source: translator/ResolvExpr/AlternativeFinder.cc @ 0b8cd722

#include <list>
#include <iterator>
#include <algorithm>
#include <functional>
#include <cassert>

#include "AlternativeFinder.h"
#include "Alternative.h"
#include "Cost.h"
#include "typeops.h"
#include "Unify.h"
#include "RenameVars.h"
#include "SynTree/Type.h"
#include "SynTree/Declaration.h"
#include "SynTree/Expression.h"
#include "SynTree/Initializer.h"
#include "SynTree/Visitor.h"
#include "SymTab/Indexer.h"
#include "SymTab/Mangler.h"
#include "SynTree/TypeSubstitution.h"
#include "SymTab/Validate.h"
#include "Designators/Processor.h"
#include "Tuples/TupleAssignment.h"
#include "Tuples/NameMatcher.h"
#include "utility.h"

extern bool resolveVerbose;
#define PRINT( text ) if ( resolveVerbose ) { text } 
//#define DEBUG_COST

namespace ResolvExpr {
    Expression *resolveInVoidContext( Expression *expr, const SymTab::Indexer &indexer, TypeEnvironment &env ) {
        CastExpr *castToVoid = new CastExpr( expr );

        AlternativeFinder finder( indexer, env );
        finder.findWithAdjustment( castToVoid );

        // it's a property of the language that a cast expression has either 1 or 0 interpretations; if it has 0
        // interpretations, an exception has already been thrown.
        assert( finder.get_alternatives().size() == 1 );
        CastExpr *newExpr = dynamic_cast< CastExpr* >( finder.get_alternatives().front().expr );
        assert( newExpr );
        env = finder.get_alternatives().front().env;
        return newExpr->get_arg()->clone();
    }

    namespace {
        void printAlts( const AltList &list, std::ostream &os, int indent = 0 ) {
            for ( AltList::const_iterator i = list.begin(); i != list.end(); ++i ) {
                i->print( os, indent );
                os << std::endl;
            }
        }

        void makeExprList( const AltList &in, std::list< Expression* > &out ) {
            for ( AltList::const_iterator i = in.begin(); i != in.end(); ++i ) {
                out.push_back( i->expr->clone() );
            }
        }

        Cost sumCost( const AltList &in ) {
            Cost total;
            for ( AltList::const_iterator i = in.begin(); i != in.end(); ++i ) {
                total += i->cost;
            }
            return total;
        }

        struct PruneStruct {
            bool isAmbiguous;
            AltList::iterator candidate;
            PruneStruct() {}
            PruneStruct( AltList::iterator candidate ): isAmbiguous( false ), candidate( candidate ) {}
        };

        template< typename InputIterator, typename OutputIterator >
        void pruneAlternatives( InputIterator begin, InputIterator end, OutputIterator out, const SymTab::Indexer &indexer ) {
            // select the alternatives that have the minimum conversion cost for a particular set of result types
            std::map< std::string, PruneStruct > selected;
            for ( AltList::iterator candidate = begin; candidate != end; ++candidate ) {
                PruneStruct current( candidate );
                std::string mangleName;
                for ( std::list< Type* >::const_iterator retType = candidate->expr->get_results().begin(); retType != candidate->expr->get_results().end(); ++retType ) {
                    Type *newType = (*retType)->clone();
                    candidate->env.apply( newType );
                    mangleName += SymTab::Mangler::mangle( newType );
                    delete newType;
                }
                std::map< std::string, PruneStruct >::iterator mapPlace = selected.find( mangleName );
                if ( mapPlace != selected.end() ) {
                    if ( candidate->cost < mapPlace->second.candidate->cost ) {
                        PRINT(
                            std::cout << "cost " << candidate->cost << " beats " << mapPlace->second.candidate->cost << std::endl;
                            )
                        selected[ mangleName ] = current;
                    } else if ( candidate->cost == mapPlace->second.candidate->cost ) {
                        PRINT(
                            std::cout << "marking ambiguous" << std::endl;
                            )
                        mapPlace->second.isAmbiguous = true;
                    }
                } else {
                    selected[ mangleName ] = current;
                }
            }

