This is such a transparently good idea that I don't know why someone hasn't already done it.

APL programming on a touch screen sounds like it would be better than regular programing on a touch screen because the terseness in that context is much more appealing -- it's a lot nicer to enter a few symbols from a software keyboard than a few words on a touch screen, which isn't at all the case for programming on a regular keyboard.

(searching for 'apl iphone' is going to suck, though)