Modularizing

Modularizing

You may be wondering at this point if every OmniMark program that outputs SGML or XML markup really has to contain over fifty lines of boilerplate code. Of course it doesn't. You may not want the processing instructions and comments from the input reproduced in the output. And perhaps your input markup never contains any escaped newline characters in attribute values. On the other hand, maybe you just haven't encountered them yet.

If you want to keep your OmniMark scripts robust, the only way to scrap your boilerplate it to modularize it away. Beginning with OmniMark 9.1, all the code we have seen so far has been packaged in two reusable library modules shipped with OmniMark: omxmlwrite.xmd and beta/omsgmlwrite.xmd. The interface for the former library is described in the OmniMark documentation. A typical use would look somewhat like this:

import "omxmlwrite.xmd" prefixed by xml.
 
process
   do xml-parse scan #main-input
      output xml.written from "%c"
   done

There is a catch, however: your rules that used to output XML markup now need to emit markup events instead. So rather than something like this:

element #implied
   output "<%q"
   repeat over specified attributes as a
      output " " || key of attribute a || "=%"" || attribute a || "%""
   again
   output ">%c</%q>"
 
element "graphical-object"
   output "<figure><image href=%"%v(object-location)%"/>%c</figure>"

your rules should look like this:

element #implied
   signal throw #markup-start #current-markup-event
   output "%c"
   signal throw #markup-end #current-markup-event
 
element "graphical-object"
   local markup-element-event figure initial { create-element-event (declared-elements of target-dtd){"figure"} }
   local markup-element-event image  initial { create-element-event (declared-elements of target-dtd){"image"}
                                                         attributes { attribute "object-location" with key "href" } }
 
   signal throw #markup-start figure
   signal throw #markup-start image
   signal throw #markup-end image
   output "%c"
   signal throw #markup-end figure

Besides the ability to use the omxmlwrite library and get rid of the boilerplate, this style of coding has the benefit of easy pipeline construction, but you can find more on that topic elsewhere.