From f9173c06b76fbbb70ff14b1a51dd1e0115a0f917 Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@me.com>
Date: Wed, 31 May 2017 15:22:32 -0400
Subject: [PATCH] Define a type family to constrain every element of a list of
 types.

---
 src/Data/Record.hs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/Data/Record.hs b/src/Data/Record.hs
index 57662d633..891275957 100644
--- a/src/Data/Record.hs
+++ b/src/Data/Record.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE DataKinds, GADTs, KindSignatures, MultiParamTypeClasses, TypeOperators #-}
+{-# LANGUAGE ConstraintKinds, DataKinds, GADTs, KindSignatures, MultiParamTypeClasses, TypeFamilies, TypeOperators #-}
 module Data.Record where
 
 import Data.Functor.Listable
@@ -30,6 +30,10 @@ class HasField (fields :: [*]) (field :: *) where
   getField :: Record fields -> field
   setField :: Record fields -> field -> Record fields
 
+type family ConstrainAll (toConstraint :: * -> Constraint) (fs :: [*]) :: Constraint where
+  ConstrainAll toConstraint (f ': fs) = (toConstraint f, ConstrainAll toConstraint fs)
+  ConstrainAll _ '[] = ()
+
 
 -- Instances