Add Ord instances for Interval, IntervalSet and IntervalMap

[googleson78]

The primary intended use case for these is to allow storage in maps and sets.

[Bodigrim]

I'm generally in favor of this.

@msakai what do you think?

[googleson78]

ping @msakai, should I put in the effort to get CI cleaned up for all versions on this, or is this patch undesirable overall?

[msakai]

Sorry for the delay. I will take a look.

[msakai]

It is a bit unnatural, just like defining Ord instances of Complex, but if there is a demand or a use case that a user wants to use Map/Set instead of HashMap/HashSet, I think it is okay to add.

[msakai]

@googleson78
The following change fixes CI failure at least on GHC-8.10.7. Could you try this?

diff --git a/src/Data/Interval/Internal.hs b/src/Data/Interval/Internal.hs
index 16890a4..ae26189 100644
--- a/src/Data/Interval/Internal.hs
+++ b/src/Data/Interval/Internal.hs
@@ -56,12 +56,12 @@ data Interval r
   | RightOpen !r !r
   | BothOpen !r !r
   deriving
-    ( Eq,
-      Ord,
+    ( Eq
+    , Ord
       -- ^ Note that this Ord is derived and not semantically meaningful.
       -- The primary intended use case is to allow using 'Interval'
       -- in maps and sets that require ordering.
-      Typeable
+    , Typeable
     )
 
 peekInterval :: (Applicative m, Monad m, Ord r) => m Int8 -> m r -> m r -> m (Interval r)
diff --git a/src/Data/IntervalMap/Base.hs b/src/Data/IntervalMap/Base.hs
index 556e763..f8a4979 100644
--- a/src/Data/IntervalMap/Base.hs
+++ b/src/Data/IntervalMap/Base.hs
@@ -124,12 +124,12 @@ import qualified GHC.Exts as GHCExts
 -- even if adjacent intervals are connected and mapped to the same value.
 newtype IntervalMap r a = IntervalMap (Map (LB r) (Interval r, a))
   deriving
-    ( Eq,
-      Ord,
+    ( Eq
+    , Ord
       -- ^ Note that this Ord is derived and not semantically meaningful.
       -- The primary intended use case is to allow using 'IntervalSet'
       -- in maps and sets that require ordering.
-      Typeable
+    , Typeable
     )
 
 #if __GLASGOW_HASKELL__ >= 708
diff --git a/src/Data/IntervalSet.hs b/src/Data/IntervalSet.hs
index 7e44647..fac557e 100644
--- a/src/Data/IntervalSet.hs
+++ b/src/Data/IntervalSet.hs
@@ -89,12 +89,12 @@ import qualified GHC.Exts as GHCExts
 -- Any connected intervals are merged together, and empty intervals are ignored.
 newtype IntervalSet r = IntervalSet (Map (Extended r) (Interval r))
   deriving
-    ( Eq,
-      Ord,
+    ( Eq
+    , Ord
       -- ^ Note that this Ord is derived and not semantically meaningful.
       -- The primary intended use case is to allow using 'IntervalSet'
       -- in maps and sets that require ordering.
-      Typeable
+    , Typeable
     )
 
 #if __GLASGOW_HASKELL__ >= 708

It seems the feature for writing comments in this location was added in GHC 8.2.1.

• https://gitlab.haskell.org/ghc/ghc/-/issues/11768
• ghc/ghc@6971430

I think it's okay to drop support for GHC <8.2. (We can update the build matrix in a separate PR)

[Bodigrim]

Dropped support of GHC < 8.2 in 4115223. @googleson78 could you please rebase and try to fix haddocks as suggested?

[googleson78]

Added Masahiro's patch and rebased on master, 🤞

[Bodigrim]

Thanks!

[googleson78]

Thanks to the both of you too!