Joshua Morey | 2014-03-27

Filter Chaining

Not long after my last post, I updated the Skhema graph generation to support filter chaining. Functions and variables are now implemented as a new type of evaluation token with a stack of filters, using a shared syntax. The following examples show basic function usage.


The cycle function is one of the built-in functions that I described previously. The only change is that the syntax has been tweaked to use bracketed options. The format-url function is one of the user-defined functions used by Bramble to generate a URL from a data context. In this case the post option requires that context has both a 'time' and 'slug' variable which can be transformed into a URL such as /2014/01/skhema-filters. It's somewhat opaque this way, since just looking at the template does not necessarily provide enough information to know which variables the model needs to provide, but I think that encapsulating this functionality in user-defined functions is better in the long run.


The filter syntax has not changed, but I updated the implementation so that filters can be stacked on variables, functions, and other filters. Bramble has enough functionality at this point to give me an assurance that the current approach should work well.