copied from js_of_ocaml/toplevel/examples/lwt_toplevel

indent.ml

@@ -0,0 +1,43 @@
+open Js_of_ocaml
+
+let textarea (textbox : Dom_html.textAreaElement Js.t) : unit =
+  let rec loop s acc (i, pos') =
+    try
+      let pos = String.index_from s pos' '\n' in
+      loop s ((i, (pos', pos)) :: acc) (succ i, succ pos)
+    with _ -> List.rev ((i, (pos', String.length s)) :: acc)
+  in
+  let rec find (l : (int * (int * int)) list) c =
+    match l with
+    | [] -> assert false
+    | (i, (lo, up)) :: _ when up >= c -> c, i, lo, up
+    | (_, (_lo, _up)) :: rem -> find rem c
+  in
+  let v = textbox##.value in
+  let pos =
+    let c1 = textbox##.selectionStart and c2 = textbox##.selectionEnd in
+    if Js.Opt.test (Js.Opt.return c1) && Js.Opt.test (Js.Opt.return c2)
+    then
+      let l = loop (Js.to_string v) [] (0, 0) in
+      Some (find l c1, find l c2)
+    else None
+  in
+  let f =
+    match pos with
+    | None -> fun _ -> true
+    | Some ((_c1, line1, _lo1, _up1), (_c2, line2, _lo2, _up2)) ->
+        fun l -> l >= line1 + 1 && l <= line2 + 1
+  in
+  let v = Ocp_indent.indent (Js.to_string v) f in
+  textbox##.value := Js.string v;
+  match pos with
+  | Some ((c1, line1, _lo1, up1), (c2, line2, _lo2, up2)) ->
+      let l = loop v [] (0, 0) in
+      let lo1'', up1'' = List.assoc line1 l in
+      let lo2'', up2'' = List.assoc line2 l in
+      let n1 = max (c1 + up1'' - up1) lo1'' in
+      let n2 = max (c2 + up2'' - up2) lo2'' in
+      let () = (Obj.magic textbox)##setSelectionRange n1 n2 in
+      textbox##focus;
+      ()
+  | None -> ()