Data/Fixed.hs

{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# OPTIONS -Wall -fno-warn-unused-binds #-}

-----------------------------------------------------------------------------
-- |
-- Module : Data.Fixed
-- Copyright : (c) Ashley Yakeley 2005, 2006, 2009
-- License : BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer : Ashley Yakeley <ashley@semantic.org>
-- Stability : experimental
-- Portability : portable
--
-- This module defines a \"Fixed\" type for fixed-precision arithmetic.
-- The parameter to Fixed is any type that's an instance of HasResolution.
-- HasResolution has a single method that gives the resolution of the Fixed type.
--
-- This module also contains generalisations of div, mod, and divmod to work
-- with any Real instance.
--
-----------------------------------------------------------------------------

module Data.Fixed
(
 div',mod',divMod',

 Fixed(..), HasResolution(..),
 showFixed,
 E0,Uni,
 E1,Deci,
 E2,Centi,
 E3,Milli,
 E6,Micro,
 E9,Nano,
 E12,Pico
) where

import Prelude -- necessary to get dependencies right
import Data.Typeable
import Data.Data
import GHC.Read
import Text.ParserCombinators.ReadPrec
import Text.Read.Lex

default () -- avoid any defaulting shenanigans

-- | generalisation of 'div' to any instance of Real
div' :: (Real a,Integral b) => a -> a -> b
div' n d = floor ((toRational n) / (toRational d))

-- | generalisation of 'divMod' to any instance of Real
divMod' :: (Real a,Integral b) => a -> a -> (b,a)
divMod' n d = (f,n - (fromIntegral f) * d) where
 f = div' n d

-- | generalisation of 'mod' to any instance of Real
mod' :: (Real a) => a -> a -> a
mod' n d = n - (fromInteger f) * d where
 f = div' n d

-- | The type parameter should be an instance of 'HasResolution'.
newtype Fixed a = MkFixed Integer -- ^ /Since: 4.7.0.0/
 deriving (Eq,Ord,Typeable)

-- We do this because the automatically derived Data instance requires (Data a) context.
-- Our manual instance has the more general (Typeable a) context.
tyFixed :: DataType
tyFixed = mkDataType "Data.Fixed.Fixed" [conMkFixed]
conMkFixed :: Constr
conMkFixed = mkConstr tyFixed "MkFixed" [] Prefix
instance (Typeable a) => Data (Fixed a) where
 gfoldl k z (MkFixed a) = k (z MkFixed) a
 gunfold k z _ = k (z MkFixed)
 dataTypeOf _ = tyFixed
 toConstr _ = conMkFixed

class HasResolution a where
 resolution :: p a -> Integer

withType :: (p a -> f a) -> f a
withType foo = foo undefined

withResolution :: (HasResolution a) => (Integer -> f a) -> f a
withResolution foo = withType (foo . resolution)

instance Enum (Fixed a) where
 succ (MkFixed a) = MkFixed (succ a)
 pred (MkFixed a) = MkFixed (pred a)
 toEnum = MkFixed . toEnum
 fromEnum (MkFixed a) = fromEnum a
 enumFrom (MkFixed a) = fmap MkFixed (enumFrom a)
 enumFromThen (MkFixed a) (MkFixed b) = fmap MkFixed (enumFromThen a b)
 enumFromTo (MkFixed a) (MkFixed b) = fmap MkFixed (enumFromTo a b)
 enumFromThenTo (MkFixed a) (MkFixed b) (MkFixed c) = fmap MkFixed (enumFromThenTo a b c)

instance (HasResolution a) => Num (Fixed a) where
 (MkFixed a) + (MkFixed b) = MkFixed (a + b)
 (MkFixed a) - (MkFixed b) = MkFixed (a - b)
 fa@(MkFixed a) * (MkFixed b) = MkFixed (div (a * b) (resolution fa))
 negate (MkFixed a) = MkFixed (negate a)
 abs (MkFixed a) = MkFixed (abs a)
 signum (MkFixed a) = fromInteger (signum a)
 fromInteger i = withResolution (\res -> MkFixed (i * res))

