Add an initial 'lazy list' for doing backtracking

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

src/Bergamot/Search.elm

@@ -0,0 +1,25 @@
+module Bergamot.Search exposing (..)
+
+type SearchStep a
+    = Empty
+    | Found a (Search a)
+
+type alias Search a = () -> SearchStep a
+
+map : (a -> b) -> Search a -> Search b
+map f s () =
+    case s () of
+        Empty -> Empty
+        Found a sp -> Found (f a) (map f sp)
+
+interleave : Search a -> Search a -> Search a
+interleave s1 s2 () =
+    case s1 () of
+        Empty -> s2 ()
+        Found a s1p -> Found a (interleave s2 s1p)
+
+one : Search a -> Maybe (a, Search a)
+one s =
+    case s () of
+        Empty -> Nothing
+        Found a sp -> Just (a, sp)