Streamly.Internal.Data.Parser.ParserD

Setup

>>> :m
>>> import Control.Applicative ((<|>))
>>> import Data.Bifunctor (second)
>>> import Data.Char (isSpace)
>>> import qualified Data.Foldable as Foldable
>>> import qualified Data.Maybe as Maybe

>>> import Streamly.Data.Fold (Fold)
>>> import Streamly.Data.Parser (Parser)

>>> import qualified Streamly.Data.Fold as Fold
>>> import qualified Streamly.Data.Parser as Parser
>>> import qualified Streamly.Data.Stream as Stream

For APIs that have not been released yet.

>>> import qualified Streamly.Internal.Data.Fold as Fold
>>> import qualified Streamly.Internal.Data.Parser as Parser

Types

data Parser a m b

A parser is a fold that can fail and is represented as Parser step initial extract. Before we drive a parser we call the initial action to retrieve the initial state of the fold. The parser driver invokes step with the state returned by the previous step and the next input element. It results into a new state and a command to the driver represented by Step type. The driver keeps invoking the step function until it stops or fails. At any point of time the driver can call extract to inspect the result of the fold. If the parser hits the end of input extract is called. It may result in an error or an output value.

Pre-release

Constructors

forall s. Parser (s -> a -> m (Step s b)) (m (Initial s b)) (s -> m (Step s b))

Instances

Monad m => MonadFail (Parser a m)

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

fail :: String -> Parser a m a0

(Monad m, MonadIO m) => MonadIO (Parser a m)

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

liftIO :: IO a0 -> Parser a m a0

Monad m => Alternative (Parser a m)

Sequential alternative. The input is first passed to the first parser, and if it succeeds, the result is returned. However, if the first parser fails, the parser driver backtracks and tries the same input on the second parser, returning the result if it succeeds.

Note: The implementation of <|> is not lazy in the second argument. The following code will fail:

>>> Stream.parse (Parser.satisfy (> 0) <|> undefined) $ Stream.fromList [1..10]
*** Exception: Prelude.undefined
...

WARNING! this is not suitable for large scale use. As a thumb rule stream fusion works well for less than 8 compositions of this operation, otherwise consider using ParserK. Do not use recursive parser implementations based on this Alternative instance.

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

empty :: Parser a m a0

(<|>) :: Parser a m a0 -> Parser a m a0 -> Parser a m a0

some :: Parser a m a0 -> Parser a m [a0]

many :: Parser a m a0 -> Parser a m [a0]

Monad m => Applicative (Parser a m)

Applicative form of splitWith.

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

pure :: a0 -> Parser a m a0

(<*>) :: Parser a m (a0 -> b) -> Parser a m a0 -> Parser a m b

liftA2 :: (a0 -> b -> c) -> Parser a m a0 -> Parser a m b -> Parser a m c

(*>) :: Parser a m a0 -> Parser a m b -> Parser a m b

(<*) :: Parser a m a0 -> Parser a m b -> Parser a m a0

Functor m => Functor (Parser a m)

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

fmap :: (a0 -> b) -> Parser a m a0 -> Parser a m b

(<$) :: a0 -> Parser a m b -> Parser a m a0

Monad m => Monad (Parser a m)

See documentation of Parser.

Although this implementation allows stream fusion, it has quadratic complexity, making it suitable only for a small number of compositions. As a thumb rule use it for less than 8 compositions, use ParserK otherwise.

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

(>>=) :: Parser a m a0 -> (a0 -> Parser a m b) -> Parser a m b

(>>) :: Parser a m a0 -> Parser a m b -> Parser a m b

return :: a0 -> Parser a m a0

newtype ParseError

This exception is used when a parser ultimately fails, the user of the parser is intimated via this exception.

Pre-release

Constructors

ParseError String

Instances

Exception ParseError

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

toException :: ParseError -> SomeException

fromException :: SomeException -> Maybe ParseError

displayException :: ParseError -> String

Show ParseError

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

showsPrec :: Int -> ParseError -> ShowS

show :: ParseError -> String

showList :: [ParseError] -> ShowS

data Step s b

The return type of a Parser step.

The parse operation feeds the input stream to the parser one element at a time, representing a parse Step. The parser may or may not consume the item and returns a result. If the result is Partial we can either extract the result or feed more input to the parser. If the result is Continue, we must feed more input in order to get a result. If the parser returns Done then the parser can no longer take any more input.

If the result is Continue, the parse operation retains the input in a backtracking buffer, in case the parser may ask to backtrack in future. Whenever a 'Partial n' result is returned we first backtrack by n elements in the input and then release any remaining backtracking buffer. Similarly, 'Continue n' backtracks to n elements before the current position and starts feeding the input from that point for future invocations of the parser.

If parser is not yet done, we can use the extract operation on the state of the parser to extract a result. If the parser has not yet yielded a result, the operation fails with a ParseError exception. If the parser yielded a Partial result in the past the last partial result is returned. Therefore, if a parser yields a partial result once it cannot fail later on.

The parser can never backtrack beyond the position where the last partial result left it at. The parser must ensure that the backtrack position is always after that.

Pre-release

Constructors

Partial !Int !s

Partial count state. The following hold on Partial result:

1. extract on state would succeed and give a result.
2. Input stream position is reset to current position - count.
3. All input before the new position is dropped. The parser can never backtrack beyond this position.

Continue !Int !s

Continue count state. The following hold on a Continue result:

1. If there was a Partial result in past, extract on state would give that result as Done otherwise it may return Error or Continue.
2. Input stream position is reset to current position - count.
3. the input is retained in a backtrack buffer.

Done !Int !b

Done with leftover input count and result.