instance (HasResolution a) => Real (Fixed a) where
 toRational fa@(MkFixed a) = (toRational a) / (toRational (resolution fa))

instance (HasResolution a) => Fractional (Fixed a) where
 fa@(MkFixed a) / (MkFixed b) = MkFixed (div (a * (resolution fa)) b)
 recip fa@(MkFixed a) = MkFixed (div (res * res) a) where
 res = resolution fa
 fromRational r = withResolution (\res -> MkFixed (floor (r * (toRational res))))

instance (HasResolution a) => RealFrac (Fixed a) where
 properFraction a = (i,a - (fromIntegral i)) where
 i = truncate a
 truncate f = truncate (toRational f)
 round f = round (toRational f)
 ceiling f = ceiling (toRational f)
 floor f = floor (toRational f)

chopZeros :: Integer -> String
chopZeros 0 = ""
chopZeros a | mod a 10 == 0 = chopZeros (div a 10)
chopZeros a = show a

-- only works for positive a
showIntegerZeros :: Bool -> Int -> Integer -> String
showIntegerZeros True _ 0 = ""
showIntegerZeros chopTrailingZeros digits a = replicate (digits - length s) '0' ++ s' where
 s = show a
 s' = if chopTrailingZeros then chopZeros a else s

withDot :: String -> String
withDot "" = ""
withDot s = '.':s

-- | First arg is whether to chop off trailing zeros
showFixed :: (HasResolution a) => Bool -> Fixed a -> String
showFixed chopTrailingZeros fa@(MkFixed a) | a < 0 = "-" ++ (showFixed chopTrailingZeros (asTypeOf (MkFixed (negate a)) fa))
showFixed chopTrailingZeros fa@(MkFixed a) = (show i) ++ (withDot (showIntegerZeros chopTrailingZeros digits fracNum)) where
 res = resolution fa
 (i,d) = divMod a res
 -- enough digits to be unambiguous
 digits = ceiling (logBase 10 (fromInteger res) :: Double)
 maxnum = 10 ^ digits
 fracNum = div (d * maxnum) res

instance (HasResolution a) => Show (Fixed a) where
 show = showFixed False

instance (HasResolution a) => Read (Fixed a) where
 readPrec = readNumber convertFixed
 readListPrec = readListPrecDefault
 readList = readListDefault

convertFixed :: forall a . HasResolution a => Lexeme -> ReadPrec (Fixed a)
convertFixed (Number n)
 | Just (i, f) <- numberToFixed r n =
 return (fromInteger i + (fromInteger f / (10 ^ r)))
 where r = resolution (undefined :: Fixed a)
convertFixed _ = pfail

data E0 = E0
 deriving (Typeable)
instance HasResolution E0 where
 resolution _ = 1
-- | resolution of 1, this works the same as Integer
type Uni = Fixed E0

data E1 = E1
 deriving (Typeable)
instance HasResolution E1 where
 resolution _ = 10
-- | resolution of 10^-1 = .1
type Deci = Fixed E1

data E2 = E2
 deriving (Typeable)
instance HasResolution E2 where
 resolution _ = 100
-- | resolution of 10^-2 = .01, useful for many monetary currencies
type Centi = Fixed E2

data E3 = E3
 deriving (Typeable)
instance HasResolution E3 where
 resolution _ = 1000
-- | resolution of 10^-3 = .001
type Milli = Fixed E3

data E6 = E6
 deriving (Typeable)
instance HasResolution E6 where
 resolution _ = 1000000
-- | resolution of 10^-6 = .000001
type Micro = Fixed E6

data E9 = E9
 deriving (Typeable)
instance HasResolution E9 where
 resolution _ = 1000000000
-- | resolution of 10^-9 = .000000001
type Nano = Fixed E9

data E12 = E12
 deriving (Typeable)
instance HasResolution E12 where
 resolution _ = 1000000000000
-- | resolution of 10^-12 = .000000000001
type Pico = Fixed E12