{-# LANGUAGE DeriveDataTypeable #-}

{- |

Module : ./Propositional/Morphism.hs

Description : Morphisms in 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 morphisms for propositional logic

copied to "Temporal.Morphism"

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 Propositional.Morphism

( Morphism (..) -- datatype for Morphisms

, pretty -- pretty printing

, idMor -- identity morphism

, isLegalMorphism -- check if morhpism is ok

, composeMor -- composition

, inclusionMap -- inclusion map

, mapSentence -- map of sentences

, mapSentenceH -- map of sentences, without Result type

, applyMap -- application function for maps

, applyMorphism -- application function for morphism

, morphismUnion

) where

import Data.Data

import qualified Data.Map as Map

import qualified Data.Set as Set

import Propositional.Sign as Sign

import qualified Propositional.AS_BASIC_Propositional as AS_BASIC

import Common.Id as Id

import Common.Result

import Common.Doc

import Common.DocUtils

import qualified Common.Result as Result

import Control.Monad (unless)

{- | The datatype for morphisms in propositional logic as

maps of sets -}

data Morphism = Morphism

{ source :: Sign

, target :: Sign

, propMap :: Map.Map Id Id

} deriving (Show, Eq, Ord, Typeable, Data)

instance Pretty Morphism where

pretty = printMorphism

-- | Constructs an id-morphism

idMor :: Sign -> Morphism

idMor a = inclusionMap a a

-- | Determines whether a morphism is valid

isLegalMorphism :: Morphism -> Result ()

isLegalMorphism pmor =

let psource = items $ source pmor

ptarget = items $ target pmor

pdom = Map.keysSet $ propMap pmor

pcodom = Set.map (applyMorphism pmor) psource

in unless (Set.isSubsetOf pcodom ptarget && Set.isSubsetOf pdom psource) $

fail "illegal Propositional morphism"

-- | Application funtion for morphisms

applyMorphism :: Morphism -> Id -> Id

applyMorphism mor idt = Map.findWithDefault idt idt $ propMap mor

-- | Application function for propMaps

applyMap :: Map.Map Id Id -> Id -> Id

applyMap pmap idt = Map.findWithDefault idt idt pmap

-- | Composition of morphisms in propositional Logic

composeMor :: Morphism -> Morphism -> Result Morphism

composeMor f g =

let fSource = source f

gTarget = target g

fMap = propMap f

gMap = propMap g

in return Morphism

{ source = fSource

, target = gTarget

, propMap = if Map.null gMap then fMap else

Set.fold ( \ i -> let j = applyMap gMap (applyMap fMap i) in

if i == j then id else Map.insert i j)

Map.empty $ items fSource }

-- | Pretty printing for Morphisms

printMorphism :: Morphism -> Doc

printMorphism m = pretty (source m) <> text "-->" <> pretty (target m)

<> vcat (map ( \ (x, y) -> lparen <> pretty x <> text ","

<> pretty y <> rparen) $ Map.assocs $ propMap m)

-- | Inclusion map of a subsig into a supersig

inclusionMap :: Sign.Sign -> Sign.Sign -> Morphism

inclusionMap s1 s2 = Morphism

{ source = s1

, target = s2

, propMap = Map.empty }

{- | sentence translation along signature morphism

here just the renaming of formulae -}

mapSentence :: Morphism -> AS_BASIC.FORMULA -> Result.Result AS_BASIC.FORMULA

mapSentence mor = return . mapSentenceH mor

mapSentenceH :: Morphism -> AS_BASIC.FORMULA -> AS_BASIC.FORMULA

mapSentenceH mor frm = case frm of

AS_BASIC.Negation form rn -> AS_BASIC.Negation (mapSentenceH mor form) rn

AS_BASIC.Conjunction form rn ->

AS_BASIC.Conjunction (map (mapSentenceH mor) form) rn

AS_BASIC.Disjunction form rn ->

AS_BASIC.Disjunction (map (mapSentenceH mor) form) rn

AS_BASIC.Implication form1 form2 rn -> AS_BASIC.Implication

(mapSentenceH mor form1) (mapSentenceH mor form2) rn

AS_BASIC.Equivalence form1 form2 rn -> AS_BASIC.Equivalence

(mapSentenceH mor form1) (mapSentenceH mor form2) rn

AS_BASIC.True_atom rn -> AS_BASIC.True_atom rn

AS_BASIC.False_atom rn -> AS_BASIC.False_atom rn

AS_BASIC.Predication predH -> AS_BASIC.Predication

$ id2SimpleId $ applyMorphism mor $ Id.simpleIdToId predH

morphismUnion :: Morphism -> Morphism -> Result.Result Morphism

morphismUnion mor1 mor2 =

let pmap1 = propMap mor1

pmap2 = propMap mor2

p1 = source mor1

p2 = source mor2

up1 = Set.difference (items p1) $ Map.keysSet pmap1

up2 = Set.difference (items p2) $ Map.keysSet pmap2

(pds, pmap) = foldr ( \ (i, j) (ds, m) -> case Map.lookup i m of

Nothing -> (ds, Map.insert i j m)

Just k -> if j == k then (ds, m) else

(Diag Error

("incompatible mapping of prop " ++ showId i " to "

++ showId j " and " ++ showId k "")

nullRange : ds, m)) ([], pmap1)

(Map.toList pmap2 ++ map (\ a -> (a, a))

(Set.toList $ Set.union up1 up2))

in if null pds then return Morphism

{ source = unite p1 p2

, target = unite (target mor1) $ target mor2

, propMap = pmap } else Result pds Nothing