There have been various times in my programming career that I've wanted an emacs macro with arguments, so that it would do things like concatenate a number in each line. Things like this in C:
#define a 0
#define b 1
...
#define l 10
#define m 11
Usually I take that as a sign that I need to write some other program to generate the lines of the C program, but for some tasks that's overkill and I want an automated way to create a list of sequential things so I don't have to type 1 down 1 down 1 down 1 down 2 down 2 down 2 down...
Surely this is a solved problem.