1 files changed, 36 insertions, 0 deletions
diff --git a/stdlib/source/lux/abstract/apply.lux b/stdlib/source/lux/abstract/apply.lux
new file mode 100644
index 000000000..5eb42b63d
--- /dev/null
+++ b/stdlib/source/lux/abstract/apply.lux
@@ -0,0 +1,36 @@
+(.module:
+  lux
+  [//
+   ["." functor (#+ Functor)]
+   [monad (#+ Monad)]])
+
+(signature: #export (Apply f)
+  {#.doc "Applicative functors."}
+  (: (Functor f)
+     &functor)
+  (: (All [a b]
+       (-> (f (-> a b)) (f a) (f b)))
+     apply))
+
+(structure: #export (compose f-monad f-apply g-apply)
+  {#.doc "Applicative functor composition."}
+  (All [F G]
+    (-> (Monad F) (Apply F) (Apply G)
+        ## TODO: Replace (All [a] (F (G a))) with (functor.Then F G)
+        (Apply (All [a] (F (G a))))))
+  
+  (def: &functor (functor.compose (get@ #&functor f-apply) (get@ #&functor g-apply)))
+  
+  (def: (apply fgf fgx)
+    ## TODO: Switch from this version to the one below (in comments) ASAP.
+    (let [fgf' (:: f-apply apply
+                   (:: f-monad wrap (:: g-apply apply))
+                   fgf)]
+      (:: f-apply apply fgf' fgx))
+    ## (let [applyF (:: f-apply apply)
+    ##       applyG (:: g-apply apply)]
+    ##   ($_ applyF
+    ##       (:: f-monad wrap applyG)
+    ##       fgf
+    ##       fgx))
+    ))