9 WXME Decoding

▼ |  | The Racket Graphical Interface Toolkit

1 | Windowing
2 | Widget Gallery
3 | Windowing Classes
4 | Windowing Functions
5 | Editors
6 | Snip and Style Classes
7 | Editor Classes
8 | Editor Functions
9 | WXME Decoding
10 | Preferences
11 | Dynamic Loading
12 | Startup Actions
13 | Platform Dependencies
| Index

► | 9 | WXME Decoding

9.1 | Snip Class Mapping
9.2 | Dr Racket Comment Boxes
9.3 | Dr Racket XML Boxes
9.4 | Dr Racket Racket Boxes
9.5 | Dr Racket Text Boxes
9.6 | Dr Racket Fractions
9.7 | Dr Racket Teachpack Images
9.8 | Dr Racket Test-Case Boxes

On this page:

is-wxme-stream?
wxme-port->text-port
wxme-port->port
extract-used-classes
register-lib-mapping!
string->lib-path
unknown-extensions-skip-enabled
broken-wxme-big-endian?
wxme-read
wxme-read-syntax
snip-reader<%>
read-header
read-snip
readable<%>
read-special
stream<%>
read-integer
read-fixed-integer
read-inexact
read-raw-bytes
read-bytes
read-editor
read-snip-from-port
9.1`` Snip Class Mapping
9.1.1`` Nested Editors
editor%
get-content-port
9.1.2`` Images
image%
get-data
get-w
get-h
get-dx
get-dy
9.2`` Dr Racket Comment Boxes
reader
comment-editor%
get-data
read-special
9.3`` Dr Racket XML Boxes
reader
xml-editor%
get-data
read-special
9.4`` Dr Racket Racket Boxes
reader
racket-editor%
get-data
read-special
9.5`` Dr Racket Text Boxes
reader
text-editor%
get-data
read-special
9.6`` Dr Racket Fractions
reader
9.7`` Dr Racket Teachpack Images
reader
cache-image%
get-argb
get-width
get-height
get-pin-x
get-pin-y
9.8`` Dr Racket Test-Case Boxes
reader
test-case%
get-comment
get-test
get-expected
get-should-raise
get-error-message
get-enabled?
get-collapsed?
get-error-box?

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### 9`` WXME Decoding

(require wxme)

The wxme library provides tools for reading WXME editor<%>-format files (see File Format) without the racket/gui library.

> procedure (is-wxme-stream? in) → boolean?
> in : input-port?

Peeks from in and returns #t if it starts with the magic bytes indicating a WXME-format stream (see File Format), #f otherwise.

> procedure (wxme-port->text-port in [close?]) → input-port?
> in : input-port?
> close? : any/c = #t

Takes an input port whose stream starts with WXME-format data and returns an input port that produces a text form of the WXME content, like the result of opening a WXME file in DrRacket and saving it as text.

Unlike wxme-port->port, this function may take liberties with the snips in a way that would render a valid program invalid. For example, if the wxme stream in contains a bitmap image, then there may not be a reasonable text-only version of it and thus wxme-port->port might turn what would have been a valid Racket program into text that is a syntax error, Nevertheless, the result may still be useful for human readers or approximate program-processing tools that run only in a GUI-less context.

If close? is true, then closing the result port closes the original port.

See Snip Class Mapping for information about the kinds of non-text content that can be read.

> procedure (wxme-port->port in [close? snip-filter]) → input-port?
> in : input-port?
> close? : any/c = #t
> snip-filter : (any/c . -> . any/c) = (lambda (x) x)

Takes an input port whose stream starts with WXME-format data and returns an input port that produces text content converted to bytes, and non-text content as “special” values (see read-char-or-special).

These special values produced by the new input port are different than the ones produced by reading a file into an editor<%> object. Instead of instances of the snip%, the special values are typically simple extensions of object%. See Snip Class Mapping for information about the kinds of non-text content that can be read.

If close? is true, then closing the result port close the original port.

The snip-filter procedure is applied to any special value generated for the stream, and its result is used as an alternate special value.

If a special value (possibly produced by the filter procedure) is an object implementing the readable<%> interface, then the object’s read-special method is called to produce the special value.

> > procedure
> > (extract-used-classes in) |  | → |  |
> > (listof string?) |  | (listof string?)
> in : input-port?

Returns two values: a list of snip-class names used by the given stream, and a list of data-class names used by the stream. If the stream is not a WXME stream, the result is two empty lists. The given stream is not closed, and only data for a WXME stream (if any) is consumed.

> procedure (register-lib-mapping! str mod-path) → void?
> str : string?
> mod-path : (cons/c 'lib (listof string?))

Maps a snip-class name to a quoted module path that provides a reader% implementation. The module path must have the form '(lib string ...), where each string contains only alpha-numeric ASCII characters, ., _, -, and spaces.

