Solve day 8 part 2

haskell/Pre.hs

@@ -25,6 +25,7 @@ module Pre (
     module Data.Void,
     module Data.Word,
     module Linear,
+    module Safe,
     module Test.Tasty,
     module Test.Tasty.Golden,
     module Test.Tasty.HUnit,
@@ -71,6 +72,7 @@ import Data.Traversable
 import Data.Void
 import Data.Word
 import Linear (V2 (..))
+import Safe
 import Test.Tasty
 import Test.Tasty.Golden hiding (Always)
 import Test.Tasty.HUnit

haskell/Puzzles/Day8.hs

@@ -24,6 +24,11 @@ puzzle =
                     -- TODO more principled way of distinguishing example and real
                     (!! ((if length boxes == 20 then 10 else if length boxes == 1000 then 1000 else undefined))) $
                         connectBoxes boxes
+            , TL.show
+                . maybe (error "sets never unified") (\((V3 x1 _ _, V3 x2 _ _), _) -> x1 * x2)
+                . lastMay
+                . takeWhile ((> 1) . DS.sets . snd)
+                . connectBoxes
             ]
         , extraTests = mempty
         }

outputs/real/8/2

@@ -0,0 +1 @@
+78894156