            PRINT(
                std::cout << "there are " << selected.size() << " alternatives before elimination" << std::endl;
                )

            // accept the alternatives that were unambiguous
            for ( std::map< std::string, PruneStruct >::iterator target = selected.begin(); target != selected.end(); ++target ) {
                if ( !target->second.isAmbiguous ) {
                    Alternative &alt = *target->second.candidate;
                    for ( std::list< Type* >::iterator result = alt.expr->get_results().begin(); result != alt.expr->get_results().end(); ++result ) {
                        alt.env.applyFree( *result );
                    }
                    *out++ = alt;
                }
            }

        }

        template< typename InputIterator, typename OutputIterator >
        void findMinCost( InputIterator begin, InputIterator end, OutputIterator out ) {
            AltList alternatives;

            // select the alternatives that have the minimum parameter cost
            Cost minCost = Cost::infinity;
            for ( AltList::iterator i = begin; i != end; ++i ) {
                if ( i->cost < minCost ) {
                    minCost = i->cost;
                    i->cost = i->cvtCost;
                    alternatives.clear();
                    alternatives.push_back( *i );
                } else if ( i->cost == minCost ) {
                    i->cost = i->cvtCost;
                    alternatives.push_back( *i );
                }
            }
            std::copy( alternatives.begin(), alternatives.end(), out );
        }

        template< typename InputIterator >
        void simpleCombineEnvironments( InputIterator begin, InputIterator end, TypeEnvironment &result ) {
            while ( begin != end ) {
                result.simpleCombine( (*begin++).env );
            }
        }

        void renameTypes( Expression *expr ) {
            for ( std::list< Type* >::iterator i = expr->get_results().begin(); i != expr->get_results().end(); ++i ) {
                (*i)->accept( global_renamer );
            }
        }
    }

    template< typename InputIterator, typename OutputIterator >
    void AlternativeFinder::findSubExprs( InputIterator begin, InputIterator end, OutputIterator out ) {
        while ( begin != end ) {
            AlternativeFinder finder( indexer, env );
            finder.findWithAdjustment( *begin );
            // XXX  either this
            //Designators::fixDesignations( finder, (*begin++)->get_argName() );
            // or XXX this
            begin++;
            PRINT(
                std::cout << "findSubExprs" << std::endl;
                printAlts( finder.alternatives, std::cout );
                )
            *out++ = finder;
        }
    }

    AlternativeFinder::AlternativeFinder( const SymTab::Indexer &indexer, const TypeEnvironment &env )
        : indexer( indexer ), env( env ) {
    }

    void AlternativeFinder::find( Expression *expr, bool adjust ) {
        expr->accept( *this );
        if ( alternatives.empty() ) {
            throw SemanticError( "No reasonable alternatives for expression ", expr );
        }
        for ( AltList::iterator i = alternatives.begin(); i != alternatives.end(); ++i ) {
            if ( adjust ) {
                adjustExprTypeList( i->expr->get_results().begin(), i->expr->get_results().end(), i->env, indexer );
            }
        }
        PRINT(
            std::cout << "alternatives before prune:" << std::endl;
            printAlts( alternatives, std::cout );
            )
        AltList::iterator oldBegin = alternatives.begin();
        pruneAlternatives( alternatives.begin(), alternatives.end(), front_inserter( alternatives ), indexer );
        if ( alternatives.begin() == oldBegin ) {
            std::ostrstream stream;
            stream << "Can't choose between alternatives for expression ";
            expr->print( stream );
            stream << "Alternatives are:";
            AltList winners;
            findMinCost( alternatives.begin(), alternatives.end(), back_inserter( winners ) );
            printAlts( winners, stream, 8 );
            throw SemanticError( std::string( stream.str(), stream.pcount() ) );
        }
        alternatives.erase( oldBegin, alternatives.end() );
        PRINT(
            std::cout << "there are " << alternatives.size() << " alternatives after elimination" << std::endl;
            )
    }

