Re: Project - Eliminating grob parents and outside-staff-priority

[Keith OHara]

On Sat, 29 Sep 2012 10:30:32 -0700, address@hidden <address@hidden> wrote:

> The way you're using "tentative" is almost exactly how pure properties are used 
> in LilyPond.

Specifically, 'pure-height being the estimated vertical extent before 
line-breaking, while 'height is its extent after line-breaking.

If there are distinct properties to describe the position at different stages, 
then each property can be evaluated just once (as HanWen suggested, and as Mike 
agreed 100%).

> I think all property look-ups should be pure until one is absolutely certain 
> that the property won't change, at which point the unpure value should be 
> cached and returned for both pure and unpure queries (impure sounds too 
> religious, thus unpure).  The pure properties need not always return the same 
> value - they can get closer and closer to the unpure as more and more 
> information gets determined.

This is the opposite approach, where some "properties" are not permanent at 
all.  The word 'tentative' is a better label than 'pure', because pure functions would 
always return the same value given the same arguments.