From 14b8c850a92ec30889f388361ed95843a46d55c8 Mon Sep 17 00:00:00 2001
From: Jaro <jaro@argonaut-constellation.org>
Date: Sun, 4 Jun 2023 06:05:10 +0200
Subject: [PATCH] Implement unions of lists of rectangles.

---
 .../Text/ParagraphLayout/Internal/Rect.hs     | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/Data/Text/ParagraphLayout/Internal/Rect.hs b/src/Data/Text/ParagraphLayout/Internal/Rect.hs
index ec5b9cd..880116d 100644
--- a/src/Data/Text/ParagraphLayout/Internal/Rect.hs
+++ b/src/Data/Text/ParagraphLayout/Internal/Rect.hs
@@ -5,6 +5,8 @@ module Data.Text.ParagraphLayout.Internal.Rect
     , Rect (Rect, x_origin, y_origin, x_size, y_size)
     , height
     , union
+    , unionMany
+    , unionMany1
     , width
     , x_max
     , x_min
@@ -15,6 +17,8 @@ module Data.Text.ParagraphLayout.Internal.Rect
     )
 where
 
+import Data.List.NonEmpty (NonEmpty, nonEmpty)
+
 -- | An axis-aligned rectangle on a 2D plane.
 data Rect a = Rect
     { x_origin :: a
@@ -101,3 +105,21 @@ union bias a b =
         hy = y_max a `max` y_max b
         dx = hx - lx
         dy = hy - ly
+
+-- | `Just` the `union` of all given rectangles, or `Nothing` if none are given.
+unionMany :: (Num a, Ord a) => Bias -> [Rect a] -> Maybe (Rect a)
+unionMany bias rects = unionMany1 bias <$> nonEmpty rects
+
+-- | The `union` of all given rectangles, where at least one must be given.
+--
+-- Note that adding a default value to the input list to make it non-empty
+-- will probably not do what you want, since the `union` operation has no
+-- identity element.
+--
+-- If you need a default output value for empty inputs, consider using:
+--
+-- @
+-- `Data.Maybe.fromMaybe` yourDefaultValue $ `unionMany` bias rects
+-- @
+unionMany1 :: (Num a, Ord a) => Bias -> NonEmpty (Rect a) -> Rect a
+unionMany1 bias rects = foldr1 (union bias) rects
-- 
2.30.2