Re: Community improvements to the Emacs Widget Library manual?

[Mauro Aranda <maurooaranda@gmail.com>]

bovine@cyberscientist.ca writes:

 > On 2023-07-14 10:41, Mauro Aranda wrote:
 >> Bryce Carson <bovine@cyberscientist.ca> writes:
 >>
 >>> Further, I can't seem to get these functions to work as documented or
 >>> expected.
 >>> Without these defined when I'm creating a widget with the following
 >>> code, I do get a button but the internal value is displayed in the
 >>> clickable
 >>> button. I'd like the external value to be displayed in the button
 >>> %v, just
 >>> as the menu-tag is is "externally facing".
 >>> <<widget>>=
 >>> (define-widget 'project-widget 'list
 >>>   :tag (let ((s "\n\tProject"))
 >>>          (put-text-property 0 (length s) 'face 'bold s) s)
 >>>   :format "%t\n%v "
 >>>   :offset 0
 >>>   :indent 0
 >>>   :convert-widget 'widget-types-convert-widget
 >>>   :args '((menu-choice
 >>>            :tag "EmacSQL-supported backend"
 >>>            :format "%[%t%]: %[%v%]"
 >>>            :value "sqlite"
 >>>            :value-to-external <<menu-choice internal value to
 >>> external lambda>>
 >>>            :value-to-internal <<menu-choice external value to
 >>> internal lambda>>
 >>>            (choice-item :menu-tag "MySQL" :value "mysql")
 >>>            (choice-item :menu-tag "PostgreSQL" :value "postgresql")
 >>>            (choice-item :menu-tag "SQLite" :value "sqlite"))))
 >>> <<menu-choice internal value to external lambda>>=
 >>> (lambda (widget internal-value)
 >>>   "Converts lowercase, internal values to the casing of trademarks."
 >>>   (pcase internal-value
 >>>     ("mysql" "MySQL")
 >>>     ("sqlite" "SQLite")
 >>>     ("postgresql" "PostgreSQL")))
 >>> <<menu-choice external value to internal lambda>>=
 >>> (lambda (widget external-value)
 >>>   "Converts the casing of trademarked names to lowercase, internal
 >>> values."
 >>>   (pcase external-value
 >>>     ("MySQL" "mysql")
 >>>     ("SQLite" "sqlite")
 >> When possible, please post code that can be evaled without making
 >> tweaks.
 >> Some things I noted:
 >> - Since the super is a list widget, then you don't need to specify
 >> :convert-widget.  The :convert-widget function is one of the few that
 >> gets called for all supers, so you end up converting twice the widget.
 >> In this case, it doesn't seem you want that.
 >> - You're specifying a value in the internal format for the
 >> menu-choice.
 >> The manual specifies that when creating a widget or defining a new
 >> one, the ‘:value’ should be in the external format.
 >> - I think you should give similar conversion functions to all
 >> choice-item, and also pass the :value in external format.
 >> Let me know if you still find problems after fixing these things.
 >
 > I fixed those issues and I do not see the invalid or void state, but
 > only nil is ever displayed in the buffer.
 > Below is the code I defined.

OK, I think you ran into something that's unsupported (maybe a bug, but
I'm not quite sure).

And thank you for providing the code, it made things easier for me to
see it.

 > (define-widget 'project-widget 'list
 >   "A mimimal example to demonstrate 'styled' choice item buttons in a
 >   choice menu."
 >   :tag (let ((s "\n\tProject"))
 >          (put-text-property 0 (length s) 'face 'bold s) s)
 >   :format "%t\n%v "
 >
 >   :args '((menu-choice
 >            :tag "EmacSQL-supported backend"
 >            :size 50
 >            :format "%[%t%]: %[%v%] \n"
 >
 >            :value "SQLite"
 >            :choice (database-choice-item :menu-tag "SQLite" :value
 >            "SQLite")
 >
 >            :value-to-external menu-choice-value-to-external
 >            :value-to-internal menu-choice-value-to-internal
 >
 >            (database-choice-item :menu-tag "MySQL" :value "MySQL")
 >            (database-choice-item :menu-tag "PostgreSQL" :value
 >            "PostgreSQL")
 >            (database-choice-item :menu-tag "SQLite" :value
 >            "SQLite"))))

The menu-choice creation assumes no difference between the internal
format and external format.  So for now, try removing the
:value-to-external and :value-to-internal.  I think it does that
because there's no big reason for converting a menu-choice value, since
the menu-choice will get its value from a valid choice, and the
individual choice is responsible for the conversion between formats.

Oh, and don't use :value and :choice at the same.  Just use :value to
give it a default value.  So this widget should be:

(define-widget 'project-widget 'list
   "A mimimal example to demonstrate 'styled' choice item buttons in a
   choice menu."
   :tag (let ((s "\n\tProject"))
          (put-text-property 0 (length s) 'face 'bold s) s)
   :format "%t\n%v "
   :args '((menu-choice
            :tag "EmacSQL-supported backend"
            :size 50
            :format "%[%t%]: %[%v%] \n"
        :value "MySQL"
            (database-choice-item :menu-tag "MySQL"      :value "MySQL")
            (database-choice-item :menu-tag "PostgreSQL" :value
            "PostgreSQL")
            (database-choice-item :menu-tag "SQLite"     :value
            "SQLite"))))

 > (define-widget 'database-choice-item 'choice-item
 >   nil
 >   :value-to-external #'menu-choice-value-to-external
 >   :value-to-internal #'menu-choice-value-to-internal)

And now, you need a :match function for this widget, so that when it
gets passed an external value, such as "MySQL", it returns non-nil.

So maybe something like this:
(define-widget 'database-choice-item 'choice-item
   nil
   :match (lambda (widget value)
        (equal (widget-get widget :value) (widget-apply widget
                                :value-to-internal
                                value)))
   :value-to-external #'menu-choice-value-to-external
   :value-to-internal #'menu-choice-value-to-internal)

You need a custom :match function because otherwise the
database-choice-item would resort to matching like an item, and that's
not good when you have different internal and external formats.
Basically, if you use different formats, you should consider providing a
:match function yourself.

I think with these fixes, your code will run just as you expect it.