> procedure (string->lib-path str gui?) → (cons/c 'lib (listof string?))
> str : string?
> gui? : any/c

Returns a quoted module path for str for either editor<%> mode when gui? is true, or wxme mode when gui? is #f. For the latter, built-in mappings and mapping registered via register-lib-mapping! are used. If str cannot be parsed as a library path, and if no mapping is available (either because the class is built-in or not known), the result is #f.

> parameter (unknown-extensions-skip-enabled) → boolean?
> (unknown-extensions-skip-enabled skip?) → void?
> skip? : any/c

A parameter. When set to #f (the default), an exception is raised when an unrecognized snip class is encountered in a WXME stream. When set to a true value, instances of unrecognized snip classes are simply omitted from the transformed stream.

> parameter (broken-wxme-big-endian?) → boolean?
> (broken-wxme-big-endian? big?) → void?
> big? : any/c

A parameter. Some old and short-lived WXME formats depended on the endian order of the machine where the file was saved. Set this parameter to pick the endian order to use when reading the file; the default is the current platform’s endian order.

> procedure (wxme-read in) → any/c
> in : input-port?

Like read, but for a stream that starts with WXME-format data. If multiple S-expressions are in the WXME data, they are all read and combined with 'begin.

If racket/gui/base is available (as determined by gui-available?), then open-input-text-editor is used. Otherwise, wxme-port->port is used.

> procedure (wxme-read-syntax source-v in) → (or/c syntax? eof-object?)
> source-v : any/c
> in : input-port?

Like read-syntax, but for a WXME-format input stream. If multiple S-expressions are in the WXME data, they are all read and combined with 'begin.

If racket/gui/base is available (as determined by gui-available?), then open-input-text-editor is used. Otherwise, wxme-port->port is used.

interface snip-reader<%> : interface?

An interface to be implemented by a reader for a specific kind of data in a WXME stream. The interface has two methods: read-header and read-snip.

> > > method
> > > (send a-snip-reader read-header |  | version |  |  |  |
> > > |  | stream) |  | → |  | any
> > version : exact-nonnegative-integer?
> > stream : (is-a?/c stream<%>)

> Called at most once per WXME stream to initialize the data type’s stream-specific information. This method usually does nothing.

> > > method
> > > (send a-snip-reader read-snip |  | text-only? |  |  |  |
> > > |  | version |  |  |  |
> > > |  | stream) |  | → |  |
> > > (if text-only?
> > > bytes?
> > > any/c)
> > text-only? : boolean?
> > version : exact-nonnegative-integer?
> > stream : (is-a?/c stream<%>)

> Called when an instance of the data type is encountered in the stream. This method reads the data and returns either bytes to be returned as part of the decoded stream or any other kind of value to be returned as a “special” value from the decoded stream. The result value can optionally be an object that implements readable<%>.

> The text-only? argument is #f when wxme-port->text-port was called and #t when wxme-port->port was called.

interface readable<%> : interface?

An interface to be implemented by values returned from a snip reader. The only method is read-special.

> > > method
> > > (send a-readable read-special |  | source |  |  |  |
> > > |  | line |  |  |  |
> > > |  | column |  |  |  |
> > > |  | position) |  | → |  | any/c
> > source : any/c
> > line : (or/c exact-nonnegative-integer? #f)
> > column : (or/c exact-nonnegative-integer? #f)
> > position : (or/c exact-nonnegative-integer? #f)

> Like read-special, but for non-graphical mode. When a value implements this interface, its read-special method is called with source-location information to obtain the “special” result from the WXME-decoding port.

interface stream<%> : interface?

Represents a WXME input stream for use by snip-reader<%> instances.

> > method (send a-stream read-integer what) → exact-integer?
> > what : any/c

> Reads an exact integer, analogous to get-exact.

> The what field describes what is being read, for error-message purposes, in case the stream does not continue with an integer.

> > method (send a-stream read-fixed-integer what) → exact-integer?
> > what : any/c

> Reads an exact integer that has a fixed size in the stream, analogous to get-fixed.

> The what argument is as for read-integer.

> > method (send a-stream read-inexact what) → (and/c real? inexact?)
> > what : any/c

> Reads an inexact real number, analogous to get-inexact.

> The what argument is as for read-integer.

> > method (send a-stream read-raw-bytes what) → bytes?
> > what : any/c

> Reads raw bytes, analogous to get-unterminated-bytes.

> The what argument is as for read-integer.

> > method (send a-stream read-bytes what) → bytes?
> > what : any/c

> Reads raw bytes, analogous to get-bytes.

> The what argument is as for read-integer.

> > method (send a-stream read-editor what) → input-port?
> > what : any/c

> Reads a nested editor, producing a new input port to extract the editor’s content.

> The what argument is as for read-integer.

