Re: [Haskell-beginners] Choosing a function randomly...

Why not just construct a list of the functions, and randomly select an element from the list? Tom On May 20, 2012 5:14 AM, "Ertugrul Söylemez" wrote:

Stuart Hungerford wrote:

...

This is kind-of related to my earlier question on looking up functions by name. Suppose I have a module with a number of functions with the same signature:

[...]

I'd like to choose and run one of these functions randomly at run time. [...]

Again the lookup approach seems most reasonable. The cleanest way is to define a simple name type for your functions:

data FuncIx = FuncA | FuncB deriving (Ord)

instance Random FuncIx where ...

funcA :: A -> B funcB :: A -> B

funcs :: Map FuncIx (A -> B) funcs = M.fromList (zip [FuncA, FuncB] [funcA, funcB])

If you want to go for maximum speed instead:

import qualified Data.Vector as V

type FuncIx = Int

...

funcs :: V.Vector (A -> B) funcs = V.fromList [funcA, funcB]

randFunc :: (RandomGen g) => g -> (A -> B, g) randFunc = first (funcs V.!) . randomR (0, 1)

Greets, Ertugrul

-- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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