Done count result means the parser has finished, it will accept no more input, last count elements from the input are unused and the result of the parser is in result.

Error !String

Parser failed without generating any output.

The parsing operation may backtrack to the beginning and try another alternative.

Instances

Bifunctor Step

Map first function over the state and second over the result.

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

bimap :: (a -> b) -> (c -> d) -> Step a c -> Step b d

first :: (a -> b) -> Step a c -> Step b c

second :: (b -> c) -> Step a b -> Step a c

Functor (Step s)

fmap = second

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

fmap :: (a -> b) -> Step s a -> Step s b

(<$) :: a -> Step s b -> Step s a

data Initial s b

The type of a Parser's initial action.

Internal

Constructors

IPartial !s

Wait for step function to be called with state s.

IDone !b

Return a result right away without an input.

IError !String

Return an error right away without an input.

Instances

Bifunctor Initial

first maps on IPartial and second maps on IDone.

Internal

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

bimap :: (a -> b) -> (c -> d) -> Initial a c -> Initial b d

first :: (a -> b) -> Initial a c -> Initial b c

second :: (b -> c) -> Initial a b -> Initial a c

Functor (Initial s)

Maps a function over the result held by IDone.

>>> fmap = second

Internal

Defined in Streamly.Internal.Data.Parser.ParserD.Type

Methods

fmap :: (a -> b) -> Initial s a -> Initial s b

(<$) :: a -> Initial s b -> Initial s a

Downgrade to Fold

toFold :: Monad m => Parser a m b -> Fold m a b

Make a Fold from a Parser. The fold just throws an exception if the parser fails or tries to backtrack.

This can be useful in combinators that accept a Fold and we know that a Parser cannot fail or failure exception is acceptable as there is no way to recover.

Pre-release

Accumulators

fromFold :: Monad m => Fold m a b -> Parser a m b

Make a Parser from a Fold. This parser sends all of its input to the fold.

fromFoldMaybe :: Monad m => String -> Fold m a (Maybe b) -> Parser a m b

Convert a Maybe returning fold to an error returning parser. The first argument is the error message that the parser would return when the fold returns Nothing.

Pre-release

fromPure :: Monad m => b -> Parser a m b

A parser that always yields a pure value without consuming any input.

fromEffect :: Monad m => m b -> Parser a m b

A parser that always yields the result of an effectful action without consuming any input.

die :: Monad m => String -> Parser a m b

A parser that always fails with an error message without consuming any input.

dieM :: Monad m => m String -> Parser a m b

A parser that always fails with an effectful error message and without consuming any input.

Pre-release

Map on input

lmap :: (a -> b) -> Parser b m r -> Parser a m r

lmap f parser maps the function f on the input of the parser.

>>> Stream.parse (Parser.lmap (\x -> x * x) (Parser.fromFold Fold.sum)) (Stream.enumerateFromTo 1 100)
Right 338350

lmap = Parser.lmapM return

lmapM :: Monad m => (a -> m b) -> Parser b m r -> Parser a m r

lmapM f parser maps the monadic function f on the input of the parser.

postscan :: Fold m a b -> Parser b m c -> Parser a m c

Stateful scan on the input of a parser using a Fold.

Unimplemented

filter :: Monad m => (a -> Bool) -> Parser a m b -> Parser a m b

Include only those elements that pass a predicate.

>>> Stream.parse (Parser.filter (> 5) (Parser.fromFold Fold.sum)) $ Stream.fromList [1..10]
Right 40

Map on output

rmapM :: Monad m => (b -> m c) -> Parser a m b -> Parser a m c

rmapM f parser maps the monadic function f on the output of the parser.

>>> rmap = fmap

Element parsers

peek :: Monad m => Parser a m a

Peek the head element of a stream, without consuming it. Fails if it encounters end of input.

>>> Stream.parse ((,) <$> Parser.peek <*> Parser.satisfy (> 0)) $ Stream.fromList [1]
Right (1,1)

peek = lookAhead (satisfy True)

one :: Monad m => Parser a m a

Consume one element from the head of the stream. Fails if it encounters end of input.

>>> one = Parser.satisfy $ const True

oneEq :: (Monad m, Eq a) => a -> Parser a m a

Match a specific element.

>>> oneEq x = Parser.satisfy (== x)

oneNotEq :: (Monad m, Eq a) => a -> Parser a m a

Match anything other than the supplied element.

>>> oneNotEq x = Parser.satisfy (/= x)

oneOf :: (Monad m, Eq a, Foldable f) => f a -> Parser a m a

Match any one of the elements in the supplied list.

>>> oneOf xs = Parser.satisfy (`Foldable.elem` xs)

When performance matters a pattern matching predicate could be more efficient than a Foldable datatype:

let p x =
   case x of
      a -> True
      e -> True
       _  -> False
in satisfy p

GHC may use a binary search instead of linear search in the list. Alternatively, you can also use an array instead of list for storage and search.

noneOf :: (Monad m, Eq a, Foldable f) => f a -> Parser a m a

See performance notes in oneOf.

>>> noneOf xs = Parser.satisfy (`Foldable.notElem` xs)

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

Succeeds if we are at the end of input, fails otherwise.

>>> Stream.parse ((,) <$> Parser.satisfy (> 0) <*> Parser.eof) $ Stream.fromList [1]
Right (1,())

satisfy :: Monad m => (a -> Bool) -> Parser a m a

Returns the next element if it passes the predicate, fails otherwise.

>>> Stream.parse (Parser.satisfy (== 1)) $ Stream.fromList [1,0,1]
Right 1

>>> toMaybe f x = if f x then Just x else Nothing
>>> satisfy f = Parser.maybe (toMaybe f)

maybe :: Monad m => (a -> Maybe b) -> Parser a m b

Map a Maybe returning function on the next element in the stream. The parser fails if the function returns Nothing otherwise returns the Just value.

