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+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+%
+\section[ListSetOps]{Set-like operations on lists}
+
+\begin{code}
+module ListSetOps (
+	unionLists, minusList, insertList,
+
+	-- Association lists
+	Assoc, assoc, assocMaybe, assocUsing, assocDefault, assocDefaultUsing,
+	emptyAssoc, unitAssoc, mapAssoc, plusAssoc_C, extendAssoc_C,
+	mkLookupFun, findInList, assocElts,
+
+	-- Duplicate handling
+	hasNoDups, runs, removeDups, findDupsEq, 
+	equivClasses, equivClassesByUniq
+
+   ) where
+
+#include "HsVersions.h"
+
+import Outputable
+import Unique	( Unique )
+import UniqFM	( eltsUFM, emptyUFM, addToUFM_C )
+import Util	( isn'tIn, isIn, mapAccumR, sortLe )
+import List	( partition )
+\end{code}
+
+
+%************************************************************************
+%*									*
+	Treating lists as sets
+	Assumes the lists contain no duplicates, but are unordered
+%*									*
+%************************************************************************
+
+\begin{code}
+insertList :: Eq a => a -> [a] -> [a]
+-- Assumes the arg list contains no dups; guarantees the result has no dups
+insertList x xs | isIn "insert" x xs = xs
+	    | otherwise		 = x : xs
+
+unionLists :: (Eq a) => [a] -> [a] -> [a]
+-- Assumes that the arguments contain no duplicates
+unionLists xs ys = [x | x <- xs, isn'tIn "unionLists" x ys] ++ ys
+
+minusList :: (Eq a) => [a] -> [a] -> [a]
+-- Everything in the first list that is not in the second list:
+minusList xs ys = [ x | x <- xs, isn'tIn "minusList" x ys]
+\end{code}
+
+
+%************************************************************************
+%*									*
+\subsection[Utils-assoc]{Association lists}
+%*									*
+%************************************************************************
+
+Inefficient finite maps based on association lists and equality.
+
+\begin{code}
+type Assoc a b = [(a,b)]	-- A finite mapping based on equality and association lists
+
+emptyAssoc	  :: Assoc a b
+unitAssoc	  :: a -> b -> Assoc a b
+assocElts	  :: Assoc a b -> [(a,b)]
+assoc		  :: (Eq a) => String -> Assoc a b -> a -> b
+assocDefault	  :: (Eq a) => b -> Assoc a b -> a -> b
+assocUsing	  :: (a -> a -> Bool) -> String -> Assoc a b -> a -> b
+assocMaybe	  :: (Eq a) => Assoc a b -> a -> Maybe b
+assocDefaultUsing :: (a -> a -> Bool) -> b -> Assoc a b -> a -> b
+mapAssoc	  :: (b -> c) -> Assoc a b -> Assoc a c
+extendAssoc_C	  :: (Eq a) => (b -> b -> b) -> Assoc a b -> (a,b)     -> Assoc a b
+plusAssoc_C	  :: (Eq a) => (b -> b -> b) -> Assoc a b -> Assoc a b -> Assoc a b
+	-- combining fn takes (old->new->result)
+
+emptyAssoc    = []
+unitAssoc a b = [(a,b)]
+assocElts xs  = xs
+
+assocDefaultUsing eq deflt ((k,v) : rest) key
+  | k `eq` key = v
+  | otherwise  = assocDefaultUsing eq deflt rest key
+
+assocDefaultUsing eq deflt [] key = deflt
+
+assoc crash_msg         list key = assocDefaultUsing (==) (panic ("Failed in assoc: " ++ crash_msg)) list key
+assocDefault deflt      list key = assocDefaultUsing (==) deflt list key
+assocUsing eq crash_msg list key = assocDefaultUsing eq (panic ("Failed in assoc: " ++ crash_msg)) list key
+
+assocMaybe alist key
+  = lookup alist
+  where
+    lookup []		  = Nothing
+    lookup ((tv,ty):rest) = if key == tv then Just ty else lookup rest
+
+mapAssoc f alist = [(key, f val) | (key,val) <- alist]
+
+plusAssoc_C combine []  new = new	-- Shortcut for common case
+plusAssoc_C combine old new = foldl (extendAssoc_C combine) old new
+
+extendAssoc_C combine old_list (new_key, new_val)
+  = go old_list
+  where
+    go [] = [(new_key, new_val)]
+    go ((old_key, old_val) : old_list) 
+	| new_key == old_key = ((old_key, old_val `combine` new_val) : old_list)
+	| otherwise	     = (old_key, old_val) : go old_list
+\end{code}
+
+
+@mkLookupFun eq alist@ is a function which looks up
+its argument in the association list @alist@, returning a Maybe type.
