John Meacham wrote:
On Fri, Dec 03, 2004 at 10:05:08AM +0000, Graham Klyne wrote:
....
BTW, if the goal is to have a random number generator as a pure (non-IO) function, I *do* think there's a reasonable semantic objection here.
Oh yes. no one is wanting that.
May I? Sometimes I am surprised how much energy goes into such details as discussed under this (or other) topic, and for weeks *nobody* says a single word about the applications. What for? When used? Personally I never paid too much attention to this monadic Random stuff, since in my applications I could always use PURE FUNCTIONAL usage of RN generators. 1. Using (lazy) streams of random numbers. I needed a noise signal, I produced a noise signal, by iterating a generator. 2. I needed a multidimensional Perlin noise. One localized loop permitted to fill an array with pseudo-random values, and then a "random" f(x,y,z) is obtained by indexing and some intricate combinatorics which decorrelates the values. 3. There exist a category of *ergodic* functions, *PURE* functions which behave erratically when the argument, integer, n= 0, 1, 2, 3, ... It looks like noise, perfectly usable. This has been used by Greg Ward in graphics, and it should be published somewhere in Graphics Gems. This function is based on a polynomial with the bits XORed and truncated to (say) 32 bits. Trivial to do in languages which work with machine integers, ignoring overflow (like Clean). More difficult in Haskell. Jerzy Karczmarczuk