Just an idea here, but would implicit-params work? It only gives you
Reader-monad capabilities, but you can always split random generators.
There might be repercussions for the quality of the generated numbers,
though, for which I have no idea.
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE RankNTypes #-}
import Data.Implicit
import System.Random
import Text.Printf
import Data.Default.Class
instance Default StdGen where
def = mkStdGen 10
newtype AlgebraicNumber = AlgebraicNumber {- your data here -} String
deriving Show
instance Implicit_ StdGen => Num AlgebraicNumber where
AlgebraicNumber x + AlgebraicNumber y =
-- You could tidy this up with a State monad.
let g = param_ :: StdGen
(g1, g2) = split g
gx = fst $ next g1 -- compute on x using left generator
gy = fst $ next g2 -- compute on y using right generator
in
AlgebraicNumber (printf ("%s computed with rand = %d,"
++ "%s computed with rand = %d")
x gx y gy)
On Sat, Nov 1, 2014 at 11:28 AM, Hiromi ISHII
Hi Bardur,
You can just use the State monad to thread the StdGen around and "update" it when you need to. You can get a pure interface by hiding away the runState behind a function:
Thank you for your rapid response! Unfortunately, I didn't describe my problem accurately.
This approach (or using MonadRandom) to pass around random generator with Monad, works fine when it's just enough to feed generator to the algorithm.
But my situation is slightly different: random generator has to be passed around to implement the instance method for `Num`, so it can't take random generator as its argument. So I need some way to hide random generator from function type signatures.
Fortunately, your response suggested me the alternative approach: converting the data-type into continuation-passing style. This should work fine when we just do some operations on data-type, but we have to feed the generator when we want to inspect its value, so it's not sufficient, though...
-- Hiromi ISHII konn.jinro@gmail.com
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