On 19 June 2010 23:51, Mike Meyer
<[email protected]> wrote:
> In any case, I don't think 10% is enough gain to justify narrowing the
> range for which naive programs are correct. An order of magnitude
> would be. A factor of two is a maybe.
QFT!
Have a look at this:
(defn fact [n]
(loop [n n r 1]
(if (zero? n)
r
(recur (dec n) (* r n)))))
This doesn't compile. To make it compile, the initial value of r has
to be given as (num 1) *or* the initial binding of the "inner" n has
to be given as (long n). Changing the ops to *' and dec' rules out the
latter option, but the (num ...) hint on r is still required. Not
surprisingly having r start off with (Long. 1) solves makes this
compile too.
The summary is that I'm finding it impossible to write a standard
tail-recursive factorial function without type hints on my literals. I
suppose I can guess what the reason is by now, but I find it
unreasonably confusing. Not sure to which degree this can be ironed
out if boxing were to remain an opt-in rather than -out...?
Oh, just in case votes on this are of interest, I like the idea of
loop' for fast-by-default looping.
Sincerely,
Michał
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