Also,

[davv]

recursion is fun! It feels more like magic.

Here's a nice functional programming exercise I did today: Given a function that increments an integer and a function that decrements it, create a function that returns the sum of two numbers, where either of the two numbers may be positive or negative.

Comments

[lhexa]

Weirldy enough, that's also how it's done in a fair chunk of mathematical logic, such as Peano arithmetic. I guess it's because you need fewer axioms, if your only operation is "add one".

[davv]

It makes sense. Logic prefers having as few axioms as possible, so defining numbers like that would let one go from first principles.

(I don't think that definition of integers would support negative ones, though. Am I right?)

[lhexa]

Yeah, it's just the natural numbers.