operations analogous to " fold " for lists .

foldlFn :: (r -> a -> b -> r) -> r -> Func a b -> r
foldlFn f a t =
    case t of
      Empty -> a
      Leaf _h l -> foldl_list f a l
      Branch _p _b l r -> foldlFn f (foldlFn f a l) r
    where
      foldl_list _f a' l =
          case l of
            [] -> a'
            (x,y) : t' -> foldl_list f (f a' x y) t'

foldrFn :: (a -> b -> r -> r) -> Func a b -> r -> r
foldrFn f t a =
    case t of
      Empty -> a
      Leaf _h l -> foldr_list f l a
      Branch _p _b l r -> foldrFn f l (foldrFn f r a)
    where
      foldr_list f' l a' =
          case l of
            [] -> a'
            (x, y) : t' -> f' x y (foldr_list f' t' a')


graph :: (Ord a, Ord b) => Func a b -> Set (a, b)
graph f = Set.fromList (foldlFn (\ a x y -> (x,y) : a) [] f)

dom :: Ord a => Func a b -> Set a
dom f = Set.fromList (foldlFn (\ a x _y -> x :a) [] f)

ran :: Ord b => Func a b -> Set b
ran f = Set.fromList (foldlFn (\ a _x y -> y : a) [] f)


applyD :: Ord k => Map k a -> k -> a -> Map k a
applyD m k a = Map.insert k a m

apply :: Ord k => Map k a -> k -> Maybe a
apply m k = Map.lookup k m

tryApplyD :: Ord k => Map k a -> k -> a -> a
tryApplyD m k d = fromMaybe d (Map.lookup k m)

tryApplyL :: Ord k => Map k [a] -> k -> [a]
tryApplyL m k = tryApplyD m k []

defined :: Ord t => Map t a -> t -> Bool
defined = flip Map.member

undefine :: forall k a. Ord k => k -> Map k a -> Map k a
undefine k mp = Map.delete k mp


 ( * Redefinition and combination .                                              * ) 

 let ( |->),combine = 
   let newbranch p1 t1 p2 t2 = 
     let zp =   p2 in 
     let b = zp land ( -zp ) in 
     let p = p1 land ( b - 1 ) in 
     if p1 land b = 0 then Branch(p , b ,  ) 
     else Branch(p , b , t2,t1 ) in 
   let rec define_list ( x , y as xy ) l = 
     match l with 
       ( a , b as ab)::t - > 
           let c = Pervasives.compare x a in 
           if c = 0 then xy::t 
           else if c < 0 then xy::l 
           else ab::(define_list xy t ) 
     | [ ] - > [ xy ] 
   and combine_list op z l1 l2 = 
     match ( l1,l2 ) with 
       [ ] , _ - > l2 
     | _ , [ ] - > l1 
     | ( (  as xy1)::t1,(x2,y2 as  ) - > 
           let c = Pervasives.compare x1 x2 in 
           if c < 0 then xy1::(combine_list op z t1 l2 ) 
           else if c > 0 then xy2::(combine_list op z l1 t2 ) else 
           let y = op y1 y2 and l = combine_list op z t1 t2 in 
           if z(y ) then l else ( x1,y)::l in 
   let ( |- > ) x y = 
     let k = Hashtbl.hash x in 
     let rec upd t = 
       match t with 
         Empty - > Leaf ( k,[x , y ] ) 
         , l ) - > 
            if h = k then  , define_list ( x , y ) l ) 
            else newbranch h t k ( Leaf(k,[x , y ] ) ) 
       | Branch(p , b , l , r ) - > 
           if k land ( b - 1 ) < > p then newbranch p t k ( Leaf(k,[x , y ] ) ) 
           else if k land b = 0 then Branch(p , b , upd l , r ) 
           else Branch(p , b , l , upd r ) in 
     upd in 
   let rec combine op z t1 t2 = 
     match ( t1,t2 ) with 
       Empty , _ - > t2 
     | _ , Empty - > t1 
     | Leaf(h1,l1),Leaf(h2,l2 ) - > 
           if h1 = h2 then 
             let l = combine_list op z l1 l2 in 
             if l = [ ] then Empty else Leaf(h1,l ) 
           else newbranch h1 t1 h2 t2 
     | ( Leaf(k , lis ) as lf),(Branch(p , b , l , r ) as br ) - > 
           if k land ( b - 1 ) = p then 
             if k land b = 0 then 
               ( match combine op z lf l with 
                  Empty - > r | l ' - > Branch(p , b ,  ) ) 
             else 
               ( match combine op z lf r with 
                  Empty - > l | r ' - > Branch(p , b , l , r ' ) ) 
           else 
             newbranch k lf p br 
     | ( Branch(p , b , l , r ) as br),(Leaf(k , lis ) as lf ) - > 
           if k land ( b - 1 ) = p then 
             if k land b = 0 then 
               ( match combine op z l lf with 
                 Empty - > r | l ' - > Branch(p , b ,  ) ) 
             else 
               ( match combine op z r lf with 
                  Empty - > l | r ' - > Branch(p , b , l , r ' ) ) 
           else 
             newbranch        ) - > 
           if b1 < b2 then 
             if p2 land ( b1 - 1 ) < > p1 then newbranch p1 t1 p2 t2 
             else if p2 land b1 = 0 then 
               ( match combine op z l1 t2 with 
                  Empty - > r1 | l - > Branch(p1,b1,l , r1 ) ) 
             else 
               ( match combine op z r1 t2 with 
                  Empty - > l1 | r - > Branch(p1,b1,l1,r ) ) 
           else if b2 < b1 then 
             if p1 land ( b2 - 1 ) < > p2 then newbranch p1 t1 p2 t2 
             else if p1 land b2 = 0 then 
               ( match combine op z t1 l2 with 
                  Empty - > r2 | l - > Branch(p2,b2,l , r2 ) ) 
             else 
               ( match combine op z t1 r2 with 
                  Empty - > l2 | r - > Branch(p2,b2,l2,r ) ) 
           else if p1 = p2 then 
            ( match ( combine op z l1 l2,combine op z r1 r2 ) with 
               ( Empty , r ) - > r | ( l , Empty ) - > l | ( l , r ) - > Branch(p1,b1,l , r ) ) 
           else 
             newbranch p1 t1 p2 t2 in 
   ( |->),combine ; ; 

