-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Peter Verswyvelen wrote: | I do have asked myself the question whether a "really random generating" | function could be regarded as "pure" somehow (actually would a true | random function still be a mathematical function?) | | E.g. the function would return a true (not pseudo) random number, | practically unpredictable (e.g. hardware assisted, using some physical | phenomenon, e.g. using atmospheric noise or something). So you surely | won't get referential transparency but since the function is really | random, this would be correct behavior? An informal definition of a function might be something like a black box that takes and input and produces an output, and for each possible input, the output must be the same. Taking this to be a function, there is really no such thing as a random function, and if there was, it wouldn't even need to be a function. (What would the input to it be?) If you wanted to mathematically represent a random number, it would, in most cases I can think of, best be represented as a free variable. In a program, such a free variable could be filled in by the runtime. Conveniently, (and by no coincidence) this is something the IO monad can provide for us! :) | Of course you could just put this random generator in the IO monad, but | certain algorithms- like Monte Carlo - intuitively don't seem to operate | in a IO monad to me. Why not? A Random monad might be more appropriate in this case anyway. Such a monad is a State monad that hold a random seed. Every time a random number is needed, the seed is passed to a deterministic psuedo-random number generator, and a new seed is put as the next state. If a truly random number is ever needed, either IO or unsafeInterleaveIO will be needed. The use of unsafeInterleaveIO would be a (rightly) controversial choice though. - - Jake -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkmLaK4ACgkQye5hVyvIUKk88QCfRksu7z80QmzgjUvmiyrzDDjl QnsAn1R5DHz2tJpWP3yb0+U+loyBdyCX =RIX9 -----END PGP SIGNATURE-----