From 3bd95d257cc8429e609418a4744c75576085a994 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Sun, 19 Nov 2023 21:47:57 -0500
Subject: [PATCH] CCList: use TRMC for many functions on 5.1

---
 src/core/CCList.ml | 101 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 90 insertions(+), 11 deletions(-)

diff --git a/src/core/CCList.ml b/src/core/CCList.ml
index 79a57708..5dd6b392 100644
--- a/src/core/CCList.ml
+++ b/src/core/CCList.ml
@@ -6,16 +6,6 @@
 
 [@@@ocaml.warning "-32"]
 
-let nth_opt l n =
-  if n < 0 then invalid_arg "nth_opt";
-  let rec aux l n =
-    match l, n with
-    | [], _ -> None
-    | x :: _, 0 -> Some x
-    | _ :: l, _ -> aux l (n - 1)
-  in
-  aux l n
-
 let rec find_opt p l =
   match l with
   | [] -> None
@@ -64,9 +54,11 @@ let mguard c =
   else
     []
 
-(* max depth for direct recursion *)
+(** max depth for direct recursion *)
 let direct_depth_default_ = 1000
 
+[@@@iflt 5.1]
+
 let tail_map f l =
   (* Unwind the list of tuples, reconstructing the full list front-to-back.
      @param tail_acc a suffix of the final list; we append tuples' content
@@ -136,6 +128,8 @@ let append l1 l2 =
   | [ x; y ] -> x :: y :: l2
   | _ -> direct direct_depth_append_ l1 l2
 
+[@@@endif]
+
 let ( @ ) = append
 let[@inline] cons' l x = x :: l
 
@@ -144,6 +138,9 @@ let cons_maybe o l =
   | Some x -> x :: l
   | None -> l
 
+(* TRMC after 5.1 *)
+[@@@iflt 5.1]
+
 let direct_depth_filter_ = 10_000
 
 let filter p l =
@@ -178,6 +175,8 @@ let fold_right f l acc =
   in
   direct direct_depth_default_ f l acc
 
+[@@@endif]
+
 let rec fold_while f acc = function
   | [] -> acc
   | e :: l ->
@@ -286,6 +285,9 @@ let fold_flat_map_i f acc l =
   in
   aux f acc 0 [] l
 
+[@@@iflt 5.1]
+
+(* keep this because it's tailrec for < 5.1 *)
 let init len f =
   let rec indirect_ i acc =
     if i = len then
@@ -311,6 +313,8 @@ let init len f =
   else
     direct_ 0
 
+[@@@endif]
+
 let rec compare f l1 l2 =
   match l1, l2 with
   | [], [] -> 0
@@ -425,6 +429,8 @@ let partition_filter_map f l =
 
 let partition_map = partition_filter_map
 
+[@@@iflt 5.1]
+
 let combine l1 l2 =
   let rec direct i l1 l2 =
     match l1, l2 with
@@ -440,6 +446,16 @@ let combine l1 l2 =
   in
   direct direct_depth_default_ l1 l2
 
+[@@@else_]
+
+let[@tail_mod_cons] rec combine l1 l2 =
+  match l1, l2 with
+  | [], [] -> []
+  | x1 :: l1', x2 :: l2' -> (x1, x2) :: combine l1' l2'
+  | _, _ -> invalid_arg "CCList.combine"
+
+[@@@endif]
+
 let combine_gen l1 l2 =
   let l1 = ref l1 in
   let l2 = ref l2 in
@@ -451,6 +467,8 @@ let combine_gen l1 l2 =
       l2 := tail2;
       Some (x1, x2)
 
+[@@@iflt 5.1]
+
 let combine_shortest l1 l2 =
   let rec direct i l1 l2 =
     match l1, l2 with
@@ -466,6 +484,15 @@ let combine_shortest l1 l2 =
   in
   direct direct_depth_default_ l1 l2
 
+[@@@else_]
+
+let[@tail_mod_cons] rec combine_shortest l1 l2 =
+  match l1, l2 with
+  | _, [] | [], _ -> []
+  | x1 :: l1', x2 :: l2' -> (x1, x2) :: combine_shortest l1' l2'
+
+[@@@endif]
+
 let split l =
   let rec direct i l =
     match l with
@@ -666,6 +693,8 @@ let sorted_diff_uniq ~cmp l1 l2 =
   in
   recurse ~cmp [] l1 l2
 
+[@@@iflt 5.1]
+
 let take n l =
   let rec direct i n l =
     match l with
@@ -684,6 +713,19 @@ let take n l =
   in
   direct direct_depth_default_ n l
 
+[@@@else_]
+
+let[@tail_mod_cons] rec take n l =
+  match l with
+  | [] -> []
+  | x :: l' ->
+    if n > 0 then
+      x :: take (n - 1) l'
+    else
+      []
+
+[@@@endif]
+
 let rec drop n l =
   match l with
   | [] -> []
@@ -748,6 +790,8 @@ let interleave l1 l2 : _ list =
   in
   aux [] l1 l2
 
+[@@@iflt 5.1]
+
 let take_while p l =
   let rec direct i p l =
     match l with
@@ -769,6 +813,19 @@ let take_while p l =
   in
   direct direct_depth_default_ p l
 
+[@@@else_]
+
+let rec take_while p l =
+  match l with
+  | [] -> []
+  | x :: l' ->
+    if p x then
+      x :: take_while p l'
+    else
+      []
+
+[@@@endif]
+
 let rec drop_while p l =
   match l with
   | [] -> []
@@ -1416,6 +1473,8 @@ let of_seq_rev l =
   in
   loop [] l
 
+[@@@iflt 5.1]
+
 let of_seq l =
   let rec direct i seq =
     if i <= 0 then
@@ -1428,6 +1487,15 @@ let of_seq l =
   in
   direct direct_depth_default_ l
 
+[@@@else_]
+
+let[@tail_mod_cons] rec of_seq seq =
+  match seq () with
+  | Seq.Nil -> []
+  | Seq.Cons (x, tl) -> x :: of_seq tl
+
+[@@@endif]
+
 let to_gen l =
   let l = ref l in
   fun () ->
@@ -1437,6 +1505,8 @@ let to_gen l =
       l := l';
       Some x
 
+[@@@iflt 5.1]
+
 let of_gen g =
   let rec direct i g =
     if i = 0 then
@@ -1453,6 +1523,15 @@ let of_gen g =
   in
   direct direct_depth_default_ g
 
+[@@@else_]
+
+let[@tail_mod_cons] rec of_gen g =
+  match g () with
+  | None -> []
+  | Some x -> x :: of_gen g
+
+[@@@endif]
+
 module Infix = struct
   let[@inline] ( >|= ) l f = map f l
   let[@inline] ( >>= ) l f = flat_map f l