(* Redefinition and combination.                                             *)

let (|->),combine =
  let newbranch p1 t1 p2 t2 =
    let zp = p1 lxor p2 in
    let b = zp land (-zp) in
    let p = p1 land (b - 1) in
    if p1 land b = 0 then Branch(p,b,t1,t2)
    else Branch(p,b,t2,t1) in
  let rec define_list (x,y as xy) l =
    match l with
      (a,b as ab)::t ->
          let c = Pervasives.compare x a in
          if c = 0 then xy::t
          else if c < 0 then xy::l
          else ab::(define_list xy t)
    | [] -> [xy]
  and combine_list op z l1 l2 =
    match (l1,l2) with
      [],_ -> l2
    | _,[] -> l1
    | ((x1,y1 as xy1)::t1,(x2,y2 as xy2)::t2) ->
          let c = Pervasives.compare x1 x2 in
          if c < 0 then xy1::(combine_list op z t1 l2)
          else if c > 0 then xy2::(combine_list op z l1 t2) else
          let y = op y1 y2 and l = combine_list op z t1 t2 in
          if z(y) then l else (x1,y)::l in
  let (|->) x y =
    let k = Hashtbl.hash x in
    let rec upd t =
      match t with
        Empty -> Leaf (k,[x,y])
      | Leaf(h,l) ->
           if h = k then Leaf(h,define_list (x,y) l)
           else newbranch h t k (Leaf(k,[x,y]))
      | Branch(p,b,l,r) ->
          if k land (b - 1) <> p then newbranch p t k (Leaf(k,[x,y]))
          else if k land b = 0 then Branch(p,b,upd l,r)
          else Branch(p,b,l,upd r) in
    upd in
  let rec combine op z t1 t2 =
    match (t1,t2) with
      Empty,_ -> t2
    | _,Empty -> t1
    | Leaf(h1,l1),Leaf(h2,l2) ->
          if h1 = h2 then
            let l = combine_list op z l1 l2 in
            if l = [] then Empty else Leaf(h1,l)
          else newbranch h1 t1 h2 t2
    | (Leaf(k,lis) as lf),(Branch(p,b,l,r) as br) ->
          if k land (b - 1) = p then
            if k land b = 0 then
              (match combine op z lf l with
                 Empty -> r | l' -> Branch(p,b,l',r))
            else
              (match combine op z lf r with
                 Empty -> l | r' -> Branch(p,b,l,r'))
          else
            newbranch k lf p br
    | (Branch(p,b,l,r) as br),(Leaf(k,lis) as lf) ->
          if k land (b - 1) = p then
            if k land b = 0 then
              (match combine op z l lf with
                Empty -> r | l' -> Branch(p,b,l',r))
            else
              (match combine op z r lf with
                 Empty -> l | r' -> Branch(p,b,l,r'))
          else
            newbranch p br k lf
    | Branch(p1,b1,l1,r1),Branch(p2,b2,l2,r2) ->
          if b1 < b2 then
            if p2 land (b1 - 1) <> p1 then newbranch p1 t1 p2 t2
            else if p2 land b1 = 0 then
              (match combine op z l1 t2 with
                 Empty -> r1 | l -> Branch(p1,b1,l,r1))
            else
              (match combine op z r1 t2 with
                 Empty -> l1 | r -> Branch(p1,b1,l1,r))
          else if b2 < b1 then
            if p1 land (b2 - 1) <> p2 then newbranch p1 t1 p2 t2
            else if p1 land b2 = 0 then
              (match combine op z t1 l2 with
                 Empty -> r2 | l -> Branch(p2,b2,l,r2))
            else
              (match combine op z t1 r2 with
                 Empty -> l2 | r -> Branch(p2,b2,l2,r))
          else if p1 = p2 then
           (match (combine op z l1 l2,combine op z r1 r2) with
              (Empty,r) -> r | (l,Empty) -> l | (l,r) -> Branch(p1,b1,l,r))
          else
            newbranch p1 t1 p2 t2 in
  (|->),combine;;
-}