    void AlternativeFinder::findWithAdjustment( Expression *expr ) {
        find( expr, true );
    }

    template< typename StructOrUnionType >
    void AlternativeFinder::addAggMembers( StructOrUnionType *aggInst, Expression *expr, const Cost &newCost, const std::string &name ) {
        std::list< Declaration* > members;
        aggInst->lookup( name, members );
        for ( std::list< Declaration* >::const_iterator i = members.begin(); i != members.end(); ++i ) {
            if ( DeclarationWithType *dwt = dynamic_cast< DeclarationWithType* >( *i ) ) {
                alternatives.push_back( Alternative( new MemberExpr( dwt->clone(), expr->clone() ), env, newCost ) );
                renameTypes( alternatives.back().expr );
            } else {
                assert( false );
            }
        }
    }

    void AlternativeFinder::visit( ApplicationExpr *applicationExpr ) {
        alternatives.push_back( Alternative( applicationExpr->clone(), env, Cost::zero ) );
    }

    Cost computeConversionCost( Alternative &alt, const SymTab::Indexer &indexer ) {
        ApplicationExpr *appExpr = dynamic_cast< ApplicationExpr* >( alt.expr );
        assert( appExpr );
        PointerType *pointer = dynamic_cast< PointerType* >( appExpr->get_function()->get_results().front() );
        assert( pointer );
        FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() );
        assert( function );

        Cost convCost( 0, 0, 0 );
        std::list< DeclarationWithType* >& formals = function->get_parameters();
        std::list< DeclarationWithType* >::iterator formal = formals.begin();
        std::list< Expression* >& actuals = appExpr->get_args();
        for ( std::list< Expression* >::iterator actualExpr = actuals.begin(); actualExpr != actuals.end(); ++actualExpr ) {
            PRINT(
                std::cout << "actual expression:" << std::endl;
                (*actualExpr)->print( std::cout, 8 );
                std::cout << "--- results are" << std::endl;
                printAll( (*actualExpr)->get_results(), std::cout, 8 );
                )
            std::list< DeclarationWithType* >::iterator startFormal = formal;
            Cost actualCost;
            for ( std::list< Type* >::iterator actual = (*actualExpr)->get_results().begin(); actual != (*actualExpr)->get_results().end(); ++actual ) {
                if ( formal == formals.end() ) {
                    if ( function->get_isVarArgs() ) {
                        convCost += Cost( 1, 0, 0 );
                        break;
                    } else {
                        return Cost::infinity;
                    }
                }
                PRINT(
                    std::cout << std::endl << "converting ";
                    (*actual)->print( std::cout, 8 );
                    std::cout << std::endl << " to ";
                    (*formal)->get_type()->print( std::cout, 8 );
                    )
                Cost newCost = conversionCost( *actual, (*formal)->get_type(), indexer, alt.env );
                PRINT(
                    std::cout << std::endl << "cost is" << newCost << std::endl;
                    )

                if ( newCost == Cost::infinity ) {
                    return newCost;
                }
                convCost += newCost;
                actualCost += newCost;

                convCost += Cost( 0, polyCost( (*formal)->get_type(), alt.env, indexer ) + polyCost( *actual, alt.env, indexer ), 0 );

                formal++;
            }
            if ( actualCost != Cost( 0, 0, 0 ) ) {
                std::list< DeclarationWithType* >::iterator startFormalPlusOne = startFormal;
                startFormalPlusOne++;
                if ( formal == startFormalPlusOne ) {
                    // not a tuple type
                    Type *newType = (*startFormal)->get_type()->clone();
                    alt.env.apply( newType );
                    *actualExpr = new CastExpr( *actualExpr, newType );
                } else {
                    TupleType *newType = new TupleType( Type::Qualifiers() );
                    for ( std::list< DeclarationWithType* >::iterator i = startFormal; i != formal; ++i ) {
                        newType->get_types().push_back( (*i)->get_type()->clone() );
                    }
                    alt.env.apply( newType );
                    *actualExpr = new CastExpr( *actualExpr, newType );
                }
            }

