Pipes.Parse

Element-agnostic parsing utilities for pipes

See Pipes.Parse.Tutorial for an extended tutorial

Parsing

pipes-parse handles end-of-input and pushback by storing a Producer in a StateT layer.

Connect Parsers to Producers using either runStateT, evalStateT, or execStateT:

runStateT  :: Parser a m r -> Producer a m x -> m (r, Producer a m x)
evalStateT :: Parser a m r -> Producer a m x -> m  r
execStateT :: Parser a m r -> Producer a m x -> m    (Producer a m x)
                                                      ^^^^^^^^^^^^^^
                                                         Leftovers

type Parser a m r = forall x. StateT (Producer a m x) m r

A Parser is an action that reads from and writes to a stored Producer

draw :: Monad m => Parser a m (Maybe a)

Draw one element from the underlying Producer, returning Nothing if the Producer is empty

skip :: Monad m => Parser a m Bool

Skip one element from the underlying Producer, returning True if successful or False if the Producer is empty

skip = fmap isJust draw

drawAll :: Monad m => Parser a m [a]

Draw all elements from the underlying Producer

Note that drawAll is not an idiomatic use of pipes-parse, but I provide it for simple testing purposes. Idiomatic pipes-parse style consumes the elements immediately as they are generated instead of loading all elements into memory. For example, you can use foldAll or foldAllM for this purpose.

skipAll :: Monad m => Parser a m ()

Drain all elements from the underlying Producer

unDraw :: Monad m => a -> Parser a m ()

Push back an element onto the underlying Producer

peek :: Monad m => Parser a m (Maybe a)

peek checks the first element of the stream, but uses unDraw to push the element back so that it is available for the next draw command.

peek = do
    x <- draw
    case x of
        Nothing -> return ()
        Just a  -> unDraw a
    return x

isEndOfInput :: Monad m => Parser a m Bool

Check if the underlying Producer is empty

isEndOfInput = fmap isNothing peek

foldAll

Arguments

:: Monad m

=> (x -> a -> x)

Step function

-> x

Initial accumulator

-> (x -> b)

Extraction function

-> Parser a m b

Fold all input values

Control.Foldl.purely foldAll :: Monad m => Fold a b -> Parser a m b

foldAllM

Arguments

:: Monad m

=> (x -> a -> m x)

Step function

-> m x

Initial accumulator

-> (x -> m b)

Extraction function

-> Parser a m b

Fold all input values monadically

Control.Foldl.impurely foldAllM :: Monad m => FoldM a m b -> Parser a m b

Parsing Lenses

Connect lenses to Producers using (^.) or view:

(^.) :: Producer a m x
     -> Lens' (Producer a m x) (Producer b m y)
     -> Producer b m y

Connect lenses to Parsers using zoom:

zoom :: Lens' (Producer a m x) (Producer b m y)
     -> Parser b m r
     -> Parser a m r

Connect lenses to each other using (.) (i.e. function composition):

(.) :: Lens' (Producer a m x) (Producer b m y)
    -> Lens' (Producer b m y) (Producer c m z)
    -> Lens' (Producer a m y) (Producer c m z)

span :: Monad m => (a -> Bool) -> Lens' (Producer a m x) (Producer a m (Producer a m x))

span is an improper lens that splits the Producer into two Producers, where the outer Producer is the longest consecutive group of elements that satisfy the predicate

splitAt :: Monad m => Int -> Lens' (Producer a m x) (Producer a m (Producer a m x))

splitAt is an improper lens that splits a Producer into two Producers after a fixed number of elements

groupBy :: Monad m => (a -> a -> Bool) -> Lens' (Producer a m x) (Producer a m (Producer a m x))

groupBy splits a Producer into two Producers after the first group of elements that are equal according to the equality predicate

group :: (Monad m, Eq a) => Lens' (Producer a m x) (Producer a m (Producer a m x))

Like groupBy, where the equality predicate is (==)

Utilities

toParser :: Monad m => Consumer (Maybe a) m r -> Parser a m r

Convert a Consumer to a Parser

Nothing signifies end of input

toParser_ :: Monad m => Consumer a m X -> Parser a m ()

Convert a never-ending Consumer to a Parser

parsed :: Monad m => Parser a m (Either e b) -> Producer a m r -> Producer b m (e, Producer a m r)

Run a Parser repeatedly on a Producer, yielding each `Right result

Returns the remainder of the Producer when the Parser returns Left

parsed_ :: Monad m => Parser a m (Maybe b) -> Producer a m r -> Producer b m (Producer a m r)

Run a Parser repeatedly on a Producer, yielding each Just result

Returns the remainder of the Producer when the Parser returns Nothing

parseForever :: Monad m => (forall n. Monad n => Parser a n (Either r b)) -> Pipe a b m r

Deprecated: Use parsed instead

Convert a Parser to a Pipe by running it repeatedly on the input

parseForever_ :: Monad m => (forall n. Monad n => Parser a n (Maybe b)) -> Pipe a b m ()

Deprecated: Use parsed_ instead

Variant of parseForever for parsers which return a Maybe instead of an Either

Re-exports

Control.Monad.Trans.Class re-exports lift.

Control.Monad.Trans.State.Strict re-exports StateT, runStateT, evalStateT, and execStateT.

Pipes re-exports Producer, yield, and next.

module Control.Monad.Trans.Class

module Control.Monad.Trans.State.Strict

module Pipes