I agree that one-liners are hard to read and completely beginner - unfriendly, but they are just about beauty and fun. In a real life task splitting this in multiple lines is a good idea, but solving katas like this is definitely great.

You are correct. =) But I solve katas for fun, and sometimes that goes against best practises.

...then I thought about this one but not sure because although it uses fewer function calls it reconcatenates the string over and over. Thoughts on speed/efficiency, anyone?

thanks, I avoid char because I program in C for which that's a keyword, so I'm just used to c.