From e85429629f0373b1484ba02250b2092fa2568e91 Mon Sep 17 00:00:00 2001
From: George Thomas <georgefsthomas@gmail.com>
Date: Tue, 9 Dec 2025 11:00:01 +0000
Subject: [PATCH] Generalise `allUnorderedPairs`

Now that it's in the prelude, the desire to remove diagonals is less obvious than it was.
---
 haskell/Pre.hs          | 4 ++--
 haskell/Puzzles/Day8.hs | 2 +-
 haskell/Puzzles/Day9.hs | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/haskell/Pre.hs b/haskell/Pre.hs
index 9447da9..7e6a5c5 100644
--- a/haskell/Pre.hs
+++ b/haskell/Pre.hs
@@ -108,5 +108,5 @@ listIndex n =
             [] -> Nothing
             x : xs -> if n == 0 then Just x else listIndex (n - 1) xs
 
-allUnorderedPairs :: [a] -> [(a, a)]
-allUnorderedPairs = concat . join (zipWith (flip $ map . (,)) . tail . tails)
+allUnorderedPairs :: Bool -> [a] -> [(a, a)]
+allUnorderedPairs diagonals = concat . join (zipWith (flip $ map . (,)) . (bool tail toList diagonals) . tails)
diff --git a/haskell/Puzzles/Day8.hs b/haskell/Puzzles/Day8.hs
index d0a730d..47d7ecf 100644
--- a/haskell/Puzzles/Day8.hs
+++ b/haskell/Puzzles/Day8.hs
@@ -40,4 +40,4 @@ puzzle =
 connectBoxes :: [V3 Int] -> [((V3 Int, V3 Int), DS.DisjointSet (V3 Int))]
 connectBoxes boxes = zip allPairs $ scanl (flip $ uncurry DS.union) (foldMap DS.singleton boxes) allPairs
   where
-    allPairs = sortOn (quadrance . uncurry (-)) $ allUnorderedPairs boxes
+    allPairs = sortOn (quadrance . uncurry (-)) $ allUnorderedPairs False boxes
diff --git a/haskell/Puzzles/Day9.hs b/haskell/Puzzles/Day9.hs
index 826eee3..740cc15 100644
--- a/haskell/Puzzles/Day9.hs
+++ b/haskell/Puzzles/Day9.hs
@@ -15,7 +15,7 @@ puzzle =
                 . fmap ((\(V2 x y) -> x * y) . (+ 1) . fmap abs . uncurry (-))
                 . fromMaybe (error "empty input")
                 . nonEmpty
-                . allUnorderedPairs
+                . allUnorderedPairs False
             ]
         , extraTests = mempty
         }