From b0b64b1593518e5e33d285934d375b08c939086a Mon Sep 17 00:00:00 2001
From: Jonathan Knowles <jonathan.knowles@iohk.io>
Date: Wed, 4 Sep 2019 06:47:16 +0000
Subject: [PATCH] Use `safe` library function `tailSafe` instead of
 locally-defined `tailOrEmpty`.

---
 lib/jormungandr/cardano-wallet-jormungandr.cabal          | 1 +
 lib/jormungandr/src/Cardano/Wallet/Jormungandr/Network.hs | 7 +++----
 nix/.stack.nix/cardano-wallet-jormungandr.nix             | 1 +
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/jormungandr/cardano-wallet-jormungandr.cabal b/lib/jormungandr/cardano-wallet-jormungandr.cabal
index 82df34f6978..5e1595ca8dc 100644
--- a/lib/jormungandr/cardano-wallet-jormungandr.cabal
+++ b/lib/jormungandr/cardano-wallet-jormungandr.cabal
@@ -49,6 +49,7 @@ library
     , http-client
     , http-types
     , memory
+    , safe
     , servant
     , servant-client
     , servant-client-core
diff --git a/lib/jormungandr/src/Cardano/Wallet/Jormungandr/Network.hs b/lib/jormungandr/src/Cardano/Wallet/Jormungandr/Network.hs
index 1aa8c5ce567..2ec00758bce 100644
--- a/lib/jormungandr/src/Cardano/Wallet/Jormungandr/Network.hs
+++ b/lib/jormungandr/src/Cardano/Wallet/Jormungandr/Network.hs
@@ -89,6 +89,8 @@ import Network.HTTP.Client
     ( Manager, defaultManagerSettings, newManager )
 import Network.HTTP.Types.Status
     ( status400 )
+import Safe
+    ( tailSafe )
 import Servant.API
     ( (:<|>) (..) )
 import Servant.Client
@@ -141,7 +143,7 @@ mkNetworkLayer j = NetworkLayer
         -- Get the descendants of the tip's /parent/.
         -- The first descendant is therefore the current tip itself. We need to
         -- skip it. Hence the 'tail'.
-        ids <- tailOrEmpty <$> getDescendantIds j (prevBlockHash tip) count
+        ids <- tailSafe <$> getDescendantIds j (prevBlockHash tip) count
                 `mappingError` \case
             ErrGetDescendantsNetworkUnreachable e ->
                 ErrGetBlockNetworkUnreachable e
@@ -165,9 +167,6 @@ mkNetworkLayer j = NetworkLayer
   where
     mappingError = flip withExceptT
 
-    tailOrEmpty [] = []
-    tailOrEmpty (_:xs) = xs
-
 {-------------------------------------------------------------------------------
                             Jormungandr Client
 -------------------------------------------------------------------------------}
diff --git a/nix/.stack.nix/cardano-wallet-jormungandr.nix b/nix/.stack.nix/cardano-wallet-jormungandr.nix
index 639cf875768..590509b32f1 100644
--- a/nix/.stack.nix/cardano-wallet-jormungandr.nix
+++ b/nix/.stack.nix/cardano-wallet-jormungandr.nix
@@ -38,6 +38,7 @@
           (hsPkgs.http-client)
           (hsPkgs.http-types)
           (hsPkgs.memory)
+          (hsPkgs.safe)
           (hsPkgs.servant)
           (hsPkgs.servant-client)
           (hsPkgs.servant-client-core)