changed names of resource-1.3; added a note on homepage on release

1 files changed, 676 insertions, 0 deletions

diff --git a/src/GF/Data/Operations.hs b/src/GF/Data/Operations.hs
new file mode 100644
index 000000000..253723876
--- /dev/null
+++ b/src/GF/Data/Operations.hs
@@ -0,0 +1,676 @@
+----------------------------------------------------------------------
+-- |
+-- Module      : Operations
+-- Maintainer  : AR
+-- Stability   : (stable)
+-- Portability : (portable)
+--
+-- > CVS $Date: 2005/11/11 16:12:41 $ 
+-- > CVS $Author: bringert $
+-- > CVS $Revision: 1.22 $
+--
+-- some auxiliary GF operations. AR 19\/6\/1998 -- 6\/2\/2001
+--
+-- Copyright (c) Aarne Ranta 1998-2000, under GNU General Public License (see GPL)
+-----------------------------------------------------------------------------
+
+module GF.Data.Operations (-- * misc functions
+		   ifNull, onSnd,
+
+		   -- * the Error monad
+		   Err(..), err, maybeErr, testErr, errVal, errIn, derrIn,
+		   performOps, repeatUntilErr, repeatUntil, okError, isNotError,
+		   showBad, lookupErr, lookupErrMsg, lookupDefault, updateLookupList,
+		   mapPairListM, mapPairsM, pairM, mapErr, mapErrN, foldErr,
+		   (!?), errList, singleton, mapsErr, mapsErrTree,
+		   
+		   -- ** checking
+		   checkUnique, titleIfNeeded, errMsg, errAndMsg,
+
+		   -- * a three-valued maybe type to express indirections
+		   Perhaps(..), yes, may, nope,
+		   mapP,
+		   unifPerhaps, updatePerhaps, updatePerhapsHard,
+
+		   -- * binary search trees; now with FiniteMap
+		   BinTree, emptyBinTree, isInBinTree, justLookupTree,
+		   lookupTree, lookupTreeMany, lookupTreeManyAll, updateTree,
+		   buildTree, filterBinTree,
+		   sorted2tree, mapTree, mapMTree, tree2list,
+ 
+
+		   -- * parsing
+		   WParser, wParseResults, paragraphs,
+
+		   -- * printing
+		   indent, (+++), (++-), (++++), (+++++),
+		   prUpper, prReplicate, prTList, prQuotedString, prParenth, prCurly, 
+		   prBracket, prArgList, prSemicList, prCurlyList, restoreEscapes,
+		   numberedParagraphs, prConjList, prIfEmpty, wrapLines,
+
+		   -- ** LaTeX code producing functions
+		   dollar, mbox, ital, boldf, verbat, mkLatexFile, 
+		   begindocument, enddocument,
+
+		   -- * extra
+		   sortByLongest, combinations, mkTextFile, initFilePath,
+
+		   -- * topological sorting with test of cyclicity
+		   topoTest, topoSort, cyclesIn,
+
+		   -- * the generic fix point iterator
+		   iterFix,
+
+		   -- * association lists
+		   updateAssoc, removeAssoc,
+
+		   -- * chop into separator-separated parts
+		   chunks, readIntArg, subSequences,
+
+		   -- * state monad with error; from Agda 6\/11\/2001
+		   STM(..), appSTM, stm, stmr, readSTM, updateSTM, writeSTM, done,
+
+		   -- * error monad class
+		   ErrorMonad(..), checkAgain, checks, allChecks, doUntil
+                
+		  ) where
+
+import Data.Char (isSpace, toUpper, isSpace, isDigit)
+import Data.List (nub, sortBy, sort, deleteBy, nubBy)
+--import Data.FiniteMap
+import Control.Monad (liftM,liftM2, MonadPlus, mzero, mplus)
+
+import GF.Data.ErrM
+
+infixr 5 +++
+infixr 5 ++-
+infixr 5 ++++
+infixr 5 +++++
+infixl 9 !?