        }
        if ( formal != formals.end() ) {
            return Cost::infinity;
        }

        for ( InferredParams::const_iterator assert = appExpr->get_inferParams().begin(); assert != appExpr->get_inferParams().end(); ++assert ) {
            PRINT(
                std::cout << std::endl << "converting ";
                assert->second.actualType->print( std::cout, 8 );
                std::cout << std::endl << " to ";
                assert->second.formalType->print( std::cout, 8 );
                )
            Cost newCost = conversionCost( assert->second.actualType, assert->second.formalType, indexer, alt.env );
            PRINT(
                std::cout << std::endl << "cost of conversion is " << newCost << std::endl;
                )
            if ( newCost == Cost::infinity ) {
                return newCost;
            }
            convCost += newCost;

            convCost += Cost( 0, polyCost( assert->second.formalType, alt.env, indexer ) + polyCost( assert->second.actualType, alt.env, indexer ), 0 );
        }

        return convCost;
    }

    void makeUnifiableVars( Type *type, OpenVarSet &unifiableVars, AssertionSet &needAssertions ) {
        for ( std::list< TypeDecl* >::const_iterator tyvar = type->get_forall().begin(); tyvar != type->get_forall().end(); ++tyvar ) {
            unifiableVars[ (*tyvar)->get_name() ] = (*tyvar)->get_kind();
            for ( std::list< DeclarationWithType* >::iterator assert = (*tyvar)->get_assertions().begin(); assert != (*tyvar)->get_assertions().end(); ++assert ) {
                needAssertions[ *assert ] = true;
            }
///     needAssertions.insert( needAssertions.end(), (*tyvar)->get_assertions().begin(), (*tyvar)->get_assertions().end() );
        }
    }

    bool AlternativeFinder::instantiateFunction( std::list< DeclarationWithType* >& formals, /*const*/ AltList &actuals, bool isVarArgs, OpenVarSet& openVars, TypeEnvironment &resultEnv, AssertionSet &resultNeed, AssertionSet &resultHave ) {
        std::list< TypeEnvironment > toBeDone;
        simpleCombineEnvironments( actuals.begin(), actuals.end(), resultEnv );
        // make sure we don't widen any existing bindings
        for ( TypeEnvironment::iterator i = resultEnv.begin(); i != resultEnv.end(); ++i ) {
            i->allowWidening  = false;
        }
        resultEnv.extractOpenVars( openVars );

        /*
          Tuples::NameMatcher matcher( formals );
          try {
          matcher.match( actuals );
          } catch ( Tuples::NoMatch &e ) {
          std::cerr << "Alternative doesn't match: " << e.message << std::endl;
          }
        */
        std::list< DeclarationWithType* >::iterator formal = formals.begin();
        for ( AltList::const_iterator actualExpr = actuals.begin(); actualExpr != actuals.end(); ++actualExpr ) {
            for ( std::list< Type* >::iterator actual = actualExpr->expr->get_results().begin(); actual != actualExpr->expr->get_results().end(); ++actual ) {
                if ( formal == formals.end() ) {
                    return isVarArgs;
                }
                PRINT(
                    std::cerr << "formal type is ";
                    (*formal)->get_type()->print( std::cerr );
                    std::cerr << std::endl << "actual type is ";
                    (*actual)->print( std::cerr );
                    std::cerr << std::endl;
                    )
                if ( !unify( (*formal)->get_type(), *actual, resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
                    return false;
                }
                formal++;
            }
        }
        // Handling of default values
        while ( formal != formals.end() ) {
            if ( ObjectDecl *od = dynamic_cast<ObjectDecl *>( *formal ) )
                if ( SingleInit *si = dynamic_cast<SingleInit *>( od->get_init() ))
                    // so far, only constant expressions are accepted as default values
                    if ( ConstantExpr *cnstexpr = dynamic_cast<ConstantExpr *>( si->get_value()) )
                        if ( Constant *cnst = dynamic_cast<Constant *>( cnstexpr->get_constant() ) )
                            if ( unify( (*formal)->get_type(), cnst->get_type(), resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
                                // XXX Don't know if this is right
                                actuals.push_back( Alternative( cnstexpr->clone(), env, Cost::zero ) );
                                formal++;
                                if ( formal == formals.end()) break;
                            }
            return false;
        }
        return true;
    }

