The following code produces a contract error; I think TR is making
assumptions that it probably shouldn’t be.
Please could someone investigate.
Thanks,
Tim
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
#lang typed/racket/gui
(define f (new frame% [label "Frame"]))
(define sldr
(new slider%
[parent f]
[max-value 0]
[min-value -1]
[init-value 0]
[callback (λ (sldr cntrl-evnt)
(displayln (get-v)))]
[label (format "It's false if negative")]))
(define (get-v) : (Option Index)
(define v (send sldr get-value))
(printf "~s ~s ~s~%" v (negative? v) (if (negative? v) #f v))
(if (negative? v)
#f
(cast v Index)))
(send f show #t)
(send sldr set-value -1)
(get-v)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Runtime error is:
----------------------------------------------------------------------
broke its own contract
promised: Index
produced: -1
in: Index
contract from: cast
blaming: cast
(assuming the contract is correct)
at: unsaved-editor:18.6
----------------------------------------------------------------------
--
Tim Brown CEng MBCS <tim.br...@cityc.co.uk>
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