--- a/src/list_util.sml	Sat Jun 13 15:42:24 2009 -0400
+++ b/src/list_util.sml	Tue Jun 16 14:38:01 2009 -0400
@@ -123,6 +123,24 @@
         fm ([], s)
     end
 
+fun foldlMapiPartial f s =
+    let
+        fun fm (n, ls', s) ls =
+            case ls of
+                nil => (rev ls', s)
+              | h :: t =>
+                let
+                    val (h', s') = f (n, h, s)
+                    val ls' = case h' of
+                                  NONE => ls'
+                                | SOME h' => h' :: ls'
+                in
+                    fm (n + 1, ls', s') t
+                end
+    in
+        fm (0, [], s)
+    end
+
 fun foldlMapAbort f s =
     let
         fun fm (ls', s) ls =
@@ -172,6 +190,19 @@
         m 0 []
     end
 
+fun mapiPartial f =
+    let
+        fun m i acc ls =
+            case ls of
+                [] => rev acc
+              | h :: t =>
+                m (i + 1) (case f (i, h) of
+                               NONE => acc
+                             | SOME v => v :: acc) t
+    in
+        m 0 []
+    end
+
 fun appi f =
     let
         fun m i ls =