[asQuirreL]

But going in the opposite direction, could you not also implement arbitrary effects using conditions? (Or delimited continuations in schemes)

[ReleaseCandidat]

I am not sure about conditions (I don't know enough about CL), but the effect system of Koka (and OCaml) uses delimited continuations. So it is doable in Scheme, with shift/reset or prompt/control or whatever primitives are defined.