[Cook] Fingerprinting recipes

[Peter Miller]

On Mon, 2003-06-16 at 17:08, Dirk Heinrichs wrote:
> Am Freitag, 13. Juni 2003 16:16 schrieb ext Brendan J Simon:
> > You could put each recipe in it's own file and inlude the recipe files
> > in the master cookbook.  Your dependencies will then include this recipe
> > file.

> A recipe can change without editing it (i.e. implizit recipe using a target 
> dependant variable). So listing the recipe file as dependency doesn't help.

It is possible to have the ingredients of a recipe fingerprinted, so the
recipe is re-run if the ingredients change, even if everything else is
up-to-date.  This is useful for libraries (usually when the ingredients
are reduced).
	
	target: ingredient
		set ingredients-fingerprint
	{
		blah blah;
	}

Fingerprinting the recipe itself is much harder.  Cook compiles recipe
bodies into byte-code.  Fingerprinting the byte-code is simple enough,
but putting the recipe itself into an included file and make it depend
on that file is easier, and requires no changes to Cook.

	target: ingredient [__FILE__]
		set ingredients-fingerprint
	{
		blah blah;
	}

I often use recipes like

	lib%.a: [%_obj]
		set unlink ingredients-fingerprint
	{
		ar cq [target] [need];
	}

which a re-run if the list of objects changes, because the list of
ingredients is known at the end of graph-building, so the ingredients
fingerprint is known at graph-walking time.

Cook makes all the power of a 3GL available in recipe bodies, not just
simple command execution.  What you asked for, to fingerprint the recipe
*after* all patterns and variables are expanded, isn't available to cook
until *after* the byte-code has been executed.  To fingerprint at this
level would require redesign of Cook *and* need more memory to remember
the dependency graph.  It also changes a number of order-of-evaluation
semantics, which could result in some users' cookbooks no longer
working.  For example the [collect] and [execute] functions mean that
you can't evaluate the recipe bodies after graph building but before
graph walking, because the files they use may not exist yet *and* you
need them in the fingerprint, too.

-- 
Regards
Peter Miller <millerp at canb.auug.org.au>
/\/\*        http://www.canb.auug.org.au/~millerp/

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