Some thoughts on Perl template processing

​”mak­ing a tem­plate draw­ing to get a clear vision of the mask your mask­ing” by Douglas R Witt is licensed under CC BY-ND 2.0

Template proces­sors and engines are one of those pieces of soft­ware where it seems every devel­op­er wants to rein­vent the wheel. Goodness knows I’ve done it ear­li­er in my career. Tell me if this sounds familiar:

1. You need to mix data into a doc­u­ment so you start with Perl’s string inter­po­la­tion in "dou­ble quotes" or sprintf for­mats. (Or maybe you inves­ti­gate formats, but the less said about them the bet­ter.)
2. You real­ize your doc­u­ments need to dis­play things based on cer­tain con­di­tions, or you want to loop over a list or some oth­er structure.
3. You add these fea­tures via key­word pars­ing and escape char­ac­ters, think­ing it’s OK since this is just a small bespoke project.
4. Before you know it you’ve invent­ed anoth­er domain-specific lan­guage (DSL) and have to sup­port it on top of the appli­ca­tion you were try­ing to deliv­er in the first place.

Stop. Just stop. Decades of oth­ers who have walked this same path have already done this for you. Especially if you’re using a web frame­work like Dancer, Mojolicious, or Catalyst, where the tem­plate proces­sor is either built-in or plug­gable from CPAN. Even if you’re not devel­op­ing a web appli­ca­tion there are sev­er­al general-purpose options of var­i­ous capa­bil­i­ties like Template Toolkit and…