Collaborative Editor
Collaborative editor patterns that I try to code could be of many kinds. There are string manipulation algorithms, CRDTs and even LLM inference. So even though a full-fledged editor is not in scope here, many algorithms like these can be explored and a functional editor can be created.
The code will be updated directly here in phases. I don’t commit this to a separate repository.
Please note that this is a random collection of algorithms that eventually could be part of a simple editor. There are too many books and papers that deal with a multitude of algorithms.
OCaml 5 Effect Handlers
I will add some sections like this to explain the reason for experimenting with new paradigms. In many cases the code is too dense and will seem complicated when new techniques are introduced needlessly but Effect handlers are interesting to learn. Application though should be selective. There will be many usecases for these in the future.
So the following is an experiment.
Breaking paragraphs into lines
The title describes the essence of one such algorithm( Plass and Knuth ) to break paragraphs.
open Stdlib
open Effect.Deep
open Effect
type entry = {
first : int;
last : int;
mutable next : int;
mutable score : int}
let l = ref []
let is_space= function ' ' -> true | _ -> false
let final_state (start, idx) =
let e = {first = start; last = idx; next = -1; score = -1} in
l := !l @ [e];
Printf.printf " Final state %d %d%!" start idx
type _ Effect.t += Skipping_spaces : (int * int ) -> unit Effect.t
let parabreak text ideal_width max_width =
let start = ref 0 in
let idx,_ =
String.fold_left (fun (idx,word_or_space) c ->
match (is_space c, word_or_space) with
| (true,true)
->
(* Printf.printf "Space at index %d, skipping\n%!" idx; *)
if !start < idx then
perform (Skipping_spaces (!start,idx));
start := idx + 1;
(idx + 1,false);
| (true,false)
-> Printf.printf "No Space at index %d, skipping\n%!" idx;
(idx + 1,false)
| (false,_)
->(idx + 1,true)) (0,false) text
in
if !start < idx then
perform (Skipping_spaces (!start,idx));
final_state (!start,idx)
let effective text =
Printf.printf "Handling effects%!";
match_with (fun () -> parabreak text 10 29)
()
{ effc = (fun (type c) (eff: c Effect.t) ->
match eff with
| Skipping_spaces (s,s1) -> Some (fun (k: (c,_) continuation) ->
(* Printf.printf "Skipping spaces \"%d %d\"\n%!" s s1; *)
let e = {first = s; last = s1; next = -1; score = -1} in
l := !l @ [e];
continue k ()
)
| _ -> None
);
exnc = (function
| e -> raise e
);
(* retc = fun _ -> failwith "Fatal error" *)
retc = (fun res -> Printf.printf "Computation returned: \n")
}
type _ Effect.t += Plass_break : int -> unit Effect.t
let rec plassbreak indent idx idealwidth maxwidth =
let
lastrecord = List.nth !l idx in
let llen = ref (lastrecord.last - lastrecord.first) in
let bscore = idealwidth - !llen in
let bscore = ref (bscore * 2) in
let btail = ref (idx + 1) in
let _ =
List.fold_left (fun acc entry ->
match entry with
| {first; last; next; score} ->
let wwidth = last - first in
if ((!llen + wwidth) >= maxwidth) then(
perform (Plass_break acc);
acc
)else(
let lscore = ref (idealwidth - (!llen + wwidth)) in
lscore := !lscore * 2;
llen := !llen + wwidth + 1;
if score == -1 then
plassbreak (indent + 1) (acc + 1) idealwidth maxwidth;
let
record = List.nth !l acc in
if ((!lscore + score) < !bscore) then(
bscore := !lscore + record.score;
btail := acc;
);
acc + 1;
)
) idx !l in
let record = List.nth !l idx in
record.next <- !btail;
record.score <- !bscore;
if (record.next + 1) = List.length !l then (
record.score <- 0;
)
let pbreak =
Printf.printf "Handling effects%!";
match_with (fun () -> plassbreak 0 10 29)
()
{ effc = (fun (type c) (eff: c Effect.t) ->
match eff with
| Plass_break s -> Some (fun (k: (c,_) continuation) ->
Printf.printf "Plass Break\"%d\"\n%!" s ;
(* continue k () *)
)
| _ -> None
);
exnc = (function
| e -> raise e
);
(* retc = fun _ -> failwith "Fatal error" *)
retc = (fun res -> Printf.printf "Computation returned: \n")
}
let rec loop_while line text lines idx next acc =
if acc > next || (acc + 1) >= List.length !l then
line
else
let {first; last; _} = List.nth lines acc in
if (last - first) <= 0 then
line
else
let new_line =
line ^ (if acc = idx then "" else " ") ^
String.sub text first (last - first)
in
loop_while new_line text lines idx next (acc + 1)
let layout text idealwidth maxwidth =
let rec loop idx lines line =
if idx < List.length !l then
let {first; last; next; _} = List.nth lines idx in
let line = loop_while line text lines idx next idx in
if (String.length line < maxwidth)
then
let line = String.make (maxwidth - String.length line) ' ' in
let subline = String.sub line 0 idealwidth in
let subline1 = String.sub line idealwidth (String.length line - idealwidth) in
let line = subline ^ "+" ^ subline1 ^ "|" in
Printf.printf "%s\n" line;
else Printf.printf "%s" line;
loop (idx + 1) !l line
in
loop 0 !l ""
(* read the entire file *)
let read_file() =
let contents = In_channel.with_open_text "/Users/anu/Documents/go/wiki.txt" In_channel.input_all in
contents
let () =
try
let file_contents = read_file() in
let _ = effective file_contents in
let _ = pbreak in
let _ = layout file_contents 10 30 in
()
with
| exn -> Printf.printf "Unhandled exception: %s\n%!" (Printexc.to_string exn)
Written on October 1, 2024