+
+ifNull :: b -> ([a] -> b) -> [a] -> b
+ifNull b f xs = if null xs then b else f xs
+
+onSnd :: (a -> b) -> (c,a) -> (c,b)
+onSnd f (x, y) = (x, f y)
+
+-- the Error monad
+
+-- | analogue of @maybe@
+err :: (String -> b) -> (a -> b) -> Err a -> b 
+err d f e = case e of
+  Ok a -> f a
+  Bad s -> d s
+
+-- | add msg s to @Maybe@ failures
+maybeErr :: String -> Maybe a -> Err a
+maybeErr s = maybe (Bad s) Ok
+
+testErr :: Bool -> String -> Err ()
+testErr cond msg = if cond then return () else Bad msg
+
+errVal :: a -> Err a -> a
+errVal a = err (const a) id
+
+errIn :: String -> Err a -> Err a
+errIn msg = err (\s -> Bad (s ++++ "OCCURRED IN" ++++ msg)) return
+
+-- | used for extra error reports when developing GF
+derrIn :: String -> Err a -> Err a
+derrIn m = errIn m -- id
+
+performOps :: [a -> Err a] -> a -> Err a
+performOps ops a = case ops of
+  f:fs -> f a >>= performOps fs
+  [] -> return a
+
+repeatUntilErr :: (a -> Bool) -> (a -> Err a) -> a -> Err a
+repeatUntilErr cond f a = if cond a then return a else f a >>= repeatUntilErr cond f
+
+repeatUntil :: (a -> Bool) -> (a -> a) -> a -> a
+repeatUntil cond f a = if cond a then a else repeatUntil cond f (f a)
+
+okError :: Err a -> a
+-- okError = err (error "no result Ok") id
+okError = err (error . ("Bad result occurred" ++++)) id
+
+isNotError :: Err a -> Bool
+isNotError = err (const False) (const True)
+
+showBad :: Show a => String -> a -> Err b
+showBad s a = Bad (s +++ show a)
+
+lookupErr :: (Eq a,Show a) => a -> [(a,b)] -> Err b
+lookupErr a abs = maybeErr ("Unknown" +++ show a) (lookup a abs)
+
+lookupErrMsg :: (Eq a,Show a) => String -> a -> [(a,b)] -> Err b
+lookupErrMsg m a abs = maybeErr (m +++ "gave unknown" +++ show a) (lookup a abs)
+
+lookupDefault :: Eq a => b -> a -> [(a,b)] -> b
+lookupDefault d x l = maybe d id $  lookup x l 
+
+updateLookupList ::  Eq a => (a,b) -> [(a,b)] -> [(a,b)]
+updateLookupList ab abs = insert ab [] abs where
+ insert c cc [] = cc ++ [c]
+ insert (a,b) cc ((a',b'):cc') = if   a == a' 
+                                 then cc ++ [(a,b)] ++ cc'
+                                 else insert (a,b) (cc ++ [(a',b')]) cc'
+
+mapPairListM :: Monad m => ((a,b) -> m c) -> [(a,b)] -> m [(a,c)]
+mapPairListM f xys = mapM (\ p@(x,_) -> liftM ((,) x) (f p)) xys
+
+mapPairsM :: Monad m => (b -> m c) -> [(a,b)] -> m [(a,c)]
+mapPairsM f xys = mapM (\ (x,y) -> liftM ((,) x) (f y)) xys
+
+pairM :: Monad a => (b -> a c) -> (b,b) -> a (c,c)
+pairM op (t1,t2) = liftM2 (,) (op t1) (op t2)
+
+-- | like @mapM@, but continue instead of halting with 'Err'
+mapErr :: (a -> Err b) -> [a] -> Err ([b], String) 
+mapErr f xs = Ok (ys, unlines ss) 
+  where
+    (ys,ss) = ([y | Ok y <- fxs], [s | Bad s <- fxs])
+    fxs = map f xs
+
+-- | alternative variant, peb 9\/6-04
+mapErrN :: Int -> (a -> Err b) -> [a] -> Err ([b], String)
