Changes in src/Tuples/TupleAssignment.cc [6eb8948:906e24d]

File:

• src/Tuples/TupleAssignment.cc (modified) (2 diffs)

src/Tuples/TupleAssignment.cc

@@ -18 +18 @@
 #include "ResolvExpr/typeops.h"
 #include "SynTree/Expression.h"
-#include "SynTree/Initializer.h"
-#include "Tuples.h"
+#include "TupleAssignment.h"
 #include "Common/SemanticError.h"
 
@@ -28 +27 @@
 #include <cassert>
 #include <set>
-#include <unordered_set>
 
 namespace Tuples {
-        class TupleAssignSpotter {
-          public:
-                // dispatcher for Tuple (multiple and mass) assignment operations
-                TupleAssignSpotter( ResolvExpr::AlternativeFinder & );
-                void spot( UntypedExpr * expr, std::list<ResolvExpr::AltList> &possibilities );
-
-          private:
-                void match();
-                // records for assignment generation
-                struct Options {
-                        void print( std::ostream & );
-                        int size() const { return options.size(); }
-                        bool empty() const { return options.empty(); }
-                        typedef std::list< ResolvExpr::AltList >::iterator iterator;
-                        iterator begin() { return options.begin(); }
-                        iterator end() { return options.end(); }
-
-                        std::list< ResolvExpr::AltList > options;
-                };
-
-                struct Matcher {
-                  public:
-                        Matcher( TupleAssignSpotter &spotter, Expression *_lhs, Expression *_rhs );
-                        virtual ~Matcher() {}
-                        virtual void match( std::list< Expression * > &out ) = 0;
-                        std::list< Expression * > lhs, rhs;
-                        TupleAssignSpotter &spotter;
-                        std::list< ObjectDecl * > tmpDecls;
-                };
-
-                struct MassAssignMatcher : public Matcher {
-                  public:
-                        MassAssignMatcher( TupleAssignSpotter &spotter, Expression *lhs, Expression *rhs ) : Matcher( spotter, lhs, rhs ) {
-                                this->rhs.push_back( rhs );
+        TupleAssignSpotter::TupleAssignSpotter( ResolvExpr::AlternativeFinder *f = 0 )
+                : currentFinder(f), matcher(0), hasMatched( false ) {}
+
+        bool TupleAssignSpotter::pointsToTuple( Expression *expr ) {
+                // also check for function returning tuple of reference types
+                if (AddressExpr *addr = dynamic_cast<AddressExpr *>(expr) )
+                        if ( isTuple(addr->get_arg() ) )
+                                return true;
+                return false;
+        }
+
+        bool TupleAssignSpotter::isTupleVar( DeclarationWithType *decl ) {
+                if ( dynamic_cast<TupleType *>(decl->get_type()) )
+                        return true;
+                return false;
+        }
+
+        bool TupleAssignSpotter::isTuple( Expression *expr, bool isRight ) {
+                // true if `expr' is an expression returning a tuple: tuple, tuple variable or MRV function
+                if ( ! expr ) return false;
+
+                if ( dynamic_cast<TupleExpr *>(expr) )
+                        return true;
+                else if ( VariableExpr *var = dynamic_cast<VariableExpr *>(expr) ) {
+                        if ( isTupleVar(var->get_var()) )
+                                return true;
+                }
+
+                return false;
+        }
+
+        bool TupleAssignSpotter::match() {
+                assert ( matcher != 0 );
+
+                std::list< Expression * > new_assigns;
+                if ( ! matcher->match(new_assigns) )
+                        return false;
+
+                if ( new_assigns.empty() ) return false;
+                /*return */matcher->solve( new_assigns );
+                if ( dynamic_cast<TupleAssignSpotter::MultipleAssignMatcher *>( matcher ) ) {
+                        // now resolve new assignments
+                        std::list< Expression * > solved_assigns;
+                        ResolvExpr::AltList solved_alts;
+                        assert( currentFinder != 0 );
+
+                        ResolvExpr::AltList current;
+                        for ( std::list< Expression * >::iterator i = new_assigns.begin(); i != new_assigns.end(); ++i ) {
+                                //try {
