From 2eb37dfb7ca72b08fb3da15d4bdb7b77b428c18f Mon Sep 17 00:00:00 2001
From: Alice McKean <mckean.kylej@gmail.com>
Date: Sun, 1 Sep 2019 22:56:06 -0700
Subject: [PATCH] add monoidal unit for Bounded Builders

---
 src/Data/ByteArray/Builder/Small/Bounded.hs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Data/ByteArray/Builder/Small/Bounded.hs b/src/Data/ByteArray/Builder/Small/Bounded.hs
index 429e0c5..892b36d 100644
--- a/src/Data/ByteArray/Builder/Small/Bounded.hs
+++ b/src/Data/ByteArray/Builder/Small/Bounded.hs
@@ -22,6 +22,7 @@ module Data.ByteArray.Builder.Small.Bounded
   , pasteGrowST
   , pasteIO
     -- * Combine
+  , empty
   , append
     -- * Bounds Manipulation
   , (<=)
@@ -136,6 +137,10 @@ construct f = Builder
 
 infixr 9 `append`
 
+-- | The monoidal unit of `append`
+empty :: Builder 0
+empty = Builder $ \_ off0 s0 -> (# s0, off0 #)
+
 -- | Concatenate two builders.
 append :: Builder n -> Builder m -> Builder (n + m)
 append (Builder f) (Builder g) =