+@mkLookupFunDef@ is similar except that it is given a value to return
+on failure.
+
+\begin{code}
+mkLookupFun :: (key -> key -> Bool)	-- Equality predicate
+	    -> [(key,val)] 		-- The assoc list
+	    -> key 			-- The key
+	    -> Maybe val		-- The corresponding value
+
+mkLookupFun eq alist s
+  = case [a | (s',a) <- alist, s' `eq` s] of
+      []    -> Nothing
+      (a:_) -> Just a
+
+findInList :: (a -> Bool) -> [a] -> Maybe a
+findInList p [] = Nothing
+findInList p (x:xs) | p x	= Just x
+		    | otherwise = findInList p xs
+\end{code}
+
+
+%************************************************************************
+%*									*
+\subsection[Utils-dups]{Duplicate-handling}
+%*									*
+%************************************************************************
+
+\begin{code}
+hasNoDups :: (Eq a) => [a] -> Bool
+
+hasNoDups xs = f [] xs
+  where
+    f seen_so_far []     = True
+    f seen_so_far (x:xs) = if x `is_elem` seen_so_far then
+				False
+			   else
+				f (x:seen_so_far) xs
+
+    is_elem = isIn "hasNoDups"
+\end{code}
+
+\begin{code}
+equivClasses :: (a -> a -> Ordering) 	-- Comparison
+	     -> [a]
+	     -> [[a]]
+
+equivClasses cmp stuff@[]     = []
+equivClasses cmp stuff@[item] = [stuff]
+equivClasses cmp items
+  = runs eq (sortLe le items)
+  where
+    eq a b = case cmp a b of { EQ -> True; _ -> False }
+    le a b = case cmp a b of { LT -> True; EQ -> True; GT -> False }
+\end{code}
+
+The first cases in @equivClasses@ above are just to cut to the point
+more quickly...
+
+@runs@ groups a list into a list of lists, each sublist being a run of
+identical elements of the input list. It is passed a predicate @p@ which
+tells when two elements are equal.
+
+\begin{code}
+runs :: (a -> a -> Bool) 	-- Equality
+     -> [a]
+     -> [[a]]
+
+runs p []     = []
+runs p (x:xs) = case (span (p x) xs) of
+		  (first, rest) -> (x:first) : (runs p rest)
+\end{code}
+
+\begin{code}
+removeDups :: (a -> a -> Ordering) 	-- Comparison function
+	   -> [a]
+	   -> ([a], 	-- List with no duplicates
+	       [[a]])	-- List of duplicate groups.  One representative from
+			-- each group appears in the first result
+
+removeDups cmp []  = ([], [])
+removeDups cmp [x] = ([x],[])
+removeDups cmp xs
+  = case (mapAccumR collect_dups [] (equivClasses cmp xs)) of { (dups, xs') ->
+    (xs', dups) }
+  where
+    collect_dups dups_so_far [x]         = (dups_so_far,      x)
+    collect_dups dups_so_far dups@(x:xs) = (dups:dups_so_far, x)
+
+findDupsEq :: (a->a->Bool) -> [a] -> [[a]]
+findDupsEq eq [] = []
+findDupsEq eq (x:xs) | null eq_xs  = findDupsEq eq xs
+		     | otherwise   = (x:eq_xs) : findDupsEq eq neq_xs
+		     where
+		       (eq_xs, neq_xs) = partition (eq x) xs
+\end{code}
+
+
+\begin{code}
+equivClassesByUniq :: (a -> Unique) -> [a] -> [[a]]
+	-- NB: it's *very* important that if we have the input list [a,b,c],
+	-- where a,b,c all have the same unique, then we get back the list
+	-- 	[a,b,c]
+	-- not
+	--	[c,b,a]
+	-- Hence the use of foldr, plus the reversed-args tack_on below
+equivClassesByUniq get_uniq xs
+  = eltsUFM (foldr add emptyUFM xs)
+  where
+    add a ufm = addToUFM_C tack_on ufm (get_uniq a) [a]
+    tack_on old new = new++old
+\end{code}
+
+