+mapErrN maxN f xs = Ok (ys, unlines (errHdr : ss2)) 
+  where
+    (ys, ss) = ([y | Ok y <- fxs], [s | Bad s <- fxs])
+    errHdr = show nss ++ " errors occured" ++ 
+	     if nss > maxN then ", showing the first " ++ show maxN else ""
+    ss2 = map ("* "++) $ take maxN ss 
+    nss = length ss
+    fxs = map f xs
+
+
+-- | like @foldM@, but also return the latest value if fails
+foldErr :: (a -> b -> Err a) -> a -> [b] -> Err (a, Maybe String)
+foldErr f s xs = case xs of
+  [] -> return (s,Nothing)
+  x:xx -> case f s x of
+    Ok v  -> foldErr f v xx
+    Bad m -> return $ (s, Just m)
+
+-- @!!@ with the error monad
+(!?) :: [a] -> Int -> Err a
+xs !? i = foldr (const . return) (Bad "too few elements in list") $ drop i xs
+
+errList :: Err [a] -> [a]
+errList = errVal []
+
+singleton :: a -> [a]
+singleton = (:[])
+
+-- checking
+
+checkUnique :: (Show a, Eq a) => [a] -> [String]
+checkUnique ss = ["overloaded" +++ show s | s <- nub overloads] where
+  overloads = filter overloaded ss
+  overloaded s = length (filter (==s) ss) > 1
+
+titleIfNeeded :: a -> [a] -> [a]
+titleIfNeeded a [] = []
+titleIfNeeded a as = a:as
+
+errMsg :: Err a -> [String]
+errMsg (Bad m) = [m]
+errMsg _ = []
+
+errAndMsg :: Err a -> Err (a,[String])
+errAndMsg (Bad m) = Bad m
+errAndMsg (Ok a) = return (a,[])
+
+-- | a three-valued maybe type to express indirections
+data Perhaps a b = Yes a | May b | Nope deriving (Show,Read,Eq,Ord)
+
+yes :: a -> Perhaps a b
+yes = Yes
+
+may :: b -> Perhaps a b
+may = May
+
+nope :: Perhaps a b
+nope = Nope
+
+mapP :: (a -> c) -> Perhaps a b -> Perhaps c b
+mapP f p = case p of
+  Yes a -> Yes (f a)
+  May b -> May b
+  Nope  -> Nope
+
+-- | this is what happens when matching two values in the same module
+unifPerhaps :: (Eq a, Eq b, Show a, Show b) => 
+               Perhaps a b -> Perhaps a b -> Err (Perhaps a b)
+unifPerhaps p1 p2 = case (p1,p2) of
+  (Nope, _)  -> return p2
+  (_, Nope)  -> return p1
+  _ -> if p1==p2 then return p1 
+                 else Bad ("update conflict between" ++++ show p1 ++++ show p2)
+
+-- | this is what happens when updating a module extension
+updatePerhaps :: (Eq a,Eq b, Show a, Show b) => 
+                 b -> Perhaps a b -> Perhaps a b -> Err (Perhaps a b)
+updatePerhaps old p1 p2 = case (p1,p2) of
+  (Yes a,    Nope)  -> return $ may old
+  (May older,Nope)  -> return $ may older
+  (_, May a)        -> Bad "strange indirection"
+  _ -> unifPerhaps p1 p2
+
+-- | here the value is copied instead of referred to; used for oper types
+updatePerhapsHard :: (Eq a, Eq b, Show a, Show b) => b -> 
+                     Perhaps a b -> Perhaps a b -> Err (Perhaps a b)
+updatePerhapsHard old p1 p2 = case (p1,p2) of
+  (Yes a,    Nope)  -> return $ yes a
+  (May older,Nope)  -> return $ may older
