src/Symantic/Compta/Calc/Flow.hs

   1 module Symantic.Compta.Calc.Flow where
   2
   3 import Control.DeepSeq (NFData)
   4 import Data.Bool
   5 import Data.Eq (Eq)
   6 import Data.Functor (Functor)
   7 import Data.Maybe (Maybe(..))
   8 import Data.Ord (Ord(..))
   9 import GHC.Generics (Generic)
  10 import Text.Show (Show(..))
  11
  12 import Symantic.Compta.Lang
  13
  14 -- ** Type 'Flow'
  15 -- | A 'Flow keeps track separatly of what goes 'In'
  16 -- and what goes 'Out' of an account.
  17 data Flow a
  18   = In !a
  19   | Out !a
  20   | Bidir !a !a
  21   deriving (Eq, Show, Generic, NFData, Functor)
  22
  23 instance FromInteger qty => FromInteger (Flow qty) where
  24   fromInteger i | i <= 0 = Out (fromInteger i)
  25                 | otherwise = In (fromInteger i)
  26
  27 flowIn :: Flow a -> Maybe a
  28 flowIn = \case
  29   In i -> Just i
  30   Out _ -> Nothing
  31   Bidir _ i -> Just i
  32
  33 flowOut :: Flow a -> Maybe a
  34 flowOut = \case
  35   In _ -> Nothing
  36   Out o -> Just o
  37   Bidir o _ -> Just o
  38
  39 flow :: Flowable a => a -> Flow a
  40 flow f =
  41   case (outOf f, inOf f) of
  42     (Just o, Nothing) -> Out o
  43     (Nothing, Just i) -> In i
  44     (Just o, Just i) -> Bidir o i
  45     (Nothing, Nothing) -> Bidir f f
  46 unFlow :: Addable a => Flow a -> a
  47 unFlow = \case
  48   In i -> i
  49   Out o -> o
  50   Bidir o i -> o + i
  51
  52 instance Zeroable a => Zeroable (Flow a) where
  53   zero = In zero
  54 instance (Nullable a, Addable a) => Nullable (Flow a) where
  55   null = \case
  56     Out o -> null o
  57     In i -> null i
  58     Bidir o i -> null (o + i)
  59 instance Addable a => Addable (Flow a) where
  60   In i  + Out o = Bidir o i
  61   In ix + In py = In (ix + py)
  62   In i  + Bidir ny py = Bidir ny (i + py)
  63
  64   Out ox + Out ny = Out (ox + ny)
  65   Out o  + In i  = Bidir o i
  66   Out ox + Bidir ny i = Bidir (ox + ny) i
  67
  68   Bidir ox ix + Out o = Bidir (ox + o) ix
  69   Bidir ox ix + In py = Bidir ox (ix + py)
  70   Bidir ox ix + Bidir ny py = Bidir (ox + ny) (ix + py)
  71 instance Negable a => Negable (Flow a) where
  72   negate = \case
  73     In i -> Out (negate i)
  74     Out o -> In (negate o)
  75     Bidir o i -> Bidir (negate i) (negate o)
  76 instance Flowable (Flow a) where
  77   outOf f = case f of
  78     In _ -> Nothing
  79     Out _ -> Just f
  80     Bidir n _ -> Just (Out n)
  81   inOf f = case f of
  82     In _ -> Just f
  83     Out _ -> Nothing
  84     Bidir _ p -> Just (In p)
  85 --instance Eq
  86
  87 -- * Class 'Flowable'
  88 class Flowable a where
  89   outOf :: a -> Maybe a
  90   inOf  :: a -> Maybe a
  91 {-
  92 instance Flowable Decimal where
  93   outOf q =
  94     case q of
  95      _ | q < 0 -> Just q
  96      _         -> Nothing
  97   inOf q =
  98     case q of
  99      _ | q <= 0 -> Nothing
 100      _          -> Just q
 101 instance Flowable a => Flowable (Map k a) where
 102   inOf q =
 103     case Map.mapMaybe inOf q of
 104      m | Map.null m -> Nothing
 105      m -> Just m
 106   outOf q =
 107     case Map.mapMaybe outOf q of
 108      m | Map.null m -> Nothing
 109      m -> Just m
 110 instance Flowable a => Flowable (k, a) where
 111   inOf (u, q) = (u,) <$> inOf q
 112   outOf (u, q) = (u,) <$> outOf q
 113 -}