Correct!
Adam tracks which values contribute to which other values through all
operations -
Any cell value contributing to an invariant is "poison".
Any cell value derived from a poison value is invalid.
Button right now are latches in a pipe (in the future, I want to change
them to be latch controls, rather than the latch itself). A button
receives a value and forwards it when clicked. If the value is invalid,
the button is disabled.
Other controls enable/disable depending on if the cell they are bound
to was "considered" or not. Every interface cell has a priority, if the
priority or value contributes, then the cell was considered. Right now,
considered isn't tracked at as fine a granularity as contributing
(priority is tracked at the sheet level).
Sean
On Apr 2, 2005, at 5:56 PM, Ralph Thomas wrote:
> can_do_element_operation is in the invariant section, meaning that it
> should be true.
>
> I think what happens is:
>
> * When "selection == @item_end" the invariant can_do_element
> operation is not satisfied
> * "selection" caused to an invariant violation.
> * .._params are dictionaries, all of which reference "selection"
> * the buttons are bound to the .._params which contain a cell
> contributing to an invariant violation and are disabled.
>
> It seems like if a dictionary contains any cell which contributed to
> an invariant violation then anything bound to the dictionary is
> disabled.
>
> Ralph
>
> On Apr 2, 2005 4:08 PM, David Catmull <unc...@un...>
> wrote:
>> I'm trying to understand how the list_box_emulator example works as
>> far
>> as disabling the Insert and Delete buttons.
>>
>> There is a 'can_do_element_operation' in the sheet, and yet it is not
>> referenced anywhere. It looks like the buttons are being disabled
>> because they are bound to 'insert/delete_params' which both reference
>> 'selection' which is referenced in the invariant, but I still don't
>> quite follow how that works. What exactly is the connection between
>> 'insert/delete_params' and 'can_do_element_operation'? Is it just the
>> fact that 'selection' is in the definition of
>> 'can_do_element_operation'?
>>
>> --
>> David Catmull
>> unc...@un...
>> http://www.uncommonplace.com/
>>
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