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Posted to dev@cocoon.apache.org by Marcus Crafter <cr...@dresdnerbank.de> on 2000/11/09 20:23:18 UTC
Matchers and Selectors (was Re: Better and Better and RT)
Hi Giacomo,
On Sun, 5 Nov 2000, Giacomo Pati wrote:
> Ross Burton wrote:
> >
> > Berin Loritsch wrote:
> > >
> > > I envision the following additional selectors to be vital
> > > to any site:
> > >
> > > ParameterSelector (select things pased on HTTP parameters)
> > > AcceptsSelector (send PNG to browsers that accept it...)
>
> Take into account that a Selector chooses between multiple possibilities
> (and a default one if neither choosen) whereas a Matcher returns a List
> (or maybe we should change that to a Map) of values you can use for
> substitution in src attributes of Generators and Transformers. I can
> imaging to have a Matcher that select values out of the environment
> objects (Request/Response/Session/Context) and a corresponsing Selector
> which chooses some component to generate the view expected. This way you
> can still refer to the values the Matcher has evaluated.
>
> <match type="uri" pattern="myuri">
> <match type="value-extractor" pattern="unused"> <-----+
> <select type="value-selector"> !
> <when test="first"> !
> <generate type="file" src="mydir/first/{value}/> --+
> </when>
> ...
> </select>
> </match>
> </match>
>
> I really think that we must think in terms of "team play" between
> components. What do you think about that?
I like the idea of having the selector working with the matcher. But I
think I'm getting myself confused between the uses of matchers and
selectors. :-(
My understanding is that a 'matcher' is used to match something
against the current request and a specific parameter passed to the
matcher. 'Selectors' on the other hand are used to test the current
request for particular values.
I wrote the RequestParamMatcherFactory which I posted a couple of days
back, and are now writing a ParameterSelectorFactory - what i want to
do is to be able to tell the selector which request parameter it
should be testing - but from what I can see, the selector interface
doesn't support parameters like matchers do ?
For example:
<select type="paramselector" param="myparameter">
<when test="on">
...
</when>
</select>
Where 'myparameter' is the what should be passed to
request.getParameter(); in the generated paramselector code.
How can something like this be implemented ? Selectors seem to be
designed to use a predefined parameter to select a value from a
defined set. What if we want to vary that parameter ?
I could set all of the 'param's in the declaration of the selector in
the selection section of the sitemap (hows that for a tounge
twister!), but then there's problems if 2 or more request parameters
are used at the same time.
Any ideas ? or have I totally misunderstood everything! :-)
Cheers,
Marcus
--
.....
,,$$$$$$$$$, Marcus Crafter
;$' '$$$$: Computer Systems Engineer
$: $$$$: Open Software Associates GmbH
$ o_)$$$: 82-84 Mainzer Landstrasse
;$, _/\ &&:' 60327 Frankfurt Germany
' /( &&&
\_&&&&' Email : Marcus.Crafter@osa.de
&&&&. Business Hours : +49 69 9757 200
&&&&&&&: After Hours : +49 69 49086750
Re: [C2 & patch] Re: Matchers and Selectors (was Re: Better and
Betterand RT)
Posted by Raphael Luta <lu...@networks.vivendi.net>.
Giacomo Pati wrote:
>
> Marcus Crafter wrote:
> >
> > On Thu, 9 Nov 2000, Giacomo Pati wrote:
> >
> > > The concept of a Matcher is much more general. You can easily write a
> > > Matcher that matches "high load on the servel" or alike.
> >
> > *nod*.. sounds good.
> >
> > > How about his:
> > >
> > > <select type="paramselector">
> > > <when test="myparameter = on">
> > > ...
> > > </when>
> > > <when test="yourparameter = on">
> > > ...
> > > </when>
> > > <otherwise>
> > > ...
> > > </otherwise>
> > > </select>
> >
> > Excellent idea. I'm putting it together at the moment. Note for the
> > above example to work, we'll need to add = to the call to 'translate' in
> > sitemap.xsl (when 'generate-name' is called, otherwise the = sign is
> > added to the generated class variable name causing a compiler error).
>
> Oh, yes of course, I didn't think of. Maybe it's better to get rid of
> trying to derivate names from the pattern and generate pure names with
> generate-id().
>
> > I also though about implementing 'greater than' and 'less than'
> > operators too. Over time I would like to expand the set of operators
> > to include many varied tests. ie:
>
> Why not. But keep in mind your operators are used by admin people not by
> programmers (and with admin people i don't meant sys admins :). So
> please keep it as simple and understandable as possible.
>
> You can use an "is" instead of "=" (good old COBOL is comming back :])
>
I'd rather have UNIX shell like operators name (my own background ;) )
eq for equal
ne for not equal
lt for lower than
gt for greater than
le for lower or equal
...
This avoids the use of restricted characters, covers all the needed operators
and is pretty intuitive for any English speaker or UNIX shell user.
--
Raphaël Luta - luta.raphael@networks.vivendi.net
Re: [C2 & patch] Re: Matchers and Selectors (was Re: Better and
Betterand RT)
Posted by Marcus Crafter <cr...@dresdnerbank.de>.
Hi All,
On Tue, 14 Nov 2000, Marcus Crafter wrote:
> On Mon, 13 Nov 2000, Marcus Crafter wrote:
>
> > Programmer style Quasi-English style
> > -----------------------------------
> > == eq
> > != ne
> > < lt
> > > gt
> > <= le
> > >= ge
> > && and
> > || or
> > ! not
Just to keep everyone updated - the selectors are coming along well, I
had to put out some other fires in the meantime which caused a little
delay, but I'll have something posted to the list in the next few days.
Looking forward to everyones comments,
Cheers,
Marcus
--
.....
,,$$$$$$$$$, Marcus Crafter
;$' '$$$$: Computer Systems Engineer
$: $$$$: Open Software Associates GmbH
$ o_)$$$: 82-84 Mainzer Landstrasse
;$, _/\ &&:' 60327 Frankfurt Germany
' /( &&&
\_&&&&' Email : Marcus.Crafter@osa.de
&&&&. Business Hours : +49 69 9757 200
&&&&&&&: After Hours : +49 69 49086750
Re: [C2 & patch] Re: Matchers and Selectors (was Re: Better and
Betterand RT)
Posted by Marcus Crafter <cr...@dresdnerbank.de>.
On Mon, 13 Nov 2000, Marcus Crafter wrote:
> On Sun, 12 Nov 2000, Giacomo Pati wrote:
>
> > Marcus Crafter wrote:
> > >
> I thought about the following operator set:
>
> Programmer style Quasi-English style
> -----------------------------------
> == eq
> != ne
> < lt
> > gt
> <= le
> >= ge
> && and
> || or
> ! not
>
> and even for the perl dudes:
>
> =~ matches (?)
After thinking about it last night, perhaps this last one should be
covered by a 'matcher' and not a 'selector' ? What I was aiming for
was a way to be able to save people needing to write '.. or ... or
.. or .. or .. or', etc. Regular expressions seemed natural enough.
I'll can implement the others first, and after a bit of usage we can
see if the last one makes sense as a selector test case ?
Comments anyone ?
Cheers,
Marcus
--
.....
,,$$$$$$$$$, Marcus Crafter
;$' '$$$$: Computer Systems Engineer
$: $$$$: Open Software Associates GmbH
$ o_)$$$: 82-84 Mainzer Landstrasse
;$, _/\ &&:' 60327 Frankfurt Germany
' /( &&&
\_&&&&' Email : Marcus.Crafter@osa.de
&&&&. Business Hours : +49 69 9757 200
&&&&&&&: After Hours : +49 69 49086750
Re: [C2 & patch] Re: Matchers and Selectors (was Re: Better and
Betterand RT)
Posted by Marcus Crafter <cr...@dresdnerbank.de>.
On Sun, 12 Nov 2000, Giacomo Pati wrote:
> Marcus Crafter wrote:
> >
> > On Thu, 9 Nov 2000, Giacomo Pati wrote:
>
> Maybe it's better to get rid of trying to derive names from the pattern
> and generate pure names with generate-id().
Might be better solution. With generate-id(.) we're guaranteed of
getting unique variables anyway.
> > I also though about implementing 'greater than' and 'less than'
> > operators too. Over time I would like to expand the set of operators
> > to include many varied tests. ie:
>
> Why not. But keep in mind your operators are used by admin people not by
> programmers (and with admin people i don't meant sys admins :). So
> please keep it as simple and understandable as possible.
>
> You can use an "is" instead of "=" (good old COBOL is comming back :])
I understand, although as a developer I tend to like 'eq' instead of
'is' like Raphael suggested. What do you think ?
I see a lot of power in creating a boolean logic evaluation engine
which could be used from a parameter selector, a session selector, a
context selector, etc, in fact any kind of selector that can provide
a context to operate in (ie. lookup between variable names and values)
and a string to evaluate. It would provide for a lot of flexibility in
the sitemap.