    static const int recursionLimit = 10;

    void addToIndexer( AssertionSet &assertSet, SymTab::Indexer &indexer ) {
        for ( AssertionSet::iterator i = assertSet.begin(); i != assertSet.end(); ++i ) {
            if ( i->second == true ) {
                i->first->accept( indexer );
            }
        }
    }

    template< typename ForwardIterator, typename OutputIterator >
    void inferRecursive( ForwardIterator begin, ForwardIterator end, const Alternative &newAlt, OpenVarSet &openVars, const SymTab::Indexer &decls, const AssertionSet &newNeed, int level, const SymTab::Indexer &indexer, OutputIterator out ) {
        if ( begin == end ) {
            if ( newNeed.empty() ) {
                *out++ = newAlt;
                return;
            } else if ( level >= recursionLimit ) {
                throw SemanticError( "Too many recursive assertions" );
            } else {
                AssertionSet newerNeed;
                PRINT(
                    std::cerr << "recursing with new set:" << std::endl;
                    printAssertionSet( newNeed, std::cerr, 8 );
                    )
                inferRecursive( newNeed.begin(), newNeed.end(), newAlt, openVars, decls, newerNeed, level+1, indexer, out );
                return;
            }
        }

        ForwardIterator cur = begin++;
        if ( !cur->second ) {
            inferRecursive( begin, end, newAlt, openVars, decls, newNeed, level, indexer, out );
        }
        DeclarationWithType *curDecl = cur->first;
        PRINT(
            std::cerr << "inferRecursive: assertion is ";
            curDecl->print( std::cerr );
            std::cerr << std::endl;
            )
        std::list< DeclarationWithType* > candidates;
        decls.lookupId( curDecl->get_name(), candidates );
///   if ( candidates.empty() ) { std::cout << "no candidates!" << std::endl; }
        for ( std::list< DeclarationWithType* >::const_iterator candidate = candidates.begin(); candidate != candidates.end(); ++candidate ) {
            PRINT(
                std::cout << "inferRecursive: candidate is ";
                (*candidate)->print( std::cout );
                std::cout << std::endl;
                )
            AssertionSet newHave, newerNeed( newNeed );
            TypeEnvironment newEnv( newAlt.env );
            OpenVarSet newOpenVars( openVars );
            Type *adjType = (*candidate)->get_type()->clone();
            adjustExprType( adjType, newEnv, indexer );
            adjType->accept( global_renamer );
            PRINT(
                std::cerr << "unifying ";
                curDecl->get_type()->print( std::cerr );
                std::cerr << " with ";
                adjType->print( std::cerr );
                std::cerr << std::endl;
                )
            if ( unify( curDecl->get_type(), adjType, newEnv, newerNeed, newHave, newOpenVars, indexer ) ) {
                PRINT(
                    std::cerr << "success!" << std::endl;
                    )
                SymTab::Indexer newDecls( decls );
                addToIndexer( newHave, newDecls );
                Alternative newerAlt( newAlt );
                newerAlt.env = newEnv;
                assert( (*candidate)->get_uniqueId() );
                Expression *varExpr = new VariableExpr( static_cast< DeclarationWithType* >( Declaration::declFromId( (*candidate)->get_uniqueId() ) ) );
                deleteAll( varExpr->get_results() );
                varExpr->get_results().clear();
                varExpr->get_results().push_front( adjType->clone() );
                PRINT(
                    std::cout << "satisfying assertion " << curDecl->get_uniqueId() << " ";
                    curDecl->print( std::cout );
                    std::cout << " with declaration " << (*candidate)->get_uniqueId() << " ";
                    (*candidate)->print( std::cout );
                    std::cout << std::endl;
                    )
                ApplicationExpr *appExpr = static_cast< ApplicationExpr* >( newerAlt.expr );
                // XXX: this is a memory leak, but adjType can't be deleted because it might contain assertions
                appExpr->get_inferParams()[ curDecl->get_uniqueId() ] = ParamEntry( (*candidate)->get_uniqueId(), adjType->clone(), curDecl->get_type()->clone(), varExpr );
                inferRecursive( begin, end, newerAlt, newOpenVars, newDecls, newerNeed, level, indexer, out );
            } else {
                delete adjType;
            }
        }
    }

