The paper "Implementing SNOBOL4 in SIL; version 3.11" by Griswold is interesting to look at (<www.regressive.org/snobol4/doc/arizona/s4d58.pdf>). It looks like there is some code at github (https://github.com/mdhender/sil/blob/main/v311.sil) but I haven't looked at the provenance of it.