Add NFData Graph instance (snowleopard#26)

.gitignore

@@ -1,5 +1,6 @@
 dist
 dist-*
+.ghc.environment.*
 cabal-dev
 *.o
 *.hi

CHANGES.md

@@ -1,5 +1,9 @@
 # Change log
 
+## next
+
+* add `NFData Graph` instance
+
 ## 0.0.5
 
 * Add `dfs`.

algebraic-graphs.cabal

@@ -69,7 +69,8 @@ library
                         Algebra.Graph.Relation.Transitive
     build-depends:      array      >= 0.5 && < 0.8,
                         base       >= 4.9 && < 5,
-                        containers >= 0.5 && < 0.8
+                        containers >= 0.5 && < 0.8,
+                        deepseq    >= 1.4.2.0 && <1.5
     default-language:   Haskell2010
     default-extensions: FlexibleContexts
                         GeneralizedNewtypeDeriving

src/Algebra/Graph.hs

@@ -47,6 +47,7 @@ module Algebra.Graph (
   ) where
 
 import Control.Applicative (Alternative, (<|>))
+import Control.DeepSeq (NFData (..))
 import Control.Monad
 
 import qualified Algebra.Graph.AdjacencyMap       as AM
@@ -138,6 +139,12 @@ data Graph a = Empty
              | Connect (Graph a) (Graph a)
              deriving (Foldable, Functor, Show, Traversable)
 
+instance NFData a => NFData (Graph a) where
+    rnf Empty         = ()
+    rnf (Vertex a)    = rnf a
+    rnf (Overlay x y) = rnf x `seq` rnf y
+    rnf (Connect x y) = rnf x `seq` rnf y
+
 instance C.Graph (Graph a) where
     type Vertex (Graph a) = a
     empty   = empty