feat: add is_empty, find_index, find_mapi (#21)

These functions were introduced in OCaml 5.1.

src/BwdLabels.ml

@@ -8,6 +8,8 @@ let compare_lengths = BwdNoLabels.compare_lengths
 
 let[@inline] compare_length_with xs ~len = BwdNoLabels.compare_length_with xs len
 
+let is_empty = BwdNoLabels.is_empty
+
 let snoc = BwdNoLabels.snoc
 
 let nth = BwdNoLabels.nth
@@ -64,8 +66,12 @@ let[@inline] find ~f = BwdNoLabels.find f
 
 let[@inline] find_opt ~f = BwdNoLabels.find_opt f
 
+let[@inline] find_index ~f = BwdNoLabels.find_index f
+
 let[@inline] find_map ~f = BwdNoLabels.find_map f
 
+let[@inline] find_mapi ~f = BwdNoLabels.find_mapi f
+
 let[@inline] filter ~f = BwdNoLabels.filter f
 
 let[@inline] find_all ~f = BwdNoLabels.find_all f

src/BwdLabels.mli

@@ -38,6 +38,7 @@ type 'a t = 'a BwdDef.bwd =
 val length : 'a t -> int
 val compare_lengths : 'a t -> 'a t -> int
 val compare_length_with : 'a t -> len:int -> int
+val is_empty : 'a t -> bool
 val snoc : 'a t -> 'a -> 'a t
 val nth : 'a t -> int -> 'a
 val nth_opt : 'a t -> int -> 'a option
@@ -97,7 +98,9 @@ val memq : 'a -> set:'a t -> bool
 
 val find : f:('a -> bool) -> 'a t -> 'a
 val find_opt : f:('a -> bool) -> 'a t -> 'a option
+val find_index : f:('a -> bool) -> 'a t -> int option
 val find_map : f:('a -> 'b option) -> 'a t -> 'b option
+val find_mapi : f:(int -> 'a -> 'b option) -> 'a t -> 'b option
 val filter : f:('a -> bool) -> 'a t -> 'a t
 val find_all : f:('a -> bool) -> 'a t -> 'a t
 val filteri : f:(int -> 'a -> bool) -> 'a t -> 'a t

src/BwdNoLabels.ml

@@ -28,6 +28,8 @@ let compare_length_with xs len =
       (go[@tailcall]) (len-1) xs
   in go len xs
 
+let is_empty = function Emp -> true | _ -> false
+
 let snoc l x = Snoc (l, x)
 
 let nth xs i =
@@ -270,16 +272,34 @@ let find_opt f =
       if f x then Some x else go xs
   in go
 
+let find_index f =
+  let rec go i =
+    function
+    | Emp -> None
+    | Snoc (xs, x) ->
+      if f x then Some i else go (i+1) xs
+  in go 0
+
 let find_map f =
   let rec go =
     function
     | Emp -> None
     | Snoc (xs, x) ->
       match f x with
-      | Some y -> Some y
+      | Some _ as r -> r
       | None -> go xs
   in go
 
+let find_mapi f =
+  let rec go i =
+    function
+    | Emp -> None
+    | Snoc (xs, x) ->
+      match f i x with
+      | Some _ as r -> r
+      | None -> go (i+1) xs
+  in go 0
+
 let filter f =
   let[@tail_mod_cons] rec go =
     function

src/BwdNoLabels.mli

@@ -38,6 +38,7 @@ type 'a t = 'a BwdDef.bwd =
 val length : 'a t -> int
 val compare_lengths : 'a t -> 'a t -> int
 val compare_length_with : 'a t -> int -> int
+val is_empty : 'a t -> bool
 val snoc : 'a t -> 'a -> 'a t
 val nth : 'a t -> int -> 'a
 val nth_opt : 'a t -> int -> 'a option
@@ -97,7 +98,9 @@ val memq : 'a -> 'a t -> bool
 
 val find : ('a -> bool) -> 'a t -> 'a
 val find_opt : ('a -> bool) -> 'a t -> 'a option
+val find_index : ('a -> bool) -> 'a t -> int option
 val find_map : ('a -> 'b option) -> 'a t -> 'b option
+val find_mapi : (int -> 'a -> 'b option) -> 'a t -> 'b option
 val filter : ('a -> bool) -> 'a t -> 'a t
 val find_all : ('a -> bool) -> 'a t -> 'a t
 val filteri : (int -> 'a -> bool) -> 'a t -> 'a t

