I'm interesting in learning more about conditional restart systems and how they work. I'm not sure where to start. I've been looking at source code but was wondering if there was any higher level guides available.
You might like to read the chapter in Practical Common Lisp
19. Beyond Exception Handling: Conditions and Restarts
An discussion on LtU, check out the comments:
Common Lisp Exception Handling
An explanation illustrating the stack state:
What's a condition system and why do you want one?
and an example with links to further references:
Simple restarts example by Paul Gresham
And a video tutorial by Patrick Stein