----------------------------------------------------------------------------- -- | -- Module : Data.SBV.BitVectors.Model -- Copyright : (c) Levent Erkok -- License : BSD3 -- Maintainer : erkokl@gmail.com -- Stability : experimental -- -- Instance declarations for our symbolic world ----------------------------------------------------------------------------- {-# OPTIONS_GHC -fno-warn-orphans #-} {-# LANGUAGE CPP #-} {-# LANGUAGE TypeSynonymInstances #-} {-# LANGUAGE BangPatterns #-} {-# LANGUAGE PatternGuards #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE Rank2Types #-} module Data.SBV.BitVectors.Model ( Mergeable(..), EqSymbolic(..), OrdSymbolic(..), SDivisible(..), Uninterpreted(..), SIntegral , sbvTestBit, sbvPopCount, setBitTo, sbvShiftLeft, sbvShiftRight, sbvSignedShiftArithRight , allEqual, allDifferent, inRange, sElem, oneIf, blastBE, blastLE, fullAdder, fullMultiplier , lsb, msb, genVar, genVar_, forall, forall_, exists, exists_ , constrain, pConstrain, sBool, sBools, sWord8, sWord8s, sWord16, sWord16s, sWord32 , sWord32s, sWord64, sWord64s, sInt8, sInt8s, sInt16, sInt16s, sInt32, sInt32s, sInt64 , sInt64s, sInteger, sIntegers, sReal, sReals, toSReal, slet ) where import Control.Monad (when, liftM) import Data.Array (Array, Ix, listArray, elems, bounds, rangeSize) import Data.Bits (Bits(..)) import Data.Int (Int8, Int16, Int32, Int64) import Data.List (genericLength, genericIndex, unzip4, unzip5, unzip6, unzip7, intercalate) import Data.Maybe (fromMaybe) import Data.Word (Word8, Word16, Word32, Word64) import Test.QuickCheck (Testable(..), Arbitrary(..)) import qualified Test.QuickCheck as QC (whenFail) import qualified Test.QuickCheck.Monadic as QC (monadicIO, run) import System.Random import Data.SBV.BitVectors.AlgReals import Data.SBV.BitVectors.Data import Data.SBV.Utils.Boolean noUnint :: String -> a noUnint x = error $ "Unexpected operation called on uninterpreted value: " ++ show x noUnint2 :: String -> String -> a noUnint2 x y = error $ "Unexpected binary operation called on uninterpreted values: " ++ show (x, y) liftSym1 :: (State -> Kind -> SW -> IO SW) -> (AlgReal -> AlgReal) -> (Integer -> Integer) -> SBV b -> SBV b liftSym1 _ opCR opCI (SBV k (Left a)) = SBV k $ Left $ mapCW opCR opCI noUnint a liftSym1 opS _ _ a@(SBV k _) = SBV k $ Right $ cache c where c st = do swa <- sbvToSW st a opS st k swa liftSW2 :: (State -> Kind -> SW -> SW -> IO SW) -> Kind -> SBV a -> SBV b -> Cached SW liftSW2 opS k a b = cache c where c st = do sw1 <- sbvToSW st a sw2 <- sbvToSW st b opS st k sw1 sw2 liftSym2 :: (State -> Kind -> SW -> SW -> IO SW) -> (CW -> CW -> Bool) -> (AlgReal -> AlgReal -> AlgReal) -> (Integer -> Integer -> Integer) -> SBV b -> SBV b -> SBV b liftSym2 _ okCW opCR opCI (SBV k (Left a)) (SBV _ (Left b)) | okCW a b = SBV k $ Left $ mapCW2 opCR opCI noUnint2 a b liftSym2 opS _ _ _ a@(SBV k _) b = SBV k $ Right $ liftSW2 opS k a b liftSym2B :: (State -> Kind -> SW -> SW -> IO SW) -> (CW -> CW -> Bool) -> (AlgReal -> AlgReal -> Bool) -> (Integer -> Integer -> Bool) -> SBV b -> SBV b -> SBool liftSym2B _ okCW opCR opCI (SBV _ (Left a)) (SBV _ (Left b)) | okCW a b = literal (liftCW2 opCR opCI noUnint2 a b) liftSym2B opS _ _ _ a b = SBV (KBounded False 1) $ Right $ liftSW2 opS (KBounded False 1) a b liftSym1Bool :: (State -> Kind -> SW -> IO SW) -> (Bool -> Bool) -> SBool -> SBool liftSym1Bool _ opC (SBV _ (Left a)) = literal $ opC $ cwToBool a liftSym1Bool opS _ a = SBV (KBounded False 1) $ Right $ cache c where c st = do sw <- sbvToSW st a opS st (KBounded False 1) sw liftSym2Bool :: (State -> Kind -> SW -> SW -> IO SW) -> (Bool -> Bool -> Bool) -> SBool -> SBool -> SBool liftSym2Bool _ opC (SBV _ (Left a)) (SBV _ (Left b)) = literal (cwToBool a `opC` cwToBool b) liftSym2Bool opS _ a b = SBV (KBounded False 1) $ Right $ cache c where c st = do sw1 <- sbvToSW st a sw2 <- sbvToSW st b opS st (KBounded False 1) sw1 sw2 mkSymOpSC :: (SW -> SW -> Maybe SW) -> Op -> State -> Kind -> SW -> SW -> IO SW mkSymOpSC shortCut op st k a b = maybe (newExpr st k (SBVApp op [a, b])) return (shortCut a b) mkSymOp :: Op -> State -> Kind -> SW -> SW -> IO SW mkSymOp = mkSymOpSC (const (const Nothing)) mkSymOp1SC :: (SW -> Maybe SW) -> Op -> State -> Kind -> SW -> IO SW mkSymOp1SC shortCut op st k a = maybe (newExpr st k (SBVApp op [a])) return (shortCut a) mkSymOp1 :: Op -> State -> Kind -> SW -> IO SW mkSymOp1 = mkSymOp1SC (const Nothing) -- Symbolic-Word class instances -- | Generate a finite symbolic bitvector, named genVar :: (Random a, SymWord a) => Maybe Quantifier -> Kind -> String -> Symbolic (SBV a) genVar q k = mkSymSBV q k . Just -- | Generate a finite symbolic bitvector, unnamed genVar_ :: (Random a, SymWord a) => Maybe Quantifier -> Kind -> Symbolic (SBV a) genVar_ q k = mkSymSBV q k Nothing -- | Generate a finite constant bitvector genLiteral :: Integral a => Kind -> a -> SBV b genLiteral k = SBV k . Left . mkConstCW k -- | Convert a constant to an integral value genFromCW :: Integral a => CW -> a genFromCW (CW _ (CWInteger x)) = fromInteger x genFromCW c = error $ "genFromCW: Unsupported non-integral value: " ++ show c -- | Generically make a symbolic var genMkSymVar :: (Random a, SymWord a) => Kind -> Maybe Quantifier -> Maybe String -> Symbolic (SBV a) genMkSymVar k mbq Nothing = genVar_ mbq k genMkSymVar k mbq (Just s) = genVar mbq k s instance SymWord Bool where mkSymWord = genMkSymVar (KBounded False 1) literal x = genLiteral (KBounded False 1) (if x then (1::Integer) else 0) fromCW = cwToBool mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Word8 where mkSymWord = genMkSymVar (KBounded False 8) literal = genLiteral (KBounded False 8) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Int8 where mkSymWord = genMkSymVar (KBounded True 8) literal = genLiteral (KBounded True 8) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Word16 where mkSymWord = genMkSymVar (KBounded False 16) literal = genLiteral (KBounded False 16) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Int16 where mkSymWord = genMkSymVar (KBounded True 16) literal = genLiteral (KBounded True 16) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Word32 where mkSymWord = genMkSymVar (KBounded False 32) literal = genLiteral (KBounded False 32) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Int32 where mkSymWord = genMkSymVar (KBounded True 32) literal = genLiteral (KBounded True 32) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Word64 where mkSymWord = genMkSymVar (KBounded False 64) literal = genLiteral (KBounded False 64) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Int64 where mkSymWord = genMkSymVar (KBounded True 64) literal = genLiteral (KBounded True 64) fromCW = genFromCW mbMaxBound = Just maxBound mbMinBound = Just minBound instance SymWord Integer where mkSymWord = genMkSymVar KUnbounded literal = SBV KUnbounded . Left . mkConstCW KUnbounded fromCW = genFromCW mbMaxBound = Nothing mbMinBound = Nothing instance SymWord AlgReal where mkSymWord = genMkSymVar KReal literal = SBV KReal . Left . CW KReal . CWAlgReal fromCW (CW _ (CWAlgReal a)) = a fromCW c = error $ "SymWord.AlgReal: Unexpected non-real value: " ++ show c -- AlgReal needs its own definition of isConcretely -- to make sure we avoid using unimplementable Haskell functions isConcretely (SBV KReal (Left (CW KReal (CWAlgReal v)))) p | isExactRational v = p v isConcretely _ _ = False mbMaxBound = Nothing mbMinBound = Nothing ------------------------------------------------------------------------------------ -- * Smart constructors for creating symbolic values. These are not strictly -- necessary, as they are mere aliases for 'symbolic' and 'symbolics', but -- they nonetheless make programming easier. ------------------------------------------------------------------------------------ -- | Declare an 'SBool' sBool :: String -> Symbolic SBool sBool = symbolic -- | Declare a list of 'SBool's sBools :: [String] -> Symbolic [SBool] sBools = symbolics -- | Declare an 'SWord8' sWord8 :: String -> Symbolic SWord8 sWord8 = symbolic -- | Declare a list of 'SWord8's sWord8s :: [String] -> Symbolic [SWord8] sWord8s = symbolics -- | Declare an 'SWord16' sWord16 :: String -> Symbolic SWord16 sWord16 = symbolic -- | Declare a list of 'SWord16's sWord16s :: [String] -> Symbolic [SWord16] sWord16s = symbolics -- | Declare an 'SWord32' sWord32 :: String -> Symbolic SWord32 sWord32 = symbolic -- | Declare a list of 'SWord32's sWord32s :: [String] -> Symbolic [SWord32] sWord32s = symbolics -- | Declare an 'SWord64' sWord64 :: String -> Symbolic SWord64 sWord64 = symbolic -- | Declare a list of 'SWord64's sWord64s :: [String] -> Symbolic [SWord64] sWord64s = symbolics -- | Declare an 'SInt8' sInt8 :: String -> Symbolic SInt8 sInt8 = symbolic -- | Declare a list of 'SInt8's sInt8s :: [String] -> Symbolic [SInt8] sInt8s = symbolics -- | Declare an 'SInt16' sInt16 :: String -> Symbolic SInt16 sInt16 = symbolic -- | Declare a list of 'SInt16's sInt16s :: [String] -> Symbolic [SInt16] sInt16s = symbolics -- | Declare an 'SInt32' sInt32 :: String -> Symbolic SInt32 sInt32 = symbolic -- | Declare a list of 'SInt32's sInt32s :: [String] -> Symbolic [SInt32] sInt32s = symbolics -- | Declare an 'SInt64' sInt64 :: String -> Symbolic SInt64 sInt64 = symbolic -- | Declare a list of 'SInt64's sInt64s :: [String] -> Symbolic [SInt64] sInt64s = symbolics -- | Declare an 'SInteger' sInteger:: String -> Symbolic SInteger sInteger = symbolic -- | Declare a list of 'SInteger's sIntegers :: [String] -> Symbolic [SInteger] sIntegers = symbolics -- | Declare an 'SReal' sReal:: String -> Symbolic SReal sReal = symbolic -- | Declare a list of 'SReal's sReals :: [String] -> Symbolic [SReal] sReals = symbolics -- | Promote an SInteger to an SReal toSReal :: SInteger -> SReal toSReal x | Just i <- unliteral x = literal $ fromInteger i | True = SBV KReal (Right (cache y)) where y st = do xsw <- sbvToSW st x newExpr st KReal (SBVApp (Extract 0 0) [xsw]) -- special encoding! -- | Symbolic Equality. Note that we can't use Haskell's 'Eq' class since Haskell insists on returning Bool -- Comparing symbolic values will necessarily return a symbolic value. -- -- Minimal complete definition: '.==' infix 4 .==, ./= class EqSymbolic a where (.==), (./=) :: a -> a -> SBool -- minimal complete definition: .== x ./= y = bnot (x .== y) -- | Symbolic Comparisons. Similar to 'Eq', we cannot implement Haskell's 'Ord' class -- since there is no way to return an 'Ordering' value from a symbolic comparison. -- Furthermore, 'OrdSymbolic' requires 'Mergeable' to implement if-then-else, for the -- benefit of implementing symbolic versions of 'max' and 'min' functions. -- -- Minimal complete definition: '.<' infix 4 .<, .<=, .>, .>= class (Mergeable a, EqSymbolic a) => OrdSymbolic a where (.<), (.<=), (.>), (.>=) :: a -> a -> SBool smin, smax :: a -> a -> a -- minimal complete definition: .< a .<= b = a .< b ||| a .== b a .> b = b .< a a .>= b = b .<= a a `smin` b = ite (a .<= b) a b a `smax` b = ite (a .<= b) b a {- We can't have a generic instance of the form: instance Eq a => EqSymbolic a where x .== y = if x == y then true else false even if we're willing to allow Flexible/undecidable instances.. This is because if we allow this it would imply EqSymbolic (SBV a); since (SBV a) has to be Eq as it must be a Num. But this wouldn't be the right choice obviously; as the Eq instance is bogus for SBV for natural reasons.. -} instance EqSymbolic (SBV a) where (.==) = liftSym2B (mkSymOpSC (eqOpt trueSW) Equal) rationalCheck (==) (==) (./=) = liftSym2B (mkSymOpSC (eqOpt falseSW) NotEqual) rationalCheck (/=) (/=) eqOpt :: SW -> SW -> SW -> Maybe SW eqOpt w x y = if x == y then Just w else Nothing instance SymWord a => OrdSymbolic (SBV a) where x .< y | Just mb <- mbMaxBound, x `isConcretely` (== mb) = false | Just mb <- mbMinBound, y `isConcretely` (== mb) = false | True = liftSym2B (mkSymOpSC (eqOpt falseSW) LessThan) rationalCheck (<) (<) x y x .<= y | Just mb <- mbMinBound, x `isConcretely` (== mb) = true | Just mb <- mbMaxBound, y `isConcretely` (== mb) = true | True = liftSym2B (mkSymOpSC (eqOpt trueSW) LessEq) rationalCheck (<=) (<=) x y x .> y | Just mb <- mbMinBound, x `isConcretely` (== mb) = false | Just mb <- mbMaxBound, y `isConcretely` (== mb) = false | True = liftSym2B (mkSymOpSC (eqOpt falseSW) GreaterThan) rationalCheck (>) (>) x y x .>= y | Just mb <- mbMaxBound, x `isConcretely` (== mb) = true | Just mb <- mbMinBound, y `isConcretely` (== mb) = true | True = liftSym2B (mkSymOpSC (eqOpt trueSW) GreaterEq) rationalCheck (>=) (>=) x y -- Bool instance EqSymbolic Bool where x .== y = if x == y then true else false -- Lists instance EqSymbolic a => EqSymbolic [a] where [] .== [] = true (x:xs) .== (y:ys) = x .== y &&& xs .== ys _ .== _ = false instance OrdSymbolic a => OrdSymbolic [a] where [] .< [] = false [] .< _ = true _ .< [] = false (x:xs) .< (y:ys) = x .< y ||| (x .== y &&& xs .< ys) -- Maybe instance EqSymbolic a => EqSymbolic (Maybe a) where Nothing .== Nothing = true Just a .== Just b = a .== b _ .== _ = false instance (OrdSymbolic a) => OrdSymbolic (Maybe a) where Nothing .< Nothing = false Nothing .< _ = true Just _ .< Nothing = false Just a .< Just b = a .< b -- Either instance (EqSymbolic a, EqSymbolic b) => EqSymbolic (Either a b) where Left a .== Left b = a .== b Right a .== Right b = a .== b _ .== _ = false instance (OrdSymbolic a, OrdSymbolic b) => OrdSymbolic (Either a b) where Left a .< Left b = a .< b Left _ .< Right _ = true Right _ .< Left _ = false Right a .< Right b = a .< b -- 2-Tuple instance (EqSymbolic a, EqSymbolic b) => EqSymbolic (a, b) where (a0, b0) .== (a1, b1) = a0 .== a1 &&& b0 .== b1 instance (OrdSymbolic a, OrdSymbolic b) => OrdSymbolic (a, b) where (a0, b0) .< (a1, b1) = a0 .< a1 ||| (a0 .== a1 &&& b0 .< b1) -- 3-Tuple instance (EqSymbolic a, EqSymbolic b, EqSymbolic c) => EqSymbolic (a, b, c) where (a0, b0, c0) .== (a1, b1, c1) = (a0, b0) .== (a1, b1) &&& c0 .== c1 instance (OrdSymbolic a, OrdSymbolic b, OrdSymbolic c) => OrdSymbolic (a, b, c) where (a0, b0, c0) .< (a1, b1, c1) = (a0, b0) .< (a1, b1) ||| ((a0, b0) .== (a1, b1) &&& c0 .< c1) -- 4-Tuple instance (EqSymbolic a, EqSymbolic b, EqSymbolic c, EqSymbolic d) => EqSymbolic (a, b, c, d) where (a0, b0, c0, d0) .== (a1, b1, c1, d1) = (a0, b0, c0) .== (a1, b1, c1) &&& d0 .== d1 instance (OrdSymbolic a, OrdSymbolic b, OrdSymbolic c, OrdSymbolic d) => OrdSymbolic (a, b, c, d) where (a0, b0, c0, d0) .< (a1, b1, c1, d1) = (a0, b0, c0) .< (a1, b1, c1) ||| ((a0, b0, c0) .== (a1, b1, c1) &&& d0 .< d1) -- 5-Tuple instance (EqSymbolic a, EqSymbolic b, EqSymbolic c, EqSymbolic d, EqSymbolic e) => EqSymbolic (a, b, c, d, e) where (a0, b0, c0, d0, e0) .== (a1, b1, c1, d1, e1) = (a0, b0, c0, d0) .== (a1, b1, c1, d1) &&& e0 .== e1 instance (OrdSymbolic a, OrdSymbolic b, OrdSymbolic c, OrdSymbolic d, OrdSymbolic e) => OrdSymbolic (a, b, c, d, e) where (a0, b0, c0, d0, e0) .< (a1, b1, c1, d1, e1) = (a0, b0, c0, d0) .< (a1, b1, c1, d1) ||| ((a0, b0, c0, d0) .== (a1, b1, c1, d1) &&& e0 .< e1) -- 6-Tuple instance (EqSymbolic a, EqSymbolic b, EqSymbolic c, EqSymbolic d, EqSymbolic e, EqSymbolic f) => EqSymbolic (a, b, c, d, e, f) where (a0, b0, c0, d0, e0, f0) .== (a1, b1, c1, d1, e1, f1) = (a0, b0, c0, d0, e0) .== (a1, b1, c1, d1, e1) &&& f0 .== f1 instance (OrdSymbolic a, OrdSymbolic b, OrdSymbolic c, OrdSymbolic d, OrdSymbolic e, OrdSymbolic f) => OrdSymbolic (a, b, c, d, e, f) where (a0, b0, c0, d0, e0, f0) .< (a1, b1, c1, d1, e1, f1) = (a0, b0, c0, d0, e0) .< (a1, b1, c1, d1, e1) ||| ((a0, b0, c0, d0, e0) .