Literate Programming Using OmniMark

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2. Template Processing

Template processing is central to the weaving process, where we build a formatted document from the literate program. The template language devised for this project is quite simple: a template consists of boilerplate text, and template parameters, which are strings bracketed by [: and :].

Templates are emitted via the emit-template function:

define string source function 
   emit-template value string source template
as
   using group "fill-in template parameters"
      submit template
    

In our case, all the templates are stored in the global string shelf templates:

global string templates variable elsewhere
    

As a result, the argument to emit-template could be a string instead of a string source. Template parameters are stored in the global string shelf template-parameters:

global string template-parameters variable
    

The substitution of template parameter values into the template is handled by find rules:

group "fill-in template parameters"
   find "[:" any ++ => parameter-name ":]" (blank* "%n")?
      output template-parameters{parameter-name} 
         when template-parameters has key parameter-name
    

A second form of template parameter, this time delimited by [? and ?] is used when a referent should be emitted rather than a value:

group "fill-in template parameters"
   find "[?" ("key:" | "name:") => p any ++ => parameter-name "?]" (blank* "%n")?
      output referent (p || template-parameters{parameter-name})
         when template-parameters has key parameter-name
    

Although the shelf of templates is shown here, the actual values are discussed later, when they are needed.

global string templates variable initial {
      <5 main page template>
   with key "main page",

      <10 section page template>
   with key "section page",

      <7 section list item template>
   with key "section list item",

      <18 template anonymous code>
   with key "anonymous code",

      <12 template code identified>
   with key "identified code",

      <14 template code identified appended>
   with key "identified code appended",

      "<filename>[:filename:]</filename><block-number>[:block number:]</block-number>"
   with key "code pointer",

      <20 template code reference>
   with key "code reference",

      "<[:element name:]>[:element content:]</[:element name:]>"
   with key "identity"
}
    

OmniMark's save-clear operation allows for rudimentary scoping of template parameters:

save-clear template-parameters
    

This is sufficient for our needs.

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