Common Text Transformation Library http://cttl.sourceforge.net/

quote(true,RM,RR) asymmetric quote

• Category:

  • Asymmetric quoted expression (deprecated.)

    • NOTE: Asymmetric quote is no longer in use and will be phased out in the future releases of CTTL. It has been replaced by the positive lookbehind assertion algorithm, lookbehind(R1,R2).

• Format:

  • 
        quote( true, RM, RR )
    
    

    where

    • RM describes grammar matching input symbols at the beginning of quote interior;

    • RR describes syntactic unit closing the quote.

• Algorithm:

  • Asymmetric quote has no opening clause. The interior of the quote begins immediately at the upper boundary of the parseable substring.

  • Asymmetric quote performs non-terminal symbol search for the input symbol matching its RR grammar clause. The search algorithm is executed only once.

  • If RR succeeds, the RM expression is evaluated by match() grammar evaluation algorithm.
    If RR fails, RM is never evaluated.

  • Parseable substring presented to the interior expression by RM is restricted by a half-open range

        [ p1, p2 )
    

    where

    • p1 is the upper boundary of the parseable substring before RR is evaluated;

    • p2 is the upper boundary of the substring after RR is evaluated.

  • Precondition: expression RR must be a bang_find −searchable grammar construct.

• Space sensitivity:

  • The space sensitivity of asymmetric quote is enabled. The interior clause RM invokes space policy grammar of the policy class specified by the parseable substring.

• Searchability:

  • Search grammar evaluation algorithms

    • terminal symbol search and

    • non-terminal symbol search

    are syntactically enabled for asymmetric quotes, but have no effect: in either case match() grammar evaluation algorithm of RM is executed by the lexer.

• Example:

  • Matching pair of opening and closing tags in XML document can be described by asymmetric quote as follows:

    
    #define CTTL_TRACE_EVERYTHING
    #include "cttl/cttl.h"
    
    using namespace cttl;
    
    int main()
    {
        std::string inp = "<element>text</element>";
        const_edge<> substring( inp );
        const_edge<> interior = substring;
    
        (
            symbol( "<element>" )
            +
            quote(
                true,
                interior( entity( isalpha ) ),
                symbol( "</element>" )
            )
        ).match( substring );
    
        assert( interior == "text" );
    
        return 0;
    }
    
    

   

• Trace output format:

  • The trace symbol of an asymmetric quote is a double quotation mark ("), enclosed in a pair of symmetrical braces:

        {"
        ...
        }
    

    The above sample generates the following trace:

        -@<element>text</element>?{;            0-23
        ---------------<element>@| T            9-23    <element>
        ----------@text</element>? {"           9-23
        ---------------<element>@|  1           9-23
        -<element>text</element>@|  T           23-23   </element>
        --------------------@text?  {e          9-13
                                     :3:1
        -----------<element>text@|   $          13-13   isalpha
        --------------------@text|   e          9-13
                                    }
                                   }
                                  }
    

   

Copyright © 1997-2009 Igor Kholodov mailto:cttl@users.sourceforge.net.

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