From 916fde61ae8c1effbf093ae73a1b5d215a3ba37b Mon Sep 17 00:00:00 2001
From: Tissevert <tissevert+devel@marvid.fr>
Date: Mon, 6 May 2019 16:47:29 +0200
Subject: [PATCH] Expose function follow to the outside of the module and use
 Map.lookup instead of (!?) for backward compatibility

---
 src/Graph.hs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/Graph.hs b/src/Graph.hs
index 88f9a67..313530d 100644
--- a/src/Graph.hs
+++ b/src/Graph.hs
@@ -3,14 +3,15 @@
 module Graph (
       Graph(..)
     , editLabel
+    , follow
     , open
     , rewind
     , singleton
     , weave
   ) where
 
-import Data.Map (Map, (!?))
-import qualified Data.Map as Map (delete, empty, insert, toList)
+import Data.Map (Map)
+import qualified Data.Map as Map (delete, empty, insert, lookup, toList)
 import Tree (Tree(..), Structure(..))
 
 data Vertex edge label = Vertex {
@@ -63,7 +64,7 @@ rewind = open . zipUp
 
 follow :: Ord edge => Graph edge label -> edge -> Maybe (Graph edge label)
 follow (Graph {focus, context}) edge =
-  edges focus !? edge >>= \vertex -> Just $ Graph {
+  Map.lookup edge (edges focus) >>= \vertex -> Just $ Graph {
       focus = vertex
     , context = Zipper {
           origin = context