== (a1, b1, c1, d1, e1) &&& f0 .< f1) -- 7-Tuple instance (EqSymbolic a, EqSymbolic b, EqSymbolic c, EqSymbolic d, EqSymbolic e, EqSymbolic f, EqSymbolic g) => EqSymbolic (a, b, c, d, e, f, g) where (a0, b0, c0, d0, e0, f0, g0) .== (a1, b1, c1, d1, e1, f1, g1) = (a0, b0, c0, d0, e0, f0) .== (a1, b1, c1, d1, e1, f1) &&& g0 .== g1 instance (OrdSymbolic a, OrdSymbolic b, OrdSymbolic c, OrdSymbolic d, OrdSymbolic e, OrdSymbolic f, OrdSymbolic g) => OrdSymbolic (a, b, c, d, e, f, g) where (a0, b0, c0, d0, e0, f0, g0) .< (a1, b1, c1, d1, e1, f1, g1) = (a0, b0, c0, d0, e0, f0) .< (a1, b1, c1, d1, e1, f1) ||| ((a0, b0, c0, d0, e0, f0) .== (a1, b1, c1, d1, e1, f1) &&& g0 .< g1) -- | Symbolic Numbers. This is a simple class that simply incorporates all number like -- base types together, simplifying writing polymorphic type-signatures that work for all -- symbolic numbers, such as 'SWord8', 'SInt8' etc. For instance, we can write a generic -- list-minimum function as follows: -- -- @ -- mm :: SIntegral a => [SBV a] -> SBV a -- mm = foldr1 (\a b -> ite (a .<= b) a b) -- @ -- -- It is similar to the standard 'Integral' class, except ranging over symbolic instances. class (SymWord a, Num a, Bits a) => SIntegral a -- 'SIntegral' Instances, including all possible variants except 'Bool', since booleans -- are not numbers. instance SIntegral Word8 instance SIntegral Word16 instance SIntegral Word32 instance SIntegral Word64 instance SIntegral Int8 instance SIntegral Int16 instance SIntegral Int32 instance SIntegral Int64 instance SIntegral Integer -- Boolean combinators instance Boolean SBool where true = literal True false = literal False bnot b | b `isConcretely` (== False) = true | b `isConcretely` (== True) = false | True = liftSym1Bool (mkSymOp1SC opt Not) not b where opt x | x == falseSW = Just trueSW | x == trueSW = Just falseSW | True = Nothing a &&& b | a `isConcretely` (== False) || b `isConcretely` (== False) = false | a `isConcretely` (== True) = b | b `isConcretely` (== True) = a | True = liftSym2Bool (mkSymOpSC opt And) (&&) a b where opt x y | x == falseSW || y == falseSW = Just falseSW | x == trueSW = Just y | y == trueSW = Just x | True = Nothing a ||| b | a `isConcretely` (== True) || b `isConcretely` (== True) = true | a `isConcretely` (== False) = b | b `isConcretely` (== False) = a | True = liftSym2Bool (mkSymOpSC opt Or) (||) a b where opt x y | x == trueSW || y == trueSW = Just trueSW | x == falseSW = Just y | y == falseSW = Just x | True = Nothing a <+> b | a `isConcretely` (== False) = b | b `isConcretely` (== False) = a | a `isConcretely` (== True) = bnot b | b `isConcretely` (== True) = bnot a | True = liftSym2Bool (mkSymOpSC opt XOr) (<+>) a b where opt x y | x == y = Just falseSW | x == falseSW = Just y | y == falseSW = Just x | True = Nothing -- | Returns (symbolic) true if all the elements of the given list are different. allDifferent :: EqSymbolic a => [a] -> SBool allDifferent (x:xs@(_:_)) = bAll (x ./=) xs &&& allDifferent xs allDifferent _ = true -- | Returns (symbolic) true if all the elements of the given list are the same. allEqual :: EqSymbolic a => [a] -> SBool allEqual (x:xs@(_:_)) = bAll (x .==) xs allEqual _ = true -- | Returns (symbolic) true if the argument is in range inRange :: OrdSymbolic a => a -> (a, a) -> SBool inRange x (y, z) = x .>= y &&& x .<= z -- | Symbolic membership test sElem :: EqSymbolic a => a -> [a] -> SBool sElem x xs = bAny (.== x) xs -- | Returns 1 if the boolean is true, otherwise 0. oneIf :: (Num a, SymWord a) => SBool -> SBV a oneIf t = ite t 1 0 -- Num instance for symbolic words. instance (Ord a, Num a, SymWord a) => Num (SBV a) where fromInteger = literal . fromIntegral x + y | x `isConcretely` (== 0) = y | y `isConcretely` (== 0) = x | True = liftSym2 (mkSymOp Plus) rationalCheck (+) (+) x y x * y | x `isConcretely` (== 0) = 0 | y `isConcretely` (== 0) = 0 | x `isConcretely` (== 1) = y | y `isConcretely` (== 1) = x | True = liftSym2 (mkSymOp Times) rationalCheck (*) (*) x y x - y | y `isConcretely` (== 0) = x | True = liftSym2 (mkSymOp Minus) rationalCheck (-) (-) x y abs a | hasSign a = ite (a .< 0) (-a) a | True = a signum a | hasSign a = ite (a .< 0) (-1) (ite (a .== 0) 0 1) | True = oneIf (a ./= 0) instance Fractional SReal where fromRational = literal . fromRational x / y = liftSym2 (mkSymOp Quot) rationalCheck (/) die x y where -- should never happen die = error $ "impossible: non-real value found in Fractional.SReal " ++ show (x, y) -- Most operations on concrete rationals require a compatibility check rationalCheck :: CW -> CW -> Bool rationalCheck a b = case (cwVal a, cwVal b) of (CWAlgReal x, CWAlgReal y) -> isExactRational x && isExactRational y _ -> True -- same as above, for SBV's rationalSBVCheck :: SBV a -> SBV a -> Bool rationalSBVCheck (SBV KReal (Left a)) (SBV KReal (Left b)) = rationalCheck a b rationalSBVCheck _ _ = True -- Some operations will never be used on Reals, but we need fillers: noReal :: String -> AlgReal -> AlgReal -> AlgReal noReal o a b = error $ "SBV.AlgReal." ++ o ++ ": Unexpected arguments: " ++ show (a, b) noRealUnary :: String -> AlgReal -> AlgReal noRealUnary o a = error $ "SBV.AlgReal." ++ o ++ ": Unexpected argument: " ++ show a -- NB. In the optimizations below, use of -1 is valid as -- -1 has all bits set to True for both signed and unsigned values instance (Num a, Bits a, SymWord a) => Bits (SBV a) where x .&. y | x `isConcretely` (== 0) = 0 | x `isConcretely` (== -1) = y | y `isConcretely` (== 0) = 0 | y `isConcretely` (== -1) = x | True = liftSym2 (mkSymOp And) (const (const True)) (noReal ".&.") (.&.) x y x .|. y | x `isConcretely` (== 0) = y | x `isConcretely` (== -1) = -1 | y `isConcretely` (== 0) = x | y `isConcretely` (== -1) = -1 | True = liftSym2 (mkSymOp Or) (const (const True)) (noReal ".|.") (.|.) x y x `xor` y | x `isConcretely` (== 0) = y | y `isConcretely` (== 0) = x | True = liftSym2 (mkSymOp XOr) (const (const True)) (noReal "xor") xor x y complement = liftSym1 (mkSymOp1 Not) (noRealUnary "Not") complement bitSize _ = intSizeOf (undefined :: a) isSigned _ = hasSign (undefined :: a) bit i = 1 `shiftL` i shiftL x y | y < 0 = shiftR x (-y) | y == 0 = x | True = liftSym1 (mkSymOp1 (Shl y)) (noRealUnary "shiftL") (`shiftL` y) x shiftR x y | y < 0 = shiftL x (-y) | y == 0 = x | True = liftSym1 (mkSymOp1 (Shr y)) (noRealUnary "shiftR") (`shiftR` y) x rotateL x y | y < 0 = rotateR x (-y) | y == 0 = x | isBounded x = let sz = bitSize x in liftSym1 (mkSymOp1 (Rol (y `mod` sz))) (noRealUnary "rotateL") (rot True sz y) x | True = shiftL x y -- for unbounded Integers, rotateL is the same as shiftL in Haskell rotateR x y | y < 0 = rotateL x (-y) | y == 0 = x | isBounded x = let sz = bitSize x in liftSym1 (mkSymOp1 (Ror (y `mod` sz))) (noRealUnary "rotateR") (rot False sz y) x | True = shiftR x y -- for unbounded integers, rotateR is the same as shiftR in Haskell -- NB. testBit is *not* implementable on non-concrete symbolic words x `testBit` i | isConcrete x = (x .&. bit i) /= 0 | True = error $ "SBV.testBit: Called on symbolic value: " ++ show x ++ ". Use sbvTestBit instead." -- NB. popCount is *not* implementable on non-concrete symbolic words popCount x | isConcrete x = let go !c 0 = c go !c w = go (c+1) (w .&. (w-1)) in go 0 x | True = error $ "SBV.popCount: Called on symbolic value: " ++ show x ++ ". Use sbvPopCount instead." -- Since the underlying representation is just Integers, rotations has to be careful on the bit-size rot :: Bool -> Int -> Int -> Integer -> Integer rot toLeft sz amt x | sz < 2 = x | True = norm x y' `shiftL` y .|. norm (x `shiftR` y') y where (y, y') | toLeft = (amt `mod` sz, sz - y) | True = (sz - y', amt `mod` sz) norm v s = v .