Merge pull request #185 from snoyberg/nonNullToNonEmpty

Add function to convert from NonNull to NonEmpty
snoyberg · Dec 24, 2019 · c6faffa · c6faffa
2 parents 4ab1d16 + 9c9e039
commit c6faffa
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diff --git a/mono-traversable/ChangeLog.md b/mono-traversable/ChangeLog.md
@@ -1,3 +1,7 @@
+## 1.0.15.0
+* Added `toNonEmpty` to `Data.NonNull`
+  [#185](https://github.com/snoyberg/mono-traversable/pull/185)
+
 ## 1.0.14.0
 * Added `WrappedMono` to `Data.MonoTraversable`
   [#182](https://github.com/snoyberg/mono-traversable/pull/182)

diff --git a/mono-traversable/package.yaml b/mono-traversable/package.yaml
@@ -1,5 +1,5 @@
 name:        mono-traversable
-version:     1.0.14.0
+version:     1.0.15.0
 synopsis:    Type classes for mapping, folding, and traversing monomorphic containers
 description: Please see the README at <https://www.stackage.org/package/mono-traversable>
 category:    Data

diff --git a/mono-traversable/src/Data/NonNull.hs b/mono-traversable/src/Data/NonNull.hs
@@ -16,6 +16,7 @@ module Data.NonNull (
   , nonNull
   , toNullable
   , fromNonEmpty
+  , toNonEmpty
   , ncons
   , nuncons
   , splitFirst
@@ -132,6 +133,12 @@ fromNonEmpty :: IsSequence seq => NE.NonEmpty (Element seq) -> NonNull seq
 fromNonEmpty = impureNonNull . fromList . NE.toList
 {-# INLINE fromNonEmpty #-}
 
+-- | __Safely__ convert from a 'NonNull' container to a 'NonEmpty' list.
+--
+-- @since 1.0.15.0
+toNonEmpty :: MonoFoldable mono => NonNull mono -> NE.NonEmpty (Element mono)
+toNonEmpty = NE.fromList . otoList
+
 -- | Specializes 'fromNonEmpty' to lists only.
 toMinList :: NE.NonEmpty a -> NonNull [a]
 toMinList = fromNonEmpty

diff --git a/mono-traversable/test/Spec.hs b/mono-traversable/test/Spec.hs
@@ -209,6 +209,9 @@ main = hspec $ do
         describe "fromNonEmpty" $ do
             prop "toMinList" $ \(NonEmpty' ne) ->
                 (NE.toList ne :: [Int]) @?= NN.toNullable (NN.toMinList ne)
+        describe "toNonEmpty" $ do
+            it "converts nonnull to nonempty" $ do
+                NN.toNonEmpty (NN.impureNonNull [1,2,3]) @?= NE.fromList [1,2,3]
 
         describe "mapNonNull" $ do
             prop "mapNonNull id == id" $ \x xs ->