[Caml-list] Evaluation order of Stream.from

[Caml-list] Evaluation order of Stream.from

[YAMAGATA yoriyuki]

Hi, folks.

I have a question about Stream.from.  If I create a stream by
Stream.from f by some function f, in what order f is called?  I mean,
is it guaranteed that f is always called as f 1, f 2, f 3, ....? or is
the order like f 1, f 3, f 5, f 7, f 2, f 4, .... possible?

The manual states nothing, so maybe I have to assume there is no
guarantee.  But then using a function with side effects
is nearly impossible, which is unfortunate.

I tried to understand the source, but it is full of magic and anyways,
the source does not make any guarantee for the future.
--
Yamagata Yoriyuki
http://www.mars.sphere.ne.jp/yoriyuki/
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Re: [Caml-list] Evaluation order of Stream.from

[Daniel de Rauglaudre]

Hi,

On Tue, May 21, 2002 at 10:09:38PM +0900, YAMAGATA yoriyuki wrote:

> I have a question about Stream.from.  If I create a stream by
> Stream.from f by some function f, in what order f is called?  I mean,
> is it guaranteed that f is always called as f 1, f 2, f 3, ....? or is
> the order like f 1, f 3, f 5, f 7, f 2, f 4, .... possible?

Yes, the order is guaranteed: in streams, to access the nth element,
you must have accessed the first n-1 ones before. But the first
element is f 0, not f 1.

-- 
Daniel de RAUGLAUDRE
daniel.de_rauglaudre@inria.fr
http://cristal.inria.fr/~ddr/
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Re: [Caml-list] Evaluation order of Stream.from

[John Max Skaller]

YAMAGATA yoriyuki wrote:

>Hi, folks.
>
>I have a question about Stream.from.  If I create a stream by
>Stream.from f by some function f, in what order f is called?  I mean,
>is it guaranteed that f is always called as f 1, f 2, f 3, ....? or is
>the order like f 1, f 3, f 5, f 7, f 2, f 4, .... possible?
>
>The manual states nothing, so maybe I have to assume there is no
>guarantee.  But then using a function with side effects
>is nearly impossible, which is unfortunate.
>
>I tried to understand the source, but it is full of magic and anyways,
>the source does not make any guarantee for the future.
>

The same issue arises for List.rev_map. By experiment, I find it applies
its function argument from the head of the list argument, in order,
which is suggested by  the statement that it is tail recursive.
But it isn't *guarranteed* by the manual, and it probably should be.

To be pedantic .. the 'tail recursive' bit is non-information.
Only source code has that property. List.rev_map is a standard library
routine. It should be characterized by saying it has
linear performance, with constant storage overhead.

-- 
John Max Skaller, mailto:skaller@ozemail.com.au
snail:10/1 Toxteth Rd, Glebe, NSW 2037, Australia.
voice:61-2-9660-0850




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