cherry pick changes to the lists lib

lib/lists.trp

@@ -9,8 +9,6 @@ let fun map f list =
             |  (x::xs) => (f (j,x)) :: (mapj (j+1) xs)
     in mapj 0 list
     end
-
-
 
     fun foldl f y [] = y
       | foldl f y (x::xs) = foldl f (f (x,y)) xs
@@ -58,6 +56,28 @@ let fun map f list =
       in  partition_aux ([],[]) ls 
       end   
 
+    fun filter f l = case l of
+    [] => []
+    | h :: t => if f h then h :: (filter f t) else filter f t
+
+    fun first l = case l of
+    [] => []
+    | h :: _ => h
+
+    fun slice beg s_end l = case (beg, s_end, l) of
+      (_, _, []) => []
+    | (0, 0, _) => []
+    | (0, n, h :: t) => h :: (slice beg (n - 1) t)
+    | (m, n, h :: t) => slice (m - 1) (n - 1) t
+    | (_, _, _) => []
+
+    fun insert_at_index l appended_l index =
+      let val beg_slice = slice 0 index l
+          val end_slice = slice index (length l) l
+      in append beg_slice (append appended_l end_slice)
+    end
+
+
 in
     [ ("map",     map)
     , ("mapi",    mapi)
@@ -69,5 +89,10 @@ in
     , ("length",  length)
     , ("append",  append)
     , ("partition", partition) 
+    , ("nth", nth)
+    , ("filter", filter)
+    , ("first", first)
+    , ("slice", slice)
+    , ("insert_at_index", insert_at_index)
     ]
 end

lib/out/lists.exports

@@ -7,4 +7,9 @@ lookup
 elem
 length
 append
-partition
+partition
+nth
+filter
+first
+slice
+insert_at_index