init with working 'exists' function for string set

src/string-set.sml

@@ -0,0 +1,144 @@
+structure StringSet =
+struct
+  datatype t =
+    CHILDREN of {keys: string vector, children: t vector}
+  | FOUND_WITH_CHILDREN of {keys: string vector, children: t vector}
+  | FOUND
+
+  fun helpBinSearch (findChr, keyPos, children, low, high) =
+    if high >= low then
+      let
+        val mid = low + ((high - low) div 2)
+        val midStr = Vector.sub (children, mid)
+        val midChr = String.sub (midStr, keyPos)
+      in
+        if midChr = findChr then
+          SOME mid
+        else if midChr < findChr then
+          helpBinSearch (findChr, keyPos, children, mid + 1, high)
+        else
+          helpBinSearch (findChr, keyPos, children, low, mid - 1)
+      end
+    else
+      NONE
+
+  fun binSearch (findChr, keyPos, children) =
+    if Vector.length children > 0 then
+      helpBinSearch (findChr, keyPos, children, 0, Vector.length children - 1)
+    else
+      NONE
+
+  datatype search_string_match =
+    NO_SEARCH_MATCH
+  | FULL_SEARCH_MATCH
+  | SEARCH_KEY_CONTAINS_TRIE_KEY
+  | TRIE_KEY_CONTAINS_SEARCH_KEY
+
+  fun searchKeyMatch (searchKey, trieKey, keyPos) =
+    if
+      keyPos < String.size searchKey
+    then
+      if keyPos < String.size trieKey then
+        let
+          val searchChr = String.sub (searchKey, keyPos)
+          val trieChr = String.sub (trieKey, keyPos)
+        in
+          if searchChr = trieChr then
+            searchKeyMatch (searchKey, trieKey, keyPos + 1)
+          else
+            NO_SEARCH_MATCH
+        end
+      else
+        SEARCH_KEY_CONTAINS_TRIE_KEY
+    else if
+      keyPos = String.size searchKey
+    then
+      if keyPos < String.size trieKey then TRIE_KEY_CONTAINS_SEARCH_KEY
+      else if keyPos = String.size trieKey then FULL_SEARCH_MATCH
+      else SEARCH_KEY_CONTAINS_TRIE_KEY
+    else 
+      (* implicit: keyPos > String.size searchKey *) 
+      if keyPos <= String.size trieKey then
+        TRIE_KEY_CONTAINS_SEARCH_KEY
+      else
+        NO_SEARCH_MATCH
+
+  fun isFoundNode node =
+    case node of
+      FOUND => true
+    | FOUND_WITH_CHILDREN _ => true
+    | CHILDREN _ => false
+
+  fun exists (searchKey, keyPos, trie) =
+    case trie of
+      CHILDREN {keys, children} =>
+        let
+          val findChr = String.sub (searchKey, keyPos)
+        in
+          (case binSearch (findChr, keyPos, keys) of
+             SOME idx =>
+               let
+                 val trieKey = Vector.sub (keys, idx)
+                 val nextKeyPos = keyPos + 1
+               in
+                 (case searchKeyMatch (searchKey, trieKey, nextKeyPos) of
+                    NO_SEARCH_MATCH => false
+                  | FULL_SEARCH_MATCH =>
+                      let val trieChild = Vector.sub (children, idx)
+                      in isFoundNode trieChild
+                      end
+                  | SEARCH_KEY_CONTAINS_TRIE_KEY =>
+                      let val trieChild = Vector.sub (children, idx)
+                      in exists (searchKey, nextKeyPos, trieChild)
+                      end
+                  | TRIE_KEY_CONTAINS_SEARCH_KEY => false)
+               end
+           | NONE => false)
+        end
+    | FOUND_WITH_CHILDREN {keys, children} =>
+        let
+          val findChr = String.sub (searchKey, keyPos)
+        in
+          (case binSearch (findChr, keyPos, keys) of
+             SOME idx =>
+               let
+                 val trieKey = Vector.sub (keys, idx)
+                 val nextKeyPos = keyPos + 1
+               in
+                 (case searchKeyMatch (searchKey, trieKey, nextKeyPos) of
+                    NO_SEARCH_MATCH => false
+                  | FULL_SEARCH_MATCH =>
+                      let val trieChild = Vector.sub (children, idx)
+                      in isFoundNode trieChild
+                      end
+                  | SEARCH_KEY_CONTAINS_TRIE_KEY =>
+                      let val trieChild = Vector.sub (children, idx)
+                      in exists (searchKey, nextKeyPos, trieChild)
+                      end
+                  | TRIE_KEY_CONTAINS_SEARCH_KEY => false)
+               end
+           | NONE => false)
+        end
+    | FOUND => keyPos = String.size searchKey
+
+  (* 
+   * todo: 
+   * Code insert function, with an insertKeyMatch helper function
+   * which is similar to the searchKeyMatch helper function,
+   * except that it may also return the index to split a node at
+   * in a new datatype.
+   *)
+
+  fun insert (insKey, keyPos, trie) =
+    case trie of
+      FOUND =>
+        if keyPos = String.size insKey then
+          FOUND
+        else
+          FOUND_WITH_CHILDREN
+            { keys = Vector.fromList [insKey]
+            , children = Vector.fromList [FOUND]
+            }
+    | CHILDREN {keys, children} => 0 (* todo *)
+    | FOUND_WITH_CHILDREN {keys, children} => 0 (* todo *)
+end