Steal a `filter_map` implementation from Karuta

2 files changed, 7 insertions, 0 deletions

diff --git a/lib/Utilities.ml b/lib/Utilities.ml
index 8f278a3..8b6b08e 100644
--- a/lib/Utilities.ml
+++ b/lib/Utilities.ml
@@ -86,6 +86,12 @@ module FingerTree = struct
 
   let join ss sep =
     BatFingerTree.print ~first:"" ~last:"" ~sep BatIO.nwrite |> Fun.flip BatIO.to_string ss
+
+  let filter_map f =
+    BatFingerTree.fold_left
+      (fun acc elem ->
+        match f elem with None -> acc | Some result -> BatFingerTree.snoc acc result)
+      BatFingerTree.empty
 end
 
 module Atomic = struct
diff --git a/lib/Utilities.mli b/lib/Utilities.mli
index 204fec3..f220b08 100644
--- a/lib/Utilities.mli
+++ b/lib/Utilities.mli
@@ -35,6 +35,7 @@ module FingerTree : sig
   val sequence : ('a, 'b) result BatFingerTree.t -> ('a BatFingerTree.t, 'b) result
   val foldm_left : ('a -> 'b -> ('a, 'e) result) -> 'a -> 'b BatFingerTree.t -> ('a, 'e) result
   val join : string BatFingerTree.t -> string -> string
+  val filter_map : ('a -> 'b option) -> 'a BatFingerTree.t -> 'b BatFingerTree.t
 end
 
 module Fun : sig