expressions

Expressions and Formulæ à la carte

Monthly Downloads: 11

Programming language: Haskell

License: BSD 3-clause "New" or "Revised" License

Tags: Math     Data     Logic    

Latest version: v0.5

README

expressions

λ> :set -XDataKinds -XFlexibleContexts -XKindSignatures -XOverloadedStrings -XRankNTypes -XTypeOperators
λ> import Data.Expression as E
λ> import Data.Maybe
λ> import Data.Singletons
λ> import Data.Text

defining expressions

λ> var "a" .+. var "b" :: ALia 'IntegralSort
(+ (a : int) (b : int))

λ> :{
let a, b, c, d, x, y, z, i :: forall f (s :: Sort). ( VarF :<: f, SingI s ) => IFix f s
    a = var "a"
    b = var "b"
    c = var "c"
    d = var "d"
    x = var "x"
    y = var "y"
    z = var "z"
    i = var "i"
:}

λ> select a (i :: ALia 'IntegralSort) .+. b :: ALia 'IntegralSort
(+ (select (a : array int int) (i : int)) (b : int))

parsing expressions

λ> :{
let in1, in2, in3 :: Text
    in1 = "(select (a : array int (array int bool)) (+ (b : int) 3))"
    in2 = "(forall ((x : int)) (exists ((y : int)) (and true (= (b : bool) (< x y)))))"
    in3 = "(and (forall ((x : int) (y : int)) (< x (+ y (z : int)))) (= z 3))"
:}

λ> parse in1 :: Maybe (QFALia ('ArraySort 'IntegralSort 'BooleanSort))
Just (select (a : array int (array int bool)) (+ 3 (b : int)))

λ> parse in2 :: Maybe (Lia 'BooleanSort)
Just (forall ((x : int)) (exists ((y : int)) (= (b : bool) (< (x : int) (y : int)))))

λ> parse in3 :: Maybe (Lia 'BooleanSort)
Just (and (forall ((x : int) (y : int)) (< (x : int) (+ (y : int) (z : int)))) (= (z : int) 3))

equating expressions

λ> a == (fromJust $ parse "(a : int)" :: ALia 'IntegralSort)
True

λ> a == (fromJust $ parse "(+ (a : int) 3)" :: ALia 'IntegralSort)
False

λ> a .+. cnst 1 == (fromJust $ parse "(+ (a : int) 1)" :: ALia 'IntegralSort)
True

substituting

λ> (a .*. (a .+. cnst 3) :: ALia 'IntegralSort) `substitute` (cnst 3 `for` (a .+. cnst 3))
(* (a : int) 3)

listing variables

λ> :{
let ai, bi :: Var 'IntegralSort
    ai = a
    bi = b

    qe :: Lia 'BooleanSort
    qe = forall [ai] (exists [bi] (a .+. b .=. c .+. d))
:}

λ> vars qe
[(a : int),(b : int),(c : int),(d : int)]

λ> freevars qe
[(c : int),(d : int)]

distinguish quantifier-free from quantified formulae

λ> isQuantified (z .&. (exists [b :: Var 'IntegralSort] (a .+. b .=. c .+. d)) :: Lia 'BooleanSort)
True

λ> isQuantifierFree (z .&. a .+. b .=. c .+. d :: Lia 'BooleanSort)
True

negation normal form

λ> nnf (E.not (z .&. (exists [b :: Var 'IntegralSort] (a .+. b .=. c .+. d)) :: Lia 'BooleanSort))
(or (not (z : bool)) (forall ((b : int)) (not (= (+ (a : int) (b : int)) (+ (c : int) (d : int))))))

prenex form

λ> :{
let cb :: Var 'BooleanSort
    cb = c
    di :: Var 'IntegralSort
    di = d
    qe :: Lia 'BooleanSort
    qe = forall [ai] (b .&. E.not (exists [cb] (c .->. d)) .&. forall [di] (d .+. a ./=. cnst 3))
:}

λ> prenex qe
(forall
  ((f2 : int) (f1 : int))
  (forall
    ((f0 : bool))
    (and
      (b : bool)
      (and (f0 : bool) (not (d : bool)))
      (not (= (+ (f1 : int) (f2 : int)) 3))
    )
  )
)

flat form

λ> flatten (select a (i .+. cnst 1) .=. cnst 3 :: ALia 'BooleanSort)
(exists ((k0 : int)) (and (= (k0 : int) (+ 1 (i : int))) (= (select (a : array int int) (k0 : int)) 3)))

λ> type L1 = UniversalF ('ArraySort 'IntegralSort 'IntegralSort) :+: ALiaF
λ> flatten (select (store a i (cnst 3)) (cnst 4) .=. b :: IFix L1 'BooleanSort)
(forall
  ((k0 : array int int))
  (or
    (not (= (k0 : array int int) (store (a : array int int) (i : int) 3)))
    (= (select (k0 : array int int) 4) (b : int))
  )
)

λ> type L2 = ExistentialF ('ArraySort 'IntegralSort 'IntegralSort) :+: L1
λ> flatten (select (store a i (cnst 3)) (cnst 4) .=. b :: IFix L2 'BooleanSort)
(exists
  ((k0 : array int int))
  (and
    (= (k0 : array int int) (store (a : array int int) (i : int) 3))
    (= (select (k0 : array int int) 4) (b : int))
  )
)

replace store terms using axiom

λ> unstore (select (store a i (cnst 3)) (cnst 4) .=. b :: IFix L2 'BooleanSort)
(exists
  ((k0 : array int int))
  (and
    (and
      (= (select (k0 : array int int) (i : int)) 3)
      (forall
        ((m0 : int))
          (or
            (= (i : int) (m0 : int))
            (= (select (k0 : array int int) (m0 : int)) (select (a : array int int) (m0 : int)))
          )
      )
    )
    (= (select (k0 : array int int) 4) (b : int))
  )
)

---

See documentation.