chapter 24 - added alt parsing example

Author: mukeshsoni

chapter24/learning-parsers/learning-parsers.cabal

@@ -19,4 +19,5 @@ executable learning-parsers
   default-language:    Haskell2010
   build-depends:       base >= 4.7 && < 5
                      , trifecta
-                     , parsers
+                     , parsers
+                     , raw-strings-qq

chapter24/learning-parsers/src/AltParsing.hs

@@ -0,0 +1,27 @@
+{-# LANGUAGE QuasiQuotes #-}
+module AltParsing where
+
+import Control.Applicative
+import Text.RawString.QQ
+import Text.Trifecta
+
+type NumberOrString =
+    Either Integer String
+
+eitherOr = [r|
+123
+def
+456
+ghi
+|]
+
+parseNos :: Parser NumberOrString
+parseNos =
+    skipMany (oneOf "\n")
+    >>
+    (Left <$> integer)
+    <|> (Right <$> some letter)
+
+main = do
+    print $ parseString parseNos mempty eitherOr
+    print $ parseString (some (token parseNos)) mempty eitherOr