1 files changed, 33 insertions, 0 deletions
diff --git a/stdlib/source/lux/data/trace.lux b/stdlib/source/lux/data/trace.lux
new file mode 100644
index 000000000..f8094565b
--- /dev/null
+++ b/stdlib/source/lux/data/trace.lux
@@ -0,0 +1,33 @@
+(;module:
+  lux
+  (lux (control ["m" monoid]
+                functor
+                comonad)
+       [macro]))
+
+(type: #export (Trace t a)
+  {#monoid (m;Monoid t)
+   #trace (-> t a)})
+
+(struct: #export Functor<Trace> (All [t] (Functor (Trace t)))
+  (def: (map f fa)
+    (update@ #trace (. f) fa)))
+
+(struct: #export CoMonad<Trace> (All [t] (CoMonad (Trace t)))
+  (def: functor Functor<Trace>)
+
+  (def: (unwrap wa)
+    ((get@ #trace wa)
+     (get@ [#monoid #m;unit] wa)))
+
+  (def: (split wa)
+    (let [monoid (get@ #monoid wa)]
+      {#monoid monoid
+       #trace (lambda [t1]
+                {#monoid monoid
+                 #trace (lambda [t2] ((get@ #trace wa)
+                                 (:: monoid append t1 t2)))})})))
+
+(def: #export (run context tracer)
+  (All [t a] (-> t (Trace t a) a))
+  (:: tracer trace context))