+
+%************************************************************************
+%* *
+\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
+\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 (sortLt lt items)
+ where
+ eq a b = case cmp a b of { EQ -> True; _ -> False }
+ lt a b = case cmp a b of { LT -> True; _ -> 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.
+