Most of the code I worked with was 30-40 years old. Often full of ad hoc DSLs. Refreshing this kind of code was easier than any other kinds - rewriting the DSL

Most of the code I worked with was 30-40 years old. Often full of ad hoc DSLs. Refreshing this kind of code was easier than any other kinds - rewriting the DSL itself with the modern technologies was sufficient, 90% of the remaining code base did not need much maintenance then.