List.filter_map (#2185)

Changes

@@ -184,6 +184,9 @@ Working version
   hint that can emit non-whitespace characters.
   (Vladimir Keleshev and Pierre Weis, review by Josh Berdine, Gabriel Radanne)
 
+- GPR#2185: Add `List.filter_map`
+  (Thomas Refis, review by Alain Frisch and Gabriel Scherer)
+
 ### Other libraries:
 
 - GPR#1061: Add ?follow parameter to Unix.link. This allows hardlinking

asmcomp/flambda_to_clambda.ml

@@ -649,7 +649,7 @@ let to_clambda_program t env constants (program : Flambda.program) =
           fields
       in
       let init_fields =
-        Misc.Stdlib.List.filter_map (function
+        List.filter_map (function
             | (i, field, None) -> Some (i, field)
             | (_, _, Some _) -> None)
           fields

middle_end/lift_constants.ml

@@ -527,7 +527,7 @@ let constant_dependencies ~backend:_
   | Allocated_const _ -> Symbol.Set.empty
   | Block (_, fields) ->
     let symbol_fields =
-      Misc.Stdlib.List.filter_map
+      List.filter_map
         (function
           | (Symbol s : Flambda.constant_defining_value_block_field) -> Some s
           | Flambda.Const _ -> None)

middle_end/remove_unused_program_constructs.ml

@@ -28,7 +28,7 @@ let constant_dependencies (const:Flambda.constant_defining_value) =
   | Allocated_const _ -> Symbol.Set.empty
   | Block (_, fields) ->
     let symbol_fields =
-      Misc.Stdlib.List.filter_map (function
+      List.filter_map (function
           | (Symbol s : Flambda.constant_defining_value_block_field) ->
             Some s
           | Flambda.Const _ -> None)

parsing/builtin_attributes.ml

@@ -97,7 +97,7 @@ let alert_attr x =
   | _ -> None
 
 let alert_attrs l =
-  Misc.Stdlib.List.filter_map alert_attr l
+  List.filter_map alert_attr l
 
 let alerts_of_attrs l =
   List.fold_left

parsing/location.ml

@@ -425,7 +425,7 @@ let highlight_quote ppf
     highlight_tag
     locs
   =
-  let iset = ISet.of_intervals @@ Misc.Stdlib.List.filter_map (fun loc ->
+  let iset = ISet.of_intervals @@ List.filter_map (fun loc ->
     let s, e = loc.loc_start, loc.loc_end in
     if s.pos_cnum = -1 || e.pos_cnum = -1 then None
     else Some ((s, s.pos_cnum), (e, e.pos_cnum - 1))

stdlib/list.ml

@@ -236,6 +236,16 @@ let find_all p =
 
 let filter = find_all
 
+let filter_map f =
+  let rec aux accu = function
+    | [] -> rev accu
+    | x :: l ->
+        match f x with
+        | None -> aux accu l
+        | Some v -> aux (v :: accu) l
+  in
+  aux []
+
 let partition p l =
   let rec part yes no = function
   | [] -> (rev yes, rev no)

stdlib/list.mli

@@ -134,6 +134,13 @@ val rev_map : ('a -> 'b) -> 'a list -> 'b list
    {!List.rev}[ (]{!List.map}[ f l)], but is tail-recursive and
    more efficient. *)
 
+val filter_map : ('a -> 'b option) -> 'a list -> 'b list
+(** [filter_map f l] applies [f] to every element of [l], filters
+    out the [None] elements and returns the list of the arguments of
+    the [Some] elements.
+    @since 4.08.0
+*)
+
 val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a
 (** [List.fold_left f a [b1; ...; bn]] is
    [f (... (f (f a b1) b2) ...) bn]. *)

stdlib/listLabels.mli

@@ -136,6 +136,13 @@ val rev_map : f:('a -> 'b) -> 'a list -> 'b list
    {!List.rev}[ (]{!List.map}[ f l)], but is tail-recursive and
    more efficient. *)
 
+val filter_map : f:('a -> 'b option) -> 'a list -> 'b list
+(** [filter_map f l] applies [f] to every element of [l], filters
+    out the [None] elements and returns the list of the arguments of
+    the [Some] elements.
+    @since 4.08.0
+*)
+
 val fold_left : f:('a -> 'b -> 'a) -> init:'a -> 'b list -> 'a
 (** [List.fold_left f a [b1; ...; bn]] is
    [f (... (f (f a b1) b2) ...) bn]. *)

testsuite/tests/lib-list/test.ml

@@ -1,6 +1,12 @@
 (* TEST
 *)
 
+let string_of_even_opt x =
+  if x mod 2 = 0 then
+    Some (string_of_int x)
+  else
+    None
+
 (* Standard test case *)
 let () =
   let l = List.init 10 (fun x -> x) in
@@ -35,6 +41,7 @@ let () =
   assert (List.compare_length_with [1] 0 > 0);
   assert (List.compare_length_with ['1'] 1 = 0);
   assert (List.compare_length_with ['1'] 2 < 0);
+  assert (List.filter_map string_of_even_opt l = ["0";"2";"4";"6";"8"]);
   ()
 ;;
 

utils/misc.ml

@@ -112,17 +112,6 @@ module Stdlib = struct
       | (hd1 :: tl1, hd2 :: tl2) -> eq hd1 hd2 && equal eq tl1 tl2
       | (_, _) -> false
 
-    let filter_map f l =
-      let rec aux acc l =
-        match l with
-        | [] -> List.rev acc
-        | h :: t ->
-          match f h with
-          | None -> aux acc t
-          | Some v -> aux (v :: acc) t
-      in
-      aux [] l
-
     let rec find_map f = function
       | x :: xs ->
           begin match f x with

utils/misc.mli

@@ -98,11 +98,6 @@ module Stdlib : sig
     (** Returns [true] iff the given lists have the same length and content
         with respect to the given equality function. *)
 
-    val filter_map : ('a -> 'b option) -> 'a t -> 'b t
-    (** [filter_map f l] applies [f] to every element of [l], filters
-        out the [None] elements and returns the list of the arguments of
-        the [Some] elements. *)
-
     val find_map : ('a -> 'b option) -> 'a t -> 'b option
     (** [find_map f l] returns the first evaluation of [f] that returns [Some],
        or returns None if there is no such element. *)