The reversible reverser

APL, 5


This reverses (, along the last axis) the input (), and is followed by a comment ( marks a line comment). Reversed, the program reverses (, along the first axis) the input, and is followed by a comment. Because the input is always going to be one dimensional, in this case and are functionally equivalent. It is perhaps even sneakier than the GolfScript solution, so here's a cleaner solution (no comments), which scores 9.


This first grabs an empty vector (), flattens it (monadic ,), and reverses it (, along the first axis). This still leaves an empty vector. Then it concatenates (dyadic ,) to the input (), leaving the input untouched. It then flattens (monadic ,) the already-flat input and reverses it (, along the last axis). Then it concatenates (dyadic ,) another empty vector () to the reversed input. This does nothing, and leaves the reversed input behind. Reversed, this program does the same thing, based again on the fact that and are functionally equivalent with one-dimesional arguments.

You really couldn't say I'm adding useless characters to break the palindrome (the two different reverse functions are different with two-or-more-dimensional input; I'm just taking advantage of the fact they act the same with one-dimensional input)

Unix shell - 8 + 25% = 10


Previous answer of cat|tac didn't actually work, tac reverses the order of lines, not the order of characters in a line.

Haskell, 53

niam=interact reverse
esrever tcaretni=main

Technically not a palindrome, but, since function declaration order doesn't matter, once reversed you have exactly the same program.