From 8d9562e94ee217a8f1d76f327b7c914fa738e598 Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@github.com>
Date: Thu, 5 Jan 2017 14:40:28 -0500
Subject: [PATCH] Define a lifting of cons3.

---
 src/Data/Functor/Listable.hs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Data/Functor/Listable.hs b/src/Data/Functor/Listable.hs
index f847c8d11..e5dcc727f 100644
--- a/src/Data/Functor/Listable.hs
+++ b/src/Data/Functor/Listable.hs
@@ -14,6 +14,7 @@ module Data.Functor.Listable
 , tiers2
 , liftCons1
 , liftCons2
+, liftCons3
 ) where
 
 import Prologue
@@ -39,6 +40,10 @@ liftCons1 tiers f = mapT f tiers `addWeight` 1
 liftCons2 :: [[a]] -> [[b]] -> (a -> b -> c) -> [[c]]
 liftCons2 tiers1 tiers2 f = mapT (uncurry f) (productWith (,) tiers1 tiers2) `addWeight` 1
 
+liftCons3 :: [[a]] -> [[b]] -> [[c]] -> (a -> b -> c -> d) -> [[d]]
+liftCons3 tiers1 tiers2 tiers3 f = mapT (uncurry3 f) (productWith (\ x (y, z) -> (x, y, z)) tiers1 (liftCons2 tiers2 tiers3 (,)) ) `addWeight` 1
+  where uncurry3 f (a, b, c) = f a b c
+
 
 -- Instances