+                                ResolvExpr::AlternativeFinder finder( currentFinder->get_indexer(), currentFinder->get_environ() );
+                                finder.findWithAdjustment(*i);
+                                // prune expressions that don't coincide with
+                                ResolvExpr::AltList alts = finder.get_alternatives();
+                                assert( alts.size() == 1 );
+                                assert(alts.front().expr != 0 );
+                                current.push_back( finder.get_alternatives().front() );
+                                solved_assigns.push_back( alts.front().expr->clone() );
+                                //solved_assigns.back()->print(std::cerr);
+                                /*} catch( ... ) {
+                                  continue; // no reasonable alternative found
+                                  }*/
                         }
-                        virtual void match( std::list< Expression * > &out );
-                };
-
-                struct MultipleAssignMatcher : public Matcher {
-                  public:
-                        MultipleAssignMatcher( TupleAssignSpotter &spot, Expression *lhs, Expression *rhs );
-                        virtual void match( std::list< Expression * > &out );
-                };
-
-                ResolvExpr::AlternativeFinder &currentFinder;
-                // Expression *rhs, *lhs;
-                Matcher *matcher = nullptr;
-                Options options;
-        };
-
-        bool isTupleVar( DeclarationWithType *decl ) {
-                return dynamic_cast< TupleType * >( decl->get_type() );
-        }
-
-        /// true if expr is an expression of tuple type, i.e. a tuple expression, tuple variable, or MRV (multiple-return-value) function
-        bool isTuple( Expression *expr ) {
-                if ( ! expr ) return false;
-
-                // xxx - used to include cast to varExpr and call to isTupleVar, but this doesn't seem like it should be necessary
-                return dynamic_cast<TupleExpr *>(expr) || expr->get_results().size() > 1;
-        }
-
-        bool pointsToTuple( Expression *expr ) {
-                // also check for function returning tuple of reference types
-                if ( AddressExpr *addr = dynamic_cast< AddressExpr * >( expr) ) {
-                        return isTuple( addr->get_arg() );
-                }
+                        options.add_option( current );
+
+                        return true;
+                } else { // mass assignment
+                        //if ( new_assigns.empty() ) return false;
+                        std::list< Expression * > solved_assigns;
+                        ResolvExpr::AltList solved_alts;
+                        assert( currentFinder != 0 );
+
+                        ResolvExpr::AltList current;
+                        if ( optMass.empty() ) {
+                                for ( std::list< Expression * >::size_type i = 0; i != new_assigns.size(); ++i )
+                                        optMass.push_back( ResolvExpr::AltList() );
+                        }
+                        int cnt = 0;
+                        for ( std::list< Expression * >::iterator i = new_assigns.begin(); i != new_assigns.end(); ++i, cnt++ ) {
+
+                                ResolvExpr::AlternativeFinder finder( currentFinder->get_indexer(), currentFinder->get_environ() );
+                                finder.findWithAdjustment(*i);
+                                ResolvExpr::AltList alts = finder.get_alternatives();
+                                assert( alts.size() == 1 );
+                                assert(alts.front().expr != 0 );
+                                current.push_back( finder.get_alternatives().front() );
+                                optMass[cnt].push_back( finder.get_alternatives().front() );
+                                solved_assigns.push_back( alts.front().expr->clone() );
+                        }
+
+                        return true;
+                }
+
                 return false;
         }
 
-        bool isTupleExpr( Expression *expr ) {
-                return expr->get_results().size() > 1;
-        }
-
-        void handleTupleAssignment( ResolvExpr::AlternativeFinder & currentFinder, UntypedExpr * expr, std::list<ResolvExpr::AltList> &possibilities ) {
-                TupleAssignSpotter spotter( currentFinder );
