[racket-dev] promise vs polym contracts

Right, that's what I thought.  This is only different in that:

    (define v (delay (+ 1 2)))
    (sum v) ; => v

Which means clients of `sum` now have to handle either Integers or
Promises.  Is that intentional?

On Sat, Jul 7, 2012 at 10:23 AM, Matthias Felleisen
<matthias at ccs.neu.edu> wrote:
>
> I may have made a mistake under time pressure:
>
>  [else (+ (force (sum (car x))) (force (sum (cdr x))))]
>
>
>
>
>
> On Jul 7, 2012, at 10:19 AM, Sam Tobin-Hochstadt wrote:
>
>> On Sat, Jul 7, 2012 at 10:14 AM, Matthias Felleisen
>> <matthias at ccs.neu.edu> wrote:
>>
>>> p.s. Sam's version forces too early because strict functions should
>>> force not variable lookups. This is a common misconception among programmers.
>>> I suspect it goes back to Abelson and Sussman getting it wrong (see what
>>> happens if you don't understand the foundations).
>>
>> I still don't think my version forces too early -- your alternative
>> contains no calls to `force` at all.  Are you suggesting that I should
>> `force` around the recursive calls to `sum`?  In that case, clients
>> are exposed to promises, and the result type is (U Integer (Promise
>> Integer)).  I can't tell from your description if you think that's an
>> acceptable result.
>> --
>> sam th
>> samth at ccs.neu.edu
>



-- 
sam th
samth at ccs.neu.edu