Re: Community improvements to the Emacs Widget Library manual?

[bovine@cyberscientist.ca]

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.

---

(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"))))

(defun menu-choice-value-to-internal (widget external-value)
   "Converts the casing of trademarked names to lowercase, internal 
values."
   (pcase external-value
     ("MySQL" "mysql")
     ("SQLite" "sqlite")
     ("PostgreSQL" "postgresql")))

(defun menu-choice-value-to-external (widget internal-value)
   "Converts lowercase, internal values to the casing of trademarks."
   (pcase internal-value
     ("mysql" "MySQL")
     ("sqlite" "SQLite")
     ("postgresql" "PostgreSQL")))

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

(defun widget-value-conversion-example ()
        (interactive)
        (switch-to-buffer "*Widget Value Conversion Example*")
        (kill-all-local-variables)
        (let ((inhibit-read-only t))
          (erase-buffer))
        (remove-overlays)
        (widget-insert "Widget value conversion example.\n\n")
        (widget-create 'repeat 'project-widget)
        (use-local-map widget-keymap)
        (widget-setup))