-                spotter.spot( expr, possibilities );
-        }
-
-        TupleAssignSpotter::TupleAssignSpotter( ResolvExpr::AlternativeFinder &f )
-                : currentFinder(f) {}
-
-        void TupleAssignSpotter::spot( UntypedExpr * expr, std::list<ResolvExpr::AltList> &possibilities ) {
+        bool TupleAssignSpotter::isMVR( Expression *expr ) {
+                return isTuple( expr );
+        }
+
+        bool TupleAssignSpotter::isTupleAssignment( UntypedExpr * expr, std::list<ResolvExpr::AltList> &possibilities ) {
                 if (  NameExpr *assgnop = dynamic_cast< NameExpr * >(expr->get_function()) ) {
+
                         if ( assgnop->get_name() == std::string("?=?") ) {
+
                                 for ( std::list<ResolvExpr::AltList>::iterator ali = possibilities.begin(); ali != possibilities.end(); ++ali ) {
                                         assert( ali->size() == 2 );
-                                        ResolvExpr::Alternative op1 = ali->front(), op2 = ali->back();
-
-                                        MultipleAssignMatcher multiMatcher( *this, op1.expr, op2.expr );
-                                        MassAssignMatcher massMatcher( *this, op1.expr, op2.expr );
+                                        ResolvExpr::AltList::iterator opit = ali->begin();
+                                        ResolvExpr::Alternative op1 = *opit, op2 = *(++opit);
+
                                         if ( pointsToTuple(op1.expr) ) { // also handles tuple vars
-                                                if ( isTuple( op2.expr ) ) {
-                                                        matcher = &multiMatcher;
-                                                } else {
+                                                if ( isTuple( op2.expr, true ) )
+                                                        matcher = new MultipleAssignMatcher(op1.expr, op2.expr);
+                                                else if ( isMVR( op2.expr ) ) {
+                                                        // handle MVR differently
+                                                } else
                                                         // mass assignment
-                                                        matcher = &massMatcher;
+                                                        matcher = new MassAssignMatcher(op1.expr, op2.expr);
+
+                                                std::list< ResolvExpr::AltList > options;
+                                                if ( match() )
+                                                        /*
+                                                          if ( hasMatched ) {
+                                                          // throw SemanticError("Ambiguous tuple assignment");
+                                                          } else {*/
+                                                        // Matched for the first time
+                                                        hasMatched = true;
+                                                /*} */
+                                        } /* else if ( isTuple( op2 ) )
+                                                 throw SemanticError("Inapplicable tuple assignment.");
+                                          */
+                                }
+
+                                if ( hasMatched ) {
+                                        if ( dynamic_cast<TupleAssignSpotter::MultipleAssignMatcher *>( matcher ) ) {
+                                                //options.print( std::cerr );
+                                                std::list< ResolvExpr::AltList >best = options.get_best();
+                                                if ( best.size() == 1 ) {
+                                                        std::list<Expression *> solved_assigns;
+                                                        for ( ResolvExpr::AltList::iterator i = best.front().begin(); i != best.front().end(); ++i ) {
+                                                                solved_assigns.push_back( i->expr );
+                                                        }
+                                                        /* assigning cost zero? */
+                                                        currentFinder->get_alternatives().push_front( ResolvExpr::Alternative(new SolvedTupleExpr(solved_assigns/*, SolvedTupleExpr::MULTIPLE*/), currentFinder->get_environ(), ResolvExpr::Cost() ) );
