&gt;<i>For example, Viaweb uses (still!) a Lisp-based DSL to provide the non-Turing-complete customization language for their customers, and I suspect that whole thing was a weekend hack.</i><p>&quot;Still&quot;? I think that thing has been scrapped for 15 years or so, as Yahoo rewrote the store engine. Or you mean just the user visible language that resulted?