Add more instances for Solo

Oleg Grenrus pointed out that `Solo` was missing `Eq`, `Ord`,
`Bounded`, `Enum`, and `Ix` instances, which were all apparently
available for the `OneTuple` type (in the `OneTuple` package).
Though only the first three really seem useful, there's no reason
not to take them all. For `Ix`, `Solo` naturally fills a gap
between `()` and `(,)`.

7 files changed, 42 insertions, 5 deletions

diff --git a/libraries/base/GHC/Enum.hs b/libraries/base/GHC/Enum.hs
index 2765dcd265..096e633894 100644
--- a/libraries/base/GHC/Enum.hs
+++ b/libraries/base/GHC/Enum.hs
@@ -36,6 +36,7 @@ import GHC.Char
 import GHC.Num.Integer
 import GHC.Num
 import GHC.Show
+import GHC.Tuple (Solo (..))
 default ()              -- Double isn't available yet
 
 -- | The 'Bounded' class is used to name the upper and lower limits of a
@@ -234,6 +235,22 @@ instance Enum () where
     enumFromTo () ()    = [()]
     enumFromThenTo () () () = let many = ():many in many
 
+instance Enum a => Enum (Solo a) where
+    succ (Solo a) = Solo (succ a)
+    pred (Solo a) = Solo (pred a)
+
+    toEnum x = Solo (toEnum x)
+
+    fromEnum (Solo x) = fromEnum x
+    enumFrom (Solo x) = [Solo a | a <- enumFrom x]
+    enumFromThen (Solo x) (Solo y) =
+      [Solo a | a <- enumFromThen x y]
+    enumFromTo (Solo x) (Solo y) =
+      [Solo a | a <- enumFromTo x y]
+    enumFromThenTo (Solo x) (Solo y) (Solo z) =
+      [Solo a | a <- enumFromThenTo x y z]
+
+deriving instance Bounded a => Bounded (Solo a)
 -- Report requires instances up to 15
 -- | @since 2.01
 deriving instance (Bounded a, Bounded b)
diff --git a/libraries/base/GHC/Ix.hs b/libraries/base/GHC/Ix.hs
index 34c4857b15..b523fe2b4f 100644
--- a/libraries/base/GHC/Ix.hs
+++ b/libraries/base/GHC/Ix.hs
@@ -26,6 +26,7 @@ import GHC.Num
 import GHC.Base
 import GHC.Real( fromIntegral )
 import GHC.Show
+import GHC.Tuple (Solo (..))
 
 -- | The 'Ix' class is used to map a contiguous subrange of values in
 -- a type onto integers.  It is used primarily for array indexing
@@ -266,6 +267,23 @@ instance Ix () where
     {-# INLINE index #-}  -- See Note [Inlining index]
     index b i = unsafeIndex b i
 
+instance Ix a => Ix (Solo a) where -- as derived
+    {-# SPECIALISE instance Ix (Solo Int) #-}
+
+    {-# INLINE range #-}
+    range (Solo l, Solo u) =
+      [ Solo i | i <- range (l,u) ]
+
+    {-# INLINE unsafeIndex #-}
+    unsafeIndex (Solo l, Solo u) (Solo i) =
+      unsafeIndex (l,u) i
+
+    {-# INLINE inRange #-}
+    inRange (Solo l, Solo u) (Solo i) =
+      inRange (l, u) i
+
+    -- Default method for index
+
 ----------------------------------------------------------------------
 -- | @since 2.01
 instance (Ix a, Ix b) => Ix (a, b) where -- as derived
diff --git a/libraries/ghc-prim/GHC/Classes.hs b/libraries/ghc-prim/GHC/Classes.hs
index fb9ea98581..2c874fb241 100644
--- a/libraries/ghc-prim/GHC/Classes.hs
+++ b/libraries/ghc-prim/GHC/Classes.hs
@@ -149,6 +149,7 @@ class  Eq a  where
     {-# MINIMAL (==) | (/=) #-}
 
