• Kagamin (2/2) Jan 07 2014 I believe, bearophile was interested in this - a strongly pure
• qznc (4/6) Jan 07 2014 I would consider this weakly pure, because the implicit parameter
• Joseph Rushton Wakeling (7/9) Jan 07 2014 Related -- the work I've been doing on an updated std.random:
• deadalnix (2/8) Jan 07 2014 Without this, http://dilbert.com/strips/comic/2001-10-25/
• Joseph Rushton Wakeling (11/12) Jan 08 2014 I guess you could do a design where you pass an immutable RNG state, and...
• monarch_dodra (5/15) Jan 08 2014 Nice :)
• Kagamin (2/8) Jan 11 2014 Formally it is immutable, see line 36.
• David Nadlinger (4/5) Jan 11 2014 Well, by breaking the type system you can make every PRNG
• Kagamin (4/4) Jan 11 2014 Only the cast breaks the type system, I go through holes. It's
• Joseph Rushton Wakeling (7/10) Jan 11 2014 That depends on your concept of a PRNG. Strictly speaking it can/should...
• bearophile (5/6) Jan 07 2014 The ER:

"Kagamin" <spam here.lot> writes:

I believe, bearophile was interested in this - a strongly pure 
immutable Xorshift32(1) PRNG: http://dpaste.dzfl.pl/5f710daf

"qznc" <qznc web.de> writes:

On Tuesday, 7 January 2014 at 12:32:23 UTC, Kagamin wrote:
 I believe, bearophile was interested in this - a strongly pure 
 immutable Xorshift32(1) PRNG: http://dpaste.dzfl.pl/5f710daf

I would consider this weakly pure, because the implicit parameter 
"this" is not immutable. A strongly pure PRNG cannot change 
internal state.

Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:

On 07/01/14 13:37, qznc wrote:
 I would consider this weakly pure, because the implicit parameter "this" is not
 immutable. A strongly pure PRNG cannot change internal state.

Related -- the work I've been doing on an updated std.random:
https://github.com/WebDrake/std.random2/blob/master/std/random2/generator.d

It's easy to make class-based PRNGs weakly pure and const (i.e. pure in 
everything bar perhaps some of the seed functions, const apart from seed 
functions and popFront).  I don't think it'd meed the criteria of a very strict 
functional-programming interpretation of purity, though.

"deadalnix" <deadalnix gmail.com> writes:

On Tuesday, 7 January 2014 at 12:37:39 UTC, qznc wrote:
 On Tuesday, 7 January 2014 at 12:32:23 UTC, Kagamin wrote:
 I believe, bearophile was interested in this - a strongly pure 
 immutable Xorshift32(1) PRNG: http://dpaste.dzfl.pl/5f710daf

 I would consider this weakly pure, because the implicit 
 parameter "this" is not immutable. A strongly pure PRNG cannot 
 change internal state.

Without this, http://dilbert.com/strips/comic/2001-10-25/

Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:

On 08/01/14 02:13, deadalnix wrote:
 Without this, http://dilbert.com/strips/comic/2001-10-25/

I guess you could do a design where you pass an immutable RNG state, and you
get 
back whatever random number you ask for plus a new immutable state (perhaps 
provided via an out parameter).  It's just that in this case it puts the 
responsibility on the user to be really careful in ensuring that the RNG state 
is passed around properly (the main PITA being getting back the updated state 
rather than passing the current one).

It's really much easier to do it as a class which updates internal state, and 
where you can apply  safe pure nothrow and (with obvious exceptions) const to 
just about every method; and I don't really see what you lose in a practical 
sense by doing it this way.

"monarch_dodra" <monarchdodra gmail.com> writes:

On Wednesday, 8 January 2014 at 01:13:12 UTC, deadalnix wrote:
 On Tuesday, 7 January 2014 at 12:37:39 UTC, qznc wrote:
 On Tuesday, 7 January 2014 at 12:32:23 UTC, Kagamin wrote:
 I believe, bearophile was interested in this - a strongly 
 pure immutable Xorshift32(1) PRNG: 
 http://dpaste.dzfl.pl/5f710daf

 I would consider this weakly pure, because the implicit 
 parameter "this" is not immutable. A strongly pure PRNG cannot 
 change internal state.

 Without this, http://dilbert.com/strips/comic/2001-10-25/

Nice :)

Of course, mandatory xkcd PRNG:
https://d.puremagic.com/issues/show_bug.cgi?id=11138

You know, it *is* pure...

"Kagamin" <spam here.lot> writes:

On Tuesday, 7 January 2014 at 12:37:39 UTC, qznc wrote:
 On Tuesday, 7 January 2014 at 12:32:23 UTC, Kagamin wrote:
 I believe, bearophile was interested in this - a strongly pure 
 immutable Xorshift32(1) PRNG: http://dpaste.dzfl.pl/5f710daf

 I would consider this weakly pure, because the implicit 
 parameter "this" is not immutable. A strongly pure PRNG cannot 
 change internal state.

Formally it is immutable, see line 36.

"David Nadlinger" <code klickverbot.at> writes:

On Saturday, 11 January 2014 at 10:19:00 UTC, Kagamin wrote:
 Formally it is immutable, see line 36.

Well, by breaking the type system you can make every PRNG 
immutable. ;)

David

"Kagamin" <spam here.lot> writes:

Only the cast breaks the type system, I go through holes. It's 
just a joke, purity and immutability are valued for their 
deterministic traits, so a random number generator is the last 
thing one would want to make pure or immutable.

Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:

On 11/01/14 15:12, Kagamin wrote:
 Only the cast breaks the type system, I go through holes. It's just a joke,
 purity and immutability are valued for their deterministic traits, so a random
 number generator is the last thing one would want to make pure or immutable.

That depends on your concept of a PRNG.  Strictly speaking it can/should
consist of

     (i) an immutable state

    (ii) a pure function that takes as input the current immutable state and
         returns a new immutable state.

In practice, of course, it's almost invariably easier to implement this as a 
type that has mutable internal state.

"bearophile" <bearophileHUGS lycos.com> writes:

Kagamin:
 I believe, bearophile was interested in this

The ER:
https://d.puremagic.com/issues/show_bug.cgi?id=5249

Bye,
bearophile