test/ListAsBwdLabels.ml

@@ -6,6 +6,8 @@ let compare_lengths = L.compare_lengths
 
 let compare_length_with = L.compare_length_with
 
+let is_empty l = l = []
+
 let snoc l x = l @ [x]
 
 let nth xs i =
@@ -83,8 +85,12 @@ let find ~f xs = L.find ~f (L.rev xs)
 
 let find_opt ~f xs = L.find_opt ~f (L.rev xs)
 
+let find_index ~f xs = L.find_map ~f:Fun.id (L.mapi ~f:(fun i x -> if f x then Some i else None) (L.rev xs))
+
 let find_map ~f xs = L.find_map ~f (L.rev xs)
 
+let find_mapi ~f xs = L.find_map ~f:Fun.id (L.mapi ~f (L.rev xs))
+
 let filter ~f xs = L.rev (L.filter ~f (L.rev xs))
 
 let find_all ~f xs = L.rev (L.find_all ~f (L.rev xs))

test/TestBwdLabels.ml

@@ -34,6 +34,11 @@ let test_compare_length_with =
     Q.Gen.(pair (small_list unit) (small_signed_int))
     ~print:Q.Print.(pair (list unit) int)
     (fun (xs, len) -> B.compare_length_with (of_list xs) ~len = L.compare_length_with xs ~len)
+let test_is_empty =
+  Q.Test.make ~count ~name:"is_empty"
+    Q.Gen.(small_list unit)
+    ~print:Q.Print.(list unit)
+    (fun xs -> B.is_empty (of_list xs) = L.is_empty xs)
 let test_snoc =
   Q.Test.make ~count ~name:"snoc" Q.Gen.(pair (small_list int) int) ~print:Q.Print.(pair (list int) int)
     (fun (xs, x) -> to_list (B.snoc (of_list xs) x) = L.snoc xs x)
@@ -208,11 +213,21 @@ let test_find_opt =
     Q.Gen.(pair (Q.fun1 Q.Observable.int bool) (small_list int))
     ~print:Q.Print.(pair Q.Fn.print (list int))
     (fun (Fun (_, f), xs) -> B.find_opt ~f (of_list xs) = L.find_opt ~f xs)
+let test_find_index =
+  Q.Test.make ~count ~name:"find_index"
+    Q.Gen.(pair (Q.fun1 Q.Observable.int bool) (small_list int))
+    ~print:Q.Print.(pair Q.Fn.print (list int))
+    (fun (Fun (_, f), xs) -> B.find_index ~f (of_list xs) = L.find_index ~f xs)
 let test_find_map =
   Q.Test.make ~count ~name:"find_map"
     Q.Gen.(pair (Q.fun1 Q.Observable.int (opt int)) (small_list int))
     ~print:Q.Print.(pair Q.Fn.print (list int))
     (fun (Fun (_, f), xs) -> B.find_map ~f (of_list xs) = L.find_map ~f xs)
+let test_find_mapi =
+  Q.Test.make ~count ~name:"find_mapi"
+    Q.Gen.(pair (Q.fun2 Q.Observable.int Q.Observable.int (opt int)) (small_list int))
+    ~print:Q.Print.(pair Q.Fn.print (list int))
+    (fun (Fun (_, f), xs) -> B.find_mapi ~f (of_list xs) = L.find_mapi ~f xs)
 let test_filter =
   Q.Test.make ~count ~name:"filter"
     Q.Gen.(pair (Q.fun1 Q.Observable.int bool) (small_list int))
@@ -301,6 +316,7 @@ let () =
       test_length;
       test_compare_lengths;
       test_compare_length_with;
+      test_is_empty;
       test_snoc;
       test_nth;
       test_nth_opt;
@@ -329,7 +345,9 @@ let () =
       test_memq;
       test_find;
       test_find_opt;
+      test_find_index;
       test_find_map;
+      test_find_mapi;
       test_filter;
       test_find_all;
       test_filteri;