xml-conduit-1.1.0.3: Pure-Haskell utilities for dealing with XML with the conduit package.

Safe Haskell | None

Text.XML.Stream.Parse

Contents

- Parsing XML files
  - Parser settings
    - Entity decoding
- Event parsing
- Attribute parsing
- Combinators
- Exceptions
- Other types

Description

This module provides both a native Haskell solution for parsing XML documents into a stream of events, and a set of parser combinators for dealing with a stream of events.

As a simple example, if you have the following XML file:

     <?xml version="1.0" encoding="utf-8"?>
     <people>
         <person age="25">Michael</person>
         <person age="2">Eliezer</person>
     </people>

Then this code:

     {-# LANGUAGE OverloadedStrings #-}
     import Control.Monad.Trans.Resource
     import Data.Conduit (($$))
     import Data.Text (Text, unpack)
     import Text.XML.Stream.Parse

     data Person = Person Int Text
         deriving Show

     parsePerson = tagName "person" (requireAttr "age") $ \age -> do
         name <- content
         return $ Person (read $ unpack age) name

     parsePeople = tagNoAttr "people" $ many parsePerson

     main = do
         people <- runResourceT $
                 parseFile def "people.xml" $$ force "people required" parsePeople
         print people

will produce:

     [Person {age = 25, name = "Michael"},Person {age = 2, name = "Eliezer"}]

Previous versions of this module contained a number of more sophisticated functions written by Aristid Breitkreuz and Dmitry Olshansky. To keep this package simpler, those functions are being moved to a separate package. This note will be updated with the name of the package(s) when available.

Synopsis

- parseBytes :: MonadThrow m => ParseSettings -> Conduit ByteString m Event
- parseBytesPos :: MonadThrow m => ParseSettings -> Conduit ByteString m EventPos
- parseText :: MonadThrow m => ParseSettings -> Conduit Text m EventPos
- detectUtf :: MonadThrow m => Conduit ByteString m Text
- parseFile :: MonadResource m => ParseSettings -> FilePath -> Producer m Event
- parseLBS :: MonadThrow m => ParseSettings -> ByteString -> Producer m Event
- data ParseSettings
- def :: Default a => a
- type DecodeEntities = Text -> Content
- psDecodeEntities :: ParseSettings -> DecodeEntities
- decodeXmlEntities :: DecodeEntities
- decodeHtmlEntities :: DecodeEntities
- tag :: MonadThrow m => (Name -> Maybe a) -> (a -> AttrParser b) -> (b -> ConduitM Event o m c) -> ConduitM Event o m (Maybe c)
- tagPredicate :: MonadThrow m => (Name -> Bool) -> AttrParser a -> (a -> ConduitM Event o m b) -> ConduitM Event o m (Maybe b)
- tagName :: MonadThrow m => Name -> AttrParser a -> (a -> ConduitM Event o m b) -> ConduitM Event o m (Maybe b)
- tagNoAttr :: MonadThrow m => Name -> ConduitM Event o m a -> ConduitM Event o m (Maybe a)
- content :: MonadThrow m => Consumer Event m Text
- contentMaybe :: MonadThrow m => Consumer Event m (Maybe Text)
- data AttrParser a
- requireAttr :: Name -> AttrParser Text
- optionalAttr :: Name -> AttrParser (Maybe Text)
- requireAttrRaw :: String -> ((Name, [Content]) -> Maybe b) -> AttrParser b
- optionalAttrRaw :: ((Name, [Content]) -> Maybe b) -> AttrParser (Maybe b)
- ignoreAttrs :: AttrParser ()
- orE :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m (Maybe a) -> Consumer Event m (Maybe a)
- choose :: Monad m => [Consumer Event m (Maybe a)] -> Consumer Event m (Maybe a)
- many :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m [a]
- force :: MonadThrow m => String -> ConduitM Event o m (Maybe a) -> ConduitM Event o m a
- data XmlException
  - = XmlException {
    - xmlErrorMessage :: String
    - xmlBadInput :: Maybe Event
    }
  - | InvalidEndElement Name
  - | InvalidEntity Text
  - | UnparsedAttributes [(Name, [Content])]
- data PositionRange
- type EventPos = (Maybe PositionRange, Event)

# Parsing XML files

parseBytes :: MonadThrow m => ParseSettings -> Conduit ByteString m Event

Parses a byte stream into `Event`s. This function is implemented fully in Haskell using attoparsec-text for parsing. The produced error messages do not give line/column information, so you may prefer to stick with the parser provided by libxml-enumerator. However, this has the advantage of not relying on any C libraries.

This relies on `detectUtf` to determine character encoding, and `parseText` to do the actual parsing.

parseBytesPos :: MonadThrow m => ParseSettings -> Conduit ByteString m EventPos

parseText :: MonadThrow m => ParseSettings -> Conduit Text m EventPos

Parses a character stream into `Event`s. This function is implemented fully in Haskell using attoparsec-text for parsing. The produced error messages do not give line/column information, so you may prefer to stick with the parser provided by libxml-enumerator. However, this has the advantage of not relying on any C libraries.

detectUtf :: MonadThrow m => Conduit ByteString m Text

Automatically determine which UTF variant is being used. This function first checks for BOMs, removing them as necessary, and then check for the equivalent of <?xml for each of UTF-8, UTF-16LEBE, and UTF-32LEBE. It defaults to assuming UTF-8.

parseFile :: MonadResource m => ParseSettings -> FilePath -> Producer m Event

A helper function which reads a file from disk using `enumFile`, detects character encoding using `detectUtf`, parses the XML using `parseBytes`, and then hands off control to your supplied parser.

parseLBS :: MonadThrow m => ParseSettings -> ByteString -> Producer m Event

Parse an event stream from a lazy `ByteString`.

## Parser settings

data ParseSettings

Instances

Default ParseSettings |

def :: Default a => a

The default value for this type.

type DecodeEntities = Text -> Content

psDecodeEntities :: ParseSettings -> DecodeEntities

### Entity decoding

decodeXmlEntities :: DecodeEntities

Default implementation of `DecodeEntities`: handles numeric entities and the five standard character entities (lt, gt, amp, quot, apos).

decodeHtmlEntities :: DecodeEntities

HTML4-compliant entity decoder. Handles numerics, the five standard character entities, and the additional 248 entities defined by HTML 4 and XHTML 1.

Note that HTML 5 introduces a drastically larger number of entities, and this code does not recognize most of them.

# Event parsing

tag :: MonadThrow m => (Name -> Maybe a) -> (a -> AttrParser b) -> (b -> ConduitM Event o m c) -> ConduitM Event o m (Maybe c)

The most generic way to parse a tag. It takes a predicate for checking if this is the correct tag name, an `AttrParser` for handling attributes, and then a parser for dealing with content.

This function automatically absorbs its balancing closing tag, and will throw an exception if not all of the attributes or child elements are consumed. If you want to allow extra attributes, see `ignoreAttrs`.

This function automatically ignores comments, instructions and whitespace.

tagPredicate :: MonadThrow m => (Name -> Bool) -> AttrParser a -> (a -> ConduitM Event o m b) -> ConduitM Event o m (Maybe b)

A simplified version of `tag` which matches against boolean predicates.

tagName :: MonadThrow m => Name -> AttrParser a -> (a -> ConduitM Event o m b) -> ConduitM Event o m (Maybe b)

A simplified version of `tag` which matches for specific tag names instead of taking a predicate function. This is often sufficient, and when combined with OverloadedStrings and the IsString instance of `Name`, can prove to be very concise.

tagNoAttr :: MonadThrow m => Name -> ConduitM Event o m a -> ConduitM Event o m (Maybe a)

A further simplified tag parser, which requires that no attributes exist.

content :: MonadThrow m => Consumer Event m Text

Grabs the next piece of content. If none if available, returns `empty`. This is simply a wrapper around `contentMaybe`.

contentMaybe :: MonadThrow m => Consumer Event m (Maybe Text)

Grabs the next piece of content if available. This function skips over any comments and instructions and concatenates all content until the next start or end tag.

# Attribute parsing

data AttrParser a

A monad for parsing attributes. By default, it requires you to deal with all attributes present on an element, and will throw an exception if there are unhandled attributes. Use the `requireAttr`, `optionalAttr` et al functions for handling an attribute, and `ignoreAttrs` if you would like to skip the rest of the attributes on an element.

`Alternative` instance behave like `First` monoid. It chooses first parser which doesn't fail.

Instances

Monad AttrParser |
Functor AttrParser |
Applicative AttrParser |
Alternative AttrParser |

requireAttr :: Name -> AttrParser Text

Require that a certain attribute be present and return its value.

optionalAttr :: Name -> AttrParser (Maybe Text)

Return the value for an attribute if present.

requireAttrRaw :: String -> ((Name, [Content]) -> Maybe b) -> AttrParser b

optionalAttrRaw :: ((Name, [Content]) -> Maybe b) -> AttrParser (Maybe b)

ignoreAttrs :: AttrParser ()

Skip the remaining attributes on an element. Since this will clear the list of attributes, you must call this after any calls to `requireAttr`, `optionalAttr`, etc.

# Combinators

orE :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m (Maybe a) -> Consumer Event m (Maybe a)

Get the value of the first parser which returns `Just`. If no parsers succeed (i.e., return `Just`), this function returns `Nothing`.

     orE a b = choose [a, b]

choose :: Monad m => [Consumer Event m (Maybe a)] -> Consumer Event m (Maybe a)

Get the value of the first parser which returns `Just`. If no parsers succeed (i.e., return `Just`), this function returns `Nothing`.

many :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m [a]

Keep parsing elements as long as the parser returns `Just`.

force

Arguments

:: MonadThrow m |
=> String | Error message
-> ConduitM Event o m (Maybe a) |
-> ConduitM Event o m a |

Force an optional parser into a required parser. All of the `tag` functions, `choose` and `many` deal with `Maybe` parsers. Use this when you want to finally force something to happen.

# Exceptions

data XmlException

Constructors

XmlException |
Fields xmlErrorMessage :: String xmlBadInput :: Maybe Event
InvalidEndElement Name |
InvalidEntity Text |
UnparsedAttributes [(Name, [Content])] |

Instances

Show XmlException |
Typeable XmlException |
Exception XmlException |

# Other types

data PositionRange

Instances

Eq PositionRange |
Ord PositionRange |
Show PositionRange |

type EventPos = (Maybe PositionRange, Event)