#lang scribble/manual
@(require 
	scribble/eval
	(for-label racket))

@title{GUIML}

This is a DSL for describing GUIs. It is inspired by SXML notation and the
HTMLPrag library. "GUIML" is a thin wrapper around Racket's standard
GUI library that allows a window and all its initial contents to
be specified in a single expression, instead of having to specify each
child widget's parent by name. 

Here is a simple GUI:

@racketblock[
(define g (guiml (frame% (|@| (label "Foobar")
                              (width 640)
                              (height 150))
                         (vertical-panel% (|@|)
                             (message% (|@| (label "Hello, world!")))
                             (editor-canvas% 'ecanvas (|@|))
                             (button% (|@| (label "Close")
                                         (style '(border))
                                         (callback (lambda ignored-args
                                                     (sendmsg g show #f)))))))))

]

@scheme[g] is actually of a subclass of @scheme[frame%]. The subclass is generated
on the fly, and allows all the widgets in the tree to be tagged with an optional
identifier, which can be used to retrieve a widget from the tree even if it's not
bound to a variable.

Usage:

@defform[ #:literals (guiml |@|)
	  (guiml
             (class% [id] (|@| (class-parameter val) ...)
	         (child-class% [child-id] (|@| ...) [grandchildren] ...)
		 [more-children] ...))]


The @scheme[|@|] subform contains all the arguments required by that object's @scheme[new]
operator, except the @scheme[parent], which is added automatically. This subform is
required even if it's empty.

Within the context of the above @scheme[guiml] form, this:

@racketblock[
      (button% (|@| (label "Close")
                    (style '(border))
                    (callback (λ ignored-args
                                 (sendmsg g show #f)))))
]

is equivalent to this:

@racketblock[
   (new button% (parent the-vertical-panel-above-this-in-the-tree)
                (label "Close")
                (style '(border))
                (callback (λ ignored-args
                             (sendmsg g show #f))))
]

The @scheme[|@|] subform is followed by all the object's children.

To give an object in the tree a name, you put the identifier in front of the @scheme[|@|] subform:

@racketblock[
   (guiml frame% ...
    (editor-canvas% 'ecanvas (|@|)))
]

The identifier can be of any type, and by default will be compared with @scheme[eq?]

Then the same object can be retrieved from the tree using @scheme[get-widget-by-id]:

@racketblock[
   (get-widget-by-id g 'ecanvas)
]

You can specify a comparator if you used an identifier that can't be compared
with @scheme[eq?]:

@racketblock[
   (get-widget-by-id g "ecanvas" string=?)
]

You can also retrieve all the objects of a given class from the tree:

@racketblock[
    (get-widgets-by-type g button%)
]

Each object in the tree has its own semaphore, which can be obtained
like this:

@racketblock[
   (send g get-semaphore)
]

The following syntax is provided for backward compatibility:

@racketblock[
(sendmsg g show #t)
]

In older versions of GUIML, the GUI objects were wrapped in a bundle of structs and lists,
and that was how they were tagged with identifiers and arranged in a tree that could be traversed.
The @scheme[sendmsg] form allowed you to somewhat still be able to treat this structure like a
class.