When I was a child, I thought up a joke and I did it all by myself. Alas, no one else seemed to understand how funny it was. It went a bit like this:

I phone up my mum from a call-box to say that I am going to be late home.

‘Why are you going to be late?’ she would ask me.

Photo: Keven Law

‘Because I have to walk home’ I would reply.

‘Why don’t you take the bus?’

‘I don’t have enough money.’

‘Why not?’

‘Because I spent it on this phone call’

‘But, why did you phone then?’

‘To tell you I was going to be late.’

‘But why are you going to be late?’

(& so on)

Of course I never  actually did this but when I told my friends my joke they just looked at me funny and said, ‘but that’s just stupid. Why would you phone your mum in the first place?’.

But that’s the whole point! Recursion means never having to say why you did anything…in the first place.

Post Script

In no way connected to this site, the students of Norwalk High School (Ohio?) have produced their own fantastic projects on recursion. I hope that for at least some of them it will be the start of a never-ending love affair with never-endingness.