Likely usage scenario: you are playing a lowbie spellcaster and have precious few spellbooks. You keep one book on hand so that you won't run out of castings of your offensive spell. As time goes by, during your adventures you reach a point where you get stuck next to an enemy and decide melee isn't working, you need to blast him with Fire Bolt instead. You go to read your spellbook at him, knowing that he will die and no other enemy is within 3 squares of you, so the energy cost isn't an issue.

But, you get the message "Do you want to exhaust yourself casting this spell?" because you weren't paying attention to your Power Points. You think "Oh. Well no, of course I don't want to do that. I'll go ahead and risk casting it from memory instead. That should be okay, my castings are only down to 138... ugh. Wish I had more spellbooks!"

But when you hit "No", and get the "You abort your attempt" message, you also get the messages "The ghul misses you. The ghul misses you. The ghul hits you. The ghul misses you. The ghul hits you. You lose blood! The ghul hits you. You die..." because three turns passed instead of zero.

Well, you still took the time to evoke the magic from the book and get ready to cast the spell which warrants the extra energy cost, you just chose not to. Although that sort of stuff is debatable.

Something related to this that I never liked is that if you 'r'ead the wrong book, you have to either cast or learn from it (assuming No_Book_Spellcasting=false, of course). There is no cancel option in case I wanted to bookcast Acid Ball but pressed the wrong key and picked my spellbook of Create Item. In this particular case I can choose to learn and immediately stop when monsters attack me, but...

It's possible to rationalize / explain away every potential bug as "working as intended," but, this one felt wrong to me. And since I couldn't find any discussion on the topic, nor any other bug reports, I figured I'd do my part and seek clarification.

As or lacking a cancel option in general... I don't know about that one. There's no cancelling reading a scroll either; or drinking a potion, or eating an herb, etc. Might be nice, but it might also just inflate the number of keypresses required for routine actions. On the other hand, since it's stopping and giving us an option anyway, one of those options may as well be cancel. Like zapping a wand or shooting a missile. Hmm....

Exactly my thoughts. If the game asked for confirmation on every action, that'd be exasperating. But here you already have to pause to pick [c]ast or [l]earn, so why not add [z] to exit :)

Fixed.

Also added a "Z = abort" when reading a spellbook like anon123 suggested.