/prog/'s own esoteric language

Fun idea. Let's make our own programming language.
Conditions:
Must be somewhat useful like ABC.
Not limited to characters only. Can include words.
1 function per post.

>>90
Guido hates folds.
"So now reduce(). This is actually the one I've always hated most, because, apart from a few examples involving + or *, almost every time I see a reduce() call with a non-trivial function argument, I need to grab pen and paper to diagram what's actually being fed into that function before I understand what the reduce() is supposed to do. So in my mind, the applicability of reduce() is pretty much limited to associative operators, and in all other cases it's better to write out the accumulation loop explicitly.