I found a solution: change the depth-first traversal to a breadth-first 
traversal -- it uses (pfds hamts) from guile-pfds instead of (guix 
sets)/(ice-9 vlist), so will need some small changes for use in Guix 
(unless the additional dependency is considered acceptable), but it 
should at least unblock the workspace implementation in antioxidant.

Greetings,
Maxime.