HTML-TEMPLATE for Clojure

Abstract

A templating system in Clojure modeled on HTML-TEMPLATE for Common Lisp, allowing for the separation of code from layout and dynamic generation of HTML pages.

What Wordstar’s MailMerge was to daisy-wheel printers, template systems are to web sites.

Usage

Tags

HTML-TEMPLATE for Clojure implements the following tags:

• TMPL_VAR
• TMPL_LOOP
• /TMPL_LOOP
• TMPL_IF
• TMPL_ELSE
• /TMPL_IF
• TMPL_UNLESS
• /TMPL_UNLESS

Templates

A template file consists of HTML markup interspersed with HTML-TEMPLATE directives: tags embedded in HTML comments, e.g.:

<!-- TMPL_VAR hello -->

Dr. Weitz provides this example in his documentation for HTML-TEMPLATE for Common Lisp:

<table border=1>
  <!-- TMPL_LOOP rows -->
  <tr>
     <!-- TMPL_LOOP cols -->
     <!-- TMPL_IF colorful-style -->
     <td align="right" bgcolor="pink"><!-- TMPL_VAR content --></td>
     <!-- TMPL_ELSE -->
     <td align="right" ><!-- TMPL_VAR content --></td>
     <!-- /TMPL_IF -->
     <!-- /TMPL_LOOP -->
 </tr>
 <!-- /TMPL_LOOP -->
</table>

This example will also compile on HTML-TEMPLATE for Clojure.

HTML-TEMPLATE compiles the foregoing example into Clojure code, functionally equivalent to the following:

(defn template-code [values]
  (println "<table border=1>")
  (doseq [rows (get values :rows)]
    (println "<tr>")
    (doseq [cols (get rows :cols)]
      (if (get cols :colorful-style)
        (do 
          (print "          <td align=\"right\" bgcolor=\"pink\">")
          (print (get cols :content))
          (println "</td>"))
        (do
          (print "          <td align=\"right\" >")
          (print (get cols :content))
          (println "</td>"))))
    (println "</tr>"))
  (println "</table>"))

Functions

parse-and-compile [template]

Compile a template into an anonymous function that takes a single argument, the hashmap of data values used to generate output from the compiled template.

For example:

(parse-and-compile "<html><body><!-- TMPL_VAR hello --></body></html>")

print-template [template context]

Parse, compile and apply a template to a provided context. E.g.:

(print-template "<html><body><!-- TMPL_VAR hello --></body></html>" { :hello "hello world!" })

produces the result:

<html><body>hello world!</body></html>

To direct the output to a string, you can enshroud print-template with the with-out-str macro:

(with-out_str
  (print-template "<html><body><!-- TMPL_VAR hello --></body></html>" { :hello "hello world!" }))

License

Copyright (c) 2011 John H. Poplett. All rights reserved.

Distributed under the MIT license.

Acknowledgements

Thanks to Dr. Edmund Weitz for the original Common Lisp implementation.