>>> toEither = Maybe.maybe (Left "maybe: predicate failed") Right
>>> maybe f = Parser.either (toEither . f)

>>> maybe f = Parser.fromFoldMaybe "maybe: predicate failed" (Fold.maybe f)

Pre-release

either :: Monad m => (a -> Either String b) -> Parser a m b

Map an Either returning function on the next element in the stream. If the function returns 'Left err', the parser fails with the error message err otherwise returns the Right value.

Pre-release

Sequence parsers (tokenizers)

Parsers chained in series, if one parser terminates the composition terminates. Currently we are using folds to collect the output of the parsers but we can use Parsers instead of folds to make the composition more powerful. For example, we can do:

takeEndByOrMax cond n p = takeEndBy cond (take n p) takeEndByBetween cond m n p = takeEndBy cond (takeBetween m n p) takeWhileBetween cond m n p = takeWhile cond (takeBetween m n p)

lookAhead :: Monad m => Parser a m b -> Parser a m b

Run a parser without consuming the input.

By length

Grab a sequence of input elements without inspecting them

takeBetween :: Monad m => Int -> Int -> Fold m a b -> Parser a m b

takeBetween m n takes a minimum of m and a maximum of n input elements and folds them using the supplied fold.

Stops after n elements. Fails if the stream ends before m elements could be taken.

Examples: -

>>> :{
  takeBetween' low high ls = Stream.parse prsr (Stream.fromList ls)
    where prsr = Parser.takeBetween low high Fold.toList
:}

>>> takeBetween' 2 4 [1, 2, 3, 4, 5]
Right [1,2,3,4]

>>> takeBetween' 2 4 [1, 2]
Right [1,2]

>>> takeBetween' 2 4 [1]
Left (ParseError "takeBetween: Expecting alteast 2 elements, got 1")

>>> takeBetween' 0 0 [1, 2]
Right []

>>> takeBetween' 0 1 []
Right []

takeBetween is the most general take operation, other take operations can be defined in terms of takeBetween. For example:

>>> take n = Parser.takeBetween 0 n
>>> takeEQ n = Parser.takeBetween n n
>>> takeGE n = Parser.takeBetween n maxBound

Pre-release

takeEQ :: Monad m => Int -> Fold m a b -> Parser a m b

Stops after taking exactly n input elements.

• Stops - after consuming n elements.
• Fails - if the stream or the collecting fold ends before it can collect exactly n elements.

>>> Stream.parse (Parser.takeEQ 2 Fold.toList) $ Stream.fromList [1,0,1]
Right [1,0]

>>> Stream.parse (Parser.takeEQ 4 Fold.toList) $ Stream.fromList [1,0,1]
Left (ParseError "takeEQ: Expecting exactly 4 elements, input terminated on 3")

takeGE :: Monad m => Int -> Fold m a b -> Parser a m b

Take at least n input elements, but can collect more.

• Stops - when the collecting fold stops.
• Fails - if the stream or the collecting fold ends before producing n elements.

>>> Stream.parse (Parser.takeGE 4 Fold.toList) $ Stream.fromList [1,0,1]
Left (ParseError "takeGE: Expecting at least 4 elements, input terminated on 3")

>>> Stream.parse (Parser.takeGE 4 Fold.toList) $ Stream.fromList [1,0,1,0,1]
Right [1,0,1,0,1]

Pre-release

takeP :: Monad m => Int -> Parser a m b -> Parser a m b

Takes at-most n input elements.

• Stops - when the collecting parser stops.
• Fails - when the collecting parser fails.

>>> Stream.parse (Parser.takeP 4 (Parser.takeEQ 2 Fold.toList)) $ Stream.fromList [1, 2, 3, 4, 5]
Right [1,2]

>>> Stream.parse (Parser.takeP 4 (Parser.takeEQ 5 Fold.toList)) $ Stream.fromList [1, 2, 3, 4, 5]
Left (ParseError "takeEQ: Expecting exactly 5 elements, input terminated on 4")

Internal

Exact match

listEq :: (Monad m, Eq a) => [a] -> Parser a m [a]

Match the input sequence with the supplied list and return it if successful.

>>> listEq = Parser.listEqBy (==)

listEqBy :: Monad m => (a -> a -> Bool) -> [a] -> Parser a m [a]

Match the given sequence of elements using the given comparison function. Returns the original sequence if successful.

Definition:

>>> listEqBy cmp xs = Parser.streamEqBy cmp (Stream.fromList xs) *> Parser.fromPure xs

Examples:

>>> Stream.parse (Parser.listEqBy (==) "string") $ Stream.fromList "string"
Right "string"

>>> Stream.parse (Parser.listEqBy (==) "mismatch") $ Stream.fromList "match"
Left (ParseError "streamEqBy: mismtach occurred")

streamEqBy :: Monad m => (a -> a -> Bool) -> Stream m a -> Parser a m ()

Like listEqBy but uses a stream instead of a list and does not return the stream.

subsequenceBy :: (a -> a -> Bool) -> Stream m a -> Parser a m ()

Match if the input stream is a subsequence of the argument stream i.e. all the elements of the input stream occur, in order, in the argument stream. The elements do not have to occur consecutively. A sequence is considered a subsequence of itself.

By predicate

takeWhile :: Monad m => (a -> Bool) -> Fold m a b -> Parser a m b

Collect stream elements until an element fails the predicate. The element on which the predicate fails is returned back to the input stream.

• Stops - when the predicate fails or the collecting fold stops.
• Fails - never.

