As I recall CHAIN comes from days QB was an interpreter and a compiler, CHAIN assumes bas code to interpret which no longer happens in QB64. RUN is usually the work around but there you need compiled proggies. (Update #2, no not according to Wiki, in fact today I just fixed a program with Run and happy I could restart a program like that.)
Update: Wiki does give impression it still works, with one really bad example!
Update: Wiki does give impression it still works, with one really bad example!
b = b + ...