Under the hood, Polyglot workflows are classes. Each one is a subclass of unlike-compiler%. An instance of unlike-compiler% models relationships between files that otherwise don’t fit together. You can use it to make a PNG depend on an XML file, if you know a way to have that make sense. Knowing the basics of the unlike-assets collection can help you customize Polyglot later.
The compile! method actually executes the given workflow and the underlying build. This method is synchronous, so if you want to add code to occur before or after a build, simply override compile! and place code around the superclass call.
(class polyglot/functional% (define/override (compile! #:changed c #:removed r) (displayln "before build") (define output (super compile! #:changed c #:removed r)) (displayln "after build") output))