From b59328cd5655071b49b2b8894004b7b37b6939f7 Mon Sep 17 00:00:00 2001
From: Michael Martin-Smucker <mlmartin13@gmail.com>
Date: Fri, 13 Dec 2019 10:52:22 -0700
Subject: [PATCH] Allow fold_map to map underlying type for Any/Plus

---
 src/interfaces/Interface.re | 4 ++--
 test/Test_List.re           | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/interfaces/Interface.re b/src/interfaces/Interface.re
index 2d2bd864..0fe15741 100644
--- a/src/interfaces/Interface.re
+++ b/src/interfaces/Interface.re
@@ -95,9 +95,9 @@ module type FOLDABLE = {
 
   module Fold_Map: (M: MONOID) => {let fold_map: ('a => M.t, t('a)) => M.t;};
   module Fold_Map_Any:
-    (M: MONOID_ANY) => {let fold_map: ('a => M.t('a), t('a)) => M.t('a);};
+    (M: MONOID_ANY) => {let fold_map: ('a => M.t('b), t('a)) => M.t('b);};
   module Fold_Map_Plus:
-    (P: PLUS) => {let fold_map: ('a => P.t('a), t('a)) => P.t('a);};
+    (P: PLUS) => {let fold_map: ('a => P.t('b), t('a)) => P.t('b);};
 };
 
 module type UNFOLDABLE = {
diff --git a/test/Test_List.re b/test/Test_List.re
index ee2e7c7c..efb5dbd4 100644
--- a/test/Test_List.re
+++ b/test/Test_List.re
@@ -114,6 +114,12 @@ describe("List", () => {
       expect(fold_map(List.Applicative.pure, [[1, 2, 3], [4, 5]]))
       |> to_be([[1, 2, 3], [4, 5]]);
     });
+
+    it("should do a map fold ('a => array('b))", () => {
+      let fold_map = ListF.Array.Fold_Map_Plus.fold_map;
+      expect(fold_map(Array.Applicative.pure <. Int.Show.show, [1, 2, 3]))
+      |> to_be([|"1", "2", "3"|])
+    });
   });
 
   describe("Unfoldable", () => {