I'm working through Write You a Haskell, and I'm on the part where he implements "Nanoparsec", a Haskell parser from first principles. I'm getting stuck on the Alternative instance of the parser, specifically the some and many implementations:
instance Alternative Parser where
-- empty = ...
-- (<|>) p q = ...
some v = some_v
where
many_v = some_v <|> pure []
some_v = (:) <$> v <*> many_v
many v = many_v
where
many_v = some_v <|> pure []
some_v = (:) <$> v <*> many_v
I have no idea what these two functions are doing. From what I can see, some takes a parser, applies it, and concatenates the result until the input is used up. But many looks like it does the same thing. What's happening here?