> procedure (read-snip-from-port name who stream) → bytes?
> name : string?
> who : any/c
> stream : (is-a?/c stream<%>)

Given name, which is expected to be the name of a snipclass, uses that snipclass to read from the given stream at the current point in that stream. Returns the processed bytes, much like the read-snip method.

#### 9.1`` Snip Class Mapping

When graphical data is marshaled to the WXME format, it is associated with a snip-class name to be matched with an implementation at load time. See also Snip Classes.

Ideally, the snip-class name is generated as

> (format "~s" (list '(lib string ...)
> '(lib string ...)))

where each element of the formated list is a quoted module path (see module-path?). The strings must contain only alpha-numeric ASCII characters, plus ., _, -, and spaces, and they must not be "." or "..".

In that case, the first quoted module path is used for loading WXME files in graphical mode; the corresponding module must provide snip-class object that implements the snip-class% class. The second quoted module path is used by the wxme library for converting WXME streams without graphical support; the corresponding module must provide a reader object that implements the snip-reader<%> interface. Naturally, the snip-class% instance and snip-reader<%> instance are expected to parse the same format, but generate different results suitable for the different contexts (i.e., graphical or not).

If a snip-class name is generated as

> (format "~s" '(lib string ...))

then graphical mode uses the sole module path, and wxme needs a compatibility mapping. Install one with register-lib-mapping!.

If a snip-class name has neither of the above formats, then graphical mode can use the data only if a snip class is registered for the name, or if it the name of one of the built-in classes: "wxtext", "wxtab", "wximage", or "wxmedia" (for nested editors). The wxme library needs a compatibility mapping installed with register-lib-mapping! if it is not one of the built-in classes.

Several compatibility mappings are installed automatically for the wxme library. They correspond to popular graphical elements supported by various versions of DrRacket, including comment boxes, fractions, XML boxes, Racket boxes, text boxes, and images generated by the htdp/image teachpack (or, more generally, from mrlib/cache-image-snip), and test-case boxes.

For a port created by wxme-port->port, nested editors are represented by instances of the editor% class provided by the wxme/editor library. This class provides a single method, get-content-port, which returns a port for the editor’s content. Images are represented as instances of the image% class provided by the wxme/image library.

Comment boxes are represented as instances of a class that extends editor% to implement readable<%>; see wxme/comment. The read form produces a special comment (created by make-special-comment), so that the comment box disappears when read is used to read the stream; the special-comment content is the readable instance. XML, Racket, and text boxes similarly produce instances of editor% and readable<%> that expand in the usual way; see wxme/xml, wxme/scheme, and wxme/text. Images from the htdp/image teachpack are packaged as instances of cache-image% from the wxme/cache-image library. Test-case boxes are packaged as instances of test-case% from the wxme/test-case library.

##### 9.1.1`` Nested Editors

(require wxme/editor)

class editor% : class?
superclass: object%

Instantiated for plain nested editors in a WXME stream in text mode.

> > method (send an-editor get-content-port) → input-port?

> Returns a port (like the one from wxme-port->port) for the editor’s content.

##### 9.1.2`` Images

(require wxme/image)

class image% : class?
superclass: image-snip%

Instantiated for images in a WXME stream in text mode. This class can just be treated like image-snip% and should behave just like it, except it has the methods below in addition in case old code still needs them. In other words, the methods below are provided for backwards compatibility with earlier verisons of Racket.

> > method (send an-image get-data) → (or/c bytes? #f)

> Returns bytes for a PNG, XBM,or XPM file for the image.

> > method (send an-image get-w) → (or/c exact-nonnegative-integer? -1)

> Returns the display width of the image, which may differ from the width of the actual image specified as data or by a filename; -1 means that the image data’s width should be used.

> > method (send an-image get-h) → (or/c exact-nonnegative-integer? -1)

> Returns the display height of the image, which may differ from the height of the actual image specified as data or by a filename; -1 means that the image data’s height should be used.

> > method (send an-image get-dx) → exact-integer?

> Returns an offset into the actual image to be used as the left of the display image.

> > method (send an-image get-dy) → exact-integer?

> Returns an offset into the actual image to be used as the top of the display image.

#### 9.2`` DrRacket Comment Boxes

(require wxme/comment)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for comment boxes.

class comment-editor% : class?
superclass: editor%
extends: | readable<%>

Instantiated for DrRacket comment boxes in a WXME stream for text mode.

> > method (send a-comment-editor get-data) → #f

> No data is available.

> > > method
> > > (send a-comment-editor read-special |  | source |  |  |  |
> > > |  | line |  |  |  |
> > > |  | column |  |  |  |
> > > |  | position) |  | → |  | any/c
> > source : any/c
> > line : (or/c exact-nonnegative-integer? #f)
> > column : (or/c exact-nonnegative-integer? #f)
> > position : (or/c exact-nonnegative-integer? #f)

> Generates a special comment using make-special-comment. The special comment contains the comment text.

