I'm working on a version of `dict/c` with chaperones, but I'm running into a 
surprising problem that only comes up because of the `failure-result` 
optional-argument to `dict-ref`.

When the `failure-result` is used, I don't want the "value" contract to apply 
to that result. But when the failure-result isn't used, and the "value" result 
happens to be exactly equal to the failure-result, I do want the "value" 
contract to apply to it. How do I distinguish those though?

I tried to take inspiration from Carl Eastlund's `dict/c` implemented in 
`mischief/contract`, but it doesn't use chaperones so it is free to both add an 
escape continuation, and change the `failure-result` input to always be a new 
synthesized procedure. That way the new synthesized failure-result procedure 
can call the escape continuation. If I'm constrained to chaperones, I don't 
know how to do either of those things.

How can I detect whether the `failure-result` is used-or-not by the dict's 
implementation of `dict-ref`, while keeping the `failure-result` a chaperone of 
the original failure-result?

Alex Knauth

You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
To view this discussion on the web visit 

Reply via email to