Am Mittwoch, 28. November 2012 16:42:32 UTC+1 schrieb Christophe Grand:
>
> Hi Ulrich,
>
> Wow, you got me scratching my head because your code should not even work.
> The problem I see with it is that your recursion has no base case. You
> have to know that 2 is prime to boot the algorithm. Eg
>
> ...
Salut Christophe,
thanks first for pointing out to the clojure source for tracking down
problems, I hadn't thought about that yet.
Considering base case, in fact, the first code I started off with, was
something similiar with starting values 2,3,5 :
(def primes
(concat
'(2 3 5)
(filter
(fn[n]
(every?
#(pos? (mod n %))
(take-while #(<=(*%%)n) primes)
)
)
(drop 6 (range))
)
)
)
What works. But with '(2,3) (or '(2) like you suggested) this doesn't work
any more, as 25 is included in the first "batch" (of the so called chunked
sequence) which is only tested against the starting value of primes.
Then I found the solution with "iterate" and then further reduced starting
values to '(2) and then to '() what worked as well,
as every? returns true for empty sequences, what is right from a logical
point of view too. And with '() as start even the concat wasn't necessary
any more. So this was no luck, but intention :)
Anyway, the question that still remains is, how one could "rechunk" a
chunked sequence?
Ulrich.
>
>
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