begin reimplementing search list data structure

fcore/search/search-line-gap.sml

@@ -0,0 +1,49 @@
+structure SearchLineGap =
+struct
+  fun searchStep (pos, hd, absIdx, tl, acc, searchPos, searchString) =
+    if searchPos < 0 then
+      (absIdx + 1) :: acc
+    else if pos < 0 then
+      case tl of
+        hd :: tl =>
+          searchStep (String.size hd - 1, hd, absIdx, tl, acc, searchPos, searchString)
+      | [] => acc
+    else
+      let
+        val bufferChr = String.sub (hd, pos)
+        val searchChr = String.sub (searchString, searchPos)
+      in
+        if bufferChr = searchChr then
+          searchStep (pos - 1, hd, absIdx - 1, tl, acc, searchPos - 1, searchString)
+        else
+          acc
+      end
+
+  fun loopSearch (pos, hd, absIdx, tl, acc, searchString) =
+    if pos < 0 then
+      case tl of
+        hd :: tl =>
+          loopSearch (String.size hd - 1, hd, absIdx, tl, acc, searchString)
+      | [] => acc
+    else
+      let
+        val acc = searchStep 
+          (pos, hd, absIdx, tl, acc, String.size searchString - 1, searchString)
+      in
+        loopSearch (pos - 1, hd, absIdx - 1, tl, acc, searchString)
+      end
+
+  fun search (buffer, searchString) =
+    if String.size searchString = 0 then
+      []
+    else
+      let
+        val buffer = LineGap.goToEnd buffer
+        val {leftStrings, idx = absIdx, ...} = buffer
+      in
+        case leftStrings of
+          hd :: tl =>
+            loopSearch (String.size hd - 1, hd, absIdx - 1, tl, [], searchString)
+        | [] => []
+      end
+end