&. ((1 `shiftL` s) - 1) -- | Replacement for 'testBit'. Since 'testBit' requires a 'Bool' to be returned, -- we cannot implement it for symbolic words. Index 0 is the least-significant bit. sbvTestBit :: (Num a, Bits a, SymWord a) => SBV a -> Int -> SBool sbvTestBit x i = (x .&. bit i) ./= 0 -- | Replacement for 'popCount'. Since 'popCount' returns an 'Int', we cannot implement -- it for symbolic words. Here, we return an 'SWord8', which can overflow when used on -- quantities that have more than 255 bits. Currently, that's only the 'SInteger' type -- that SBV supports, all other types are safe. Even with 'SInteger', this will only -- overflow if there are at least 256-bits set in the number, and the smallest such -- number is 2^256-1, which is a pretty darn big number to worry about for practical -- purposes. In any case, we do not support 'sbvPopCount' for unbounded symbolic integers, -- as the only possible implementation wouldn't symbolically terminate. So the only overflow -- issue is with really-really large concrete 'SInteger' values. sbvPopCount :: (Num a, Bits a, SymWord a) => SBV a -> SWord8 sbvPopCount x | isReal x = error "SBV.sbvPopCount: Called on a real value" | isConcrete x = go 0 x | not (isBounded x) = error "SBV.sbvPopCount: Called on an infinite precision symbolic value" | True = sum [ite b 1 0 | b <- blastLE x] where -- concrete case go !c 0 = c go !c w = go (c+1) (w .&. (w-1)) -- | Generalization of 'setBit' based on a symbolic boolean. Note that 'setBit' and -- 'clearBit' are still available on Symbolic words, this operation comes handy when -- the condition to set/clear happens to be symbolic. setBitTo :: (Num a, Bits a, SymWord a) => SBV a -> Int -> SBool -> SBV a setBitTo x i b = ite b (setBit x i) (clearBit x i) -- | Generalization of 'shiftL', when the shift-amount is symbolic. Since Haskell's -- 'shiftL' only takes an 'Int' as the shift amount, it cannot be used when we have -- a symbolic amount to shift with. The shift amount must be an unsigned quantity. sbvShiftLeft :: (SIntegral a, SIntegral b) => SBV a -> SBV b -> SBV a sbvShiftLeft x i | isSigned i = error "sbvShiftLeft: shift amount should be unsigned" | True = select [x `shiftL` k | k <- [0 .. bitSize x - 1]] 0 i -- | Generalization of 'shiftR', when the shift-amount is symbolic. Since Haskell's -- 'shiftR' only takes an 'Int' as the shift amount, it cannot be used when we have -- a symbolic amount to shift with. The shift amount must be an unsigned quantity. -- -- NB. If the shiftee is signed, then this is an arithmetic shift; otherwise it's logical, -- following the usual Haskell convention. See 'sbvSignedShiftArithRight' for a variant -- that explicitly uses the msb as the sign bit, even for unsigned underlying types. sbvShiftRight :: (SIntegral a, SIntegral b) => SBV a -> SBV b -> SBV a sbvShiftRight x i | isSigned i = error "sbvShiftRight: shift amount should be unsigned" | True = select [x `shiftR` k | k <- [0 .. bitSize x - 1]] 0 i -- | Arithmetic shift-right with a symbolic unsigned shift amount. This is equivalent -- to 'sbvShiftRight' when the argument is signed. However, if the argument is unsigned, -- then it explicitly treats its msb as a sign-bit, and uses it as the bit that -- gets shifted in. Useful when using the underlying unsigned bit representation to implement -- custom signed operations. Note that there is no direct Haskell analogue of this function. sbvSignedShiftArithRight:: (SIntegral a, SIntegral b) => SBV a -> SBV b -> SBV a sbvSignedShiftArithRight x i | isSigned i = error "sbvSignedShiftArithRight: shift amount should be unsigned" | isSigned x = sbvShiftRight x i | True = ite (msb x) (complement (sbvShiftRight (complement x) i)) (sbvShiftRight x i) -- | Full adder. Returns the carry-out from the addition. -- -- N.B. Only works for unsigned types. Signed arguments will be rejected. fullAdder :: SIntegral a => SBV a -> SBV a -> (SBool, SBV a) fullAdder a b | isSigned a = error "fullAdder: only works on unsigned numbers" | True = (a .> s ||| b .> s, s) where s = a + b -- | Full multiplier: Returns both the high-order and the low-order bits in a tuple, -- thus fully accounting for the overflow. -- -- N.B. Only works for unsigned types. Signed arguments will be rejected. -- -- N.B. The higher-order bits are determined using a simple shift-add multiplier, -- thus involving bit-blasting. It'd be naive to expect SMT solvers to deal efficiently -- with properties involving this function, at least with the current state of the art. fullMultiplier :: SIntegral a => SBV a -> SBV a -> (SBV a, SBV a) fullMultiplier a b | isSigned a = error "fullMultiplier: only works on unsigned numbers" | True = (go (bitSize a) 0 a, a*b) where go 0 p _ = p go n p x = let (c, p') = ite (lsb x) (fullAdder p b) (false, p) (o, p'') = shiftIn c p' (_, x') = shiftIn o x in go (n-1) p'' x' shiftIn k v = (lsb v, mask .|. (v `shiftR` 1)) where mask = ite k (bit (bitSize v - 1)) 0 -- | Little-endian blasting of a word into its bits. Also see the 'FromBits' class. blastLE :: (Num a, Bits a, SymWord a) => SBV a -> [SBool] blastLE x | isReal x = error "SBV.blastLE: Called on a real value" | not (isBounded x) = error "SBV.blastLE: Called on an infinite precision value" | True = map (sbvTestBit x) [0 .. intSizeOf x - 1] -- | Big-endian blasting of a word into its bits. Also see the 'FromBits' class. blastBE :: (Num a, Bits a, SymWord a) => SBV a -> [SBool] blastBE = reverse . blastLE -- | Least significant bit of a word, always stored at index 0. lsb :: (Num a, Bits a, SymWord a) => SBV a -> SBool lsb x = sbvTestBit x 0 -- | Most significant bit of a word, always stored at the last position. msb :: (Num a, Bits a, SymWord a) => SBV a -> SBool msb x | isReal x = error "SBV.msb: Called on a real value" | not (isBounded x) = error "SBV.msb: Called on an infinite precision value" | True = sbvTestBit x (intSizeOf x - 1) -- Enum instance. These instances are suitable for use with concrete values, -- and will be less useful for symbolic values around. Note that `fromEnum` requires -- a concrete argument for obvious reasons. Other variants (succ, pred, [x..]) etc are similarly -- limited. While symbolic variants can be defined for many of these, they will just diverge -- as final sizes cannot be determined statically. instance (Show a, Bounded a, Integral a, Num a, SymWord a) => Enum (SBV a) where succ x | v == (maxBound :: a) = error $ "Enum.succ{" ++ showType x ++ "}: tried to take `succ' of maxBound" | True = fromIntegral $ v + 1 where v = enumCvt "succ" x pred x | v == (minBound :: a) = error $ "Enum.pred{" ++ showType x ++ "}: tried to take `pred' of minBound" | True = fromIntegral $ v - 1 where v = enumCvt "pred" x toEnum x | xi < fromIntegral (minBound :: a) || xi > fromIntegral (maxBound :: a) = error $ "Enum.toEnum{" ++ showType r ++ "}: " ++ show x ++ " is out-of-bounds " ++ show (minBound :: a, maxBound :: a) | True = r where xi :: Integer xi = fromIntegral x r :: SBV a r = fromIntegral x fromEnum x | r < fromIntegral (minBound :: Int) || r > fromIntegral (maxBound :: Int) = error $ "Enum.fromEnum{" ++ showType x ++ "}: value " ++ show r ++ " is outside of Int's bounds " ++ show (minBound :: Int, maxBound :: Int) | True = fromIntegral r where r :: Integer r = enumCvt "fromEnum" x enumFrom x = map fromIntegral [xi .. fromIntegral (maxBound :: a)] where xi :: Integer xi = enumCvt "enumFrom" x enumFromThen x y | yi >= xi = map fromIntegral [xi, yi .. fromIntegral (maxBound :: a)] | True = map fromIntegral [xi, yi .. fromIntegral (minBound :: a)] where xi, yi :: Integer xi = enumCvt "enumFromThen.x" x yi = enumCvt "enumFromThen.y" y enumFromThenTo x y z = map fromIntegral [xi, yi .. zi] where xi, yi, zi :: Integer xi = enumCvt "enumFromThenTo.x" x yi = enumCvt "enumFromThenTo.y" y zi = enumCvt "enumFromThenTo.z" z -- | Helper function for use in enum operations enumCvt :: (SymWord a, Integral a, Num b) => String -> SBV a -> b enumCvt w x = case unliteral x of Nothing -> error $ "Enum." ++ w ++ "{" ++ showType x ++ "}: Called on symbolic value " ++ show x Just v -> fromIntegral v -- | The 'SDivisible' class captures the essence of division. -- Unfortunately we cannot use Haskell's 'Integral' class since the 'Real' -- and 'Enum' superclasses are not implementable for symbolic bit-vectors. -- However, 'quotRem' and 'divMod' makes perfect sense, and the 'SDivisible' class captures -- this operation. One issue is how division by 0 behaves. The verification -- technology requires total functions, and there are several design choices -- here. We follow Isabelle/HOL approach of assigning the value 0 for division -- by 0. Therefore, we impose the following law: -- -- @ x `sQuotRem` 0 = (0, x) @ -- @ x `sDivMod` 0 = (0, x) @ -- -- Note that our instances implement this law even when @x@ is @0@ itself. -- -- NB. 