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{-# LANGUAGE DeriveGeneric, DeriveTraversable, TupleSections #-}
-- | A list of entities with relative frequencies of appearance.
module Game.LambdaHack.Core.Frequency
( -- * The @Frequency@ type
Frequency
-- * Construction
, uniformFreq, toFreq, maxBoundInt32
-- * Transformation
, scaleFreq
-- * Consumption
, nullFreq, runFrequency, nameFrequency
) where
import Prelude ()
import Game.LambdaHack.Core.Prelude
import Control.Applicative
import Data.Int (Int32)
import GHC.Generics (Generic)
maxBoundInt32 :: Int
maxBoundInt32 = toIntegralCrash (maxBound :: Int32)
-- | The frequency distribution type. Not normalized (operations may
-- or may not group the same elements and sum their frequencies). However,
-- elements with less than zero frequency are removed upon construction.
--
-- The @Eq@ instance compares raw representations, not relative,
-- normalized frequencies, so operations don't need to preserve
-- the expected equalities.
data Frequency a = Frequency
{ runFrequency :: [(Int, a)] -- ^ give acces to raw frequency values
, nameFrequency :: Text -- ^ short description for debug, etc.
}
deriving (Show, Eq, Ord, Foldable, Traversable, Generic)
instance Monad Frequency where
Frequency xs name >>= f =
Frequency [
#ifdef WITH_EXPENSIVE_ASSERTIONS
assert (toInteger p * toInteger q <= toInteger maxBoundInt32
`blame` (name, map fst xs))
#endif
(p * q, y)
| (p, x) <- xs
, (q, y) <- runFrequency (f x)
]
("bind (" <> name <> ")")
instance Functor Frequency where
fmap f (Frequency xs name) = Frequency (map (second f) xs) name
instance Applicative Frequency where
{-# INLINE pure #-}
pure x = Frequency [(1, x)] "pure"
Frequency fs fname <*> Frequency ys yname =
Frequency [
#ifdef WITH_EXPENSIVE_ASSERTIONS
assert (toInteger p * toInteger q <= toInteger maxBoundInt32
`blame` (fname, map fst fs, yname, map fst ys))
#endif
(p * q, f y)
| (p, f) <- fs
, (q, y) <- ys
]
("(" <> fname <> ") <*> (" <> yname <> ")")
instance MonadPlus Frequency where
mplus (Frequency xs xname) (Frequency ys yname) =
let name = case (xs, ys) of
([], []) -> "[]"
([], _) -> yname
(_, []) -> xname
_ -> "(" <> xname <> ") ++ (" <> yname <> ")"
in Frequency (xs ++ ys) name
mzero = Frequency [] "[]"
instance Alternative Frequency where
(<|>) = mplus
empty = mzero
-- | Uniform discrete frequency distribution.
uniformFreq :: Text -> [a] -> Frequency a
uniformFreq name l = Frequency (map (1,) l) name
-- | Takes a name and a list of frequencies and items
-- into the frequency distribution.
toFreq :: Text -> [(Int, a)] -> Frequency a
toFreq name l =
#ifdef WITH_EXPENSIVE_ASSERTIONS
assert (all (\(p, _) -> toInteger p <= toInteger maxBoundInt32) l
`blame` (name, map fst l)) $
#endif
Frequency (filter ((> 0 ) . fst) l) name
-- | Scale frequency distribution, multiplying it
-- by a positive integer constant.
scaleFreq :: Show a => Int -> Frequency a -> Frequency a
scaleFreq n (Frequency xs name) =
assert (n > 0 `blame` "non-positive frequency scale" `swith` (name, n, xs)) $
let multN p =
#ifdef WITH_EXPENSIVE_ASSERTIONS
assert (toInteger p * toInteger n <= toInteger maxBoundInt32
`blame` (n, Frequency xs name)) $
#endif
p * n
in Frequency (map (first multN) xs) name
-- | Test if the frequency distribution is empty.
nullFreq :: Frequency a -> Bool
nullFreq (Frequency fs _) = null fs
|
