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list: Use efficient chunking algorithm for tail-recursive list map

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See discussion at
https://discuss.ocaml.org/t/a-new-list-map-that-is-both-stack-safe-and-fast/865/32
This commit is contained in:
Yotam Barnoy 2017-10-03 17:45:26 -04:00
parent 4096122979
commit 0aaab670f7
1 changed files with 21 additions and 1 deletions
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22
src/core/CCList.ml
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@ -20,13 +20,33 @@ let is_empty = function
(* max depth for direct recursion *)
let direct_depth_default_ = 1000
let tail_map f l =
(* Unwind the list of tuples, reconstructing the full list front-to-back *)
let rec rise ys = function
| [] -> ys
| (y0, y1, y2, y3, y4, y5, y6, y7, y8) :: bs ->
rise (y0 :: y1 :: y2 :: y3 :: y4 :: y5 :: y6 :: y7 :: y8 :: ys) bs
in
(* Create a compressed reverse-list representation using tuples *)
let rec dive acc = function
| x0 :: x1 :: x2 :: x3 :: x4 :: x5 :: x6 :: x7 :: x8 :: xs ->
let y0 = f x0 in let y1 = f x1 in let y2 = f x2 in
let y3 = f x3 in let y4 = f x4 in let y5 = f x5 in
let y6 = f x6 in let y7 = f x7 in
dive ((y0, y1, y2, y3, y4, y5, y6, y7, f x8) :: acc) xs
| xs ->
(* Reverse direction, finishing off with a direct map *)
rise (List.map f xs) acc
in
dive [] l
let map f l =
let rec direct f i l = match l with
| [] -> []
| [x] -> [f x]
| [x1;x2] -> let y1 = f x1 in [y1; f x2]
| [x1;x2;x3] -> let y1 = f x1 in let y2 = f x2 in [y1; y2; f x3]
| _ when i=0 -> List.rev (List.rev_map f l)
| _ when i=0 -> tail_map f l
| x1::x2::x3::x4::l' ->
let y1 = f x1 in
let y2 = f x2 in