Write You a Haskell Stephen Diehl

many_v = some_v pure []
some_v = (:) v many_v
-- | Zero or more.
many :: f a -> f [a]
many v = many_v
where
many_v = some_v pure []
some_v = (:) v many_v
On top of this we can add functionality for checking whether the current character in the stream matches
a given predicate ( i.e is it a digit, is it a letter, a specific word, etc).
satisfy :: (Char -> Bool) -> Parser Char
satisfy p = item ‘bind‘ \c ->
if p c
then unit c
else (Parser (\cs -> []))
Essentially this 50 lines code encodes the entire core of the parser combinator machinery. All higher
order behavior can be written on top of just this logic. Now we can write down several higher level
functions which operate over sections of the stream.
chainl1 parses one or more occurrences of p, separated by op and returns a value obtained by a recursing
until failure on the left hand side of the stream. is can be used to parse left-recursive grammar.
oneOf :: [Char] -> Parser Char
oneOf s = satisfy (flip elem s)
chainl :: Parser a -> Parser (a -> a -> a) -> a -> Parser a
chainl p op a = (p ‘chainl1‘ op) return a
chainl1 :: Parser a -> Parser (a -> a -> a) -> Parser a
p ‘chainl1‘ op = do {a