funclang series4: Implemented insert function for ass9.

funclang-taddeus/series4/ass9.ml

@@ -9,24 +9,30 @@ let rec starts_with l s =
     | h::t -> h = (hd l) && starts_with (tl l) t
 ;;
 
+(* Insert a new (key, value) pair into a trie *)
 let rec insert trie key value =
     match trie with
     | Empty -> Node (key, value, []) (* Root *)
     | Node (k, v, children) ->
-        if starts_with key k then
-            (* Check all children for a longer prefix *)
-            if (length k) = (length key) - 1 then
-                (* Direct child *)
-                Node (k, v, children @ [Node (key, value, [])])
-            else
-                (* Add another nde between the matched node and the child,
-                 * with the length of the matched node plus one *)
-                Empty
+        if k = key then
+            raise (Failure "Inserted key already exists in trie")
+        else if starts_with key k then
+            (* Inserted key should be in this node because it starts with
+             * the node's key *)
+            let matches_key = function
+                | Empty -> false
+                | Node (k, _, c) -> starts_with key k
+            in
+            (* 'move' are the children that are moved to be the children of the
+             * inserted node, 'siblings' are the children that remain in the
+             * current matched node *)
+            let move, siblings = partition matches_key children in
+            Node (k, v, siblings @ [Node (key, value, move)])
         else
             raise (Failure "Inserted key does not start with node key")
 ;;
 
-(**)
+(* Look up a value associated with a key *)
 let rec lookup trie key =
     match trie with
     | Empty -> None (* Trie is empty, so no result *)
@@ -49,6 +55,7 @@ let rec lookup trie key =
             None
 ;;
 
+(* Find all (key, value) pairs whose key start with a given prefix *)
 let rec matches trie key =
     match trie with
     | Empty -> []