Substitutor.h

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/*
 * Substitutor.h
 *
 * Copyright (C) 2015 OpenCog Foundation
 *
 * Author: William Ma <https://github.com/williampma>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License v3 as
 * published by the Free Software Foundation and including the exceptions
 * at http://opencog.org/wiki/Licenses
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program; if not, write to:
 * Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#ifndef _OPENCOG_SUBSTITUTOR
#define _OPENCOG_SUBSTITUTOR


#include <opencog/atomspace/AtomSpace.h>


namespace opencog
{

class Substitutor
{
private:
    AtomSpace *_as;
    const std::map<Handle, Handle> *_vmap;

    Handle walk_tree(const Handle& expr)
    {
        std::map<Handle,Handle>::const_iterator it = _vmap->find(expr);
        if (_vmap->end() != it )
            return it->second;

        LinkPtr lexpr(LinkCast(expr));

        // if not a link, and not mapped, just return it
        if (not lexpr)
            return Handle(expr);

        HandleSeq oset_results;
        for (const Handle& h : lexpr->getOutgoingSet())
        {
            Handle hg = walk_tree(h);
            oset_results.push_back(hg);
        }

        // Now create a duplicate link with the substitution
        return Handle(createLink(expr->getType(), oset_results, expr->getTruthValue()));
    }

public:
    Substitutor(AtomSpace* as) : _as(as) {}

    Handle substitute(const Handle& expr, const std::map<Handle, Handle> &vars)
    {
        // throw, not assert, because this is a user error ...
        if (Handle::UNDEFINED == expr)
            throw InvalidParamException(TRACE_INFO,
                "Asked to substitute a null expression");

        _vmap = &vars;

        // The returned handle is not yet in the atomspace. Add it now.
        Handle hn = walk_tree(expr);
        if (NULL != hn)
            return _as->add_atom(hn);
        return hn;
    }
};

}

#endif // _OPENCOG_SUBSTITUTOR