From f44bf6259e4b8de1e3a41a24d2d6663a6733c24a Mon Sep 17 00:00:00 2001
From: Tissevert <tissevert+devel@marvid.fr>
Date: Mon, 13 May 2019 18:27:49 +0200
Subject: [PATCH] Clarify a mapping over a Maybe for clearer syntax

---
 src/Graph.hs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/Graph.hs b/src/Graph.hs
index 09a2f7d..891ce4d 100644
--- a/src/Graph.hs
+++ b/src/Graph.hs
@@ -63,9 +63,9 @@ rewind graph = graph {focus = root graph}
 
 follow :: Ord edge => Graph edge label -> edge -> Maybe (Graph edge label)
 follow graph@(Graph {vertices, focus}) edge =
-  Map.lookup edge (edges $ vertices ! focus) >>= \vertexID -> Just $ graph {
-      focus = vertexID
-    }
+  setFocus <$> Map.lookup edge (edges $ vertices ! focus)
+  where
+    setFocus vertexID = graph {focus = vertexID}
 
 stitch :: (Monoid label, Ord edge) => Graph edge label -> edge -> Graph edge label
 stitch graph edge =