I have the same issue for ->i contracts. I'll write multiple #:pre/desc checks with nice messages, which are promptly rendered useless by the fact that ->i prints out the whole contract instead of just the precondition check that failed. On Friday, October 30, 2020 at 7:16:59 PM UTC-7 Ben Greenman wrote:
> > Ben: if you have an example of the bad hash/dc error message I'd be > > interested to see it. > > > > Robby > > Here's the kind of message that turned me off: > > ``` > ctc.rkt:34:0: broke its own contract > promised: (hash/dc (k (or/c (quote a) (quote b) (quote c))) (v (k) > (config-value/c k)) #:immutable #t #:kind (quote flat)) > produced: '#hash((a . 1) (b . #t) (c . #<void>)) > in: (hash/dc > (k (or/c 'a 'b 'c)) > (v (k) (config-value/c k)) > #:immutable > #t > #:kind > 'flat) > contract from: + > blaming: + > (assuming the contract is correct) > ``` > > It prints the whole hash and contract, leaving me to figure out the > two key parts: (1) what piece of the hash failed, and (2) what the > contract expected for that piece. > > Now that I think of it ->* is bad in the same way --- especially for > `plot` functions. > > > Here's the code that made that error message. The #;(lambda ....) > comment is the contract that I ended up using instead of hash/dc (it > still doesn't explain bad values well). > > ``` > #lang racket/base > > (require racket/contract) > > (provide config/c) > > (define config-key/c > (or/c 'a 'b 'c)) > > (define (config-value/c k) > (case k > ((a) > string?) > ((b) > boolean?) > ((c) > void?))) > > (define config/c > #;(lambda (h) > (for ((k (in-list (list 'a 'b 'c)))) > (unless (hash-has-key? h k) > (raise-arguments-error 'config/c "missing key" "key" k "hash" h)) > (define v (hash-ref h k)) > (unless ((config-value/c k) v) > (raise-arguments-error 'config/c "bad value for key" "key" k > "value" v "hash" h)) > (void))) > (hash/dc > [k config-key/c] > [v (k) (config-value/c k)] > #:immutable #true > #:kind 'flat)) > > (contract > config/c > (hash 'a 1 'b #true 'c (void)) > '+ > '-) > ``` > -- 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 https://groups.google.com/d/msgid/racket-users/3b0ed32b-4875-4cfa-9b2b-e4398e4318d1n%40googlegroups.com.
