yamlp performs string interpolation from YAML files:
I reuse my library in my text editor:
The text editor can interpolate strings in a variety of contexts (such as Markdown, R Markdown, XML, and R XML documents):
As far as I can tell, there is no performance degradation from the recursive interpolation; the editor reads, interpolates key/value pairs, and substitutes the resulting values into R Markdown documents riddled with up to a thousand simple formulas in about 600 milliseconds (on my desktop computer).
Also, the editor provides a way to maintain the interpolated variables in a tree-like view:
The substituted values appear in the preview pane in their final form. This is all real-time and pure Java.