Add basic definition of Parser type

Author: evturn

13-monadic-parsing.hs/13.04-basic-definitions.hs

@@ -0,0 +1,13 @@
+import           Control.Applicative
+import           Data.Char
+
+newtype Parser a = P (String -> [(a, String)])
+
+parse :: Parser a -> String -> [(a, String)]
+parse (P p) inp = p inp
+
+item :: Parser Char
+item = P $ \inp ->
+  case inp of
+    []     -> []
+    (x:xs) -> [(x, xs)]