Introduce new domain concepts (e.g. label) for increasing abstraction.
It can look like a step backwards but...
Make labels with make-label
Inline join-strings to rearrange the code
Keep is a map that only "keeps" non-nil values
when-let is very useful to do stuff depending on something being null
We move from when-let to if-let to simplify the expression
We pay back the inlining of join-strings by extracting a different fn, label-seq
Garbage collection