Handle error function

[dvanhorn]

This program should not verify (error is currently unbound):

(module f racket
  (provide (contract-out [f (integer? . -> . integer?)]))
  (define (f n)
    (error "Asdf")))

Does it work just to give error a ... -> none/c contract?

[philnguyen]

If we take the blamed party into account:

This:

(module lib racket
  (provide/contract [error (any/c . -> . none/c)]))

will blame the module providing error, while this:

(module lib racket
  (provide/contract [error (none/c . -> . any/c)]))

will blame whoever calling error. Is the second closer to what we want?

[samth]

There are some deep questions about what we want here, but I think we want no one to be blamed, at least to start.