{- |

Module : $Header$

Description : Free variables; getting rid of superfluous quantifications

Copyright : (c) Till Mossakowski and Uni Bremen 2002-2005

License : similar to LGPL, see HetCATS/LICENSE.txt or LIZENZ.txt

Maintainer : Christian.Maeder@dfki.de

Stability : provisional

Portability : portable

Free variables; getting rid of superfluous quantifications

-}

module CASL.Quantification where

import CASL.AS_Basic_CASL

import CASL.Fold

import Common.Id

import Data.List

import qualified Data.Set as Set

flatVAR_DECLs :: [VAR_DECL] -> [(VAR, SORT)]

flatVAR_DECLs = concatMap (\ (Var_decl vs s _) -> map (\ v -> (v, s)) vs)

type VarSet = Set.Set (VAR, SORT)

freeVarsRecord :: (f -> VarSet) -> Record f VarSet VarSet

freeVarsRecord mf = (constRecord mf Set.unions Set.empty)

{ foldQual_var = \ _ v s _ -> Set.singleton (v, s)

, foldQuantification = \ _ _ vdecl phiVars _ ->

Set.difference phiVars $

Set.fromList $ flatVAR_DECLs vdecl

}

freeVars :: FORMULA f -> VarSet

freeVars = foldFormula $ freeVarsRecord $ const Set.empty

-- | quantify only over free variables (and only once)

effQuantify :: QUANTIFIER -> [VAR_DECL] -> FORMULA f -> Range -> FORMULA f

effQuantify q vdecls phi pos =

let flatVAR_DECL (Var_decl vs s ps) =

map (\v -> Var_decl [v] s ps) vs

joinVarDecl = foldr1 ( \ (Var_decl v1 s1 ps) (Var_decl v2 _s2 _) ->

Var_decl (v1 ++ v2) s1 ps)

cleanDecls =

map joinVarDecl . myGroup . reverse . myNub . reverse .

concatMap flatVAR_DECL

myGroup = groupBy ( \ (Var_decl _ s1 _) (Var_decl _ s2 _) -> s1 == s2)

myNub = nubBy ( \ (Var_decl v1 _ _) (Var_decl v2 _ _) -> v1 == v2)

in case q of

Unique_existential -> Quantification q (cleanDecls vdecls) phi pos

_ -> let fvs = freeVars phi

filterVAR_DECL (Var_decl vs s ps) =

Var_decl (filter (\ v -> Set.member (v,s) fvs) vs) s ps

newDecls = cleanDecls $ map filterVAR_DECL vdecls

in if null newDecls then phi else

Quantification q newDecls phi pos

stripRecord :: (f -> f) -> Record f (FORMULA f) (TERM f)

stripRecord mf = (mapRecord mf)

{ foldQuantification = \ _ quant vdecl newF pos ->

let qF = effQuantify quant vdecl newF pos in

case newF of

Quantification quant2 vd2 f2 ps ->

if quant == quant2 then

effQuantify quant (vdecl ++ vd2) f2 (pos `appRange` ps)

else qF

_ -> qF

}

-- | strip superfluous (or nested) quantifications

stripQuant :: FORMULA f -> FORMULA f

stripQuant = foldFormula $ stripRecord id

-- | strip all universal quantifications

stripAllQuant :: FORMULA f -> FORMULA f

stripAllQuant (Quantification Universal _ phi _) =

stripAllQuant phi

stripAllQuant phi = phi