rot13 (string manipulation example)

The other day, I was thinking about how Robb Sherwin's Necrotic Drift paid specific homage to the old Magnetic Scrolls games.  I remembered how the MS games used a letter-substitution code for their hints (actually, the whole point of this article is that I misremembered it as rot13 but looking now, I see it was just one-letter-away substitution) and thought, huh, wouldn't it be neat if something like that was put into a future version of Necrotic Drift, where the game itself would both provide the coded text and decode it?  I thought it'd be fun to code up an example to share here.

First off, if  you're not familiar with ASCII, each letter has its own numerical value.  You can see them in this chart:

String manipulation in Hugo is mainly a matter of checking for these values and changing them to what you want.

For my "rot13" code to work, the game would have to use a "string" grammar token (the one where the string has to be provided in quoted text, like >WRITE "KILROY WAS HERE" ON ELEVATOR WALL)- something I've found is very hard to train the player to do, but, oh well, this post isn't about how to teach players to use quotation marks where we want them.



EDIT:  Ok, I was wrong about the one-letter-off thing, too, even though I guess some of the official hint books were like that.  This actually the Magnetic Scrolls code I remembered:

Of course, I'd have to find out how it worked before I could decide whether I could replicate it in Hugo!