From 2b97d32db53ffb773e10d585e0a184ab40666036 Mon Sep 17 00:00:00 2001
From: Fraser Tweedale <frase@frase.id.au>
Date: Thu, 29 Sep 2022 22:50:31 +1000
Subject: [PATCH] renderBox: avoid unnecessary use of dlist

`renderBox` uses dlist to grow the result list while doing a render
traversal.  An ordinary fmap'd list construction suffices and offers
a very small but measurable performance boost.

Furthermore this is the only place the *dlist* library was used so
*brick* no longer depends on it.
---
 brick.cabal               |  1 -
 src/Brick/Widgets/Core.hs | 11 +++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/brick.cabal b/brick.cabal
index d7f341a..d89293f 100644
--- a/brick.cabal
+++ b/brick.cabal
@@ -123,7 +123,6 @@ library
                        bimap >= 0.5 && < 0.6,
                        data-clist >= 0.1,
                        directory >= 1.2.5.0,
-                       dlist,
                        exceptions >= 0.10.0,
                        filepath,
                        containers >= 0.5.7,
diff --git a/src/Brick/Widgets/Core.hs b/src/Brick/Widgets/Core.hs
index 68a1c74..2c16ace 100644
--- a/src/Brick/Widgets/Core.hs
+++ b/src/Brick/Widgets/Core.hs
@@ -126,7 +126,6 @@ import Control.Monad.State.Strict
 import Control.Monad.Reader
 import qualified Data.Foldable as F
 import qualified Data.Text as T
-import qualified Data.DList as DL
 import qualified Data.Map as M
 import qualified Data.Set as S
 import qualified Data.IMap as I
@@ -642,15 +641,15 @@ renderBox br ws =
       let availPrimary = c^.(contextPrimary br)
           availSecondary = c^.(contextSecondary br)
 
-          renderHis _ prev [] = return $ DL.toList prev
-          renderHis remainingPrimary prev ((i, prim):rest) = do
+          renderHis _ [] = pure []
+          renderHis remainingPrimary ((i, prim):rest) = do
               result <- render $ limitPrimary br remainingPrimary
                                $ limitSecondary br availSecondary
                                $ cropToContext prim
-              renderHis (remainingPrimary - (result^.imageL.(to $ imagePrimary br)))
-                        (DL.snoc prev (i, result)) rest
+              let newRem = remainingPrimary - (result^.imageL.(to $ imagePrimary br))
+              ((i, result) :) <$> renderHis newRem rest
 
-      renderedHis <- renderHis availPrimary DL.empty his
+      renderedHis <- renderHis availPrimary his
 
       renderedLows <- case lows of
           [] -> return []