'quot' truncates toward zero, while 'div' truncates toward negative infinity. -- -- Minimal complete definition: 'sQuotRem', 'sDivMod' class SDivisible a where sQuotRem :: a -> a -> (a, a) sDivMod :: a -> a -> (a, a) sQuot :: a -> a -> a sRem :: a -> a -> a sDiv :: a -> a -> a sMod :: a -> a -> a x `sQuot` y = fst $ x `sQuotRem` y x `sRem` y = snd $ x `sQuotRem` y x `sDiv` y = fst $ x `sDivMod` y x `sMod` y = snd $ x `sDivMod` y instance SDivisible Word64 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Int64 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Word32 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Int32 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Word16 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Int16 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Word8 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Int8 where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible Integer where sQuotRem x 0 = (0, x) sQuotRem x y = x `quotRem` y sDivMod x 0 = (0, x) sDivMod x y = x `divMod` y instance SDivisible CW where sQuotRem a b | CWInteger x <- cwVal a, CWInteger y <- cwVal b = let (r1, r2) = sQuotRem x y in (a { cwVal = CWInteger r1 }, b { cwVal = CWInteger r2 }) sQuotRem a b = error $ "SBV.sQuotRem: impossible, unexpected args received: " ++ show (a, b) sDivMod a b | CWInteger x <- cwVal a, CWInteger y <- cwVal b = let (r1, r2) = sDivMod x y in (a { cwVal = CWInteger r1 }, b { cwVal = CWInteger r2 }) sDivMod a b = error $ "SBV.sDivMod: impossible, unexpected args received: " ++ show (a, b) instance SDivisible SWord64 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SInt64 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SWord32 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SInt32 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SWord16 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SInt16 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SWord8 where sQuotRem = liftQRem sDivMod = liftDMod instance SDivisible SInt8 where sQuotRem = liftQRem sDivMod = liftDMod liftQRem :: (SymWord a, Num a, SDivisible a) => SBV a -> SBV a -> (SBV a, SBV a) liftQRem x y = ite (y .== 0) (0, x) (qr x y) where qr (SBV sgnsz (Left a)) (SBV _ (Left b)) = let (q, r) = sQuotRem a b in (SBV sgnsz (Left q), SBV sgnsz (Left r)) qr a@(SBV sgnsz _) b = (SBV sgnsz (Right (cache (mk Quot))), SBV sgnsz (Right (cache (mk Rem)))) where mk o st = do sw1 <- sbvToSW st a sw2 <- sbvToSW st b mkSymOp o st sgnsz sw1 sw2 -- Conversion from quotRem (truncate to 0) to divMod (truncate towards negative infinity) liftDMod :: (SymWord a, Num a, SDivisible a, SDivisible (SBV a)) => SBV a -> SBV a -> (SBV a, SBV a) liftDMod x y = ite (y .== 0) (0, x) $ ite (signum r .== negate (signum y)) (q-1, r+y) qr where qr@(q, r) = x `sQuotRem` y -- SInteger instance for quotRem/divMod are tricky! -- SMT-Lib only has Euclidean operations, but Haskell -- uses "truncate to 0" for quotRem, and "truncate to negative infinity" for divMod. -- So, we cannot just use the above liftings directly. instance SDivisible SInteger where sDivMod = liftDMod sQuotRem x y | not (isSymbolic x || isSymbolic y) = liftQRem x y | True = ite (y .== 0) (0, x) (qE+i, rE-i*y) where (qE, rE) = liftQRem x y -- for integers, this is euclidean due to SMTLib semantics i = ite (x .>= 0 ||| rE .== 0) 0 $ ite (y .> 0) 1 (-1) -- Quickcheck interface -- The Arbitrary instance for SFunArray returns an array initialized -- to an arbitrary element instance (SymWord b, Arbitrary b) => Arbitrary (SFunArray a b) where arbitrary = arbitrary >>= \r -> return $ SFunArray (const r) instance (SymWord a, Arbitrary a) => Arbitrary (SBV a) where arbitrary = liftM literal arbitrary -- | Symbolic choice operator, parameterized via a class -- 'select' is a total-indexing function, with the default. -- -- Minimal complete definition: 'symbolicMerge' class Mergeable a where -- | Merge two values based on the condition. This is intended -- to be a "structural" copy, walking down the values and merging -- recursively through the structure of @a@. In particular, -- symbolicMerge should *not* waste its time testing whether the -- condition might be a literal; that will be handled by 'ite' -- which should be used in all user code. In particular, any -- implementation of 'symbolicMerge' should just call 'symbolicMerge' -- recursively in the constituents of @a@, instead of 'ite'. symbolicMerge :: SBool -> a -> a -> a -- | Choose one or the other element, based on the condition. -- This is similar to 'symbolicMerge', but it has a default -- implementation that makes sure it's short-cut if the condition is concrete. -- The idea is that use symbolicMerge if you know the condition is symbolic, -- otherwise use ite, if there's a chance it might be concrete. ite :: SBool -> a -> a -> a -- | Total indexing operation. @select xs default index@ is intuitively -- the same as @xs !! index@, except it evaluates to @default@ if @index@ -- overflows select :: (SymWord b, Num b) => [a] -> a -> SBV b -> a -- default definitions ite s a b | Just t <- unliteral s = if t then a else b | True = symbolicMerge s a b -- NB. Earlier implementation of select used the binary-search trick -- on the index to chop down the search space. While that is a good trick -- in general, it doesn't work for SBV since we do not have any notion of -- "concrete" subwords: If an index is symbolic, then all its bits are -- symbolic as well. So, the binary search only pays off only if the indexed -- list is really humongous, which is not very common in general. (Also, -- for the case when the list is bit-vectors, we use SMT tables anyhow.) select xs err ind | isReal ind = error "SBV.select: unsupported real valued select/index expression" | True = walk xs ind err where walk [] _ acc = acc walk (e:es) i acc = walk es (i-1) (ite (i .== 0) e acc) -- SBV instance SymWord a => Mergeable (SBV a) where -- the strict match and checking of literal equivalence is essential below, -- as otherwise we risk hanging onto huge closures and blow stack! This is -- against the feel that merging shouldn't look at branches if the test -- expression is constant. However, it's OK to do it this way since we -- expect "ite" to be used in such cases which already checks for that. That -- is the use case of the symbolicMerge should be when the test is symbolic. -- Of course, we do not have a way of enforcing that in the user code, but -- at least our library code respects that invariant. symbolicMerge t a@(SBV{}) b@(SBV{}) | Just av <- unliteral a, Just bv <- unliteral b, rationalSBVCheck a b, av == bv = a | True = SBV k $ Right $ cache c where k = kindOf a c st = do swt <- sbvToSW st t case () of () | swt == trueSW -> sbvToSW st a -- these two cases should never be needed as we expect symbolicMerge to be () | swt == falseSW -> sbvToSW st b -- called with symbolic tests, but just in case.. () -> do {- It is tempting to record the choice of the test expression here as we branch down to the 'then' and 'else' branches. That is, when we evaluate 'a', we can make use of the fact that the test expression is True, and similarly we can use the fact that it is False when b is evaluated. In certain cases this can cut down on symbolic simulation significantly, for instance if repetitive decisions are made in a recursive loop. Unfortunately, the implementation of this idea is quite tricky, due to our sharing based implementation. As the 'then' branch is evaluated, we will create many expressions that are likely going to be "reused" when the 'else' branch is executed. But, it would be *dead wrong* to share those values, as they were "cached" under the incorrect assumptions. To wit, consider the following: foo x y = ite (y .