On 09/23/2010 09:50 AM, Daniel Lidström wrote:
> Hello,
>
> I am trying out Antlr for the very first time. My task is to define a string
> template language, similar to
> StringTemplate but with some formatting requirements. So I thought Antlr
> would be suitable for this
> task. I have managed to define the first part, well almost. I'd like to get
> some feedback on my approach
> as I feel I might be heading down the wrong path. Given a format string
> "[yyyy]-[M]-[d] [H]:[m]"
> the desired result is "2010-9-23 15:28". Right now I am getting
> "20109231528".
> How do I "capture" the dash and colon? Here's my grammar:
If the "-" and ":" are a part of your format string, then they are not a
part of your input, are they? I would think that outputting them would
be a function of how you handle your format string (which you included
above). It looks like you are outputting just the "variable" part of
your format string and not the "constant" part....
When you parse your format string, you will need to save the constant
parts verbatim.
Perhaps you can use the "dot notation" (of the lexer) to save anything
that isn't one of your tokens listed below, and output them verbatim.
So, you need another token type to catch "anything else".
> grammar TemplateCommand;
>
> options {
> language=CSharp2;
> }
>
> tokens {
> TIMEFILTER = 'TimeFilter';
> YEAR = 'yyyy';
> MONTH = 'M';
> DAY = 'd';
> HOUR = 'H';
> MINUTE = 'm';
> }
>
> @header {
> using System.Text;
> using System.Collections.Generic;
> }
>
> @members {
> // Build template command using a StringBuilder
> private StringBuilder builder = new StringBuilder();
>
> // Used to resolve variables
> private readonly IDictionary<string, string> resolver;
>
> public TemplateCommandParser(ITokenStream input, IDictionary<string, string>
> resolver)
> : this(input)
> {
> this.resolver = resolver;
> }
>
> public string Result
> { get { return builder.ToString(); } }
> }
>
> // parser rules:
>
> prog returns [string result]
> : expression=templateExpression
> { result = $expression.text; }
> ;
>
> templateExpression
> : var=(WS | Text | Number | variable)+
> { builder.Append($var.text); }
> ;
>
> variable
> : '[' var=(TIMEFILTER | YEAR | MONTH | DAY | HOUR | MINUTE) ']'
> { builder.Append(resolver[$var.text]); }
> ;
>
> // lexer rules:
>
> Text : ('a'..'z' | 'A'..'Z' | ':' | ';' | '-')+ ;
>
> Number : '1'..'9' ('0'..'9')* ;
>
> WS : ' '+ ;
>
> I pass a dictionary to the parser during construction. This dictionary
> contains the variable
> substitutions. Why isn't the templateExpression action able to capture the
> dash and colon?
> Is there an approach better suited to my task than using actions in this
> way?
>
> Thanks in advance!
>
> (I have read up on StringTemplate and it doesn't quite fit with our
> requirements.)
>
> Daniel
>
>
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--
Kevin J. Cummings
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[email protected]
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Registered Linux User #1232 (http://counter.li.org)
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