>>> Stream.parse (Parser.takeWhile (== 0) Fold.toList) $ Stream.fromList [0,0,1,0,1]
Right [0,0]

>>> takeWhile cond f = Parser.takeWhileP cond (Parser.fromFold f)

We can implement a breakOn using takeWhile:

breakOn p = takeWhile (not p)

takeWhileP :: Monad m => (a -> Bool) -> Parser a m b -> Parser a m b

Like takeWhile but uses a Parser instead of a Fold to collect the input. The combinator stops when the condition fails or if the collecting parser stops.

Other interesting parsers can be implemented in terms of this parser:

>>> takeWhile1 cond p = Parser.takeWhileP cond (Parser.takeBetween 1 maxBound p)
>>> takeWhileBetween cond m n p = Parser.takeWhileP cond (Parser.takeBetween m n p)

Stops: when the condition fails or the collecting parser stops. Fails: when the collecting parser fails.

Pre-release

takeWhile1 :: Monad m => (a -> Bool) -> Fold m a b -> Parser a m b

Like takeWhile but takes at least one element otherwise fails.

>>> takeWhile1 cond p = Parser.takeWhileP cond (Parser.takeBetween 1 maxBound p)

dropWhile :: Monad m => (a -> Bool) -> Parser a m ()

Drain the input as long as the predicate succeeds, running the effects and discarding the results.

This is also called skipWhile in some parsing libraries.

>>> dropWhile p = Parser.takeWhile p Fold.drain

Separated by elements

Separator could be in prefix postion (takeStartBy), or suffix position (takeEndBy). See deintercalate, sepBy etc for infix separator parsing, also see intersperseQuotedBy fold.

takeEndBy :: Monad m => (a -> Bool) -> Parser a m b -> Parser a m b

takeEndBy cond parser parses a token that ends by a separator chosen by the supplied predicate. The separator is also taken with the token.

This can be combined with other parsers to implement other interesting parsers as follows:

>>> takeEndByLE cond n p = Parser.takeEndBy cond (Parser.fromFold $ Fold.take n p)
>>> takeEndByBetween cond m n p = Parser.takeEndBy cond (Parser.takeBetween m n p)

>>> takeEndBy = Parser.takeEndByEsc (const False)

See also "Streamly.Data.Fold.takeEndBy". Unlike the fold, the collecting parser in the takeEndBy parser can decide whether to fail or not if the stream does not end with separator.

Pre-release

takeEndBy_ :: (a -> Bool) -> Parser a m b -> Parser a m b

Like takeEndBy but the separator is dropped.

See also "Streamly.Data.Fold.takeEndBy_".

Pre-release

takeEndByEsc :: Monad m => (a -> Bool) -> (a -> Bool) -> Parser a m b -> Parser a m b

Like takeEndBy but the separator elements can be escaped using an escape char determined by the first predicate. The escape characters are removed.

pre-release

takeStartBy :: Monad m => (a -> Bool) -> Fold m a b -> Parser a m b

Parse a token that starts with an element chosen by the predicate. The parser fails if the input does not start with the selected element.

• Stops - when the predicate succeeds in non-leading position.
• Fails - when the predicate fails in the leading position.

>>> splitWithPrefix p f = Stream.parseMany (Parser.takeStartBy p f)

Examples: -

>>> p = Parser.takeStartBy (== ',') Fold.toList
>>> leadingComma = Stream.parse p . Stream.fromList
>>> leadingComma "a,b"
Left (ParseError "takeStartBy: missing frame start")
...
>>> leadingComma ",,"
Right ","
>>> leadingComma ",a,b"
Right ",a"
>>> leadingComma ""
Right ""

Pre-release

takeStartBy_ :: Monad m => (a -> Bool) -> Fold m a b -> Parser a m b

Like takeStartBy but drops the separator.

>>> takeStartBy_ isBegin = Parser.takeFramedByGeneric Nothing (Just isBegin) Nothing

takeEitherSepBy :: (a -> Bool) -> Fold m (Either a b) c -> Parser a m c

Take either the separator or the token. Separator is a Left value and token is Right value.

Unimplemented

wordBy :: Monad m => (a -> Bool) -> Fold m a b -> Parser a m b

Like splitOn but strips leading, trailing, and repeated separators. Therefore, ".a..b." having . as the separator would be parsed as ["a","b"]. In other words, its like parsing words from whitespace separated text.

• Stops - when it finds a word separator after a non-word element
• Fails - never.

>>> wordBy = Parser.wordFramedBy (const False) (const False) (const False)

S.wordsBy pred f = S.parseMany (PR.wordBy pred f)

Grouped by element comparison

groupBy :: Monad m => (a -> a -> Bool) -> Fold m a b -> Parser a m b

Given an input stream [a,b,c,...] and a comparison function cmp, the parser assigns the element a to the first group, then if a `cmp` b is True b is also assigned to the same group. If a `cmp` c is True then c is also assigned to the same group and so on. When the comparison fails the parser is terminated. Each group is folded using the Fold f and the result of the fold is the result of the parser.

• Stops - when the comparison fails.
• Fails - never.

>>> :{
 runGroupsBy eq =
     Stream.fold Fold.toList
         . Stream.parseMany (Parser.groupBy eq Fold.toList)
         . Stream.fromList
:}

>>> runGroupsBy (<) []
[]

>>> runGroupsBy (<) [1]
[Right [1]]

>>> runGroupsBy (<) [3, 5, 4, 1, 2, 0]
[Right [3,5,4],Right [1,2],Right [0]]

groupByRolling :: Monad m => (a -> a -> Bool) -> Fold m a b -> Parser a m b

Unlike groupBy this combinator performs a rolling comparison of two successive elements in the input stream. Assuming the input stream is [a,b,c,...] and the comparison function is cmp, the parser first assigns the element a to the first group, then if a `cmp` b is True b is also assigned to the same group. If b `cmp` c is True then c is also assigned to the same group and so on. When the comparison fails the parser is terminated. Each group is folded using the Fold f and the result of the fold is the result of the parser.

