{- |

Module : $Header$

Description : Some additional helper functions

Copyright : (c) Dominik Luecke, Uni Bremen 2007

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

Maintainer : luecke@informatik.uni-bremen.de

Stability : experimental

Portability : non-portable (imports Logic.Logic)

Some helper functions for Propositional Logic

-}

{-

Ref.

http://en.wikipedia.org/wiki/Propositional_logic

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.Tools

( flatten -- "flattening" of specs

, flattenDis -- "flattening" of disjunctions

, negateFormula

) where

import Common.Id

import Propositional.AS_BASIC_Propositional

-- | the flatten functions use associtivity to "flatten" the syntax

-- | tree of the formulae

-- | flatten \"flattens\" formulae under the assumption of the

-- | semantics of basic specs, this means that we put each

-- | \"clause\" into a single formula for CNF we really will obtain

-- | clauses

flatten :: FORMULA -> [FORMULA]

flatten f = case f of

Conjunction fs _ -> concatMap flatten fs

_ -> [f]

-- | "flattening" for disjunctions

flattenDis :: FORMULA -> [FORMULA]

flattenDis f = case f of

Disjunction fs _ -> concatMap flattenDis fs

_ -> [f]

-- | negate a formula

negateFormula :: FORMULA -> FORMULA

negateFormula f = case f of

False_atom ps -> True_atom ps

True_atom ps -> False_atom ps

Negation nf _ -> nf

_ -> Negation f nullRange