The only hoops I can see there is the regular caveats that apply to all parallel programming (don't introduce deadlocks, be careful: other threads might mutate

The only hoops I can see there is the regular caveats that apply to all parallel programming (don't introduce deadlocks, be careful: other threads might mutate the data you are currently using). That applies only if you are executing guile code in parallel in the same interpreter and environment (or asynchronously accessing interpreter data) which is impossible in insert_other_embeddable_language_here. You don't have to use embedded guile like that. From my experience: if you want to embed a language and only need it in a single thread, it is just as easy to use lua. If you want several interpreters in isolated threads without any communication Lua is easily the simplest solution. But if you need communication between multiple embedded language threads or interpreters you are better of with guile or TCL depending on what threading model you prefer.