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Date: Wed, 11 Apr 2001 20:40:37 -0400
From: esr@thyrsus.com
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Michael Elizabeth Chastain <chastain@cygnus.com>, davej@suse.de,
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Subject: Re: [kbuild-devel] Re: CML2 1.0.0 release announcement
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Alan Cox <alan@lxorguk.ukuu.org.uk>:
> CML2 seems to have two other problems in my mind. Inability to parse
> the existing config files.

I gave upon that early for two reasons.  One was practical; Michael tried this
with mconfig, and (apparently) failed.  Or, at least, appeared to have decided
that path was not worth pursuing.

The other was the procedural vs. declarative problem.  I spent about a
month after the kbuild team originally encouraged me to tackle the
problem working on a design which I later labeled Thesis.  This was an
attempt to build a cleaned-up CML1, basically the existing language
without the syntactic warts.  I got as far as spinning up an
incomplete implementation that could check toy configurations.

But the design basically didn't work.  The problem is that a
procedural language imposes a kind of time order that makes it very
difficult to (a) do backtracking and (b) prove the correctness of your
result.  Perhaps a clearer way to put it is that configuration (like, say,
screen widget layout) is fundamentally a constraint problem rather
than a control problem.

A constraint problem needs a declarative rather than imperative
language, and it needs a baby reasoning engine to generate a
constraint-satisfying solution (Tk approaches screen-widget layout
this way; that's thye source of its power).  Neither of my strawman
designs had significant advantage over CML1 until I bit the bullet and
wrote a theorem prover to reason about timeless constraints.

>                        Also the draw ordering in the menu based
> config doesnt appear right. Menuconfig has a rather undocumented but
> very important property of doing roughly the right thing with
> screenreaders. Something to bear in mind when fixing the menu
> redrawing stuff.

Yes, I have plans for this.
-- 
		<a href="http://www.tuxedo.org/~esr/">Eric S. Raymond</a>

Militias, when properly formed, are in fact the people themselves and
include all men capable of bearing arms. [...] To preserve liberty it is
essential that the whole body of the people always possess arms and be
taught alike, especially when young, how to use them.
        -- Senator Richard Henry Lee, 1788, on "militia" in the 2nd Amendment