+  (_, May a)        -> Bad "strange indirection"
+  _ -> unifPerhaps p1 p2
+
+-- binary search trees
+--- FiniteMap implementation is slower in crucial tests
+
+data BinTree a b = NT | BT (a,b) !(BinTree a b) !(BinTree a b) deriving (Show)
+-- type BinTree a b = FiniteMap a b
+
+emptyBinTree :: BinTree a b
+emptyBinTree = NT
+-- emptyBinTree = emptyFM
+
+isInBinTree :: (Ord a) => a -> BinTree a b -> Bool
+isInBinTree x = err (const False) (const True) .  justLookupTree x
+-- isInBinTree = elemFM
+
+justLookupTree :: (Monad m,Ord a) => a -> BinTree a b -> m b
+justLookupTree = lookupTree (const [])
+
+lookupTree :: (Monad m,Ord a) => (a -> String) -> a -> BinTree a b -> m b
+lookupTree pr x tree = case tree of
+ NT -> fail ("no occurrence of element" +++ pr x)
+ BT (a,b) left right 
+   | x < a  -> lookupTree pr x left
+   | x > a  -> lookupTree pr x right
+   | x == a -> return b
+--lookupTree pr x tree = case lookupFM tree x of
+--  Just y -> return y
+--  _ -> fail ("no occurrence of element" +++ pr x)
+
+lookupTreeMany :: Ord a => (a -> String) -> [BinTree a b] -> a -> Err b
+lookupTreeMany pr (t:ts) x = case lookupTree pr x t of
+  Ok v -> return v
+  _ -> lookupTreeMany pr ts x
+lookupTreeMany pr [] x = Bad $ "failed to find" +++ pr x
+
+lookupTreeManyAll :: Ord a => (a -> String) -> [BinTree a b] -> a -> [b]
+lookupTreeManyAll pr (t:ts) x = case lookupTree pr x t of
+  Ok v -> v : lookupTreeManyAll pr ts x
+  _ -> lookupTreeManyAll pr ts x
+lookupTreeManyAll pr [] x = []
+
+-- | destructive update
+updateTree :: (Ord a) => (a,b) -> BinTree a b -> BinTree a b
+-- updateTree (a,b) tr = addToFM tr a b
+updateTree = updateTreeGen True
+
+-- | destructive or not
+updateTreeGen :: (Ord a) => Bool -> (a,b) -> BinTree a b -> BinTree a b
+updateTreeGen destr z@(x,y) tree = case tree of
+ NT -> BT z NT NT
+ BT c@(a,b) left right 
+   | x < a  -> let left' = updateTree z left in   BT c left' right 
+   | x > a  -> let right' = updateTree z right in BT c left right' 
+   | otherwise -> if destr
+                    then BT z left right -- removing the old value of a
+                    else tree            -- retaining the old value if one exists
+
+buildTree :: (Ord a) => [(a,b)] -> BinTree a b
+buildTree = sorted2tree . sortBy fs where
+  fs (x,_) (y,_) 
+    | x < y = LT
+    | x > y = GT
+    | True  = EQ 
+-- buildTree = listToFM
+
+sorted2tree :: Ord a => [(a,b)] -> BinTree a b
+sorted2tree [] = NT
+sorted2tree xs = BT x (sorted2tree t1) (sorted2tree t2) where
+  (t1,(x:t2)) = splitAt (length xs `div` 2) xs
+--sorted2tree = listToFM
+
+--- dm less general than orig
+mapTree :: ((a,b) -> (a,c)) -> BinTree a b -> BinTree a c
+mapTree f NT = NT
+mapTree f (BT a left right) = BT (f a) (mapTree f left) (mapTree f right)
+--mapTree f = mapFM (\k v -> snd (f (k,v)))
+
+--- fm less efficient than orig?
