{- |

Module : $Header$

Description : Signature for propositional logic

Copyright : (c) Dominik Luecke, Uni Bremen 2007

License : GPLv2 or higher, see LICENSE.txt

Maintainer : luecke@informatik.uni-bremen.de

Stability : experimental

Portability : portable

Definition of signatures for propositional logic

Ref.

Till Mossakowski, Joseph Goguen, Razvan Diaconescu, Andrzej Tarlecki.

What is a Logic?.

In Jean-Yves Beziau (Ed.), Logica Universalis, pp. 113-@133. Birkhaeuser.

2005.

-}

module Temporal.Sign

(Sign (..) -- Propositional Signatures

, pretty -- pretty printing

, isLegalSignature -- is a signature ok?

, addToSig -- adds an id to the given Signature

, unite -- union of sigantures

, emptySig -- empty signature

, isSubSigOf -- is subsiganture?

, sigDiff -- Difference of Signatures

, sigUnion -- Union for Logic.Logic

) where

import qualified Data.Set as Set

import Common.Id

import Common.Result

import Common.Doc

import Common.DocUtils

{- | Datatype for propositional Signatures

Signatures are just sets -}

newtype Sign = Sign {items :: Set.Set Id} deriving (Eq, Ord, Show)

instance Pretty Sign where

pretty = printSign

{- | determines whether a signature is vaild

all sets are ok, so glued to true -}

isLegalSignature :: Sign -> Bool

isLegalSignature _ = True

-- | pretty printing for Signatures

printSign :: Sign -> Doc

printSign s =

hsep [text "prop", sepByCommas $ map pretty $ Set.toList $ items s]

-- | Adds an Id to the signature

addToSig :: Sign -> Id -> Sign

addToSig sig tok = Sign {items = Set.insert tok $ items sig}

-- | Union of signatures

unite :: Sign -> Sign -> Sign

unite sig1 sig2 = Sign {items = Set.union (items sig1) $ items sig2}

-- | The empty signature

emptySig :: Sign

emptySig = Sign {items = Set.empty}

-- | Determines if sig1 is subsignature of sig2

isSubSigOf :: Sign -> Sign -> Bool

isSubSigOf sig1 sig2 = Set.isSubsetOf (items sig1) $ items sig2

-- | difference of Signatures

sigDiff :: Sign -> Sign -> Sign

sigDiff sig1 sig2 = Sign {items = Set.difference (items sig1) $ items sig2}

{- | union of Signatures

or do I have to care about more things here? -}

sigUnion :: Sign -> Sign -> Result Sign

sigUnion s1 s2 = Result [Diag Debug "All fine sigUnion" nullRange]

$ Just $ unite s1 s2