[darcs-devel] darcs patch: Cache pristine directory within NoPristine.

[Juliusz Chroboczek]

> I'm not sure that we *want* invalidatePristine.  Couldn't we just update
> the pristine, if we've already got one?

We could.  But we don't want to ;-)

As far as I can see, there's no Darcs command that will call
surely_slurp_Pristine after invalidating a pristine.  In other words,
we could update the pristine, but if we did, we'll never read it anyway.

So it would be safe in practice to never invalidate a pristine.  Think
of invalidatePristine as a belt+suspenders type of thing.

> It does seem like a lazy field and unsafePerformIO would be the way to go
> about this, and then we just have to keep the cache up-to-date if it
> exists.

except that...

> The catch is that we have to be able to *know* if it exists...

on the other hand...

> I'm sure this is a soluble problem

.. but this Haskell newbie has no idea how it can be done.  Feel free
to hack my code into any shape that suits you.

                                        Juliusz