+mapMTree :: (Ord a,Monad m) => ((a,b) -> m (a,c)) -> BinTree a b -> m (BinTree a c)
+mapMTree f NT = return NT
+mapMTree f (BT a left right) = do
+  a'     <- f a
+  left'  <- mapMTree f left 
+  right' <- mapMTree f right
+  return $ BT a' left' right'
+--mapMTree f t = liftM listToFM $ mapM f $ fmToList t
+
+filterBinTree :: Ord a => (a -> b -> Bool) -> BinTree a b -> BinTree a b
+-- filterFM f t
+filterBinTree f = sorted2tree . filter (uncurry f) . tree2list
+
+tree2list :: BinTree a b -> [(a,b)] -- inorder
+tree2list NT = []
+tree2list (BT z left right) = tree2list left ++ [z] ++ tree2list right
+--tree2list = fmToList
+
+-- parsing
+
+type WParser a b = [a] -> [(b,[a])] -- old Wadler style parser
+
+wParseResults :: WParser a b -> [a] -> [b]
+wParseResults p aa = [b | (b,[]) <- p aa]
+
+paragraphs :: String -> [String]
+paragraphs = map unlines . chop . lines where
+  chop [] = []
+  chop ss = let (ps,rest) = break empty ss in ps : chop (dropWhile empty rest)
+  empty = all isSpace
+
+-- printing
+
+indent :: Int -> String -> String
+indent i s = replicate i ' ' ++ s
+
+(+++), (++-), (++++), (+++++) :: String -> String -> String
+a +++ b   = a ++ " "    ++ b
+a ++- ""  = a 
+a ++- b   = a +++ b
+a ++++ b  = a ++ "\n"   ++ b
+a +++++ b = a ++ "\n\n" ++ b
+
+prUpper :: String -> String
+prUpper s = s1 ++ s2' where
+ (s1,s2) = span isSpace s
+ s2' = case s2 of
+   c:t -> toUpper c : t
+   _ -> s2
+
+prReplicate :: Int -> String -> String
+prReplicate n s = concat (replicate n s)
+
+prTList :: String -> [String] -> String
+prTList t ss = case ss of
+  []   -> ""
+  [s]  -> s
+  s:ss -> s ++ t ++ prTList t ss
+
+prQuotedString :: String -> String
+prQuotedString x = "\"" ++ restoreEscapes x ++ "\""
+
+prParenth :: String -> String
+prParenth s = if s == "" then "" else "(" ++ s ++ ")"
+
+prCurly, prBracket :: String -> String
+prCurly   s = "{" ++ s ++ "}"
+prBracket s = "[" ++ s ++ "]"
+
+prArgList, prSemicList, prCurlyList :: [String] -> String
+prArgList   = prParenth . prTList "," 
+prSemicList = prTList " ; "
+prCurlyList = prCurly . prSemicList
+
+restoreEscapes :: String -> String
+restoreEscapes s = 
+  case s of 
+    []       -> []
+    '"' : t  -> '\\' : '"'  : restoreEscapes t
+    '\\': t  -> '\\' : '\\' : restoreEscapes t
+    c   : t  -> c : restoreEscapes t
+
+numberedParagraphs :: [[String]] -> [String]
+numberedParagraphs t = case t of 
+  []   -> []
+  p:[] -> p
+  _    -> concat [(show n ++ ".") : s | (n,s) <- zip [1..] t]
+
+prConjList :: String -> [String] -> String
+prConjList c []     = ""
+prConjList c [s]    = s
+prConjList c [s,t]  = s +++ c +++ t
+prConjList c (s:tt) = s ++ "," +++ prConjList c tt
+
+prIfEmpty :: String -> String -> String -> String -> String
+prIfEmpty em _    _    [] = em
+prIfEmpty em nem1 nem2 s  = nem1 ++ s ++ nem2
+
+-- | Thomas Hallgren's wrap lines
+wrapLines :: Int -> String -> String
+wrapLines n "" = ""
+wrapLines n s@(c:cs) =
+      if isSpace c
+      then c:wrapLines (n+1) cs
+      else case lex s of
+            [(w,rest)] -> if n'>=76
+                          then '\n':w++wrapLines l rest
+                          else w++wrapLines n' rest
+               where n' = n+l
+                     l = length w
+            _ -> s -- give up!!
+
+--- optWrapLines = if argFlag "wraplines" True then wrapLines 0 else id
+
+-- LaTeX code producing functions
+dollar, mbox, ital, boldf, verbat :: String -> String
+dollar s = '$' : s ++ "$"
+mbox s   = "\\mbox{" ++ s ++ "}"
+ital s   = "{\\em" +++ s ++ "}"
+boldf s  = "{\\bf" +++ s ++ "}"
+verbat s = "\\verbat!" ++ s ++ "!"