                                                 }
-                                                match();
-                                        } else if ( isTuple( op2.expr ) ) {
-                                                throw SemanticError("Cannot assign a tuple value into a non-tuple lvalue.", expr);
+                                        } else {
+                                                assert( ! optMass.empty() );
+                                                ResolvExpr::AltList winners;
+                                                for ( std::vector< ResolvExpr::AltList >::iterator i = optMass.begin(); i != optMass.end(); ++i )
+                                                        findMinCostAlt( i->begin(), i->end(), back_inserter(winners) );
+
+                                                std::list< Expression *> solved_assigns;
+                                                for ( ResolvExpr::AltList::iterator i = winners.begin(); i != winners.end(); ++i )
+                                                        solved_assigns.push_back( i->expr );
+                                                currentFinder->get_alternatives().push_front( ResolvExpr::Alternative(new SolvedTupleExpr(solved_assigns/*, SolvedTupleExpr::MASS*/), currentFinder->get_environ(), ResolvExpr::Cost() ) );
                                         }
                                 }
                         }
                 }
-        }
-
-        void TupleAssignSpotter::match() {
-                assert ( matcher != 0 );
-
-                std::list< Expression * > new_assigns;
-                matcher->match( new_assigns );
-
-                if ( new_assigns.empty() ) return;
-                ResolvExpr::AltList current;
-                // now resolve new assignments
-                for ( std::list< Expression * >::iterator i = new_assigns.begin(); i != new_assigns.end(); ++i ) {
-                        ResolvExpr::AlternativeFinder finder( currentFinder.get_indexer(), currentFinder.get_environ() );
-                        finder.findWithAdjustment(*i);
-                        // prune expressions that don't coincide with
-                        ResolvExpr::AltList alts = finder.get_alternatives();
-                        assert( alts.size() == 1 );
-                        assert( alts.front().expr != 0 );
-                        current.push_back( alts.front() );
-                }
-
-                // extract expressions from the assignment alternatives to produce a list of assignments that
-                // together form a single alternative
-                std::list< Expression *> solved_assigns;
-                for ( ResolvExpr::Alternative & alt : current ) {
-                        solved_assigns.push_back( alt.expr->clone() );
-                }
-                // xxx - need to do this??
-                // TypeEnvironment compositeEnv;
-                // simpleCombineEnvironments( i->begin(), i->end(), compositeEnv );
-                currentFinder.get_alternatives().push_front( ResolvExpr::Alternative(new TupleAssignExpr(solved_assigns, matcher->tmpDecls), currentFinder.get_environ(), ResolvExpr::sumCost( current ) ) );
-        }
-
-        TupleAssignSpotter::Matcher::Matcher( TupleAssignSpotter &spotter, Expression *lhs, Expression *rhs ) : spotter(spotter) {
-                // xxx - shouldn't need to be &<tuple-expr>, just &<lvalue-tuple-type>
-                if (AddressExpr *addr = dynamic_cast<AddressExpr *>(lhs) )
+                return hasMatched;
+        }
+
+        void TupleAssignSpotter::Matcher::init( Expression *_lhs, Expression *_rhs ) {
+                lhs.clear();
+                if (AddressExpr *addr = dynamic_cast<AddressExpr *>(_lhs) )
                         if ( TupleExpr *tuple = dynamic_cast<TupleExpr *>(addr->get_arg()) )
-                                std::copy( tuple->get_exprs().begin(), tuple->get_exprs().end(), back_inserter(this->lhs) );
-        }
-
-        TupleAssignSpotter::MultipleAssignMatcher::MultipleAssignMatcher( TupleAssignSpotter &spotter, Expression *lhs, Expression *rhs ) : Matcher( spotter, lhs, rhs ) {
-
-                if ( TupleExpr *tuple = dynamic_cast<TupleExpr *>(rhs) )
-                        std::copy( tuple->get_exprs().begin(), tuple->get_exprs().end(), back_inserter(this->rhs) );
