6.4. Embperl

SSI and HTML::Template are simple template solutions that allow you to add basic tags to static and dynamic HTML files. The HTML::Embperl module, often referred to simply as Embperl, takes a different approach; it parses HTML files for Perl code, allowing you to shift your code into your HTML documents. This approach is similar to Java Server Pages or Microsoft's ASP technology that moves programming languages into documents. There are actually several modules available for embedding Perl within HTML documents, including Embperl, ePerl, HTML::EP, HTML::Mason, and Apache::ASP. We'll look at Embperl and Mason in this chapter.

The theory behind moving code into HTML pages is somewhat different from the standard reason for using HTML templates. Both strategies attempt to separate the interface from the program logic, but they draw the lines at different places (see Figure 6.2). Basic template solutions like HTML::Template draw the line between HTML and all code, at least as much as possible. For Embperl and similar solutions, the logic for creating the page is folded into the HTML for the page, but common business rules are collected into modules that can be shared across pages. Business rules are those core elements of your application or applications that are separate from the interface, data management, etc. Of course, in practice not everyone creates as many modules as the model suggests, and you can create modules like this with any of the approaches (as the dotted lines suggest). Thus, the model for complex template solutions like Embperl and ASP often end up looking like CGI.pm, except that instead of including HTML in the code, the code is included in the HTML. This isn't a bad thing, of course. Both CGI.pm and Embperl are excellent solutions for tying together HTML and program code, and you should choose whatever solution makes the most sense to you for each project. The point is simply that those who argue about the different approaches of using CGI.pm versus templates sometimes are not as far apart as they may seem; the extremes of each seem more alike than different.^[1]

^[1] Jason Hunter (author of Java Servlet Programming from O'Reilly & Associates) made a similar argument from a Java perspective. His article, "The Problem with JSP," is available at http://www.servlets.com/soapbox/problems-jsp.html.