(|=>) :: Ord k => k -> a -> Map k a
x |=> y = Map.singleton x y


(|->) :: Ord k => k -> a -> Map k a -> Map k a
(|->) = Map.insert

fpf :: Ord a => Map a b -> a -> Maybe b
fpf = flip Map.lookup


choose :: Map k a -> (k, a)
choose = Map.findMin


 ( * Install a ( trivial ) printer for finite partial functions .                  * ) 

 let print_fpf ( f:('a,'b)func ) = print_string " < func > " ; ; 

 # install_printer print_fpf ; ; 

 ( * Related stuff for standard functions .                                      * ) 

 let  a y f x = if x = a then y else f(x ) ; ; 

 let undef x = failwith " undefined function " ; ; 

 ( * Union - find algorithm .                                                      * ) 

 type ( ' a)pnode = Nonterminal of ' a | Terminal of ' a * int ; ; 

 type ( ' a)partition = Partition of ( ' a,('a)pnode)func ; ; 

 let rec terminus ( Partition f as ptn ) a = 
   match ( apply f a ) with 
     Nonterminal(b ) - > terminus ptn b 
   | Terminal(p , q ) - > ( p , q ) ; ; 

 let tryterminus ptn a = 
   try terminus ptn a with Failure _ - > ( a,1 ) ; ; 

 let canonize ptn a = fst(tryterminus ptn a ) ; ; 

 let equivalent eqv a b = canonize eqv a = canonize eqv b ; ; 

 let equate ( a , b ) ( Partition f as ptn ) = 
   let ( a',na ) = tryterminus ptn a 
   and ( b',nb ) = tryterminus ptn b in 
   Partition 
    ( if a ' = b ' then f else 
     if na < = nb then 
        itlist identity [ a ' |- > Nonterminal b ' ; b ' |- > Terminal(b',na+nb ) ] f 
     else 
        itlist identity [ b ' |- > Nonterminal a ' ; a ' |- > Terminal(a',na+nb ) ] f ) ; ; 

 let unequal = Partition undefined ; ; 

 let equated ( Partition f ) = dom f ; ; 

 ( * First number starting at n for which p succeeds .                           * ) 

 let rec first n p = if p(n ) then n else first ( n + / Int 1 ) p ; ; 

(* Install a (trivial) printer for finite partial functions.                 *)

let print_fpf (f:('a,'b)func) = print_string "<func>";;

#install_printer print_fpf;;

(* Related stuff for standard functions.                                     *)

let valmod a y f x = if x = a then y else f(x);;

let undef x = failwith "undefined function";;

(* Union-find algorithm.                                                     *)

type ('a)pnode = Nonterminal of 'a | Terminal of 'a * int;;

type ('a)partition = Partition of ('a,('a)pnode)func;;

let rec terminus (Partition f as ptn) a =
  match (apply f a) with
    Nonterminal(b) -> terminus ptn b
  | Terminal(p,q) -> (p,q);;

let tryterminus ptn a =
  try terminus ptn a with Failure _ -> (a,1);;

let canonize ptn a = fst(tryterminus ptn a);;

let equivalent eqv a b = canonize eqv a = canonize eqv b;;

let equate (a,b) (Partition f as ptn) =
  let (a',na) = tryterminus ptn a
  and (b',nb) = tryterminus ptn b in
  Partition
   (if a' = b' then f else
    if na <= nb then
       itlist identity [a' |-> Nonterminal b'; b' |-> Terminal(b',na+nb)] f
    else
       itlist identity [b' |-> Nonterminal a'; a' |-> Terminal(a',na+nb)] f);;

let unequal = Partition undefined;;

let equated (Partition f) = dom f;;

(* First number starting at n for which p succeeds.                          *)

let rec first n p = if p(n) then n else first (n +/ Int 1) p;;
-}

deepen :: (Depth -> Failing t) -> Depth -> Maybe Depth -> Failing (t, Depth)
deepen _ n (Just m) | n > m = Failure ["Exceeded maximum depth limit"]
deepen f n m =
    let n' = maybe (trace ("Searching with depth limit " ++ show n) n) (\_ -> n) m in
    case f n' of
      Failure _ -> deepen f (succ n) m
      Success x -> Success (x, n)

newtype Depth = Depth Int deriving (Eq, Ord, Show)

instance Enum Depth where
    toEnum = Depth
    fromEnum (Depth n) = n

instance Pretty Depth where
    pPrint = text . show

testLib :: Test
testLib = TestLabel "Lib" (TestList [test01])
