feat(wpcarro/compiler): Support Vector type

Support an array that dynamically resizes itself, and replace usages of `List`,
`Array`, and `Queue` with `Vec`.

Change-Id: I910b140b7c1bdddae40e08f8191986dccbc6fddf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7080
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>

users/wpcarro/scratch/compiler/vec.ml

@@ -0,0 +1,127 @@
+(****************************************************************************** 
+ * Similar to Python's list
+ *
+ * - mutable
+ * - dynamically resized
+ * - O(1) read
+ * - O(1) write
+ * - O(1) append (average case)
+ *
+ ******************************************************************************)
+
+type 'a vec = {
+  mutable length: int;
+  mutable capacity: int;
+  mutable xs: 'a array;
+}
+
+(****************************************************************************** 
+ * Constructors
+ ******************************************************************************)
+
+let make (size : int) (seed : 'a) : 'a vec = { 
+  length = size;
+  capacity = size;
+  xs = Array.make size seed;
+}
+
+let create () = {
+  length = 0;
+  capacity = 0;
+  xs = [||];
+}
+
+let from_array (xs : 'a array) : 'a vec = {
+  length = Array.length xs;
+  capacity = Array.length xs;
+  xs = xs;
+}
+
+let from_list (xs : 'a list) : 'a vec = 
+  match xs with
+  | [] -> create ()
+  | y::ys -> 
+    let result = {
+      length = List.length xs;
+      capacity = List.length xs;
+      xs = Array.make (List.length xs) y;
+    } in
+    List.iteri (fun i x -> Array.set result.xs i x) xs;
+    result
+
+(****************************************************************************** 
+ * Miscellaneous
+ ******************************************************************************)
+
+let append (x : 'a) (v : 'a vec) =
+  if v.capacity = 0 then
+    begin
+      v.length <- 1;
+      v.capacity <- 1;
+      v.xs <- [|x|];
+    end
+  else if v.length = v.capacity then
+    begin
+      (* According to Wikipedia, Python uses 1.25 as the growth factor *)
+      let new_cap = v.capacity |> float_of_int |> Float.mul 1.25 |> ceil |> int_of_float in
+      let new_xs = Array.make new_cap x in
+      Array.iteri (fun i x -> Array.set new_xs i x) v.xs;
+      v.capacity <- new_cap;
+      v.xs <- new_xs;
+      Array.set v.xs v.length x;
+      v.length <- v.length + 1;
+    end
+  else
+    begin
+      Array.set v.xs v.length x;
+      v.length <- v.length + 1;
+    end
+
+let get (i : int) (v : 'a vec) : 'a option =
+  if i >= v.length then
+    None
+  else
+    Some v.xs.(i)
+
+let get_unsafe (i : int) (v : 'a vec) : 'a =
+  v.xs.(i)
+
+let set (i : int) (x : 'a) (v : 'a vec) : unit =
+  if i < v.length then
+    Array.set v.xs i x
+
+let length (v : 'a vec) : int = 
+  v.length
+
+let update (i : int) (f : 'a -> 'a) (v : 'a vec) : unit =
+  match get i v with
+  | None -> ()
+  | Some x -> set i (f x) v
+
+let iter (f : 'a -> unit) (v : 'a vec) : unit =
+  let n = ref 0 in
+  while !n < v.length do
+    f v.xs.(!n);
+    n := !n + 1;
+  done
+
+let join (sep : string) (v : string vec) : string =
+  if length v = 0 then
+    ""
+  else
+    let i = ref 1 in
+    let result = ref v.xs.(0) in
+    while !i < v.length do
+      result := !result ^ sep ^ v.xs.(!i);
+      i := !i + 1;
+    done;
+    !result
+
+let map (f : 'a -> 'b) (v : 'a vec) : 'b vec =
+  let result = create () in
+  iter (fun x -> append (f x) result) v;
+  result
+
+let append_to (dst : 'a vec) (xs : 'a vec) : unit =
+  iter (fun x -> append x dst) xs
+