Merge pull request rescript-lang#3334 from bloodyowl/array-getby

Add Array.getBy

Author: bobzhang

jscomp/others/belt_Array.ml

@@ -265,6 +265,22 @@ let mapU a f =
 
 let map a f = mapU a (fun[@bs] a -> f a)
 
+let getByU a p =
+  let l = length a in
+  let i = ref 0 in
+  let r = ref None in
+  while !r = None && !i < l do
+    let v = (getUnsafe a !i) in
+    if p v [@bs] then
+      begin
+        r := Some v;
+      end;
+    incr i
+  done;
+  !r
+
+let getBy a p = getByU a (fun[@bs] a -> p a)
+
 let keepU a f =
   let l = length a in
   let r = makeUninitializedUnsafe l in

jscomp/others/belt_Array.mli

@@ -369,6 +369,16 @@ val map: 'a array ->  ('a -> 'b ) -> 'b array
 
 *)
 
+val getByU: 'a array -> ('a -> bool [@bs]) -> 'a option
+val getBy: 'a array -> ('a -> bool) -> 'a option
+(** [getBy xs p] returns [Some value] for the first value in [xs] that satisifies the predicate function [p]; returns [None] if no element satisifies the function.
+
+  @example {[
+      getBy [|1;4;3;2|] (fun x -> x mod 2 = 0) = Some 4
+      getBy [|15;13;11|] (fun x -> x mod 2 = 0) = None
+    ]}
+*)
+
 val keepU: 'a array -> ('a -> bool [@bs]) -> 'a array
 val keep: 'a array -> ('a -> bool ) -> 'a array
 (** [keep xs p ]

jscomp/test/bs_array_test.js

@@ -1542,7 +1542,23 @@ b("File \"bs_array_test.ml\", line 331, characters 4-11", Belt_Array.cmp(/* arra
           3
         ], Caml_primitive.caml_int_compare) > 0);
 
-Mt.from_pair_suites("File \"bs_array_test.ml\", line 334, characters 23-30", suites[0]);
+eq("File \"bs_array_test.ml\", line 334, characters 5-12", Belt_Array.getBy(/* array */[
+          1,
+          2,
+          3
+        ], (function (x) {
+            return x > 1;
+          })), 2);
+
+eq("File \"bs_array_test.ml\", line 335, characters 5-12", Belt_Array.getBy(/* array */[
+          1,
+          2,
+          3
+        ], (function (x) {
+            return x > 3;
+          })), undefined);
+
+Mt.from_pair_suites("File \"bs_array_test.ml\", line 337, characters 23-30", suites[0]);
 
 var A = 0;
 

jscomp/test/bs_array_test.ml

@@ -328,7 +328,10 @@ let () =
   b __LOC__ (A.cmp [|0;1;2;3|] [|1;2;3|]  compare > 0) ;
   b __LOC__ (A.cmp [|1;2;3|] [|0;1;2|]  (fun x y -> compare  x y) > 0);
   b __LOC__ (A.cmp [|1;2;3|] [|1;2;3|]  (fun x y -> compare x y) = 0);
-  b __LOC__ (A.cmp [|1;2;4|] [|1;2;3|]  (fun x y -> compare x y) > 0);
+  b __LOC__ (A.cmp [|1;2;4|] [|1;2;3|]  (fun x y -> compare x y) > 0)
 
+let () =
+  eq __LOC__ (A.getBy [|1;2;3|] (fun x -> x > 1)) (Some 2);
+  eq __LOC__ (A.getBy [|1;2;3|] (fun x -> x > 3)) None;
 
 ;; Mt.from_pair_suites __LOC__ !suites

lib/js/belt_Array.js

@@ -311,6 +311,24 @@ function map(a, f) {
   return mapU(a, Curry.__1(f));
 }
 
+function getByU(a, p) {
+  var l = a.length;
+  var i = 0;
+  var r = undefined;
+  while(r === undefined && i < l) {
+    var v = a[i];
+    if (p(v)) {
+      r = Caml_option.some(v);
+    }
+    i = i + 1 | 0;
+  };
+  return r;
+}
+
+function getBy(a, p) {
+  return getByU(a, Curry.__1(p));
+}
+
 function keepU(a, f) {
   var l = a.length;
   var r = new Array(l);
@@ -657,6 +675,8 @@ exports.forEachU = forEachU;
 exports.forEach = forEach;
 exports.mapU = mapU;
 exports.map = map;
+exports.getByU = getByU;
+exports.getBy = getBy;
 exports.keepU = keepU;
 exports.keep = keep;
 exports.keepWithIndexU = keepWithIndexU;