1 files changed, 44 insertions, 0 deletions
diff --git a/utils/ext-core/Env.hs b/utils/ext-core/Env.hs
new file mode 100644
index 0000000000..6f6973c558
--- /dev/null
+++ b/utils/ext-core/Env.hs
@@ -0,0 +1,44 @@
+{- Environments.
+   Uses lists for simplicity and to make the semantics clear.
+   A real implementation should use balanced trees or hash tables.
+-}
+
+module Env (Env,
+	    eempty,
+	    elookup,
+	    eextend,
+            edomain,
+	    efromlist,
+	    efilter,
+	    eremove)
+where
+
+import List
+
+data Env a b = Env [(a,b)] 
+ deriving (Show)
+
+eempty :: Env a b 
+eempty = Env []
+
+{- In case of duplicates, returns most recently added entry. -}
+elookup :: (Eq a) => Env a b -> a -> Maybe b
+elookup (Env l) k = lookup k l 
+
+{- May hide existing entries. -}
+eextend :: Env a b -> (a,b) -> Env a b
+eextend (Env l) (k,d) = Env ((k,d):l)
+
+edomain :: (Eq a) => Env a b -> [a]
+edomain (Env l) = nub (map fst l)
+
+{- In case of duplicates, first entry hides others. -}
+efromlist :: [(a,b)] -> Env a b
+efromlist l = Env l
+
+eremove :: (Eq a)  => Env a b -> a -> Env a b
+eremove (Env l) k = Env (filter ((/= k).fst) l)
+
+efilter :: Env a b -> (a -> Bool) -> Env a b
+efilter (Env l) p = Env (filter (p.fst) l)
+