#### 9.3`` DrRacket XML Boxes

(require wxme/xml)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for XML boxes.

class xml-editor% : class?
superclass: editor%
extends: | readable<%>

Instantiated for DrRacket XML boxes in a WXME stream for text mode.

> > method (send a-xml-editor get-data) → any/c

> Returns #t if whitespace is elimited from the contained XML literal, #f otherwise.

> > > method
> > > (send a-xml-editor read-special |  | source |  |  |  |
> > > |  | line |  |  |  |
> > > |  | column |  |  |  |
> > > |  | position) |  | → |  | any/c
> > source : any/c
> > line : (or/c exact-nonnegative-integer? #f)
> > column : (or/c exact-nonnegative-integer? #f)
> > position : (or/c exact-nonnegative-integer? #f)

> Generates a quasiquote S-expression that enclosed the XML, with unquote and unquote-splicing escapes for nested Racket boxes.

#### 9.4`` DrRacket Racket Boxes

(require wxme/scheme)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for Racket boxes.

class racket-editor% : class?
superclass: editor%
extends: | readable<%>

Instantiated for DrRacket Racket boxes in a WXME stream for text mode.

> > method (send a-racket-editor get-data) → any/c

> Returns #t if the box corresponds to a splicing unquote, #f for a non-splicing unquote.

> > > method
> > > (send a-racket-editor read-special |  | source |  |  |  |
> > > |  | line |  |  |  |
> > > |  | column |  |  |  |
> > > |  | position) |  | → |  | any/c
> > source : any/c
> > line : (or/c exact-nonnegative-integer? #f)
> > column : (or/c exact-nonnegative-integer? #f)
> > position : (or/c exact-nonnegative-integer? #f)

> Generates an S-expression for the code in the box.

#### 9.5`` DrRacket Text Boxes

(require wxme/text)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for text boxes.

class text-editor% : class?
superclass: editor%
extends: | readable<%>

Instantiated for DrRacket text boxes in a WXME stream for text mode.

> > method (send a-text-editor get-data) → #f

> No data is available.

> > > method
> > > (send a-text-editor read-special |  | source |  |  |  |
> > > |  | line |  |  |  |
> > > |  | column |  |  |  |
> > > |  | position) |  | → |  | any/c
> > source : any/c
> > line : (or/c exact-nonnegative-integer? #f)
> > column : (or/c exact-nonnegative-integer? #f)
> > position : (or/c exact-nonnegative-integer? #f)

> Generates a string containing the text.

#### 9.6`` DrRacket Fractions

(require wxme/number)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for DrRacket fractions that generates exact, rational numbers.

#### 9.7`` DrRacket Teachpack Images

(require wxme/cache-image)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for images in a WXME stream generated by the htdp/image teachpack—or, more generally, by mrlib/cache-image-snip.

class cache-image% : class?
superclass: object%

Instantiated for DrRacket teachpack boxes in a WXME stream for text mode.

> > method (send a-cache-image get-argb) → (vectorof byte?)

> Returns a vector of bytes representing the content of the image.

> > method (send a-cache-image get-width) → exact-nonnegative-integer?

> Returns the width of the image.

> > method (send a-cache-image get-height) → exact-nonnegative-integer?

> Returns the height of the image.

> > method (send a-cache-image get-pin-x) → exact-integer?

> Returns an offset across into the image for the pinhole.

> > method (send a-cache-image get-pin-y) → exact-integer?

> Returns an offset down into the image for the pinhole.

#### 9.8`` DrRacket Test-Case Boxes

(require wxme/test-case)

> value reader : (is-a?/c snip-reader<%>)

A text-mode reader for DrRacket test-case boxes in a WXME stream. It generates instances of test-case%.

class test-case% : class?
superclass: object%

Instantiated for old-style DrRacket test-case boxes in a WXME stream for text mode.

> > method (send a-test-case get-comment) → (or/c #f input-port?)

> Returns a port for the comment field, if any.

> > method (send a-test-case get-test) → input-port?

> Returns a port for the “test” field.

> > method (send a-test-case get-expected) → input-port?

> Returns a port for the “expected” field.

> > method (send a-test-case get-should-raise) → (or/c #f input-port?)

> Returns a port for the “should raise” field, if any.

> > method (send a-test-case get-error-message) → (or/c #f input-port?)

> Returns a port for the “error msg” field, if any.

> > method (send a-test-case get-enabled?) → boolean?

> Returns #t if the test is enabled.

> > method (send a-test-case get-collapsed?) → boolean?

> Returns #t if the test is collapsed.

> > method (send a-test-case get-error-box?) → boolean?

> Returns #t if the test is for an exception.

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