agda-spa/Analysis/Sign.agda

module Analysis.Sign where

open import Data.String using (String) renaming (_≟_ to _≟ˢ_)
open import Relation.Binary.PropositionalEquality using (_≡_; refl; sym; trans)
open import Relation.Nullary using (¬_; Dec; yes; no)

open import Language
open import Lattice
import Lattice.Bundles.FiniteValueMap

private module FixedHeightFiniteMap = Lattice.Bundles.FiniteValueMap.FromFiniteHeightLattice

data Sign : Set where
    + : Sign
    - : Sign
    0ˢ : Sign

-- g for siGn; s is used for strings and i is not very descriptive.
_≟ᵍ_ : IsDecidable (_≡_ {_} {Sign})
_≟ᵍ_ + + = yes refl
_≟ᵍ_ + - = no (λ ())
_≟ᵍ_ + 0ˢ = no (λ ())
_≟ᵍ_ - + = no (λ ())
_≟ᵍ_ - - = yes refl
_≟ᵍ_ - 0ˢ = no (λ ())
_≟ᵍ_ 0ˢ + = no (λ ())
_≟ᵍ_ 0ˢ - = no (λ ())
_≟ᵍ_ 0ˢ 0ˢ = yes refl

module _ (prog : Program) where
    open Program prog

    -- embelish 'sign' with a top and bottom element.
    open import Lattice.AboveBelow Sign _≡_ (record { ≈-refl = refl; ≈-sym = sym; ≈-trans = trans }) _≟ᵍ_ as AB renaming (AboveBelow to SignLattice; ≈-dec to ≈ᵍ-dec)
    -- 'sign' has no underlying lattice structure, so use the 'plain' above-below lattice.
    open AB.Plain using () renaming (finiteHeightLattice to finiteHeightLatticeᵍ-if-inhabited)


    finiteHeightLatticeᵍ = finiteHeightLatticeᵍ-if-inhabited 0ˢ

    -- The variable -> sign map is a finite value-map with keys strings. Use a bundle to avoid explicitly specifying operators.
    open FixedHeightFiniteMap String SignLattice _≟ˢ_ finiteHeightLatticeᵍ vars-Unique ≈ᵍ-dec
        renaming
            ( finiteHeightLattice to finiteHeightLatticeᵛ
            ; FiniteMap to VariableSigns
            ; _≈_ to _≈ᵛ_
            ; ≈-dec to ≈ᵛ-dec
            )

    -- Finally, the map we care about is (state -> (variables -> sign)). Bring that in.
    open FixedHeightFiniteMap State VariableSigns _≟_ finiteHeightLatticeᵛ states-Unique ≈ᵛ-dec
        renaming
            ( finiteHeightLattice to finiteHeightLatticeᵐ
            ; FiniteMap to StateVariables
            )