Re^2: Functional shuffle

Isn't it the case that random number generators do not entirely fit into the "pure functional" programming paradigm? I seem to recall reading somewhere that obtaining random numbers in Haskell involves the use of Monads, which is a kind of stretching of the concept of pure functional programming (maybe this is why I have never been able to really understand Monads?)...

This leads me to think that pure functional progamming is not the best way to attack the list shuffle problem...

rg0now

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Re^3: Functional shuffle by tall_man (Parson) on Apr 02, 2005 at 16:19 UTC
Indeed a "functional shuffle" is a contradiction in terms. In functional programming, if you give a function the same inputs you must get the same outputs. Rand is resetting a seed somewhere, which is a disallowed side-effect in a pure functional program. However, one could define a shuffle that took a list of random numbers from some outside source as an input. The paper referenced by the OP does this.	[reply]
Re^3: Functional shuffle by tlm (Prior) on Apr 02, 2005 at 16:19 UTC
You may very well be right. I did notice that in the article that Roy Johnson linked on the Haskell implementation the author spent longer than I would have expected on the discussion of the random numbers, which gave me the impression that the generation of random numbers has a conceptually different place, or different standing if you will, in the Haskell world than I'm used to from other programming languages. But to be honest, I barely understand what this requirement that the shuffle be "functional" is, as is probably plainly obvious from my various stabs at it. the lowliest monk	[reply]