Filtered functions
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From: Raffael Cavallaro on 22 Dec 2009 23:07 On 2009-12-22 20:06:52 -0500, Pascal Costanza <pc(a)p-cos.net> said: > These parties may not even know of each other. So how do they agree > what ranking to use? Clearly any such declarative programming sytem would have to define a ranking scale for rules with sensible defaults. Since end users may want to change the relative priorities of libraries of rules, there would need to be a means of modifying the priority of an existing (i.e. library) rule. Two parties (i.e. library writers) may not be aware of each other, but the end user must be aware of both (this is true of simple clos libraries and filtered functions as well) in order for things to work together properly. I don't see a declarative, rule-based system being any different in this regard. -- Raffael Cavallaro
From: Raffael Cavallaro on 22 Dec 2009 19:44 On 2009-12-22 11:09:02 -0500, Pascal Costanza <pc(a)p-cos.net> said: > Sure, but at least you need an agreement on the range of possible > values. Now, what happens if there is a method provided by party A with > priority 2, and a method provided by party B with priority 3, and you > are party C that wants to add a method exactly in between? Well pretty clearly you wouldn't use integers :^) Seriously, simple floating point values between 0.0d0 and 1000.0d0 for example would give users plenty of room to adjust rule ranking in the examples you give. By default, each rule would call call-next-rule (which would be translated to call-next-method of course) but this could be overridden if a user wants a particular rule to run last. -- Raffael Cavallaro
From: Pascal Costanza on 22 Dec 2009 20:06 On 23/12/2009 01:44, Raffael Cavallaro wrote: > On 2009-12-22 11:09:02 -0500, Pascal Costanza <pc(a)p-cos.net> said: > >> Sure, but at least you need an agreement on the range of possible >> values. Now, what happens if there is a method provided by party A >> with priority 2, and a method provided by party B with priority 3, and >> you are party C that wants to add a method exactly in between? > > Well pretty clearly you wouldn't use integers :^) > > Seriously, simple floating point values between 0.0d0 and 1000.0d0 for > example would give users plenty of room to adjust rule ranking in the > examples you give. This doesn't really help. An important use case is integrating separately developed methods, including methods implemented by third parties. These parties may not even know of each other. So how do they agree what ranking to use? This is an essential point in object systems. If you don't care about integrating separately developed code, OOP doesn't buy you that much... > By default, each rule would call call-next-rule (which would be > translated to call-next-method of course) but this could be overridden > if a user wants a particular rule to run last. Pascal -- My website: http://p-cos.net Common Lisp Document Repository: http://cdr.eurolisp.org Closer to MOP & ContextL: http://common-lisp.net/project/closer/
From: Pascal Costanza on 23 Dec 2009 05:58 On 23/12/2009 05:07, Raffael Cavallaro wrote: > On 2009-12-22 20:06:52 -0500, Pascal Costanza <pc(a)p-cos.net> said: > >> These parties may not even know of each other. So how do they agree >> what ranking to use? > > Clearly any such declarative programming sytem would have to define a > ranking scale for rules with sensible defaults. Since end users may want > to change the relative priorities of libraries of rules, there would > need to be a means of modifying the priority of an existing (i.e. > library) rule. > > Two parties (i.e. library writers) may not be aware of each other, but > the end user must be aware of both (this is true of simple clos > libraries and filtered functions as well) in order for things to work > together properly. I don't see a declarative, rule-based system being > any different in this regard. Ok, then we agree. ;) Pascal -- My website: http://p-cos.net Common Lisp Document Repository: http://cdr.eurolisp.org Closer to MOP & ContextL: http://common-lisp.net/project/closer/
From: Kenneth Tilton on 25 Dec 2009 18:12
Pascal Costanza wrote: > Hi, > > I am very excited that I can finally annouce a public release of > 'filtered functions', an extension of generic functions that Charlotte > Herzeel, Jorge Vallejos, and myself have developed some time ago and > that we are very excited about because it seems to be quite powerful in > a number of very different scenarios. This is puzzling. It sounds as if it has been used quite heavily yet both examples provided are trivial and more easily done other ways. C'mon, give up the beef! Other thought: in the paper I did not like the hand-waving about performance probably not being too bad. You have guessed wrong before about CLOS performance. If you don't know, just say so. I imagine any intense use would be a lot faster done without involving CLOS, leaving as always the question of whether programming with f/fn is so much more powerful as to be worth the hit. Also: you said more than one filter could be used. I did not see an example, nor did I know if you meant on two different parameters or methods or what. The syntax feels like exposed wiring. I'd get a macro in there so one could just say (n 1) instead of (n (eql 1)). Anyway, that's not why I am writing. I was looking at my Algebra code where I used deftype a couple of places and got to wondering if you could make CLOS dispatch off deftypes. That could be fun. kt |