## Monday, March 31, 2008

### Finger Exercises

Wow. Three months, no update. Hm.

I've been working on a bunch of little projects recently that individually don't amount to much, yet. I should have something to post about that soon.

In the mean time, here is a cute little problem (via Uri to the fun with Perl list):

What is an easy way to get all possible combinations of Y/N of length 5? (i.e., "YYYYY", "YYYYN", etc.)

Coming up with a solution to this exact problem seemed to cry out for a list comprehension:

`[[a,b,c,d,e] | let l <- "YN",                a <- l, b <- l, c <- l, d <- l, e <- l]`

but as soon as I wrote that, I saw how unsatisfactory it was. A better solution would produce all possible combinations of Y and N for a list of any integer n > 0:

`yn i = (iterate f [""]) !! i  where f l = map ('Y':) l ++ map ('N':) l`

This problem itself isn't very interesting, but it's good to have little diversions like this when you want to take a break while the coffee is steeping, waiting for the Guinness to settle, or whatnot. (Something that's more than a function from the Prelude, but less involved than something from Project Euler.)

Do you have any cute little "finger exercise" problems like these? I'd love to hear about them!