Merge pull request #380 from jmid/map-renaming

The Great Renaming, Chapter 10: `map` renaming

Author: jmid

CHANGELOG.md

@@ -81,6 +81,7 @@
 - Renamed monadic and applicative generator combinators:
   - Add missing `QCheck.Gen.bind` for consistency
   - Add missing `QCheck.Gen.ap` for consistency
+- Add missing `QCheck2.Gen.map_keep_input` for consistency
 
 
 ## 0.27 (2025-10-31)

src/core/QCheck2.ml

@@ -352,6 +352,8 @@ module Gen = struct
 
   let map5 = liftA5
 
+  let map_keep_input f x = fun st -> Tree.map (fun a -> a, f a) (x st)
+
   let return = pure
 
   let bind (gen : 'a t) (f : 'a -> ('b t)) : 'b t = fun st ->

src/core/QCheck2.mli

@@ -1181,6 +1181,15 @@ module Gen : sig
       @since 0.25
   *)
 
+  val map_keep_input : ('a -> 'b) -> 'a t -> ('a * 'b) t
+  (** [map_keep_input f g] transforms a generator [g] by applying [f] to each generated element.
+      Returns both the generated element from [g] and the output from [f].
+
+      Shrinks towards the shrinks of [g] with [f] applied to them.
+
+      @since NEXT_RELEASE
+  *)
+
   val ap : ('a -> 'b) t -> 'a t -> 'b t
   (** [ap fgen gen] composes a function generator and an argument generator
       into a result generator.