module Data.CRF.Chain2.Generic.External ( Word (obs, lbs) , mkWord , Sent , Dist (unDist) , mkDist , WordL , SentL ) where import qualified Data.Set as S import qualified Data.Map as M -- | A word with 'a' representing the observation type and 'b' representing -- the compound label type. data Word a b = Word { -- | Set of observations. obs :: S.Set a -- | Non-empty set of potential labels. , lbs :: S.Set b } deriving (Show, Eq, Ord) -- | A word constructor which checks non-emptiness of the potential -- set of labels. mkWord :: S.Set a -> S.Set b -> Word a b mkWord _obs _lbs | S.null _lbs = error "mkWord: empty set of potential labels" | otherwise = Word _obs _lbs type Sent a b = [Word a b] -- | A probability distribution defined over elements of type a. -- All elements not included in the map have probability equal -- to 0. newtype Dist a = Dist { unDist :: M.Map a Double } -- | Construct the probability distribution. mkDist :: Ord a => [(a, Double)] -> Dist a mkDist = Dist . normalize . M.fromListWith (+) where normalize dist = let z = sum (M.elems dist) in fmap (/z) dist -- | A WordL is a labeled word, i.e. a word with probability distribution -- defined over labels. We assume that every label from the distribution -- domain is a member of the set of potential labels corresponding to the -- word. TODO: Ensure the assumption using the smart constructor. type WordL a b = (Word a b, Dist b) -- | A sentence of labeled words. type SentL a b = [WordL a b]