• Stops - when the comparison fails.
• Fails - never.

>>> :{
 runGroupsByRolling eq =
     Stream.fold Fold.toList
         . Stream.parseMany (Parser.groupByRolling eq Fold.toList)
         . Stream.fromList
:}

>>> runGroupsByRolling (<) []
[]

>>> runGroupsByRolling (<) [1]
[Right [1]]

>>> runGroupsByRolling (<) [3, 5, 4, 1, 2, 0]
[Right [3,5],Right [4],Right [1,2],Right [0]]

Pre-release

groupByRollingEither :: Monad m => (a -> a -> Bool) -> Fold m a b -> Fold m a c -> Parser a m (Either b c)

Like groupByRolling, but if the predicate is True then collects using the first fold as long as the predicate holds True, if the predicate is False collects using the second fold as long as it remains False. Returns Left for the first case and Right for the second case.

For example, if we want to detect sorted sequences in a stream, both ascending and descending cases we can use 'groupByRollingEither (<=) Fold.toList Fold.toList'.

Pre-release

Framed by elements

Also see intersperseQuotedBy fold. Framed by a one or more ocurrences of a separator around a word like spaces or quotes. No nesting.

wordFramedBy

Arguments

:: Monad m

=> (a -> Bool)

Matches escape elem?

-> (a -> Bool)

Matches left quote?

-> (a -> Bool)

matches right quote?

-> (a -> Bool)

matches word separator?

-> Fold m a b

-> Parser a m b

Like wordBy but treats anything inside a pair of quotes as a single word, the quotes can be escaped by an escape character. Recursive quotes are possible if quote begin and end characters are different, quotes must be balanced. Outermost quotes are stripped.

>>> braces = Parser.wordFramedBy (== '\\') (== '{') (== '}') isSpace Fold.toList
>>> Stream.parse braces $ Stream.fromList "{ab} cd"
Right "ab"
>>> Stream.parse braces $ Stream.fromList "{ab}{cd}"
Right "abcd"
>>> Stream.parse braces $ Stream.fromList "a{b} cd"
Right "ab"
>>> Stream.parse braces $ Stream.fromList "a{{b}} cd"
Right "a{b}"

>>> quotes = Parser.wordFramedBy (== '\\') (== '"') (== '"') isSpace Fold.toList
>>> Stream.parse quotes $ Stream.fromList "\"a\"\"b\""
Right "ab"

wordWithQuotes

Arguments

:: (Monad m, Eq a)

=> Bool

Retain the quotes and escape chars in the output

-> (a -> a -> Maybe a)

quote char -> escaped char -> translated char

-> a

Matches an escape elem?

-> (a -> Maybe a)

If left quote, return right quote, else Nothing.

-> (a -> Bool)

Matches a word separator?

-> Fold m a b

-> Parser a m b

Quote and bracket aware word splitting with escaping. Like wordBy but word separators within specified quotes or brackets are ignored. Quotes and escape characters can be processed. If the end quote is different from the start quote it is called a bracket. The following quoting rules apply:

• In an unquoted string a character may be preceded by an escape character. The escape character is removed and the character following it is treated literally with no special meaning e.g. e.g. h e l l o is a single word, n is same as n.
• Any part of the word can be placed within quotes. Inside quotes all characters are treated literally with no special meaning. Quoting character itself cannot be used within quotes unless escape processing within quotes is applied to allow it.
• Optionally escape processing for quoted part can be specified. Escape character has no special meaning inside quotes unless it is followed by a character that has a escape translation specified, in that case the escape character is removed, and the specified translation is applied to the character following it. This can be used to escape the quoting character itself within quotes.
• There can be multiple quoting characters, when a quote starts, all other quoting characters within that quote lose any special meaning until the quote is closed.
• A starting quote char without an ending char generates a parse error. An ending bracket char without a corresponding bracket begin is ignored.
• Brackets can be nested.

We should note that unquoted and quoted escape processing are different. In unquoted part escape character is always removed. In quoted part it is removed only if followed by a special meaning character. This is consistent with how shell performs escape processing.

wordKeepQuotes

Arguments

:: (Monad m, Eq a)

=> a

Escape char

-> (a -> Maybe a)

If left quote, return right quote, else Nothing.

-> (a -> Bool)

Matches a word separator?

-> Fold m a b

-> Parser a m b

wordWithQuotes without processing the quotes and escape function supplied to escape the quote char within a quote. Can be used to parse words keeping the quotes and escapes intact.

>>> wordKeepQuotes = Parser.wordWithQuotes True (\_ _ -> Nothing)

wordProcessQuotes

Arguments

:: (Monad m, Eq a)

=> a

Escape char

-> (a -> Maybe a)

If left quote, return right quote, else Nothing.

-> (a -> Bool)

Matches a word separator?

-> Fold m a b

-> Parser a m b

wordWithQuotes with quote processing applied and escape function supplied to escape the quote char within a quote. Can be ysed to parse words and processing the quoting and escaping at the same time.

>>> wordProcessQuotes = Parser.wordWithQuotes False (\_ _ -> Nothing)

takeFramedBy_ :: Monad m => (a -> Bool) -> (a -> Bool) -> Fold m a b -> Parser a m b

takeFramedBy_ isBegin isEnd fold parses a token framed by a begin and an end predicate.

