fixed initTails for [a]

mono-traversable/src/Data/Sequences.hs

@@ -474,13 +474,13 @@ class (Monoid seq, MonoTraversable seq, SemiSequence seq, MonoPointed seq) => Is
 
     -- | Returns all the final segments of 'seq' with the longest first.
     --
-    -- @since 1.0.15.4
+    -- @since ????
     tails :: seq -> [seq]
     tails x = x : maybe mempty tails (tailMay x)
 
     -- | Return all the initial segments of 'seq' with the shortest first.
     --
-    -- @since 1.0.15.4
+    -- @since ????
     inits :: seq -> [seq]
     inits seq = is seq [seq]
       where
@@ -493,7 +493,7 @@ class (Monoid seq, MonoTraversable seq, SemiSequence seq, MonoPointed seq) => Is
     -- [([],[1,2]), ([1],[2]), ([1,2],[])]
     -- @
     --
-    -- @since 1.0.15.4
+    -- @since ????
     initTails :: seq -> [(seq,seq)]
     initTails seq = List.zip (inits seq) (tails seq)
 
@@ -641,7 +641,7 @@ instance IsSequence [a] where
       where
         its :: ([a] -> [a]) -> [a] -> [([a],[a])]
         its f xs@(y:ys) = (f [], xs) : its (f . (y:)) ys
-        its _ [] = []
+        its f [] = [(f [], [])]
     {-# INLINE fromList #-}
     {-# INLINE break #-}
     {-# INLINE span #-}

mono-traversable/test/Main.hs

@@ -205,9 +205,31 @@ main = hspec $ do
         test "works on strict texts" T.empty
         test "works on lazy texts" TL.empty
 
+    describe "inits" $ do
+        let test typ emptyTyp = describe typ $ do
+              it "empty" $ inits emptyTyp @?= [""]
+              it "one element" $ inits ("a" <> emptyTyp) @?= ["", "a"]
+              it "two elements" $ inits ("ab" <> emptyTyp) @?= ["", "a", "ab"]
+        test "StrictBytestring" S.empty
+        test "LazyBytestring" L.empty
+        test "StrictText" T.empty
+        test "LazyText" TL.empty
+        test "String" (mempty :: String)
+
+    describe "tails" $ do
+        let test typ emptyTyp = describe typ $ do
+              it "empty" $ tails emptyTyp @?= [""]
+              it "one element" $ tails ("a" <> emptyTyp) @?= ["a", ""]
+              it "two elements" $ tails ("ab" <> emptyTyp) @?= ["ab", "b", ""]
+        test "StrictBytestring" S.empty
+        test "LazyBytestring" L.empty
+        test "StrictText" T.empty
+        test "LazyText" TL.empty
+        test "String" (mempty :: String)
+
     describe "initTails" $ do
         let test typ emptyTyp = describe typ $ do
-              it "empty" $ initTails emptyTyp @?= []
+              it "empty" $ initTails emptyTyp @?= [("","")]
               it "one element" $ initTails ("a" <> emptyTyp) @?= [("","a"), ("a","")]
               it "two elements" $ initTails ("ab" <> emptyTyp) @?= [("","ab"), ("a","b"), ("ab","")]
         test "StrictBytestring" S.empty