    template< typename OutputIterator >
    void AlternativeFinder::inferParameters( const AssertionSet &need, AssertionSet &have, const Alternative &newAlt, OpenVarSet &openVars, OutputIterator out ) {
//      PRINT(
//          std::cout << "inferParameters: assertions needed are" << std::endl;
//          printAll( need, std::cout, 8 );
//          )
        SymTab::Indexer decls( indexer );
        PRINT(
            std::cout << "============= original indexer" << std::endl;
            indexer.print( std::cout );
            std::cout << "============= new indexer" << std::endl;
            decls.print( std::cout );
            )
        addToIndexer( have, decls );
        AssertionSet newNeed;
        inferRecursive( need.begin(), need.end(), newAlt, openVars, decls, newNeed, 0, indexer, out );
//      PRINT(
//          std::cout << "declaration 14 is ";
//          Declaration::declFromId
//          *out++ = newAlt;
//          )
    }

    template< typename OutputIterator >
    void AlternativeFinder::makeFunctionAlternatives( const Alternative &func, FunctionType *funcType, AltList &actualAlt, OutputIterator out ) {
        OpenVarSet openVars;
        AssertionSet resultNeed, resultHave;
        TypeEnvironment resultEnv;
        makeUnifiableVars( funcType, openVars, resultNeed );
        if ( instantiateFunction( funcType->get_parameters(), actualAlt, funcType->get_isVarArgs(), openVars, resultEnv, resultNeed, resultHave ) ) {
            ApplicationExpr *appExpr = new ApplicationExpr( func.expr->clone() );
            Alternative newAlt( appExpr, resultEnv, sumCost( actualAlt ) );
            makeExprList( actualAlt, appExpr->get_args() );
            PRINT(
                std::cout << "need assertions:" << std::endl;
                printAssertionSet( resultNeed, std::cout, 8 );
                )
            inferParameters( resultNeed, resultHave, newAlt, openVars, out );
        }
    }

    void AlternativeFinder::visit( UntypedExpr *untypedExpr ) {
        bool doneInit = false;
        AlternativeFinder funcOpFinder( indexer, env );

        AlternativeFinder funcFinder( indexer, env ); {
            NameExpr *fname;
            if ( ( fname = dynamic_cast<NameExpr *>( untypedExpr->get_function()))
                 && ( fname->get_name() == std::string("LabAddress")) ) {
                alternatives.push_back( Alternative( untypedExpr, env, Cost()) );
                return;
            }
        }

        funcFinder.findWithAdjustment( untypedExpr->get_function() );
        std::list< AlternativeFinder > argAlternatives;
        findSubExprs( untypedExpr->begin_args(), untypedExpr->end_args(), back_inserter( argAlternatives ) );

        std::list< AltList > possibilities;
        combos( argAlternatives.begin(), argAlternatives.end(), back_inserter( possibilities ) );

        Tuples::TupleAssignSpotter tassign( this );
        if ( tassign.isTupleAssignment( untypedExpr, possibilities ) ) {
            // take care of possible tuple assignments, or discard expression
            return;
        } // else ...

