1 files changed, 27 insertions, 0 deletions
diff --git a/src/Binary.hs b/src/Binary.hs
new file mode 100644
index 0000000..4575c49
--- /dev/null
+++ b/src/Binary.hs
@@ -0,0 +1,27 @@
+module Binary
+  ( toBinary
+  , fromBinary
+  ) where
+
+import           Control.Applicative
+import           Data.Char
+import           Helper
+
+toBinary :: Expression -> String
+toBinary (Bruijn      x        ) = (replicate x '1') ++ "0"
+toBinary (Abstraction exp      ) = "00" ++ toBinary exp
+toBinary (Application exp1 exp2) = "01" ++ (toBinary exp1) ++ (toBinary exp2)
+
+-- Stolen from John Tromp
+fromBinary :: String -> Expression
+fromBinary = foldr
+  (\x -> Abstraction . (Application . Application (Bruijn 0) . code $ x))
+  nil
+ where
+  nil = code '1'
+  code '0' = Abstraction (Abstraction (Bruijn 1))
+  code '1' = Abstraction (Abstraction (Bruijn 0))
+  code x   = fromBinary (showsBin 8 (ord x) "")
+  showsBin n x = if n == 0
+    then id
+    else let (x', b) = divMod x 2 in showsBin (n - 1) x' . (intToDigit b :)