Unique dependencies in dot graph (#713)

* Add dotgen to stack.yaml

* Generate strict dot graph (prune redundant connections)

dhall/src/Dhall/Main.hs

@@ -300,7 +300,7 @@ command (Options {..}) = do
                 State.runStateT (Dhall.Import.loadWith expression) status
 
             if   dot
-            then putStr . Text.Dot.showDot $
+            then putStr . ("strict " <>) . Text.Dot.showDot $
                  Text.Dot.attribute ("rankdir", "LR") >> _dot
             else render System.IO.stdout resolvedExpression
 

stack.yaml

@@ -9,6 +9,7 @@ extra-deps:
   - repline-0.2.0.0
   - serialise-0.2.1.0
   - neat-interpolation-0.3.2.4
+  - dotgen-0.4.2@sha256:309b7cc8a3593a8e48bee7b53020d5f72db156d58edf78a0214f58fbb84b292b
 nix:
   packages:
     - ncurses