address sequenceTuple issue

src/Swarm/Game/Scenario/Topography/Navigation/Portal.hs

@@ -257,22 +257,36 @@ ensureSpatialConsistency xs =
   nonUniform :: Map (SubworldName, SubworldName) (NonEmpty (V2 Int32))
   nonUniform = M.filter ((not . allEqual) . NE.toList) vectorized
 
--- | This signature looks a lot like the Traversable instance:
+-- |
+-- An implementation of 'sequenceA' for 'Signed' that does not
+-- require an 'Applicative' instance for the inner 'Functor'.
+--
+-- == Discussion
+-- Compare to the 'Traversable' instance of 'Signed':
 -- @
 -- instance Traversable Signed where
 --   traverse f (Positive x) = Positive <$> f x
 --   traverse f (Negative x) = Negative <$> f x
 -- @
 --
--- if we were to substitute "id" for f:
+-- if we were to substitute 'id' for f:
 -- @
 --   traverse id (Positive x) = Positive <$> id x
 --   traverse id (Negative x) = Negative <$> id x
 -- @
+-- our implementation essentially becomes @traverse id@.
+--
+-- However, we cannot simply write our implementation as @traverse id@, because
+-- the 'traverse' function has an 'Applicative' constraint, which is superfluous
+-- for our purpose.
+--
+-- Perhaps there is an opportunity to invent a typeclass for datatypes which
+-- consist exclusively of unary (or more ambitiously, non-nullary?) data constructors,
+-- for which a less-constrained 'sequence' function could be automatically derived.
 sequenceSigned ::
   Functor f =>
   Signed (f a) ->
   f (Signed a)
 sequenceSigned = \case
   Positive x -> Positive <$> x
-  Negative x -> Negative <$> x
+  Negative x -> Negative <$> x

src/Swarm/Util.hs

@@ -22,7 +22,7 @@ module Swarm.Util (
   findDup,
   both,
   allEqual,
-  
+
   -- * Directory utilities
   readFileMay,
   readFileMayT,