Simon Peyton-Jones <[EMAIL PROTECTED]> wrote on Feb 2 2000: > The library is currently based on the RandomGen class, > whose signature is: > > class RandomGen g wher > next :: g -> (Int, g) > split :: g -> (g, g) > > The difficulty is that there is absolutely no robust way to > use such a generator to generate random numbers uniformly > distributed in a given range. Why not? Because there's no > clue as to the precise range of Ints produced by next. > [..] Fergus Henderson <[EMAIL PROTECTED]> replies H> [..] H> Wouldn't it be easiest if the RNG just guaranteed to H> return integers that range over the whole range of `Int'? H> Note that the range of `Int' can be obtained using the `minBound' H> and `maxBound' functions in the standard prelude. Exactly. | * The next operation allows one to extract at least 30 bits (one | Int's worth) from the generator, returning a new generator as | well. The integer returned may be positive or negative. H> That wording is a little unclear, so I suggest clarifying H> it as follows: H> H> * The next operation allows one to extract a pseudo-random Int H> from the generator, returning a new generator as well. H> The integer returned may be positive or negative. H> Over a sufficiently large sequence of calls to next, H> the integers returned should be uniformly distributed H> over the whole range of Int (from minBound to maxBound, H> inclusive). H> H> If that clarification were made, there would be no need to H> introduce the `genRange' method that Simon P-J suggested. Indeed, why not follow this simple approach? And the line `The integer returned may be positive or negative.' can be omitted. Because it follows from the next sentence. ------------------ Sergey Mechveliani [EMAIL PROTECTED]