I'm itching to write such a thing, even if it is a little overkill! :-)
We could please both developers and admins with the operator names ?
I thought about the following operator set:
Programmer style Quasi-English style
-----------------------------------
== eq
!= ne
< lt
> gt
<= le
>= ge
&& and
|| or
! not
and even for the perl dudes:
=~ matches (?)
with the ability to nest expressions using parentheses ().
Any others that I'm missing ?
Implementation wise, my intention was to base the logic evaluator on
the Interpreter and Composite patterns, perhaps in combination with
the Visitor and Flyweight patterns where appropriate.
I thought about also using jlex/cups to build up the logics AST easily.
Any suggestions, I'd be interested in peoples comments ?
Cheers,
Marcus
--
.....
,,$$$$$$$$$, Marcus Crafter
;$' '$$$$: Computer Systems Engineer
$: $$$$: Open Software Associates GmbH
$ o_)$$$: 82-84 Mainzer Landstrasse
;$, _/\ &&:' 60327 Frankfurt Germany
' /( &&&
\_&&&&' Email : Marcus.Crafter@osa.de
&&&&. Business Hours : +49 69 9757 200
&&&&&&&: After Hours : +49 69 49086750
Re: [C2 & patch] Re: Matchers and Selectors (was Re: Better and
Betterand RT)
Posted by Giacomo Pati <gi...@apache.org>.
Marcus Crafter wrote:
>
> On Thu, 9 Nov 2000, Giacomo Pati wrote:
>
> > The concept of a Matcher is much more general. You can easily write a
> > Matcher that matches "high load on the servel" or alike.
>
> *nod*.. sounds good.
>
> > How about his:
> >
> > <select type="paramselector">
> > <when test="myparameter = on">
> > ...
> > </when>
> > <when test="yourparameter = on">
> > ...
> > </when>
> > <otherwise>
> > ...
> > </otherwise>
> > </select>
>
> Excellent idea. I'm putting it together at the moment. Note for the
> above example to work, we'll need to add = to the call to 'translate' in
> sitemap.xsl (when 'generate-name' is called, otherwise the = sign is
> added to the generated class variable name causing a compiler error).
Oh, yes of course, I didn't think of. Maybe it's better to get rid of
trying to derivate names from the pattern and generate pure names with
generate-id().
> I also though about implementing 'greater than' and 'less than'
> operators too. Over time I would like to expand the set of operators
> to include many varied tests. ie:
Why not. But keep in mind your operators are used by admin people not by
programmers (and with admin people i don't meant sys admins :). So
please keep it as simple and understandable as possible.
You can use an "is" instead of "=" (good old COBOL is comming back :])
> <when test="yourparameter > 30">
> ...
> </when>
>
> However there is a problem in sitemap.xsl here. The translate method
> can turn the < and > symbols into _ symbols which is fine, but the
> call to 'generate-id()' will give the same id for both generated class
> variables (because generate-id() is called with .. as a parameter).
Yes, see above.
> This means the 2 variables can have the same name (eg. if you use <
> or > in 2 equal leveled when statements).
Yup.
> I've changed the call to generate-id() to use . (ie. the current node,
> instead of its parent) to fix this problem - why was it
> using .. anyway ? Have I possible broken something else ?
I wanted to have the same id based on the <select> element and not on
the <when> or <otherwise>. But yes, anyway, I'll have to change the hole
name generation stuff.
> I've attached a patch with the changes.
Thanks, it's a workaround for now.
Giacomo
[C2 & patch] Re: Matchers and Selectors (was Re: Better and Better
and RT)
Posted by Marcus Crafter <cr...@dresdnerbank.de>.
On Thu, 9 Nov 2000, Giacomo Pati wrote:
> The concept of a Matcher is much more general. You can easily write a
> Matcher that matches "high load on the servel" or alike.
*nod*.. sounds good.
> How about his:
>
> <select type="paramselector">
> <when test="myparameter = on">
> ...
> </when>
> <when test="yourparameter = on">
> ...
> </when>
> <otherwise>
> ...
> </otherwise>
> </select>
Excellent idea. I'm putting it together at the moment. Note for the
above example to work, we'll need to add = to the call to 'translate' in
sitemap.xsl (when 'generate-name' is called, otherwise the = sign is
added to the generated class variable name causing a compiler error).
I also though about implementing 'greater than' and 'less than'
operators too. Over time I would like to expand the set of operators
to include many varied tests. ie:
<when test="yourparameter > 30">
...