        AltList candidates;

        for ( AltList::const_iterator func = funcFinder.alternatives.begin(); func != funcFinder.alternatives.end(); ++func ) {
            PRINT(
                std::cout << "working on alternative: " << std::endl;
                func->print( std::cout, 8 );
                )
            // check if the type is pointer to function
            PointerType *pointer;
            if ( func->expr->get_results().size() == 1 && ( pointer = dynamic_cast< PointerType* >( func->expr->get_results().front() ) ) ) {
                if ( FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() ) ) {
                    for ( std::list< AltList >::iterator actualAlt = possibilities.begin(); actualAlt != possibilities.end(); ++actualAlt ) {
                        // XXX
                        //Designators::check_alternative( function, *actualAlt );
                        makeFunctionAlternatives( *func, function, *actualAlt, std::back_inserter( candidates ) );
                    }
                } else if ( TypeInstType *typeInst = dynamic_cast< TypeInstType* >( pointer->get_base() ) ) {
                    EqvClass eqvClass;
                    if ( func->env.lookup( typeInst->get_name(), eqvClass ) && eqvClass.type ) {
                        if ( FunctionType *function = dynamic_cast< FunctionType* >( eqvClass.type ) ) {
                            for ( std::list< AltList >::iterator actualAlt = possibilities.begin(); actualAlt != possibilities.end(); ++actualAlt ) {
                                makeFunctionAlternatives( *func, function, *actualAlt, std::back_inserter( candidates ) );
                            }
                        }
                    }
                }
            } else {
                // seek a function operator that's compatible
                if ( !doneInit ) {
                    doneInit = true;
                    NameExpr *opExpr = new NameExpr( "?()" );
                    try {
                        funcOpFinder.findWithAdjustment( opExpr );
                    } catch( SemanticError &e ) {
                        // it's ok if there aren't any defined function ops
                    }
                    PRINT(
                        std::cout << "known function ops:" << std::endl;
                        printAlts( funcOpFinder.alternatives, std::cout, 8 );
                        )
                }

                for ( AltList::const_iterator funcOp = funcOpFinder.alternatives.begin(); funcOp != funcOpFinder.alternatives.end(); ++funcOp ) {
                    // check if the type is pointer to function
                    PointerType *pointer;
                    if ( funcOp->expr->get_results().size() == 1
                        && ( pointer = dynamic_cast< PointerType* >( funcOp->expr->get_results().front() ) ) ) {
                        if ( FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() ) ) {
                            for ( std::list< AltList >::iterator actualAlt = possibilities.begin(); actualAlt != possibilities.end(); ++actualAlt ) {
                                AltList currentAlt;
                                currentAlt.push_back( *func );
                                currentAlt.insert( currentAlt.end(), actualAlt->begin(), actualAlt->end() );
                                makeFunctionAlternatives( *funcOp, function, currentAlt, std::back_inserter( candidates ) );
                            }
                        }
                    }
                }
            }
        }

        for ( AltList::iterator withFunc = candidates.begin(); withFunc != candidates.end(); ++withFunc ) {
            Cost cvtCost = computeConversionCost( *withFunc, indexer );

            PRINT(
                ApplicationExpr *appExpr = dynamic_cast< ApplicationExpr* >( withFunc->expr );
                assert( appExpr );
                PointerType *pointer = dynamic_cast< PointerType* >( appExpr->get_function()->get_results().front() );
                assert( pointer );
                FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() );
                assert( function );
                std::cout << "Case +++++++++++++" << std::endl;
                std::cout << "formals are:" << std::endl;
                printAll( function->get_parameters(), std::cout, 8 );
                std::cout << "actuals are:" << std::endl;
                printAll( appExpr->get_args(), std::cout, 8 );
                std::cout << "bindings are:" << std::endl;
                withFunc->env.print( std::cout, 8 );
                std::cout << "cost of conversion is:" << cvtCost << std::endl;
                )
            if ( cvtCost != Cost::infinity ) {
                withFunc->cvtCost = cvtCost;
                alternatives.push_back( *withFunc );
            }
        }
        candidates.clear();
        candidates.splice( candidates.end(), alternatives );

