Using the for(;;) loop in Awk, and the C preprocessor, in a project called cppawk, I created a loop facility that has multiple clauses of different types, that can combine in parallel or as Cartesian-product, and are programmer-definable.

https://www.kylheku.com/cgit/cppawk/tree/cppawk-iter.1

The above manual page includes an example of how to define an alpha_range clause that iterates over string ranges like alpha_range(var, "000", "999") or alpha_range(var, "AAA", "ZZZ").