-        }
-
-        UntypedExpr * createAssgn( ObjectDecl *left, ObjectDecl *right ) {
-                assert( left && right );
-                std::list< Expression * > args;
-                args.push_back( new AddressExpr( new UntypedExpr( new NameExpr("*?"), std::list< Expression * >{ new VariableExpr( left ) } ) ) );
-                args.push_back( new VariableExpr( right ) );
-                return new UntypedExpr( new NameExpr( "?=?" ), args );
-        }
-
-        ObjectDecl * newObject( UniqueName & namer, Expression * expr ) {
-                Type * type;
-                assert( expr->get_results().size() >= 1 );
-                if ( expr->get_results().size() > 1 ) {
-                        TupleType * tt = new TupleType( Type::Qualifiers() );
-                        cloneAll( expr->get_results(), tt->get_types() );
-                        type = tt;
-                } else {
-                        type = expr->get_results().front()->clone();
-                }
-                return new ObjectDecl( namer.newName(), DeclarationNode::NoStorageClass, LinkageSpec::Cforall, nullptr, type, new SingleInit( expr->clone() ) );
-        }
-
-        void TupleAssignSpotter::MassAssignMatcher::match( std::list< Expression * > &out ) {
-                static UniqueName lhsNamer( "__massassign_L" );
-                static UniqueName rhsNamer( "__massassign_R" );
-                assert ( ! lhs.empty() && rhs.size() == 1);
-
-                ObjectDecl * rtmp = newObject( rhsNamer, rhs.front() );
-                for ( Expression * l : lhs ) {
-                        ObjectDecl * ltmp = newObject( lhsNamer, new AddressExpr( l ) );
-                        out.push_back( createAssgn( ltmp, rtmp ) );
-                        tmpDecls.push_back( ltmp );
-                }
-                tmpDecls.push_back( rtmp );
-        }
-
-        void TupleAssignSpotter::MultipleAssignMatcher::match( std::list< Expression * > &out ) {
-                static UniqueName lhsNamer( "__multassign_L" );
-                static UniqueName rhsNamer( "__multassign_R" );
-                // xxx - need more complicated matching?
+                                std::copy( tuple->get_exprs().begin(), tuple->get_exprs().end(), back_inserter(lhs) );
+
+                rhs.clear();
+        }
+
+        TupleAssignSpotter::Matcher::Matcher( /*TupleAssignSpotter &spot,*/ Expression *_lhs, Expression *_rhs ) /*: own_spotter(spot) */{
+                init(_lhs,_rhs);
+        }
+
+        TupleAssignSpotter::MultipleAssignMatcher::MultipleAssignMatcher( Expression *_lhs, Expression *_rhs )/* : own_spotter(spot) */{
+                init(_lhs,_rhs);
+
+                if ( TupleExpr *tuple = dynamic_cast<TupleExpr *>(_rhs) )
+                        std::copy( tuple->get_exprs().begin(), tuple->get_exprs().end(), back_inserter(rhs) );
+        }
+
+        UntypedExpr *TupleAssignSpotter::Matcher::createAssgn( Expression *left, Expression *right ) {
+                if ( left && right ) {
+                        std::list< Expression * > args;
+                        args.push_back(new AddressExpr(left->clone()));  args.push_back(right->clone());
+                        return new UntypedExpr(new NameExpr("?=?"), args);
+                } else
+                        throw 0; // xxx - diagnose the problem
+        }
+
+        bool TupleAssignSpotter::MassAssignMatcher::match( std::list< Expression * > &out ) {
+                if ( lhs.empty() || (rhs.size() != 1) ) return false;
+
+                for ( std::list< Expression * >::iterator l = lhs.begin(); l != lhs.end(); l++ ) {
+                        std::list< Expression * > args;
+                        args.push_back( new AddressExpr(*l) );
+                        args.push_back( rhs.front() );
+                        out.push_back( new UntypedExpr(new NameExpr("?=?"), args) );
+                }
+
+                return true;
+        }
+
+        bool TupleAssignSpotter::MassAssignMatcher::solve( std::list< Expression * > &assigns ) {
+                /*
+                  std::list< Expression * > solved_assigns;
+                  ResolvExpr::AltList solved_alts;
+                  assert( currentFinder != 0 );
+
+                  ResolvExpr::AltList current;
+                  if ( optMass.empty() ) {
+                  for ( std::list< Expression * >::size_type i = 0; i != new_assigns.size(); ++i )
