[antlr-interest] newbi question : operator + any

Mon Feb 13 08:46:59 PST 2012

Hi Marco,

I see.  Perhaps you will discover classes (email, name, stock symbol,
whatever) each of which is suuficiently constrained to facilitate your
work.

Good luck,
Kyle
 On Feb 13, 2012 2:28 AM, "Marco Laponder" <marco.laponder at kewill.com>
wrote:

>  Well, although @4dUbb%ez_5&q is not likely, it is a valid filter string,
> as all the characters could be present in a field of the table to be
> filtered. A ‘@’ could e.g. be present in a mail address, the ‘&’ in a name
> (Bang & Olufsen), etc. So I would consider  @4dUbb%ez_5&q valid. I
> understand parsing for an identifier would be more simple, but not
> sufficient for my case.****
>
> ** **
>
> Kind regards,
> Marco****
>
> ** **
>  ------------------------------
>
> *Van:* Kyle Ferrio [mailto:kferrio at gmail.com]
> *Verzonden:* vrijdag 10 februari 2012 21:10
> *Aan:* Marco Laponder
> *Onderwerp:* RE: [antlr-interest] newbi question : operator + any****
>
> ** **
>
> Ok.  You do want to parse grouped  combinations of Boolean expressions.
> So you almost certainly want a parser, not an awk filter.****
>
> But I note with interest that the instances of ANYTHING in your examples
> are limited to lower case alpha.  Ask yourself this... Would @4dUbb%ez_5&q
> be a valid ANYTHING in your language?  If not, why not?  A non-null answer
> will define an identifier pattern which restricts the class, so that the
> kind of awkward problem you're encountering now simply won't arise.  This
> is easier to see after doing than before doing.****
>
> BTW, you're actually grappling with the edges of a pretty profound
> linguistic/semiotic question, namely what do we mean by 'language' and how
> do we discriminate (much less parse) language from noise.  I'm not smart
> enough to answer that, which is off-topic for this listserv anyway.  So I
> just try to make things simple and get work done.  I think specifying an
> IDENTIFIER class in place of your ANYTHING will make your task much easier.
> ****
>
> Kyle****
>
> On Feb 9, 2012 11:08 PM, "Marco Laponder" <marco.laponder at kewill.com>
> wrote:****
>
> Hi,****
>
>  ****
>
> Let tackle your questions:****
>
>  ****
>
> Q1: I was struggling with this question myself, as I was explaining
> earlier for now it is pretty simple, a comparison operator followed by a
> string which is nog problem to handle with a regular expression. However I
> would like to enhance this later on, with parenthesis, ‘and’, ‘or’
> constructions etc. So in the future I might be able to handle a string like
> :
> ( > a && < b) || ( (<=c and >=f )  or (== f) )
> which is harder (for me anyway) to handle with a regular expression****
>
>  ****
>
> Q2: ANYTHING is really anything, the grammar is for a filter language on a
> table for a specific column, and as the user (especially my users I think
> ;-) ) must best be able to filter on anything in the table I have no
> additional restrictions there. The data in the table can contain anything,
> and therefore the filter can contain anything****
>
>  ****
>
> I am working with antlr v3 right now, but if v4 is the better way to go
> there is no problem there as I am just getting started. Regarding the
> books, there you have a fair point. I will look what the ANLTR bibles are.
> ****
>
>  ****
>
> Kind regards,****
>
> Marco****
>
>  ****
>  ------------------------------
>
> *Van:* Kyle Ferrio [mailto:kferrio at gmail.com]
> *Verzonden:* woensdag 8 februari 2012 15:52
> *Aan:* Marco Laponder
> *Onderwerp:* Re: [antlr-interest] newbi question : operator + any****
>
>  ****
>
> Hi,
>
> I'm joining the thread late, but this sounds a bit like an experience I
> have seen a few times. Sometimes trying to make things "too simple"