+
+mkLatexFile :: String -> String
+mkLatexFile s = begindocument +++++ s +++++ enddocument
+
+begindocument, enddocument :: String
+begindocument =
+ "\\documentclass[a4paper,11pt]{article}" ++++ -- M.F. 25/01-02
+ "\\setlength{\\parskip}{2mm}" ++++
+ "\\setlength{\\parindent}{0mm}" ++++
+ "\\setlength{\\oddsidemargin}{0mm}" ++++
+ ("\\setlength{\\evensidemargin}{"++"-2mm}") ++++ -- peb 27/5-04: to prevent hugs-mode 
+ ("\\setlength{\\topmargin}{"++"-8mm}") ++++      -- from treating the rest as comments
+ "\\setlength{\\textheight}{240mm}" ++++
+ "\\setlength{\\textwidth}{158mm}" ++++
+ "\\begin{document}\n"
+enddocument =
+ "\n\\end{document}\n"
+
+
+sortByLongest :: [[a]] -> [[a]]
+sortByLongest = sortBy longer where
+ longer x y 
+  | x' > y' = LT
+  | x' < y' = GT
+  | True    = EQ
+  where
+   x' = length x
+   y' = length y
+
+-- | 'combinations' is the same as @sequence@!!!
+-- peb 30\/5-04
+combinations :: [[a]] -> [[a]]
+combinations t = case t of 
+  []    -> [[]]
+  aa:uu -> [a:u | a <- aa, u <- combinations uu]
+
+
+mkTextFile :: String -> IO ()
+mkTextFile name = do
+  s <- readFile name
+  let s' = prelude name ++ "\n\n" ++ heading name  ++ "\n" ++ object s
+  writeFile (name ++ ".hs") s'
+ where
+   prelude name = "module " ++ name ++ " where" 
+   heading name = "txt" ++ name ++ " ="
+   object s = mk s ++ " \"\""
+   mk s = unlines ["  \"" ++ escs line ++ "\" ++ \"\\n\" ++" | line <- lines s]
+   escs s = case s of
+     c:cs | elem c "\"\\" -> '\\' : c : escs cs
+     c:cs -> c : escs cs
+     _ -> s
+
+initFilePath :: FilePath -> FilePath
+initFilePath f = reverse (dropWhile (/='/') (reverse f))
+
+-- | topological sorting with test of cyclicity
+topoTest :: Eq a => [(a,[a])] -> Either [a] [[a]]
+topoTest g = if length g' == length g then Left g' else Right (cyclesIn g ++[[]]) 
+  where
+    g' = topoSort g
+  
+cyclesIn :: Eq a => [(a,[a])] -> [[a]]
+cyclesIn deps = nubb $ clean $ filt $ iterFix findDep immediate where
+  immediate = [[y,x] | (x,xs) <- deps, y <- xs] 
+  findDep chains = [y:x:chain | 
+                      x:chain <- chains, (x',xs) <- deps, x' == x, y <- xs, 
+                      notElem y (init chain)]
+
+  clean = map remdup
+  nubb = nubBy (\x y -> y == reverse x) 
+  filt = filter (\xs -> last xs == head xs)
+  remdup (x:xs) = x : remdup xs' where xs' = dropWhile (==x) xs
+  remdup [] = []
+
+
+-- | topological sorting 
+topoSort :: Eq a => [(a,[a])] -> [a]
+topoSort g = reverse $ tsort 0 [ffs | ffs@(f,_) <- g, inDeg f == 0] [] where
+  tsort _ []     r = r
+  tsort k (ffs@(f,fs) : cs) r
+    | elem f r  = tsort k cs r
+    | k > lx    = r  
+    | otherwise = tsort (k+1) cs (f : tsort (k+1) (info fs) r)
+  info hs = [(f,fs) | (f,fs) <- g, elem f hs]
+  inDeg f = length [t | (h,hs) <- g, t <- hs, t == f]
+  lx = length g
+
+-- | the generic fix point iterator
+iterFix :: Eq a => ([a] -> [a]) -> [a] -> [a]
+iterFix more start = iter start start 
+  where
+    iter old new = if (null new')
+                      then old
+                      else iter (new' ++ old) new'
+      where
+        new' = filter (`notElem` old) (more new)
+
+-- association lists
+
+updateAssoc :: Eq a => (a,b) -> [(a,b)] -> [(a,b)]
