[Haskell] Re: About Random Integer without IO

[Thomas Davie]

On 11 Nov 2004, at 22:02, karczma wrote:

> Thomas Davie writes:
>> This method unfortunately depends on having a seed first though.
>
> Which "this method"? Please, quote the text you are referring to 
> *before*
> your answer.
>> 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.
>
> I understand that you mean the seed-propagation method.
> You are *partly* right, that the same program executed several times 
> will
> generate the same sequence, if initialized identically. But there is no
> need for monads, it suffices to pass a parameter, or to read a 
> different
> initialization file each time.
> Of course, anybody, especially somebody contributing to this list has
> the right to be a nit-picker. But, if one is a *practical* user of
> random stuff, then he/she usually knows such details. Moreover, it is
> sometimes very useful to control absolutely the initialization, to be
> able to repeat the experiment, so, professionals in Monte Carlo, etc.
> rarely if ever, use time, or system-dependent (and hidden) random 
> values.
> For me the initialization is a *context* problem, which I separate from
> the properties of the random generator. It is its quality, lack of
> correlations, etc. which is important.  Do you know of many problems
> requiring an automated, truly random initialization? In this case one
> may well delegate this issue to the *launching* of the functional 
> program,
> instead of struggling with it from within.
> This is my personal philosophy, everybody is entitled to his/hers.
>
While I agree that it is often useful to start your program with 
different parameters each time to seed the random number generator, I 
would argue that this is often inappropriate - supposing we are writing 
a very simple program to roll a virtual dice.  If the user finds one 
input that rolls a six, they can then use this repeatedly.  Reading an 
initialisation file is back to the situation of using IO to generate 
our seed.

Thanks

Tom Davie