PXP Reference : Pxp_event

# Module Pxp_event

    module Pxp_event: sig .. end

Dealing with events (for pull parsing)

Dealing with events (for pull parsing)

## Events as lists

    val to_list : (unit -> Pxp_types.event option) -> Pxp_types.event list

Fetch all events from the pull function, and return the corresponding list of events.

    val of_list : Pxp_types.event list -> unit -> Pxp_types.event option

`of_list l`: Create a pull function fetching the events from `l`

    val concat : (unit -> Pxp_types.event option) list -> unit -> Pxp_types.event option

`let p = concat l`: The pull functions contained in the list `l` are concatenated, and a new pull function `p` is created that pulls from the functions of the list in turn (when one function indicates the end of the events, it is continued with the next function in the list).

    val iter : (Pxp_types.event -> unit) -> (unit -> Pxp_types.event option) -> unit

`iter f p`: The pull function `p` is repeatedly called to get a stream of events `e`. For each event the function `f` is called.

    val extract : Pxp_types.event ->
           (unit -> Pxp_types.event option) -> unit -> Pxp_types.event option

`let next' = extract e next`: Extracts a subexpression from the pull function `next` prepended by `e`. A subexpression consists of either

- a single data, comment, PI, or error event
- a start tag, either of an element, a super root, or a document, until the corresponding end tag
- a position event followed by a subexpression

The returned pull function contains all events of the subexpression. When the extracted stream is read, the original stream is read, too.

Example:

     let l = [ E_pinstr; E_start_tag; E_data; E_start_tag; E_end_tag;

               E_comment; E_end_tag; E_data ];;

     let g = of_list l;;

     g();;

     let Some e = g();;         (* e = E_start_tag *)

     let g' = extract e g;;

     g'();;                     (* returns Some E_start_tag *)

     ...

     g'();;                     (* returns Some E_end_tag *)

     g'();;                     (* returns None, end of subexpression *)

     g();;                      (* returns Some E_data *)

     g();;                      (* returns None *)

## Filters

    type pull_fn = unit -> Pxp_types.event option

The result type of `Pxp_ev_parser.create_pull_parser`

    type filter = pull_fn -> pull_fn

A filter transforms a pull function into another pull function

    val norm_cdata_filter : filter

This filter

- removes empty `E_char_data` events
- concatenates adjacent `E_char_data` events

but does not touch any other parts of the event stream.

    val drop_ignorable_whitespace_filter : filter

This filter

- checks whether character data between elements in a "regexp" or "non-PCDATA mixed" content model consists only of whitespace, and
- removes these whitespace characters from the event stream.

If the check fails, a `WF_Error` will be raised.

This filter works only if the DTD found in the event stream actually contains element declarations. This is usually enabled by including the ``Extend_dtd_fully` or ``Val_mode_dtd` options to the `entry` passed to the `create_pull_parser` call. Furthermore, there must be an `E_start_doc` event.

This filter does not perform any other validation checks.

    val pfilter : (Pxp_types.event -> bool) -> filter

Filters an event stream by a predicate

Example: Remove comments:

     pfilter (function E_comment _ -> false | _ -> true) g

    val unwrap_document : pull_fn -> (unit -> string * Pxp_dtd.dtd) * pull_fn

This filter removes the document wrapping from the stream (see The wrapping for closed documents for a definition what this is). It is called like

             let (get_doc_details, next') = unwrap_document next

             let (version, dtd) = get_doc_details()

The returned `filter` removes any `E_start_doc`, `E_end_doc`, `E_start_super`, `E_end_super`, and `E_end_of_stream` events. If an `E_error` event is encountered, the contained exception is raised. All other events of the stream remain.

The function `get_doc_details` can be called to get details about the document definition. If an `E_start_doc` event is found in the stream, the XML version string and the DTD object are returned. The function fails if `E_start_doc` is not the first event of the stream.

## Helpers for namespace processing

The names in `E_start_tag` can be analyzed with the following.

    val namespace_split : string -> string * string

`let (p,l) = namespace_split name`: Splits `name` into the prefix `p` and the local name `l`. If there is no colon in `name`, the function returns `p=""`, and `l=name`.

    val extract_prefix : string -> string

Returns the prefix in the name, or `""` if there is no prefix. Same as `fst(namespace_split name)`.

## Printing event streams

    type dtd_style = [ `Ignore | `Include | `Reference ]

    val write_events : ?default:string ->
           ?dtd_style:dtd_style ->
           ?minimization:[ `AllEmpty | `None ] ->
           Pxp_types.output_stream ->
           Pxp_types.encoding ->
           Pxp_types.rep_encoding -> (unit -> Pxp_types.event option) -> unit

Writes the events to the `output_stream`. The events must be encoded as indicated by the `rep_encoding` argument, but the output is written as specified by the `encoding` argument.

The normalized namespace prefixes are declared as needed. Additionally, one can set the default namespace by passing `default`, which must be the normalized prefix of the default namespace.

For `E_doc_start` events, the DTD may be written. This is controlled by `dtd_style`:

- ``Ignore`: No `DOCTYPE` clause is written
- ``Include`: The `DOCTYPE` clause is written, and the DTD is included in the internal subset (the default)
- ``Reference`: The `DOCTYPE` clause is written as a reference to an external DTD

Option `minimization`: How to write out empty elements. ``AllEmpty` means that all empty elements are minimized (using the `<name/>` form). ``None` does not minimize at all and is the default.

    val display_events : ?dtd_style:dtd_style ->
           ?minimization:[ `AllEmpty | `None ] ->
           Pxp_types.output_stream ->
           Pxp_types.encoding ->
           Pxp_types.rep_encoding -> (unit -> Pxp_types.event option) -> unit

Writes the events to the `output_stream`. The events must be encoded as indicated by the `rep_encoding` argument, but the output is written as specified by the `encoding` argument.

Namespace prefixes are declared as defined in the namespace scopes. Missing prefixes are invented on the fly.

The way the DTD is printed can be set as in `write_events`.

    val string_of_event : Pxp_types.event -> string

Returns a string representation of events, for debugging