I was thinking of something along the lines of the following:

  print TQIS::Primitive::typeis("1") ;
> string
  print TQIS::Primitive::typeis(1) ;
> integer
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Here is the code:

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#include "ppport.h"

SV* typeis ( SV* what ) ;

SV* typeis ( SV* what )
{
        if ( SvIOK( what ) )
                return newSVpvs( "integer" ) ;
        else if ( SvNOK( what ) )
                return newSVpvs( "double" ) ;
        else if ( SvPOK( what ) )
                return newSVpvs( "string" ) ;

        return newSVpvs( "unknown" ) ;
}


MODULE = TQIS::Primitive                PACKAGE = TQIS::Primitive

PROTOTYPES: ENABLE

SV*
typeis( what )
        SV* what
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