>>> takeFramedBy_ = Parser.takeFramedByEsc_ (const False)

takeFramedByEsc_ :: Monad m => (a -> Bool) -> (a -> Bool) -> (a -> Bool) -> Fold m a b -> Parser a m b

takeFramedByEsc_ isEsc isBegin isEnd fold parses a token framed using a begin and end predicate, and an escape character. The frame begin and end characters lose their special meaning if preceded by the escape character.

Nested frames are allowed if begin and end markers are different, nested frames must be balanced unless escaped, nested frame markers are emitted as it is.

For example,

>>> p = Parser.takeFramedByEsc_ (== '\\') (== '{') (== '}') Fold.toList
>>> Stream.parse p $ Stream.fromList "{hello}"
Right "hello"
>>> Stream.parse p $ Stream.fromList "{hello {world}}"
Right "hello {world}"
>>> Stream.parse p $ Stream.fromList "{hello \\{world}"
Right "hello {world"
>>> Stream.parse p $ Stream.fromList "{hello {world}"
Left (ParseError "takeFramedByEsc_: missing frame end")

Pre-release

takeFramedByGeneric :: Monad m => Maybe (a -> Bool) -> Maybe (a -> Bool) -> Maybe (a -> Bool) -> Fold m a b -> Parser a m b

blockWithQuotes

Arguments

:: (Monad m, Eq a)

=> (a -> Bool)

escape char

-> (a -> Bool)

quote char, to quote inside brackets

-> a

Block opening bracket

-> a

Block closing bracket

-> Fold m a b

-> Parser a m b

Parse a block enclosed within open, close brackets. Block contents may be quoted, brackets inside quotes are ignored. Quoting characters can be used within quotes if escaped. A block can have a nested block inside it.

Quote begin and end chars are the same. Block brackets and quote chars must not overlap. Block start and end brackets must be different for nesting blocks within blocks.

>>> p = Parser.blockWithQuotes (== '\\') (== '"') '{' '}' Fold.toList
>>> Stream.parse p $ Stream.fromList "{msg: \"hello world\"}"
Right "msg: \"hello world\""

Spanning

span :: Monad m => (a -> Bool) -> Fold m a b -> Fold m a c -> Parser a m (b, c)

span p f1 f2 composes folds f1 and f2 such that f1 consumes the input as long as the predicate p is True. f2 consumes the rest of the input.

> let span_ p xs = Stream.parse (Parser.span p Fold.toList Fold.toList) $ Stream.fromList xs

> span_ (< 1) 1,2,3

> span_ (< 2) 1,2,3

> span_ (< 4) 1,2,3

Pre-release

spanBy :: Monad m => (a -> a -> Bool) -> Fold m a b -> Fold m a c -> Parser a m (b, c)

Break the input stream into two groups, the first group takes the input as long as the predicate applied to the first element of the stream and next input element holds True, the second group takes the rest of the input.

Pre-release

spanByRolling :: Monad m => (a -> a -> Bool) -> Fold m a b -> Fold m a c -> Parser a m (b, c)

Like spanBy but applies the predicate in a rolling fashion i.e. predicate is applied to the previous and the next input elements.

Pre-release

Binary Combinators

Sequential Applicative

splitWith :: Monad m => (a -> b -> c) -> Parser x m a -> Parser x m b -> Parser x m c

Sequential parser application.

Apply two parsers sequentially to an input stream. The first parser runs and processes the input, the remaining input is then passed to the second parser. If both parsers succeed, their outputs are combined using the supplied function. If either parser fails, the operation fails.

This implementation is strict in the second argument, therefore, the following will fail:

>>> Stream.parse (Parser.splitWith const (Parser.satisfy (> 0)) undefined) $ Stream.fromList [1]
*** Exception: Prelude.undefined
...

Although this implementation allows stream fusion, it has quadratic complexity, making it suitable only for a small number of compositions. As a thumb rule use it for less than 8 compositions, use ParserK otherwise.

Below are some common idioms that can be expressed using splitWith and other parser primitives:

>>> span p f1 f2 = Parser.splitWith (,) (Parser.takeWhile p f1) (Parser.fromFold f2)
>>> spanBy eq f1 f2 = Parser.splitWith (,) (Parser.groupBy eq f1) (Parser.fromFold f2)

Pre-release

split_ :: Monad m => Parser x m a -> Parser x m b -> Parser x m b

Sequential parser application ignoring the output of the first parser. Apply two parsers sequentially to an input stream. The input is provided to the first parser, when it is done the remaining input is provided to the second parser. The output of the parser is the output of the second parser. The operation fails if any of the parsers fail.

This implementation is strict in the second argument, therefore, the following will fail:

>>> Stream.parse (Parser.split_ (Parser.satisfy (> 0)) undefined) $ Stream.fromList [1]
*** Exception: Prelude.undefined
...

Although this implementation allows stream fusion, it has quadratic complexity, making it suitable only for a small number of compositions. As a thumb rule use it for less than 8 compositions, use ParserK otherwise.

Pre-release

Sequential Alternative

alt :: Monad m => Parser x m a -> Parser x m a -> Parser x m a

Sequential alternative. The input is first passed to the first parser, and if it succeeds, the result is returned. However, if the first parser fails, the parser driver backtracks and tries the same input on the second parser, returning the result if it succeeds.

Note: This implementation is not lazy in the second argument. The following will fail:

> Stream.parse (Parser.satisfy (> 0) `Parser.alt` undefined) $ Stream.fromList [1..10]

• ** Exception: Prelude.undefined

Although this implementation allows stream fusion, it has quadratic complexity, making it suitable only for a small number of compositions. As a thumb rule use it for less than 8 compositions, use ParserK otherwise.