 deriving instance Eq ()
+deriving instance Eq a => Eq (Solo a)
 deriving instance (Eq  a, Eq  b) => Eq  (a, b)
 deriving instance (Eq  a, Eq  b, Eq  c) => Eq  (a, b, c)
 deriving instance (Eq  a, Eq  b, Eq  c, Eq  d) => Eq  (a, b, c, d)
@@ -359,6 +360,7 @@ class  (Eq a) => Ord a  where
     {-# MINIMAL compare | (<=) #-}
 
 deriving instance Ord ()
+deriving instance Ord a => Ord (Solo a)
 deriving instance (Ord a, Ord b) => Ord (a, b)
 deriving instance (Ord a, Ord b, Ord c) => Ord (a, b, c)
 deriving instance (Ord a, Ord b, Ord c, Ord d) => Ord (a, b, c, d)
diff --git a/testsuite/tests/ado/T13242a.stderr b/testsuite/tests/ado/T13242a.stderr
index eb2bf062ca..f5dce341ac 100644
--- a/testsuite/tests/ado/T13242a.stderr
+++ b/testsuite/tests/ado/T13242a.stderr
@@ -29,7 +29,7 @@ T13242a.hs:13:13: error:
         instance Eq Ordering -- Defined in ‘GHC.Classes’
         instance Eq Integer -- Defined in ‘GHC.Num.Integer’
         instance Eq () -- Defined in ‘GHC.Classes’
-        ...plus 21 others
+        ...plus 22 others
         ...plus five instances involving out-of-scope types
         (use -fprint-potential-instances to see them all)
     • In a stmt of a 'do' block: return (x == x)
diff --git a/testsuite/tests/partial-sigs/should_fail/T10999.stderr b/testsuite/tests/partial-sigs/should_fail/T10999.stderr
index 356b068031..71bab83508 100644
--- a/testsuite/tests/partial-sigs/should_fail/T10999.stderr
+++ b/testsuite/tests/partial-sigs/should_fail/T10999.stderr
@@ -25,7 +25,7 @@ T10999.hs:8:28: error:
         instance Ord a => Ord (Set.Set a) -- Defined in ‘Data.Set.Internal’
         instance Ord Ordering -- Defined in ‘GHC.Classes’
         instance Ord Integer -- Defined in ‘GHC.Num.Integer’
-        ...plus 22 others
+        ...plus 23 others
         ...plus two instances involving out-of-scope types
         (use -fprint-potential-instances to see them all)
     • In the second argument of ‘($)’, namely ‘f ()’
diff --git a/testsuite/tests/typecheck/should_fail/T5095.stderr b/testsuite/tests/typecheck/should_fail/T5095.stderr
index 0bfbc41c80..e30898f74f 100644
--- a/testsuite/tests/typecheck/should_fail/T5095.stderr
+++ b/testsuite/tests/typecheck/should_fail/T5095.stderr
@@ -5,8 +5,8 @@ T5095.hs:9:11: error:
         instance [overlappable] Show a => Eq a -- Defined at T5095.hs:5:31
         instance Eq Ordering -- Defined in ‘GHC.Classes’
         instance Eq a => Eq (Maybe a) -- Defined in ‘GHC.Maybe’
-        ...plus 23 others
-        ...plus 7 instances involving out-of-scope types
+        ...plus 24 others
+        ...plus six instances involving out-of-scope types
         (use -fprint-potential-instances to see them all)
       (The choice depends on the instantiation of ‘a’
        To pick the first instance above, use IncoherentInstances
diff --git a/testsuite/tests/typecheck/should_fail/tcfail072.stderr b/testsuite/tests/typecheck/should_fail/tcfail072.stderr
index 0b69f4ef63..b91f96bf37 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail072.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail072.stderr
@@ -10,7 +10,7 @@ tcfail072.hs:23:13: error:
         instance Ord Ordering -- Defined in ‘GHC.Classes’
         instance Ord Integer -- Defined in ‘GHC.Num.Integer’
         instance Ord () -- Defined in ‘GHC.Classes’
-        ...plus 21 others
+        ...plus 22 others
         ...plus two instances involving out-of-scope types
         (use -fprint-potential-instances to see them all)
     • In the expression: g A