Thank you everyone, for the replies:
- The macro expansion was helpful
- Andy, thanks for pointing out where the lines are -- very helpful
- Ambrose, both (number? %) and number? are valid post-condition forms;
the issue is that the post-condition check bumps the recur out of tail
position
I guess the real question: is this worth filing a ticket for?
Thanks all,
Michael
On Thursday, July 24, 2014 9:17:23 PM UTC-6, Ambrose Bonnaire-Sergeant
wrote:
>
> Hi Michael,
>
> I believe your post condition should read {:post [(number? %)]}.
>
> Thanks,
> Ambrose
>
>
> On Fri, Jul 25, 2014 at 6:56 AM, Michael O'Keefe <michael....@gmail.com
> <javascript:>> wrote:
>
>> Hello All,
>>
>> I encountered the following behavior in Clojure 1.6 and wanted to check
>> if it should be considered a bug or not. I would say yes but wanted to
>> double check on the list first.
>>
>> Here's a minimal test case that elicited the error:
>>
>> (defn f
>>
>> [xs acc]
>> (if (nil? xs)
>> acc
>> (recur (next xs) (+ (first xs) acc))))
>>
>> (f [1 2 3 4] 0) => 10
>>
>>
>> Now, if I want to add pre/post conditions, the following happens:
>>
>> (defn g
>>
>> [xs acc]
>> {:pre [(or (nil? xs) (sequential? xs)) (number? acc)]
>> :post [number?]}
>> (if (nil? xs)
>> acc
>> (recur (next xs) (+ (first xs) acc))))
>>
>>
>> => this fails to compile with "CompilerException
>> java.lang.UnsupportedOperationException: Can only recur from tail position"
>>
>>
>> In fact, it is only the post-condition that triggers the issue.
>>
>> My guess would be that the recur statement is being knocked out of tail
>> position by the mechanism for handling the post-condition assertion. It can
>> be fixed in the code by adding an explicit loop:
>>
>> (defn g2 [xs acc]
>> {:pre [(or (nil? xs) (sequential? xs)) (number? acc)]
>> :post [number?]}
>> (loop [xs xs
>> acc acc]
>> (if (nil? xs)
>> acc
>> (recur (next xs) (+ (first xs) acc)))))
>>
>>
>> Thanks,
>>
>> Michael O'Keefe
>>
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