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.p.oke...@gmail.com
> 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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