> actually makes lexing and parsing more difficult.  While is is often good
> to defer decisions in software as long as possible, it is also helpful to
> use all of the information at our disposal.  That probably seems vague, so
> here are some questions to consider.
>
> Q1: Is your application likely to grow in syntactic and/or semantic
> complexity to a point that its needs cannot be economically met by a simple
> filter implemented, say, with GNU awk?  I'm not trying to discourage you
> from using ANTLR.  ANTLR is awesome.  But the difference in costs between
> the two approaches is large, so it makes sense to ask.
>
> Q2: Do you have any stronger guarantees on the form of the input?  For
> example, is  ANYTHING really *anything* (excluding a finite set of
> operators)?  Or are legal operands actually restricted, say, to the set of
> common alphanumeric identifiers and possibly literal values?  If so, your
> work just got vastly easier.
>
> I don't recall whether you mentioned that you're working with antlr v3 or
> the yet-to-be-released v4.  I suggest pursuing the examples appropriate to
> your version from the antlr website.  (Note that antlr v4 provides greatly
> enhanced expressiveness for expression-parsing, but examples for v3 are
> much more plentiful at the moment.)
>
> Also, definitely get your hands on the two ANTLR books.  They'll save you
> time and are actually a lot of fun if you're into this sort of thing.
>
> Best Luck,
> Kyle****
>
> On Tue, Feb 7, 2012 at 11:58 PM, Marco Laponder <marco.laponder at kewill.com>
> wrote:****
>
> Lets explain what I am trying to accomplish, maybe you can provide me
> the most impressive grammars :-)
>
>
>
> I am trying to parse a filter string which filter on a column of a
> table, so I need to know the operator. In my example I stated the '>'
> but of course I would like to expand it to '<','>=' etc and alter on
> even add parenthesis, 'and' and 'or' etc. But I would like to start
> simple as I am new at ANTLR.
>
>
>
> Your sample does the trick, however looks hard to maintain, e.g., when I
> add the '<' to COMPARE I also need to add it to ANYTHING. (Well it seems
> still more maintainable than a single regular expression no one
> understands to do the trick ;-) )
>
>
>
> Kind regards,
> Marco
>
>
>
> ________________________________
>
> Van: Marco Laponder
> Verzonden: dinsdag 7 februari 2012 8:45
> Aan: 'Gokulakannan Somasundaram'
> CC: antlr-interest at antlr.org
> Onderwerp: RE: [antlr-interest] newbi question : operator + any
>
>
>
> This still gives me the same error, any other ideas ? Of is antlr just
> not appropriate for this ?
>
>
>
> Kind regards,
>
> Marco
>
>
>
> ________________________________
>
> Van: Gokulakannan Somasundaram [mailto:gokul007 at gmail.com]
> Verzonden: maandag 6 februari 2012 16:56
> Aan: Marco Laponder
> CC: antlr-interest at antlr.org
> Onderwerp: Re: [antlr-interest] newbi question : operator + any
>
>
>
> COMPARE : '>';
>
> ANYTHING : (~'>')(.)*;
>
> testExpression : COMPARE ANYTHING;
>
>
>
>
>
> Try this.
>
>
>
> Gokul.
>
> On Mon, Feb 6, 2012 at 8:30 PM, Marco Laponder
> <marco.laponder at kewill.com> wrote:
>
> Hi All,
>
>
>
> I am trying to setup a very simple grammar, ik should be able to handle
>
>
>
> "> thiscouldbeanything"
>
>
>
> So I tried:
>
>
>
> COMPARE : '>';
>
> ANYTHING : (.)+;
>
> testExpression : COMPARE ANYTHING;
>
>
>
> but when generating java resources it gave me the error:
>
>
>
> "The following alternatives can never be matched: 1"
>
>
>
> The problems seems to be the ANYTHING, so how should I define a grammar
> to be able to handle this ?
>
>
>
> Kind regards,
>
> Marco
>
>
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