test.txt


1
2
3
4
5
6
7
8
9
10

fmap f p = Parser ((.) (fmapEither (fmap1st f)) (runParser p));

fmapEither f e = case e of {
    Left x  -> Left x;
    Right x -> Right (f x)
};

fmap1st f p = case p of {
    (l, r) -> (f l, r)
};