It depends on what you mean by scale, PG's Viaweb sold for $49 million and it was built completely around this approach. Lisp has a debugger that allows you to

It depends on what you mean by scale, PG's Viaweb sold for $49 million and it was built completely around this approach. Lisp has a debugger that allows you to edit code while it is running, and allows you to continue half-finished evaluations with the fixed version, so what it means to "fail" in any given circumstance is altered by that meaning.