+                  optMass.push_back( ResolvExpr::AltList() );
+                  }
+                  int cnt = 0;
+                  for ( std::list< Expression * >::iterator i = new_assigns.begin(); i != new_assigns.end(); ++i, cnt++ ) {
+
+                  ResolvExpr::AlternativeFinder finder( currentFinder->get_indexer(), currentFinder->get_environ() );
+                  finder.findWithAdjustment(*i);
+                  ResolvExpr::AltList alts = finder.get_alternatives();
+                  assert( alts.size() == 1 );
+                  assert(alts.front().expr != 0 );
+                  current.push_back( finder.get_alternatives().front() );
+                  optMass[cnt].push_back( finder.get_alternatives().front() );
+                  solved_assigns.push_back( alts.front().expr->clone() );
+                  }
+                */
+                return true;
+        }
+
+        bool TupleAssignSpotter::MultipleAssignMatcher::match( std::list< Expression * > &out ) {
+                // need more complicated matching
                 if ( lhs.size() == rhs.size() ) {
-                        std::list< ObjectDecl * > ltmp;
-                        std::list< ObjectDecl * > rtmp;
-                        std::transform( lhs.begin(), lhs.end(), back_inserter( ltmp ), []( Expression * expr ){
-                                return newObject( lhsNamer, new AddressExpr( expr ) );
-                        });
-                        std::transform( rhs.begin(), rhs.end(), back_inserter( rtmp ), []( Expression * expr ){
-                                return newObject( rhsNamer, expr );
-                        });
-                        zipWith( ltmp.begin(), ltmp.end(), rtmp.begin(), rtmp.end(), back_inserter(out), createAssgn );
-                        tmpDecls.splice( tmpDecls.end(), ltmp );
-                        tmpDecls.splice( tmpDecls.end(), rtmp );
-                }
+                        zipWith( lhs.begin(), lhs.end(), rhs.begin(), rhs.end(), back_inserter(out), TupleAssignSpotter::Matcher::createAssgn );
+                        return true;
+                } //else
+                //std::cerr << "The length of (left, right) is: (" << lhs.size() << "," << rhs.size() << ")" << std::endl;*/
+                return false;
+        }
+
+        bool TupleAssignSpotter::MultipleAssignMatcher::solve( std::list< Expression * > &assigns ) {
+                /*
+                  std::list< Expression * > solved_assigns;
+                  ResolvExpr::AltList solved_alts;
+                  assert( currentFinder != 0 );
+
+                  ResolvExpr::AltList current;
+                  for ( std::list< Expression * >::iterator i = new_assigns.begin(); i != new_assigns.end(); ++i ) {
+                  //try {
+                  ResolvExpr::AlternativeFinder finder( currentFinder->get_indexer(), currentFinder->get_environ() );
+                  finder.findWithAdjustment(*i);
+                  // prune expressions that don't coincide with
+                  ResolvExpr::AltList alts = finder.get_alternatives();
+                  assert( alts.size() == 1 );
+                  assert(alts.front().expr != 0 );
+                  current.push_back( finder.get_alternatives().front() );
+                  solved_assigns.push_back( alts.front().expr->clone() );
+                  //solved_assigns.back()->print(std::cerr);
+                  //} catch( ... ) {
+                  //continue; // no reasonable alternative found
+                  //}
+                  }
+                  options.add_option( current );
+                */
+
+                return true;
+        }
+
+        void TupleAssignSpotter::Options::add_option( ResolvExpr::AltList &opt ) {
+                using namespace std;
+
+                options.push_back( opt );
+                /*
+                  vector< Cost > costs;
+                  costs.reserve( opt.size() );
+                  transform( opt.begin(), opt.end(), back_inserter(costs), ptr_fun(extract_cost) );
+                */
+                // transpose matrix
+                if ( costMatrix.empty() )
+                        for ( unsigned int i = 0; i< opt.size(); ++i)
+                                costMatrix.push_back( vector<ResolvExpr::Cost>() );
+
+                int cnt = 0;
+                for ( ResolvExpr::AltList::iterator i = opt.begin(); i != opt.end(); ++i, cnt++ )
+                        costMatrix[cnt].push_back( i->cost );