Time Complexity: O(n^2) where n is the number of compositions.

Pre-release

N-ary Combinators

Sequential Collection

sequence :: Monad m => Stream m (Parser a m b) -> Fold m b c -> Parser a m c

sequence f p collects sequential parses of parsers in a serial stream p using the fold f. Fails if the input ends or any of the parsers fail.

Pre-release

concatMap :: Monad m => (b -> Parser a m c) -> Parser a m b -> Parser a m c

Map a Parser returning function on the result of a Parser.

Pre-release

Sequential Repetition

count :: Int -> Parser a m b -> Fold m b c -> Parser a m c

count n f p collects exactly n sequential parses of parser p using the fold f. Fails if the input ends or the parser fails before n results are collected.

>>> count n = Parser.countBetween n n
>>> count n p f = Parser.manyP p (Parser.takeEQ n f)

Unimplemented

countBetween :: Int -> Int -> Parser a m b -> Fold m b c -> Parser a m c

countBetween m n f p collects between m and n sequential parses of parser p using the fold f. Stop after collecting n results. Fails if the input ends or the parser fails before m results are collected.

>>> countBetween m n p f = Parser.manyP p (Parser.takeBetween m n f)

Unimplemented

manyP :: Parser a m b -> Parser b m c -> Parser a m c

Like many but uses a Parser instead of a Fold to collect the results. Parsing stops or fails if the collecting parser stops or fails.

Unimplemented

many :: Monad m => Parser a m b -> Fold m b c -> Parser a m c

Collect zero or more parses. Apply the supplied parser repeatedly on the input stream and push the parse results to a downstream fold.

Stops: when the downstream fold stops or the parser fails. Fails: never, produces zero or more results.

>>> many = Parser.countBetween 0 maxBound

Compare with many.

some :: Monad m => Parser a m b -> Fold m b c -> Parser a m c

Collect one or more parses. Apply the supplied parser repeatedly on the input stream and push the parse results to a downstream fold.

Stops: when the downstream fold stops or the parser fails. Fails: if it stops without producing a single result.

>>> some p f = Parser.manyP p (Parser.takeGE 1 f)
>>> some = Parser.countBetween 1 maxBound

Compare with some.

Interleaved Repetition

deintercalate :: Monad m => Parser a m x -> Parser a m y -> Fold m (Either x y) z -> Parser a m z

Apply two parsers alternately to an input stream. The input stream is considered an interleaving of two patterns. The two parsers represent the two patterns. Parsing starts at the first parser and stops at the first parser. It can be used to parse a infix style pattern e.g. p1 p2 p1 . Empty input or single parse of the first parser is accepted.

>>> p1 = Parser.takeWhile1 (not . (== '+')) Fold.toList
>>> p2 = Parser.satisfy (== '+')
>>> p = Parser.deintercalate p1 p2 Fold.toList
>>> Stream.parse p $ Stream.fromList ""
Right []
>>> Stream.parse p $ Stream.fromList "1"
Right [Left "1"]
>>> Stream.parse p $ Stream.fromList "1+"
Right [Left "1"]
>>> Stream.parse p $ Stream.fromList "1+2+3"
Right [Left "1",Right '+',Left "2",Right '+',Left "3"]

deintercalate1 :: Monad m => Parser a m x -> Parser a m y -> Fold m (Either x y) z -> Parser a m z

Apply two parsers alternately to an input stream. The input stream is considered an interleaving of two patterns. The two parsers represent the two patterns. Parsing starts at the first parser and stops at the first parser. It can be used to parse a infix style pattern e.g. p1 p2 p1 . Empty input or single parse of the first parser is accepted.

>>> p1 = Parser.takeWhile1 (not . (== '+')) Fold.toList
>>> p2 = Parser.satisfy (== '+')
>>> p = Parser.deintercalate1 p1 p2 Fold.toList
>>> Stream.parse p $ Stream.fromList ""
Left (ParseError "takeWhile1: end of input")
>>> Stream.parse p $ Stream.fromList "1"
Right [Left "1"]
>>> Stream.parse p $ Stream.fromList "1+"
Right [Left "1"]
>>> Stream.parse p $ Stream.fromList "1+2+3"
Right [Left "1",Right '+',Left "2",Right '+',Left "3"]

deintercalateAll :: Monad m => Parser a m x -> Parser a m y -> Fold m (Either x y) z -> Parser a m z

Like deintercalate but the entire input must satisfy the pattern otherwise the parser fails. This is many times faster than deintercalate.

>>> p1 = Parser.takeWhile1 (not . (== '+')) Fold.toList
>>> p2 = Parser.satisfy (== '+')
>>> p = Parser.deintercalateAll p1 p2 Fold.toList
>>> Stream.parse p $ Stream.fromList ""
Right []
>>> Stream.parse p $ Stream.fromList "1"
Right [Left "1"]
>>> Stream.parse p $ Stream.fromList "1+"
Left (ParseError "takeWhile1: end of input")
>>> Stream.parse p $ Stream.fromList "1+2+3"
Right [Left "1",Right '+',Left "2",Right '+',Left "3"]

Special cases

TODO: traditional implmentations of these may be of limited use. For example, consider parsing lines separated by \r\n. The main parser will have to detect and exclude the sequence \r\n anyway so that we can apply the "sep" parser.

We can instead implement these as special cases of deintercalate.

, endBy
, sepEndBy
, beginBy
, sepBeginBy
, sepAroundBy

sepBy1 :: Monad m => Parser a m b -> Parser a m x -> Fold m b c -> Parser a m c

Like sepBy but requires at least one successful parse.

