{-# OPTIONS -fno-implicit-prelude #-} module Number.ResidueClass.Check where import qualified Number.ResidueClass as Res import qualified Algebra.PrincipalIdealDomain as PID import qualified Algebra.IntegralDomain as Integral import qualified Algebra.Field as Field import qualified Algebra.Ring as Ring import qualified Algebra.Additive as Additive import qualified Algebra.ZeroTestable as ZeroTestable import Algebra.ZeroTestable(isZero) import PreludeBase import NumericPrelude import NumericPrelude.Condition (toMaybe) import NumericPrelude.Text (showsInfixPrec, readsInfixPrec) infix 7 /:, `Cons` {- | The best solution seems to let 'modulus' be part of the type. Then operations with non-matching moduli could be detected at compile time and 'zero' and 'one' could be generated with the correct modulus. An alternative trial can be found in module ResidueClassMaybe. -} data T a = Cons {modulus :: !a ,representative :: !a } factorPrec :: Int factorPrec = read "7" instance (Show a) => Show (T a) where showsPrec prec (Cons m r) = showsInfixPrec "/:" factorPrec prec r m instance (Read a, Integral.C a) => Read (T a) where readsPrec prec = readsInfixPrec "/:" factorPrec prec (/:) -- | @r \/: m@ is the residue class containing @r@ with respect to the modulus @m@ (/:) :: (Integral.C a) => a -> a -> T a (/:) r m = Cons m (mod r m) -- | Check if two residue classes share the same modulus isCompatible :: (Eq a) => T a -> T a -> Bool isCompatible x y = modulus x == modulus y maybeCompatible :: (Eq a) => T a -> T a -> Maybe a maybeCompatible x y = let mx = modulus x my = modulus y in toMaybe (mx==my) mx fromRepresentative :: (Integral.C a) => a -> a -> T a fromRepresentative m x = Cons m (mod x m) lift1 :: (Eq a) => (a -> a -> a) -> T a -> T a lift1 f x = let m = modulus x in Cons m (f m (representative x)) lift2 :: (Eq a) => (a -> a -> a -> a) -> T a -> T a -> T a lift2 f x y = maybe (errIncompat) (\m -> Cons m (f (modulus x) (representative x) (representative y))) (maybeCompatible x y) errIncompat :: a errIncompat = error "Residue class: Incompatible operands" zero :: (Additive.C a) => a -> T a zero m = Cons m Additive.zero one :: (Ring.C a) => a -> T a one m = Cons m NumericPrelude.one fromInteger :: (Integral.C a) => a -> Integer -> T a fromInteger m x = fromRepresentative m (NumericPrelude.fromInteger x) instance (Eq a) => Eq (T a) where (==) x y = maybe errIncompat (const (representative x == representative y)) (maybeCompatible x y) instance (ZeroTestable.C a) => ZeroTestable.C (T a) where isZero (Cons _ r) = isZero r instance (Eq a, Integral.C a) => Additive.C (T a) where zero = error "no generic zero in a residue class, use ResidueClass.zero" (+) = lift2 Res.add (-) = lift2 Res.sub negate = lift1 Res.neg instance (Eq a, Integral.C a) => Ring.C (T a) where one = error "no generic one in a residue class, use ResidueClass.one" (*) = lift2 Res.mul fromInteger = error "no generic integer in a residue class, use ResidueClass.fromInteger" instance (Eq a, PID.C a) => Field.C (T a) where (/) = lift2 Res.divide recip = lift1 (flip Res.divide NumericPrelude.one) fromRational' = error "no conversion from rational to residue class"