[project @ 2004-02-24 15:57:52 by simonpj]

[ghc-hetmet.git] / ghc / compiler / utils / ListSetOps.lhs

diff --git a/ghc/compiler/utils/ListSetOps.lhs b/ghc/compiler/utils/ListSetOps.lhs
index db43da5..8d4912d 100644 (file)
--- a/ghc/compiler/utils/ListSetOps.lhs
+++ b/ghc/compiler/utils/ListSetOps.lhs
@@ -5,7 +5,7 @@
 
 \begin{code}
 module ListSetOps (
-       unionLists, minusList,
+       unionLists, minusList, insertList,
 
        -- Association lists
        Assoc, assoc, assocMaybe, assocUsing, assocDefault, assocDefaultUsing,
@@ -30,22 +30,24 @@ import List ( union )
 
 %************************************************************************
 %*                                                                     *
-\subsection{Treating lists as sets}
+       Treating lists as sets
+       Assumes the lists contain no duplicates, but are unordered
 %*                                                                     *
 %************************************************************************
 
 \begin{code}
-unionLists :: (Eq a) => [a] -> [a] -> [a]
-unionLists = union
-\end{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
 
-Everything in the first list that is not in the second list:
+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
 
-\begin{code}
 minusList :: (Eq a) => [a] -> [a] -> [a]
-minusList xs ys = [ x | x <- xs, x `not_elem` ys]
-  where
-    not_elem = isn'tIn "minusList"
+-- 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}