== 0) k (k+1) where k = ite (y .== 0) x (x+1) When we reduce the 'then' branch of the first ite, we'd record the assumption that y is 0. But while reducing the 'then' branch, we'd like to share 'k', which would evaluate (correctly) to 'x' under the given assumption. When we backtrack and evaluate the 'else' branch of the first ite, we'd see 'k' is needed again, and we'd look it up from our sharing map to find (incorrectly) that its value is 'x', which was stored there under the assumption that y was 0, which no longer holds. Clearly, this is unsound. A sound implementation would have to precisely track which assumptions were active at the time expressions get shared. That is, in the above example, we should record that the value of 'k' was cached under the assumption that 'y' is 0. While sound, this approach unfortunately leads to significant loss of valid sharing when the value itself had nothing to do with the assumption itself. To wit, consider: foo x y = ite (y .== 0) k (k+1) where k = x+5 If we tracked the assumptions, we would recompute 'k' twice, since the branch assumptions would differ. Clearly, there is no need to re-compute 'k' in this case since its value is independent of y. Note that the whole SBV performance story is based on agressive sharing, and losing that would have other significant ramifications. The "proper" solution would be to track, with each shared computation, precisely which assumptions it actually *depends* on, rather than blindly recording all the assumptions present at that time. SBV's symbolic simulation engine clearly has all the info needed to do this properly, but the implementation is not straightforward at all. For each subexpression, we would need to chase down its dependencies transitively, which can require a lot of scanning of the generated program causing major slow-down; thus potentially defeating the whole purpose of sharing in the first place. Design choice: Keep it simple, and simply do not track the assumption at all. This will maximize sharing, at the cost of evaluating unreachable branches. I think the simplicity is more important at this point than efficiency. Also note that the user can avoid most such issues by properly combining if-then-else's with common conditions together. That is, the first program above should be written like this: foo x y = ite (y .== 0) x (x+2) In general, the following transformations should be done whenever possible: ite e1 (ite e1 e2 e3) e4 --> ite e1 e2 e4 ite e1 e2 (ite e1 e3 e4) --> ite e1 e2 e4 This is in accordance with the general rule-of-thumb stating conditionals should be avoided as much as possible. However, we might prefer the following: ite e1 (f e2 e4) (f e3 e5) --> f (ite e1 e2 e3) (ite e1 e4 e5) especially if this expression happens to be inside 'f's body itself (i.e., when f is recursive), since it reduces the number of recursive calls. Clearly, programming with symbolic simulation in mind is another kind of beast alltogether. -} swa <- sbvToSW st a -- evaluate 'then' branch swb <- sbvToSW st b -- evaluate 'else' branch case () of -- merge: () | swa == swb -> return swa () | swa == trueSW && swb == falseSW -> return swt () | swa == falseSW && swb == trueSW -> newExpr st k (SBVApp Not [swt]) () -> newExpr st k (SBVApp Ite [swt, swa, swb]) -- Custom version of select that translates to SMT-Lib tables at the base type of words select xs err ind | SBV _ (Left c) <- ind = case cwVal c of CWInteger i -> if i < 0 || i >= genericLength xs then err else xs `genericIndex` i _ -> error "SBV.select: unsupported real valued select/index expression" select xs err ind = SBV kElt $ Right $ cache r where kInd = kindOf ind kElt = kindOf err r st = do sws <- mapM (sbvToSW st) xs swe <- sbvToSW st err if all (== swe) sws -- off-chance that all elts are the same then return swe else do idx <- getTableIndex st kInd kElt sws swi <- sbvToSW st ind let len = length xs newExpr st kElt (SBVApp (LkUp (idx, kInd, kElt, len) swi swe) []) -- Unit instance Mergeable () where symbolicMerge _ _ _ = () select _ _ _ = () -- Mergeable instances for List/Maybe/Either/Array are useful, but can -- throw exceptions if there is no structural matching of the results -- It's a question whether we should really keep them.. -- Lists instance Mergeable a => Mergeable [a] where symbolicMerge t xs ys | lxs == lys = zipWith (symbolicMerge t) xs ys | True = error $ "SBV.Mergeable.List: No least-upper-bound for lists of differing size " ++ show (lxs, lys) where (lxs, lys) = (length xs, length ys) -- Maybe instance Mergeable a => Mergeable (Maybe a) where symbolicMerge _ Nothing Nothing = Nothing symbolicMerge t (Just a) (Just b) = Just $ symbolicMerge t a b symbolicMerge _ a b = error $ "SBV.Mergeable.Maybe: No least-upper-bound for " ++ show (k a, k b) where k Nothing = "Nothing" k _ = "Just" -- Either instance (Mergeable a, Mergeable b) => Mergeable (Either a b) where symbolicMerge t (Left a) (Left b) = Left $ symbolicMerge t a b symbolicMerge t (Right a) (Right b) = Right $ symbolicMerge t a b symbolicMerge _ a b = error $ "SBV.Mergeable.Either: No least-upper-bound for " ++ show (k a, k b) where k (Left _) = "Left" k (Right _) = "Right" -- Arrays instance (Ix a, Mergeable b) => Mergeable (Array a b) where symbolicMerge t a b | ba == bb = listArray ba (zipWith (symbolicMerge t) (elems a) (elems b)) | True = error $ "SBV.Mergeable.Array: No least-upper-bound for rangeSizes" ++ show (k ba, k bb) where [ba, bb] = map bounds [a, b] k = rangeSize -- Functions instance Mergeable b => Mergeable (a -> b) where symbolicMerge t f g x = symbolicMerge t (f x) (g x) {- Following definition, while correct, is utterly inefficient. Since the application is delayed, this hangs on to the inner list and all the impending merges, even when ind is concrete. Thus, it's much better to simply use the default definition for the function case. -} -- select xs err ind = \x -> select (map ($ x) xs) (err x) ind -- 2-Tuple instance (Mergeable a, Mergeable b) => Mergeable (a, b) where symbolicMerge t (i0, i1) (j0, j1) = (i i0 j0, i i1 j1) where i a b = symbolicMerge t a b select xs (err1, err2) ind = (select as err1 ind, select bs err2 ind) where (as, bs) = unzip xs -- 3-Tuple instance (Mergeable a, Mergeable b, Mergeable c) => Mergeable (a, b, c) where symbolicMerge t (i0, i1, i2) (j0, j1, j2) = (i i0 j0, i i1 j1, i i2 j2) where i a b = symbolicMerge t a b select xs (err1, err2, err3) ind = (select as err1 ind, select bs err2 ind, select cs err3 ind) where (as, bs, cs) = unzip3 xs -- 4-Tuple instance (Mergeable a, Mergeable b, Mergeable c, Mergeable d) => Mergeable (a, b, c, d) where symbolicMerge t (i0, i1, i2, i3) (j0, j1, j2, j3) = (i i0 j0, i i1 j1, i i2 j2, i i3 j3) where i a b = symbolicMerge t a b select xs (err1, err2, err3, err4) ind = (select as err1 ind, select bs err2 ind, select cs err3 ind, select ds err4 ind) where (as, bs, cs, ds) = unzip4 xs -- 5-Tuple instance (Mergeable a, Mergeable b, Mergeable c, Mergeable d, Mergeable e) => Mergeable (a, b, c, d, e) where symbolicMerge t (i0, i1, i2, i3, i4) (j0, j1, j2, j3, j4) = (i i0 j0, i i1 j1, i i2 j2, i i3 j3, i i4 j4) where i a b = symbolicMerge t a b select xs (err1, err2, err3, err4, err5) ind = (select as err1 ind, select bs err2 ind, select cs err3 ind, select ds err4 ind, select es err5 ind) where (as, bs, cs, ds, es) = unzip5 xs -- 6-Tuple instance (Mergeable a, Mergeable b, Mergeable c, Mergeable d, Mergeable e, Mergeable f) => Mergeable (a, b, c, d, e, f) where symbolicMerge t (i0, i1, i2, i3, i4, i5) (j0, j1, j2, j3, j4, j5) = (i i0 j0, i i1 j1, i i2 j2, i i3 j3, i i4 j4, i i5 j5) where i a b = symbolicMerge t a b select xs (err1, err2, err3, err4, err5, err6) ind = (select as err1 ind, select bs err2 ind, select cs err3 ind, select ds err4 ind, select es err5 ind, select fs err6 ind) where (as, bs, cs, ds, es, fs) = unzip6 xs -- 7-Tuple instance (Mergeable a, Mergeable b, Mergeable c, Mergeable d, Mergeable e, Mergeable f, Mergeable g) => Mergeable (a, b, c, d, e, f, g) where symbolicMerge t (i0, i1, i2, i3, i4, i5, i6) (j0, j1, j2, j3, j4, j5, j6) = (i i0 j0, i i1 j1, i i2 j2, i i3 j3, i i4 j4, i i5 j5, i i6 j6) where i a b = symbolicMerge t a b select xs (err1, err2, err3, err4, err5, err6, err7) ind = (select as err1 ind, select bs err2 ind, select cs err3 ind, select ds err4 ind, select es err5 ind, select fs err6 ind, select gs err7 ind) where (as, bs, cs, ds, es, fs, gs) = unzip7 xs -- Bounded instances instance (SymWord a, Bounded a) => Bounded (SBV a) where minBound = literal minBound maxBound = literal maxBound -- Arrays -- SArrays are both "EqSymbolic" and "Mergeable" instance EqSymbolic (SArray a b) where (SArray _ a) .== (SArray _ b) = SBV (KBounded False 1) $ Right $ cache c where c st = do ai <- uncacheAI a st bi <- uncacheAI b st newExpr st (KBounded False 1) (SBVApp (ArrEq ai bi) []) instance SymWord b => Mergeable (SArray a b) where symbolicMerge = mergeArrays -- SFunArrays are only "Mergeable". Although a brute -- force equality can be defined, any non-toy instance -- will suffer from efficiency issues; so we don't define it instance SymArray SFunArray where newArray _ = newArray_ -- the name is irrelevant in this case newArray_ mbiVal = return $ SFunArray $ const $ fromMaybe (error "Reading from an uninitialized array entry") mbiVal readArray (SFunArray f) = f resetArray (SFunArray _) a = SFunArray $ const a writeArray (SFunArray f) a b = SFunArray (\a' -> ite (a .== a') b (f a')) mergeArrays t (SFunArray f) (SFunArray g) = SFunArray (\x -> ite t (f x) (g x)) instance SymWord b => Mergeable (SFunArray a b) where symbolicMerge = mergeArrays -- | Uninterpreted constants and functions. An uninterpreted constant is -- a value that is indexed by its name. The only property the prover assumes -- about these values are that they are equivalent to themselves; i.e., (for -- functions) they return the same results when applied to same arguments. -- We support uninterpreted-functions as a general means of black-box'ing -- operations that are /irrelevant/ for the purposes of the proof; i.e., when -- the proofs can be performed without any knowledge about the function itself. -- -- Minimal complete definition: 'sbvUninterpret'. However, most instances in -- practice are already provided by SBV, so end-users should not need to define their -- own instances. class Uninterpreted a where -- | Uninterpret a value, receiving an object that can be used instead. Use this version -- when you do not need to add an axiom about this value. uninterpret :: String -> a -- | Uninterpret a value, only for the purposes of code-generation. For execution -- and verification the value is used as is. For code-generation, the alternate -- definition is used. This is useful when we want to take advantage of native -- libraries on the target languages. cgUninterpret :: String -> [String] -> a -> a -- | Most generalized form of uninterpretation, this function should not be needed -- by end-user-code, but is rather useful for the library development. sbvUninterpret :: Maybe ([String], a) -> String -> a -- minimal complete definition: 'sbvUninterpret' uninterpret = sbvUninterpret Nothing cgUninterpret nm code v = sbvUninterpret (Just (code, v)) nm -- Plain constants instance HasKind a => Uninterpreted (SBV a) where sbvUninterpret mbCgData nm | Just (_, v) <- mbCgData = v | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st v | True = do newUninterpreted st nm (SBVType [ka]) (fst `fmap` mbCgData) newExpr st ka $ SBVApp (Uninterpreted nm) [] -- Forcing an argument; this is a necessary evil to make sure all the arguments -- to an uninterpreted function are evaluated before called; the semantics of -- such functions is necessarily strict; deviating from Haskell's forceArg :: SW -> IO () forceArg (SW k n) = k `seq` n `seq` return () -- Functions of one argument instance (SymWord b, HasKind a) => Uninterpreted (SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 | Just (_, v) <- mbCgData, isConcrete arg0 = v arg0 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0) | True = do newUninterpreted st nm (SBVType [kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 mapM_ forceArg [sw0] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0] -- Functions of two arguments instance (SymWord c, SymWord b, HasKind a) => Uninterpreted (SBV c -> SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 arg1 | Just (_, v) <- mbCgData, isConcrete arg0, isConcrete arg1 = v arg0 arg1 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) kc = kindOf (undefined :: c) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0 arg1) | True = do newUninterpreted st nm (SBVType [kc, kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 sw1 <- sbvToSW st arg1 mapM_ forceArg [sw0, sw1] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0, sw1] -- Functions of three arguments instance (SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted (SBV d -> SBV c -> SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 arg1 arg2 | Just (_, v) <- mbCgData, isConcrete arg0, isConcrete arg1, isConcrete arg2 = v arg0 arg1 arg2 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) kc = kindOf (undefined :: c) kd = kindOf (undefined :: d) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0 arg1 arg2) | True = do newUninterpreted st nm (SBVType [kd, kc, kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 sw1 <- sbvToSW st arg1 sw2 <- sbvToSW st arg2 mapM_ forceArg [sw0, sw1, sw2] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0, sw1, sw2] -- Functions of four arguments instance (SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted (SBV e -> SBV d -> SBV c -> SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 arg1 arg2 arg3 | Just (_, v) <- mbCgData, isConcrete arg0, isConcrete arg1, isConcrete arg2, isConcrete arg3 = v arg0 arg1 arg2 arg3 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) kc = kindOf (undefined :: c) kd = kindOf (undefined :: d) ke = kindOf (undefined :: e) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0 arg1 arg2 arg3) | True = do newUninterpreted st nm (SBVType [ke, kd, kc, kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 sw1 <- sbvToSW st arg1 sw2 <- sbvToSW st arg2 sw3 <- sbvToSW st arg3 mapM_ forceArg [sw0, sw1, sw2, sw3] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0, sw1, sw2, sw3] -- Functions of five arguments instance (SymWord f, SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted (SBV f -> SBV e -> SBV d -> SBV c -> SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 arg1 arg2 arg3 arg4 | Just (_, v) <- mbCgData, isConcrete arg0, isConcrete arg1, isConcrete arg2, isConcrete arg3, isConcrete