From 938550b784269855dcc2a77a29fc3bbfe181be73 Mon Sep 17 00:00:00 2001
From: Andrzej Rybczak <andrzej@rybczak.net>
Date: Sat, 22 Jan 2022 16:56:09 +0100
Subject: [PATCH] Add :>> for more concise type signatures

---
 effectful-core/src/Effectful.hs                 |  1 +
 effectful-core/src/Effectful/Internal/Effect.hs | 11 +++++++++++
 effectful-core/src/Effectful/Monad.hs           |  1 +
 3 files changed, 13 insertions(+)

diff --git a/effectful-core/src/Effectful.hs b/effectful-core/src/Effectful.hs
index 5e02b37d..bc83c155 100644
--- a/effectful-core/src/Effectful.hs
+++ b/effectful-core/src/Effectful.hs
@@ -7,6 +7,7 @@ module Effectful
   , Dispatch(..)
   , DispatchOf
   , (:>)
+  , (:>>)
 
   -- * Running the 'Eff' monad
 
diff --git a/effectful-core/src/Effectful/Internal/Effect.hs b/effectful-core/src/Effectful/Internal/Effect.hs
index 58714a83..84a0fa26 100644
--- a/effectful-core/src/Effectful/Internal/Effect.hs
+++ b/effectful-core/src/Effectful/Internal/Effect.hs
@@ -8,6 +8,7 @@
 module Effectful.Internal.Effect
   ( Effect
   , (:>)(..)
+  , (:>>)
 
   -- * Re-exports
   , Type
@@ -51,3 +52,13 @@ instance {-# OVERLAPPING #-} e :> (e : es) where
 
 instance e :> es => e :> (x : es) where
   reifyIndex = 1 + reifyIndex @e @es
+
+----------------------------------------
+
+-- | Convenience operator for expressing that a function uses multiple effects
+-- in a more concise way than enumerating them all with '(:>)'.
+--
+-- @[E1, E2, ..., En] ':>>' es ≡ (E1 ':>' es, E2 ':>' es, ..., En :> es)@
+type family effs :>> es :: Constraint where
+  '[]        :>> es = ()
+  (e : effs) :>> es = (e :> es, effs :>> es)
diff --git a/effectful-core/src/Effectful/Monad.hs b/effectful-core/src/Effectful/Monad.hs
index 0e909cc9..0b7bccf0 100644
--- a/effectful-core/src/Effectful/Monad.hs
+++ b/effectful-core/src/Effectful/Monad.hs
@@ -8,6 +8,7 @@ module Effectful.Monad
   , Dispatch(..)
   , DispatchOf
   , (:>)
+  , (:>>)
 
   -- * Arbitrary I/O
   , IOE