+
+                return;
+        }
+
+        std::list< ResolvExpr::AltList > TupleAssignSpotter::Options::get_best() {
+                using namespace std;
+                using namespace ResolvExpr;
+                list< ResolvExpr::AltList > ret;
+                list< multiset<int> > solns;
+                for ( vector< vector<Cost> >::iterator i = costMatrix.begin(); i != costMatrix.end(); ++i ) {
+                        list<int> current;
+                        findMinCost( i->begin(), i->end(), back_inserter(current) );
+                        solns.push_back( multiset<int>(current.begin(), current.end()) );
+                }
+                // need to combine
+                multiset<int> result;
+                lift_intersection( solns.begin(), solns.end(), inserter( result, result.begin() ) );
+                if ( result.size() != 1 )
+                        throw SemanticError("Ambiguous tuple expression");
+                ret.push_back(get_option( *(result.begin() )));
+                return ret;
         }
 
         void TupleAssignSpotter::Options::print( std::ostream &ostr ) {
-                for ( ResolvExpr::AltList & l : options ) {
-                        for ( ResolvExpr::Alternative & alt : l ) {
-                                alt.print( ostr );
-                                ostr << " ";
-                        }
+                using namespace std;
+
+                for ( vector< vector < ResolvExpr::Cost > >::iterator i = costMatrix.begin(); i != costMatrix.end(); ++i ) {
+                        for ( vector < ResolvExpr::Cost >::iterator j = i->begin(); j != i->end(); ++j )
+                                ostr << *j << " " ;
                         ostr << std::endl;
                 } // for
+                return;
+        }
+
+        ResolvExpr::Cost extract_cost( ResolvExpr::Alternative &alt ) {
+                return alt.cost;
+        }
+
+        template< typename InputIterator, typename OutputIterator >
+        void TupleAssignSpotter::Options::findMinCost( InputIterator begin, InputIterator end, OutputIterator out ) {
+                using namespace ResolvExpr;
+                std::list<int> alternatives;
+
+                // select the alternatives that have the minimum parameter cost
+                Cost minCost = Cost::infinity;
+                unsigned int index = 0;
+                for ( InputIterator i = begin; i != end; ++i, index++ ) {
+                        if ( *i < minCost ) {
+                                minCost = *i;
+                                alternatives.clear();
+                                alternatives.push_back( index );
+                        } else if ( *i == minCost ) {
+                                alternatives.push_back( index );
+                        }
+                }
+                std::copy( alternatives.begin(), alternatives.end(), out );
+        }
+
+        template< class InputIterator, class OutputIterator >
+        void TupleAssignSpotter::Options::lift_intersection( InputIterator begin, InputIterator end, OutputIterator out ) {
+                if ( begin == end ) return;
+                InputIterator test = begin;
+
+                if (++test == end)
+                        { copy(begin->begin(), begin->end(), out); return; }
+
+
+                std::multiset<int> cur; // InputIterator::value_type::value_type
+                copy( begin->begin(), begin->end(), inserter( cur, cur.begin() ) );
+
+                while ( test != end ) {
+                        std::multiset<int> temp;
+                        set_intersection( cur.begin(), cur.end(), test->begin(), test->end(), inserter(temp,temp.begin()) );
+                        cur.clear();
+                        copy( temp.begin(), temp.end(), inserter(cur,cur.begin()));
+                        ++test;
+                }
+
+                copy( cur.begin(), cur.end(), out );
+                return;
+        }
+
+        ResolvExpr::AltList TupleAssignSpotter::Options::get_option( std::list< ResolvExpr::AltList >::size_type index ) {
+                if ( index >= options.size() )
+                        throw 0; // XXX
+                std::list< ResolvExpr::AltList >::iterator it = options.begin();
+                for ( std::list< ResolvExpr::AltList >::size_type i = 0; i < index; ++i, ++it );
+                return *it;
         }
 } // namespace Tuples