+updateAssoc ab@(a,b) as = case as of
+  (x,y): xs | x == a -> (a,b):xs
+  xy   : xs          -> xy : updateAssoc ab xs
+  []                 -> [ab]
+
+removeAssoc :: Eq a => a -> [(a,b)] -> [(a,b)]
+removeAssoc a = filter ((/=a) . fst)
+
+-- | chop into separator-separated parts
+chunks :: Eq a => a -> [a] -> [[a]]
+chunks sep ws = case span (/= sep) ws of
+  (a,_:b) -> a : bs where bs = chunks sep b
+  (a, []) -> if null a then [] else [a]
+
+readIntArg :: String -> Int
+readIntArg n = if (not (null n) && all isDigit n) then read n else 0
+
+
+-- state monad with error; from Agda 6/11/2001
+
+newtype STM s a = STM (s -> Err (a,s)) 
+
+appSTM :: STM s a -> s -> Err (a,s)
+appSTM (STM f) s = f s
+
+stm :: (s -> Err (a,s)) -> STM s a
+stm = STM
+
+stmr :: (s -> (a,s)) -> STM s a
+stmr f = stm (\s -> return (f s))
+
+instance  Monad (STM s) where
+  return a    = STM (\s -> return (a,s))
+  STM c >>= f = STM (\s -> do 
+                        (x,s') <- c s
+                        let STM f' = f x
+                        f' s')
+
+readSTM :: STM s s
+readSTM = stmr (\s -> (s,s))
+
+updateSTM :: (s -> s) -> STM s () 
+updateSTM f = stmr (\s -> ((),f s))
+
+writeSTM :: s -> STM s ()
+writeSTM s = stmr (const ((),s))
+
+done :: Monad m => m ()
+done = return ()
+
+class Monad m => ErrorMonad m where
+  raise   :: String -> m a
+  handle  :: m a -> (String -> m a) -> m a
+  handle_ :: m a -> m a -> m a
+  handle_ a b =  a `handle` (\_ -> b)
+
+instance ErrorMonad Err where
+  raise  = Bad
+  handle a@(Ok _) _ = a
+  handle (Bad i) f  = f i
+
+instance ErrorMonad (STM s) where
+  raise msg = STM (\s -> raise msg)
+  handle (STM f) g = STM (\s -> (f s) 
+                                `handle` (\e -> let STM g' = (g e) in
+                                                    g' s))
+
+-- error recovery with multiple reporting AR 30/5/2008
+mapsErr :: (a -> Err b) -> [a] -> Err [b]
+
+mapsErr f = seqs . map f where
+  seqs es = case es of
+    Ok v : ms -> case seqs ms of
+      Ok vs -> return (v : vs)
+      b     -> b
+    Bad s : ms -> case seqs ms of
+      Ok vs  -> Bad s
+      Bad ss -> Bad (s +++++ ss)
+    [] -> return []
+
+mapsErrTree :: (Ord a) => ((a,b) -> Err (a,c)) -> BinTree a b -> Err (BinTree a c)
+mapsErrTree f t =  mapsErr f (tree2list t) >>= return . sorted2tree
+
+
+-- | if the first check fails try another one
+checkAgain :: ErrorMonad m => m a -> m a -> m a
+checkAgain c1 c2 = handle_ c1 c2
+
+checks :: ErrorMonad m => [m a] -> m a
+checks [] = raise "no chance to pass"
+checks cs = foldr1 checkAgain cs
+
+allChecks :: ErrorMonad m => [m a] -> m [a]
+allChecks ms = case ms of
+  (m: ms) -> let rs = allChecks ms in handle_ (liftM2 (:) m rs) rs
+  _ -> return []
+
+doUntil :: ErrorMonad m => (a -> Bool) -> [m a] -> m a
+doUntil cond ms = case ms of
+  a:as -> do
+    v <- a
+    if cond v then return v else doUntil cond as
+  _ -> raise "no result"
+
+-- subsequences sorted from longest to shortest ; their number is 2^n
+subSequences :: [a] -> [[a]]
+subSequences = sortBy (\x y -> compare (length y) (length x)) . subs where
+  subs xs = case xs of
+    [] -> [[]]
+    x:xs -> let xss = subs xs in [x:y | y <- xss] ++ xss