Racket, 147 bytes
At least it beats QBasic.
((λ(x)(display(string-join(x(build-list 26(λ(n)(list->string(map integer->char(x(range 65(+ 66 n))))))))"\n")))(λ(m)(append m(cdr(reverse m)))))
At least it beats QBasic.
((λ(x)(display(string-join(x(build-list 26(λ(n)(list->string(map integer->char(x(range 65(+ 66 n))))))))"\n")))(λ(m)(append m(cdr(reverse m)))))