Control.Monad.Yoctoparsec

Documentation

type Parser b t a = FreeT ((->) t) b a

A Parser b t a is a parser that consumes a stream of t tokens and as a result yields a value of type a, while operating under the b non-determinism monad. For most purposes b should be a MonadPlus. Useful examples include [] if you want backtracking, Maybe if you want no backtracking, StateT [] if you want to maintain a state that is automatically reverted when backtracking, and so on. hoistFreeT can be used to change the backtracking monad.

FreeT provides us with instances for Functor, Applicative, Monad, Alternative and MonadPlus.

token :: Applicative b => Parser b t t

A trivial parser that consumes a single token and yields it. Other parsers can be derived from this one using methods of the aforementioned typeclasses. For example, char x = mfilter (== x) token

parseStream :: Monad b => (s -> b (t, s)) -> Parser b t a -> s -> b (a, s)

Apply a parser to a stream given a function that obtains the next character from the stream within the same non-determinism monad.

parseString :: MonadPlus b => Parser b t a -> [t] -> b (a, [t])

Parse a string. When the end of the string is encountered, empty is yielded into the non-determinism monad.