From: Ramakrishnan Muthukrishnan <ram@rkrishnan.org>
Date: Sat, 27 Dec 2014 09:59:51 +0000 (+0530)
Subject: hw10: exercises 4 and 5
X-Git-Url: https://git.rkrishnan.org/%5B/frontends/%22news.html/?a=commitdiff_plain;h=0bb04c08d8232187dc73265e9a675f84c8e48d26;p=yorgey.git

hw10: exercises 4 and 5
---

diff --git a/hw10/AParser.hs b/hw10/AParser.hs
index f506fcb..04eb6ad 100644
--- a/hw10/AParser.hs
+++ b/hw10/AParser.hs
@@ -96,3 +96,17 @@ abParser_ = (\_ _ -> ()) <$> char 'a' <*> char 'b'
 
 intPair :: Parser [Integer]
 intPair = (\x _ z -> x : z : []) <$> posInt <*> char ' ' <*> posInt
+
+-- Exercise 4
+-- class Applicative f => Alternative f where
+--     empty :: f a
+--     (<|>) :: f a -> f a -> f a
+instance Alternative Parser where
+    empty = Parser(\_ -> Nothing)
+    (Parser p1) <|> (Parser p2) = Parser (\inp -> case (p1 inp) of
+                                                    Nothing -> (p2 inp)
+                                                    Just v -> Just v)
+
+-- exercise 5: int or Uppercase
+intOrUppercase :: Parser ()
+intOrUppercase = ((\_ -> ()) <$> posInt) <|> ((\_ -> ()) <$> (satisfy isUpper))