Definition:

>>> sepBy1 p1 p2 f = Parser.deintercalate1 p1 p2 (Fold.catLefts f)

Examples:

>>> p1 = Parser.takeWhile1 (not . (== '+')) Fold.toList
>>> p2 = Parser.satisfy (== '+')
>>> p = Parser.sepBy1 p1 p2 Fold.toList
>>> Stream.parse p $ Stream.fromList ""
Left (ParseError "takeWhile1: end of input")
>>> Stream.parse p $ Stream.fromList "1"
Right ["1"]
>>> Stream.parse p $ Stream.fromList "1+"
Right ["1"]
>>> Stream.parse p $ Stream.fromList "1+2+3"
Right ["1","2","3"]

sepBy :: Monad m => Parser a m b -> Parser a m x -> Fold m b c -> Parser a m c

Apply two parsers alternately to an input stream. Parsing starts at the first parser and stops at the first parser. The output of the first parser is emiited and the output of the second parser is discarded. It can be used to parse a infix style pattern e.g. p1 p2 p1 . Empty input or single parse of the first parser is accepted.

Definitions:

>>> sepBy p1 p2 f = Parser.deintercalate p1 p2 (Fold.catLefts f)
>>> sepBy p1 p2 f = Parser.sepBy1 p1 p2 f <|> Parser.fromEffect (Fold.extractM f)

Examples:

>>> p1 = Parser.takeWhile1 (not . (== '+')) Fold.toList
>>> p2 = Parser.satisfy (== '+')
>>> p = Parser.sepBy p1 p2 Fold.toList
>>> Stream.parse p $ Stream.fromList ""
Right []
>>> Stream.parse p $ Stream.fromList "1"
Right ["1"]
>>> Stream.parse p $ Stream.fromList "1+"
Right ["1"]
>>> Stream.parse p $ Stream.fromList "1+2+3"
Right ["1","2","3"]

sepByAll :: Monad m => Parser a m b -> Parser a m x -> Fold m b c -> Parser a m c

Non-backtracking version of sepBy. Several times faster.

manyTillP :: Parser a m b -> Parser a m x -> Parser b m c -> Parser a m c

Like manyTill but uses a Parser to collect the results instead of a Fold. Parsing stops or fails if the collecting parser stops or fails.

We can implemnent parsers like the following using manyTillP:

countBetweenTill m n f p = manyTillP (takeBetween m n f) p

Unimplemented

manyTill :: Monad m => Parser a m b -> Parser a m x -> Fold m b c -> Parser a m c

manyTill chunking test f tries the parser test on the input, if test fails it backtracks and tries chunking, after chunking succeeds test is tried again and so on. The parser stops when test succeeds. The output of test is discarded and the output of chunking is accumulated by the supplied fold. The parser fails if chunking fails.

Stops when the fold f stops.

manyThen :: Parser a m b -> Parser a m x -> Fold m b c -> Parser a m c

manyThen f collect recover repeats the parser collect on the input and collects the output in the supplied fold. If the the parser collect fails, parser recover is run until it stops and then we start repeating the parser collect again. The parser fails if the recovery parser fails.

For example, this can be used to find a key frame in a video stream after an error.

Unimplemented

Interleaved collection

1. Round robin
2. Priority based

roundRobin :: t (Parser a m b) -> Fold m b c -> Parser a m c

Apply a collection of parsers to an input stream in a round robin fashion. Each parser is applied until it stops and then we repeat starting with the the first parser again.

Unimplemented

Collection of Alternatives

Unimplemented

, shortestN
, longestN
, fastestN -- first N successful in time
, choiceN  -- first N successful in position

, choice -- first successful in position

Repeated Alternatives

retryMaxTotal :: Int -> Parser a m b -> Fold m b c -> Parser a m c

Keep trying a parser up to a maximum of n failures. When the parser fails the input consumed till now is dropped and the new instance is tried on the fresh input.

Unimplemented

retryMaxSuccessive :: Int -> Parser a m b -> Fold m b c -> Parser a m c

Like retryMaxTotal but aborts after n successive failures.

Unimplemented

retry :: Parser a m b -> Parser a m b

Keep trying a parser until it succeeds. When the parser fails the input consumed till now is dropped and the new instance is tried on the fresh input.

Unimplemented

Zipping Input

zipWithM :: Monad m => (a -> b -> m c) -> Stream m a -> Fold m c x -> Parser b m x

zip :: Monad m => Stream m a -> Fold m (a, b) x -> Parser b m x

Zip the input of a fold with a stream.

Pre-release

indexed :: forall m a b. Monad m => Fold m (Int, a) b -> Parser a m b

Pair each element of a fold input with its index, starting from index 0.

Pre-release

makeIndexFilter :: (Fold m (s, a) b -> Parser a m b) -> (((s, a) -> Bool) -> Fold m (s, a) b -> Fold m (s, a) b) -> ((s, a) -> Bool) -> Fold m a b -> Parser a m b

makeIndexFilter indexer filter predicate generates a fold filtering function using a fold indexing function that attaches an index to each input element and a filtering function that filters using @(index, element) -> Bool) as predicate.

For example:

filterWithIndex = makeIndexFilter indexed filter
filterWithAbsTime = makeIndexFilter timestamped filter
filterWithRelTime = makeIndexFilter timeIndexed filter

Pre-release

sampleFromthen :: Monad m => Int -> Int -> Fold m a b -> Parser a m b

sampleFromthen offset stride samples the element at offset index and then every element at strides of stride.

Pre-release

Deprecated

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

Deprecated: Please use "fromFold Fold.one" instead

Return the next element of the input. Returns Nothing on end of input. Also known as head.

Pre-release