Haskell Nondeterminism

nondeterminism.hs

data CoinType = Fair | Biased deriving (Show)
data Coin = Head | Tail deriving (Eq,Show)

toss Fair   = [Head, Tail]
toss Biased = [Head, Head]

pick = [Fair, Biased]

experiment = do
  coin   <- pick         -- Pick a coin at random
  result <- toss coin    -- Toss it, to get a result
  guard (result == Head) -- We only care about results that come up Heads
  return coin            -- Return which coin was used in this case


---  
>> experiment
[Biased, Biased, Fair]

Credit to https://stackoverflow.com/a/20644753