I've had a productive coding session in a lucid dream at least once. But it was just a small number of lines of code (a few blocks) I was playing around with, and I had been thinking about it all day. The visual and semantic memory was sort of stuck in my mind, consciously and subconsciously. In any event, it was insanely precise (I was editing on a giant terminal screen) and when I woke up I typed in my refactored algorithm verbatim.
But reading text coherently in a dream is, AFAIU, quite uncommon as you suggest. I used to lucid dream regularly and deliberately as an adolescent. I would hesitate to say you can't focus in a lucid dream--consciously focusing on elements of the dream, or trying to shape the dream, is kind of the point of lucid dreaming. (Of course, what you have most control over is yourself.) But, yeah, you can't usually control things in such fine detail for the duration necessary to coherently manipulate it. Reading any non-trivial text in a dream isn't very common, lucid or not-lucid, AFAIU. Though, I would imagine it's more common for people with experience lucid dreaming.
I'm sure some people can read and write as much as they want, but at a certain point on the curve we're probably dealing with people with abnormal neurology. Sort of like how there's memory palaces and other mnemonic techniques, which anybody can learn, and then there's people with Hyperthymesia.
Something I tried testing once was practicing the guitar while in a lucid dream. I was really interested in whether I'd be able to practice inside a dream and see improvement outside of it. Unfortunately the one time I attempted this, the guitar didn't sound correct, and I woke up moments later. I'm still interested in whether it would be possible, but I unfortunately no longer have the ability to test it.
It should be feasible, given that mental practice seems to work in general (from both studies and anecdotes). When I've tried practicing piano in lucid dreams, I've found the wrong notes sounding even when I press the right keys to be distracting, but if you can ignore 'dream effects', the practice will probably help.
Sure. I've also had a couple non-lucid dreams where I've read a longish excerpt of text. (Memorable because of the extraordinary detail, and because it seemed original.) And I've certainly had non-lucid dreams where I've resolved abstract problems in some inarticulable, non-visual manner. And then there's the experience of your subconscious figuring something out and it pops into your conscious mind, which can happen when sleeping or awake.
I've had enough lucid dreams when I was kid to know the difference. These days lucid dreaming for me is rare and not deliberate--i.e. if I have the presence of mind to wake up in a dream, it's mostly by chance, not because I orchestrated it through habituation. It came mostly naturally as a kid, after I stumbled upon a reproducible technique. Adults usually have to practice at it, and I'm just too lazy (and too tired). The vast majority of my dreams now are non-lucid, or quasi-lucid (i.e. I'm not in deep sleep) such that I know it's not like a proper lucid dream. The experiences are quite different.
But reading text coherently in a dream is, AFAIU, quite uncommon as you suggest. I used to lucid dream regularly and deliberately as an adolescent. I would hesitate to say you can't focus in a lucid dream--consciously focusing on elements of the dream, or trying to shape the dream, is kind of the point of lucid dreaming. (Of course, what you have most control over is yourself.) But, yeah, you can't usually control things in such fine detail for the duration necessary to coherently manipulate it. Reading any non-trivial text in a dream isn't very common, lucid or not-lucid, AFAIU. Though, I would imagine it's more common for people with experience lucid dreaming.
I'm sure some people can read and write as much as they want, but at a certain point on the curve we're probably dealing with people with abnormal neurology. Sort of like how there's memory palaces and other mnemonic techniques, which anybody can learn, and then there's people with Hyperthymesia.