This method unfortunately depends on having a seed first though. One must use a different value every time the program is started, commonly time or the first few bytes from /dev/random. Any one of these is going to require a monadic function to generate (i.e. it must come from the environment in some way - it must change every time you run the program) So while this eliminates the IO monad from most of the program, it must still be initiated using it. Thanks Tom Davie -- Computer Science is as much about computers as astronomy is about telescopes -- Edsgar Dijkstra On 11 Nov 2004, at 20:58, karczma wrote:
Georg Martius answers the request of: Jose Manuel Hernando Cobeña
I need generate random numbers by create polygons with "wxHaskell", I am searching in the web, but all I only find IO functions like
test :: Integer -> IO Integer ... I need this but with types :: Integer -> Integer
you need to reallise that Haskell is a pure language. That means a function has the same result if you call it with the same arguments (deterministic). A function that produces random numbers are not of such kind in the first place.
All depends on how you organize your computations. 1. You may in a purely functional, non-monadic way produce an infinite list, a stream of numbers, and use them as you wish, incrementally. gener seed =(aaa*seed + ccc) `mod` mmm -- or something alike... strm = st seed0 where st x = x : st (gener x) Eventually, you can directly pass the updated seed from one function to another in your program. In two words, write your programs in CPS, or a little 'monadized' style. Of course, you can transform the result from an integer between 0 and mmm-1 to other thing. 2. Despite what G. Martius says, you CAN USE a pure, deterministic function to produce something which looks randomly, it suffices to change the argument. Concretely, Ward in Graphics Gems, and other people in other places propose 'chaotic', *ergodic* functions, which vary wildly from arg to arg, even neighbouring. This is a "kind of hashing function". An example can be found in this tutorial http://freespace.virgin.net/hugo.elias/models/m_perlin.htm You take an integer, and mix its bits by taking xors, modulo, polynomials, etc. Then, such a function sampled for j=0,1,2,3, ... N will look like a genuinely random signal, without any need to 'propagate' anything.
Jerzy Karczmarczuk PS. Georg Martius concludes:
PS: this question is more appropriate for haskell-cafe.
Well, why not haskell-bratwurst-mit-pils? The protocol of making/using random stuff within Haskell is a specific problem which is not very well developed nor taught, but it is not anecdotical, it may be important. _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell