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

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