1 files changed, 17 insertions, 0 deletions
diff --git a/stdlib/source/library/lux/abstract/fold.lux b/stdlib/source/library/lux/abstract/fold.lux
new file mode 100644
index 000000000..168d743be
--- /dev/null
+++ b/stdlib/source/library/lux/abstract/fold.lux
@@ -0,0 +1,17 @@
+(.module:
+  [library
+   [lux #*]]
+  [//
+   [monoid (#+ Monoid)]])
+
+(interface: #export (Fold F)
+  {#.doc "Iterate over a structure's values to build a summary value."}
+  (: (All [a b]
+       (-> (-> b a a) a (F b) a))
+     fold))
+
+(def: #export (with-monoid monoid fold value)
+  (All [F a]
+    (-> (Monoid a) (Fold F) (F a) a))
+  (let [(^open "/\.") monoid]
+    (fold /\compose /\identity value)))