From: Ramakrishnan Muthukrishnan Date: Sat, 27 Dec 2014 06:15:50 +0000 (+0530) Subject: Add functor instance of parser X-Git-Url: https://git.rkrishnan.org/%5B/%5D%20/file/URI:LIT:krugkidfnzsc4/frontends/something?a=commitdiff_plain;h=981fe0e31a3314dd7b7533f1c3eb6ae8409aa057;p=yorgey.git Add functor instance of parser --- diff --git a/hw10/AParser.hs b/hw10/AParser.hs index 0ee3090..7860c07 100644 --- a/hw10/AParser.hs +++ b/hw10/AParser.hs @@ -57,3 +57,13 @@ posInt = Parser f ------------------------------------------------------------ -- Your code goes below here ------------------------------------------------------------ + +-- Exercise 1. functor instance for Parser +instance Functor Parser where + -- Parser a == String -> (a, String) + -- first :: (a -> b) -> (a, c) -> (b, c) + -- fmap :: (a -> b) -> Parser a -> Parser b + fmap f (Parser pf) = Parser (\s -> case (pf s) of + Nothing -> Nothing + Just v -> Just $ (uncurry (first f) v)) + where first f' a b = (f' a, b)