add Vec2.origin for (0,0)

src/day12.ml

@@ -6,18 +6,16 @@ type node =
   { char : char
   ; mutable visited : bool
   ; mutable distance : int
-  ; mutable previous : (Vec2.t * node) option
   }
 [@@deriving show]
 
 let parse_grid start_anywhere =
-  let s = ref @@ Vec2.of_tuple (0, 0) in
+  let s = ref @@ Vec2.origin in
-  let e = ref @@ Vec2.of_tuple (0, 0) in
+  let e = ref @@ Vec2.origin in
   let unvisited = ref [] in
   let grid =
     Utils.lines_of_input 12
-    |> Vec2.parse_grid (fun char ->
+    |> Vec2.parse_grid (fun char -> { char; visited = false; distance = infinity })
-      { char; visited = false; distance = infinity; previous = None })
   in
   Vec2.iter_grid grid (fun pos ->
     let n = Vec2.at_e grid pos in
@@ -45,16 +43,13 @@ let reachable f t =
 
 let rec path grid goal current unvisited =
   let current_node = Vec2.at_e grid current in
-  let neighbors = Vec2.directions |> List.map (fun dir -> Vec2.(current + dir)) in
+  Vec2.directions
-  neighbors
+  |> List.map (fun dir -> Vec2.(current + dir))
   |> List.iter (fun neighbor ->
     match Vec2.at grid neighbor with
     | Some node when (not node.visited) && reachable current_node.char node.char ->
       let new_distance = current_node.distance + 1 in
-      if new_distance < node.distance
+      if new_distance < node.distance then node.distance <- new_distance;
-      then (
-        node.distance <- new_distance;
-        node.previous <- Some (current, current_node));
       if Option.is_none @@ List.find_opt (fun x -> Vec2.(x = neighbor)) !unvisited
       then unvisited := neighbor :: !unvisited
     | _ -> ());

src/day9.ml

@@ -37,7 +37,7 @@ let next_pos head tail =
 
 let solve length =
   let moves = parse_input () in
-  let start = Vec2.of_tuple (0, 0) in
+  let start = Vec2.origin in
   let tail = List.init (length - 1) (fun _ -> start) in
   let _, _, last_knot_hist =
     List.fold_left

src/vec2.ml

@@ -9,6 +9,7 @@ type 'a grid =
   }
 [@@deriving show]
 
+let origin = 0, 0
 let up = 0, 1
 let down = 0, -1
 let left = -1, 0

src/vec2.mli

@@ -1,6 +1,7 @@
 type t [@@deriving show]
 type 'a grid [@@deriving show]
 
+val origin : t
 val up : t
 val down : t
 val left : t