arg4 = v arg0 arg1 arg2 arg3 arg4 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) kc = kindOf (undefined :: c) kd = kindOf (undefined :: d) ke = kindOf (undefined :: e) kf = kindOf (undefined :: f) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0 arg1 arg2 arg3 arg4) | True = do newUninterpreted st nm (SBVType [kf, ke, kd, kc, kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 sw1 <- sbvToSW st arg1 sw2 <- sbvToSW st arg2 sw3 <- sbvToSW st arg3 sw4 <- sbvToSW st arg4 mapM_ forceArg [sw0, sw1, sw2, sw3, sw4] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0, sw1, sw2, sw3, sw4] -- Functions of six arguments instance (SymWord g, SymWord f, SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted (SBV g -> SBV f -> SBV e -> SBV d -> SBV c -> SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 arg1 arg2 arg3 arg4 arg5 | Just (_, v) <- mbCgData, isConcrete arg0, isConcrete arg1, isConcrete arg2, isConcrete arg3, isConcrete arg4, isConcrete arg5 = v arg0 arg1 arg2 arg3 arg4 arg5 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) kc = kindOf (undefined :: c) kd = kindOf (undefined :: d) ke = kindOf (undefined :: e) kf = kindOf (undefined :: f) kg = kindOf (undefined :: g) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0 arg1 arg2 arg3 arg4 arg5) | True = do newUninterpreted st nm (SBVType [kg, kf, ke, kd, kc, kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 sw1 <- sbvToSW st arg1 sw2 <- sbvToSW st arg2 sw3 <- sbvToSW st arg3 sw4 <- sbvToSW st arg4 sw5 <- sbvToSW st arg5 mapM_ forceArg [sw0, sw1, sw2, sw3, sw4, sw5] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0, sw1, sw2, sw3, sw4, sw5] -- Functions of seven arguments instance (SymWord h, SymWord g, SymWord f, SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted (SBV h -> SBV g -> SBV f -> SBV e -> SBV d -> SBV c -> SBV b -> SBV a) where sbvUninterpret mbCgData nm = f where f arg0 arg1 arg2 arg3 arg4 arg5 arg6 | Just (_, v) <- mbCgData, isConcrete arg0, isConcrete arg1, isConcrete arg2, isConcrete arg3, isConcrete arg4, isConcrete arg5, isConcrete arg6 = v arg0 arg1 arg2 arg3 arg4 arg5 arg6 | True = SBV ka $ Right $ cache result where ka = kindOf (undefined :: a) kb = kindOf (undefined :: b) kc = kindOf (undefined :: c) kd = kindOf (undefined :: d) ke = kindOf (undefined :: e) kf = kindOf (undefined :: f) kg = kindOf (undefined :: g) kh = kindOf (undefined :: h) result st | Just (_, v) <- mbCgData, inProofMode st = sbvToSW st (v arg0 arg1 arg2 arg3 arg4 arg5 arg6) | True = do newUninterpreted st nm (SBVType [kh, kg, kf, ke, kd, kc, kb, ka]) (fst `fmap` mbCgData) sw0 <- sbvToSW st arg0 sw1 <- sbvToSW st arg1 sw2 <- sbvToSW st arg2 sw3 <- sbvToSW st arg3 sw4 <- sbvToSW st arg4 sw5 <- sbvToSW st arg5 sw6 <- sbvToSW st arg6 mapM_ forceArg [sw0, sw1, sw2, sw3, sw4, sw5, sw6] newExpr st ka $ SBVApp (Uninterpreted nm) [sw0, sw1, sw2, sw3, sw4, sw5, sw6] -- Uncurried functions of two arguments instance (SymWord c, SymWord b, HasKind a) => Uninterpreted ((SBV c, SBV b) -> SBV a) where sbvUninterpret mbCgData nm = let f = sbvUninterpret (uc2 `fmap` mbCgData) nm in uncurry f where uc2 (cs, fn) = (cs, curry fn) -- Uncurried functions of three arguments instance (SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted ((SBV d, SBV c, SBV b) -> SBV a) where sbvUninterpret mbCgData nm = let f = sbvUninterpret (uc3 `fmap` mbCgData) nm in \(arg0, arg1, arg2) -> f arg0 arg1 arg2 where uc3 (cs, fn) = (cs, \a b c -> fn (a, b, c)) -- Uncurried functions of four arguments instance (SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted ((SBV e, SBV d, SBV c, SBV b) -> SBV a) where sbvUninterpret mbCgData nm = let f = sbvUninterpret (uc4 `fmap` mbCgData) nm in \(arg0, arg1, arg2, arg3) -> f arg0 arg1 arg2 arg3 where uc4 (cs, fn) = (cs, \a b c d -> fn (a, b, c, d)) -- Uncurried functions of five arguments instance (SymWord f, SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted ((SBV f, SBV e, SBV d, SBV c, SBV b) -> SBV a) where sbvUninterpret mbCgData nm = let f = sbvUninterpret (uc5 `fmap` mbCgData) nm in \(arg0, arg1, arg2, arg3, arg4) -> f arg0 arg1 arg2 arg3 arg4 where uc5 (cs, fn) = (cs, \a b c d e -> fn (a, b, c, d, e)) -- Uncurried functions of six arguments instance (SymWord g, SymWord f, SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted ((SBV g, SBV f, SBV e, SBV d, SBV c, SBV b) -> SBV a) where sbvUninterpret mbCgData nm = let f = sbvUninterpret (uc6 `fmap` mbCgData) nm in \(arg0, arg1, arg2, arg3, arg4, arg5) -> f arg0 arg1 arg2 arg3 arg4 arg5 where uc6 (cs, fn) = (cs, \a b c d e f -> fn (a, b, c, d, e, f)) -- Uncurried functions of seven arguments instance (SymWord h, SymWord g, SymWord f, SymWord e, SymWord d, SymWord c, SymWord b, HasKind a) => Uninterpreted ((SBV h, SBV g, SBV f, SBV e, SBV d, SBV c, SBV b) -> SBV a) where sbvUninterpret mbCgData nm = let f = sbvUninterpret (uc7 `fmap` mbCgData) nm in \(arg0, arg1, arg2, arg3, arg4, arg5, arg6) -> f arg0 arg1 arg2 arg3 arg4 arg5 arg6 where uc7 (cs, fn) = (cs, \a b c d e f g -> fn (a, b, c, d, e, f, g)) -- | Adding arbitrary constraints. constrain :: SBool -> Symbolic () constrain c = addConstraint Nothing c (bnot c) -- | Adding a probabilistic constraint. The 'Double' argument is the probability -- threshold. Probabilistic constraints are useful for 'genTest' and 'quickCheck' -- calls where we restrict our attention to /interesting/ parts of the input domain. pConstrain :: Double -> SBool -> Symbolic () pConstrain t c = addConstraint (Just t) c (bnot c) -- Quickcheck interface on symbolic-booleans.. instance Testable SBool where property (SBV _ (Left b)) = property (cwToBool b) property s = error $ "Cannot quick-check in the presence of uninterpreted constants! (" ++ show s ++ ")" instance Testable (Symbolic SBool) where property m = QC.whenFail (putStrLn msg) $ QC.monadicIO test where runOnce g = do (r, Result _ _ tvals _ _ cs _ _ _ _ _ cstrs _) <- runSymbolic' (Concrete g) m let cval = fromMaybe (error "Cannot quick-check in the presence of uninterpeted constants!") . (`lookup` cs) cond = all (cwToBool . cval) cstrs when (isSymbolic r) $ error $ "Cannot quick-check in the presence of uninterpreted constants! (" ++ show r ++ ")" if cond then if r `isConcretely` id then return False else do putStrLn $ complain tvals return True else runOnce g -- cstrs failed, go again test = do die <- QC.run $ newStdGen >>= runOnce when die $ fail "Falsifiable" msg = "*** SBV: See the custom counter example reported above." complain [] = "*** SBV Counter Example: Predicate contains no universally quantified variables." complain qcInfo = intercalate "\n" $ "*** SBV Counter Example:" : map ((" " ++) . info) qcInfo where maxLen = maximum (0:[length s | (s, _) <- qcInfo]) shN s = s ++ replicate (maxLen - length s) ' ' info (n, cw) = shN n ++ " = " ++ show cw -- | Explicit sharing combinator. The SBV library has internal caching/hash-consing mechanisms -- built in, based on Andy Gill's type-safe obervable sharing technique (see: <http://ittc.ku.edu/~andygill/paper.php?label=DSLExtract09>). -- However, there might be times where being explicit on the sharing can help, especially in experimental code. The 'slet' combinator -- ensures that its first argument is computed once and passed on to its continuation, explicitly indicating the intent of sharing. Most -- use cases of the SBV library should simply use Haskell's @let@ construct for this purpose. slet :: (HasKind a, HasKind b) => SBV a -> (SBV a -> SBV b) -> SBV b slet x f = SBV k $ Right $ cache r where k = kindOf (undefined `asTypeOf` f x) r st = do xsw <- sbvToSW st x let xsbv = SBV (kindOf x) (Right (cache (const (return xsw)))) res = f xsbv sbvToSW st res {-# ANN module "HLint: ignore Eta reduce" #-} {-# ANN module "HLint: ignore Reduce duplication" #-}