[racket-dev] Release Announcement for v6.1.1, Second Draft

On Wed, Oct 29, 2014 at 5:47 PM, Robby Findler
<robby at eecs.northwestern.edu> wrote:
> Yes, that's what I mean. I don't think that the sentence "This may
> break existing programs that rely on unsafe behavior." is accurate.
> How about "This may break existing programs." or "Closing this hole
> requires us to disallow some programs that do not signal runtime
> errors." or something like that?

How about "This may result in type errors in existing programs that
rely on the original behavior; specifically, programs that `raise`
higher-order values."

Sam

>
> Robby
>
> On Wed, Oct 29, 2014 at 4:35 PM, Sam Tobin-Hochstadt
> <samth at cs.indiana.edu> wrote:
>> There were two holes.
>>
>> 1. We allowed exception handlers to assume that they received values
>> of type `exn`, even when that wasn't right.
>> 2. We allowed typed programs to throw arbitrary values, which means
>> that you could throw a typed function to an untyped handler, which
>> could then misuse it.
>>
>> Both of these changes could lead to type errors in programs that won't
>> fail at runtime, but that's true of just about everything in Typed
>> Racket, so I don't really understand what you're asking. Here are
>> examples of programs that will now type-error for each change.
>>
>> 1. (with-handlers ([void exn-message]) #f)
>> 2. (raise (lambda ([x : Integer]) x))
>>
>> I think the second problem is more what you mean, in that the first
>> program is "wrong" in some sense, even though it doesn't go wrong, but
>> the second example is a perfectly fine Racket program (if perhaps poor
>> style), but not one that can be allowed in the presence of untyped
>> code.
>>
>> Does that help explain things?
>> Sam
>>
>> On Wed, Oct 29, 2014 at 5:17 PM, Robby Findler
>> <robby at eecs.northwestern.edu> wrote:
>>> Sam: can you elaborate on precisely what the hole was? In particular,
>>> if there are any safe programs that the type system now rejects, I'd
>>> be in favor of a slightly different wording.
>>>
>>> Robby
>>>
>>> On Wed, Oct 29, 2014 at 2:35 PM, Sam Tobin-Hochstadt
>>> <samth at cs.indiana.edu> wrote:
>>>> On Wed, Oct 29, 2014 at 3:30 PM, Ryan Culpepper <ryanc at ccs.neu.edu> wrote:
>>>>>
>>>>> * Exception handling changed to be safe. This may break existing
>>>>>   programs that rely on unsafe behavior.
>>>>>
>>>>> * Casts and predicates are supported in typed regions.
>>>>
>>>> I think these two bullets (esp the first one) need to make clear that
>>>> they're about Typed Racket.
>>>>
>>>> How about:
>>>>
>>>> * Typed Racket's rules for exception handlers are now more
>>>> restrictive, as required for safety. This may cause type errors for
>>>> existing programs that rely on unsafe behavior.
>>>> * Typed Racket now supports casts and predicates in typed regions.
>>>>
>>>> Sam
>>>> _________________________
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