1 files changed, 31 insertions, 0 deletions
diff --git a/stdlib/source/specification/lux/abstract/functor/contravariant.lux b/stdlib/source/specification/lux/abstract/functor/contravariant.lux
new file mode 100644
index 000000000..cba839e94
--- /dev/null
+++ b/stdlib/source/specification/lux/abstract/functor/contravariant.lux
@@ -0,0 +1,31 @@
+(.module:
+  [library
+   [lux #*
+    ["_" test (#+ Test)]
+    [abstract
+     [equivalence (#+ Equivalence)]
+     [monad (#+ do)]]
+    [control
+     ["." function]]
+    [math
+     ["." random]
+     [number
+      ["n" nat]]]]]
+  [\\library
+   ["." / (#+ Functor)]])
+
+(def: (identity equivalence value (^open "@//."))
+  (All [f a] (-> (Equivalence (f a)) (f a) (Functor f) Test))
+  (_.test "Law of identity."
+          (equivalence
+           (@//map function.identity value)
+           value)))
+
+(def: #export (spec equivalence value functor)
+  (All [f a] (-> (Equivalence (f a)) (f a) (Functor f) Test))
+  (do random.monad
+    [sample random.nat]
+    (<| (_.for [/.Functor])
+        ($_ _.and
+            (..identity equivalence value functor)
+            ))))