</when>
However there is a problem in sitemap.xsl here. The translate method
can turn the < and > symbols into _ symbols which is fine, but the
call to 'generate-id()' will give the same id for both generated class
variables (because generate-id() is called with .. as a parameter).
This means the 2 variables can have the same name (eg. if you use <
or > in 2 equal leveled when statements).
I've changed the call to generate-id() to use . (ie. the current node,
instead of its parent) to fix this problem - why was it
using .. anyway ? Have I possible broken something else ?
I've attached a patch with the changes.
I'll send in the selector as soon as I have something up and working.
> I hope my examples will help you understand the generality of those
> components :)
Sure have. Thanks :-)
Cheers,
M.
--
.....
,,$$$$$$$$$, Marcus Crafter
;$' '$$$$: Computer Systems Engineer
$: $$$$: Open Software Associates GmbH
$ o_)$$$: 82-84 Mainzer Landstrasse
;$, _/\ &&:' 60327 Frankfurt Germany
' /( &&&
\_&&&&' Email : Marcus.Crafter@osa.de
&&&&. Business Hours : +49 69 9757 200
&&&&&&&: After Hours : +49 69 49086750
Re: Matchers and Selectors (was Re: Better and Better and RT)
Posted by Giacomo Pati <gi...@apache.ch>.
Marcus Crafter wrote:
>
> Hi Giacomo,
>
> On Sun, 5 Nov 2000, Giacomo Pati wrote:
>
> > Ross Burton wrote:
> > >
> > > Berin Loritsch wrote:
> > > >
> > > > I envision the following additional selectors to be vital
> > > > to any site:
> > > >
> > > > ParameterSelector (select things pased on HTTP parameters)
> > > > AcceptsSelector (send PNG to browsers that accept it...)
> >
> > Take into account that a Selector chooses between multiple possibilities
> > (and a default one if neither choosen) whereas a Matcher returns a List
> > (or maybe we should change that to a Map) of values you can use for
> > substitution in src attributes of Generators and Transformers. I can
> > imaging to have a Matcher that select values out of the environment
> > objects (Request/Response/Session/Context) and a corresponsing Selector
> > which chooses some component to generate the view expected. This way you
> > can still refer to the values the Matcher has evaluated.
> >
> > <match type="uri" pattern="myuri">
> > <match type="value-extractor" pattern="unused"> <-----+
> > <select type="value-selector"> !
> > <when test="first"> !
> > <generate type="file" src="mydir/first/{value}/> --+
> > </when>
> > ...
> > </select>
> > </match>
> > </match>
> >
> > I really think that we must think in terms of "team play" between
> > components. What do you think about that?
>
> I like the idea of having the selector working with the matcher. But I
> think I'm getting myself confused between the uses of matchers and
> selectors. :-(
>
> My understanding is that a 'matcher' is used to match something
> against the current request and a specific parameter passed to the
> matcher.
The concept of a Matcher is much more general. You can easily write a
Matcher that matches "high load on the servel" or alike.
> 'Selectors' on the other hand are used to test the current
> request for particular values.
Even here, think of a Selector based on the time of day.
<select type="daytime-selector">
<when test="on">
...
</when>
<when test="noon">
...
</when>
<when test="afternoon">
...
</when>
<otherwise>
...
</otherwise>
</select>
>
> I wrote the RequestParamMatcherFactory which I posted a couple of days
> back, and are now writing a ParameterSelectorFactory - what i want to
> do is to be able to tell the selector which request parameter it
> should be testing - but from what I can see, the selector interface
> doesn't support parameters like matchers do ?
>
> For example:
>
> <select type="paramselector" param="myparameter">
> <when test="on">
> ...
> </when>
> </select>
>
> Where 'myparameter' is the what should be passed to
> request.getParameter(); in the generated paramselector code.
>
> How can something like this be implemented ? Selectors seem to be
> designed to use a predefined parameter to select a value from a
> defined set. What if we want to vary that parameter ?
How about his:
<select type="paramselector">
<when test="myparameter = on">
...
</when>
<when test="yourparameter = on">
...
</when>
<otherwise>
...
</otherwise>
</select>
> I could set all of the 'param's in the declaration of the selector in
> the selection section of the sitemap (hows that for a tounge
> twister!), but then there's problems if 2 or more request parameters
> are used at the same time.
>
> Any ideas ? or have I totally misunderstood everything! :-)
I hope my examples will help you understand the generality of those
components :)
Giacomo