        findMinCost( candidates.begin(), candidates.end(), std::back_inserter( alternatives ) );
    }

    bool isLvalue( Expression *expr ) {
        for ( std::list< Type* >::const_iterator i = expr->get_results().begin(); i != expr->get_results().end(); ++i ) {
            if ( !(*i)->get_isLvalue() ) return false;
        }
        return true;
    }

    void AlternativeFinder::visit( AddressExpr *addressExpr ) {
        AlternativeFinder finder( indexer, env );
        finder.find( addressExpr->get_arg() );
        for ( std::list< Alternative >::iterator i = finder.alternatives.begin(); i != finder.alternatives.end(); ++i ) {
            if ( isLvalue( i->expr ) ) {
                alternatives.push_back( Alternative( new AddressExpr( i->expr->clone() ), i->env, i->cost ) );
            }
        }
    }

    void AlternativeFinder::visit( CastExpr *castExpr ) {
        for ( std::list< Type* >::iterator i = castExpr->get_results().begin(); i != castExpr->get_results().end(); ++i ) {
            SymTab::validateType( *i, &indexer );
            adjustExprType( *i, env, indexer );
        }

        AlternativeFinder finder( indexer, env );
        finder.findWithAdjustment( castExpr->get_arg() );

        AltList candidates;
        for ( std::list< Alternative >::iterator i = finder.alternatives.begin(); i != finder.alternatives.end(); ++i ) {
            AssertionSet needAssertions, haveAssertions;
            OpenVarSet openVars;

            // It's possible that a cast can throw away some values in a multiply-valued expression.  (An example is a
            // cast-to-void, which casts from one value to zero.)  Figure out the prefix of the subexpression results
            // that are cast directly.  The candidate is invalid if it has fewer results than there are types to cast
            // to.
            int discardedValues = (*i).expr->get_results().size() - castExpr->get_results().size();
            if ( discardedValues < 0 ) continue;
            std::list< Type* >::iterator candidate_end = (*i).expr->get_results().begin();
            std::advance( candidate_end, castExpr->get_results().size() );
            if ( !unifyList( (*i).expr->get_results().begin(), candidate_end,
                            castExpr->get_results().begin(), castExpr->get_results().end(), i->env, needAssertions, haveAssertions, openVars, indexer ) ) continue;
            Cost thisCost = castCostList( (*i).expr->get_results().begin(), candidate_end,
                                          castExpr->get_results().begin(), castExpr->get_results().end(), indexer, i->env );
            if ( thisCost != Cost::infinity ) {
                // count one safe conversion for each value that is thrown away
                thisCost += Cost( 0, 0, discardedValues );
                CastExpr *newExpr = castExpr->clone();
                newExpr->set_arg( i->expr->clone() );
                candidates.push_back( Alternative( newExpr, i->env, i->cost, thisCost ) );
            }
        }

        // findMinCost selects the alternatives with the lowest "cost" members, but has the side effect of copying the
        // cvtCost member to the cost member (since the old cost is now irrelevant).  Thus, calling findMinCost twice
        // selects first based on argument cost, then on conversion cost.
        AltList minArgCost;
        findMinCost( candidates.begin(), candidates.end(), std::back_inserter( minArgCost ) );
        findMinCost( minArgCost.begin(), minArgCost.end(), std::back_inserter( alternatives ) );
    }

    void AlternativeFinder::visit( UntypedMemberExpr *memberExpr ) {
        AlternativeFinder funcFinder( indexer, env );
        funcFinder.findWithAdjustment( memberExpr->get_aggregate() );

        for ( AltList::const_iterator agg = funcFinder.alternatives.begin(); agg != funcFinder.alternatives.end(); ++agg ) {
            if ( agg->expr->get_results().size() == 1 ) {
                if ( StructInstType *structInst = dynamic_cast< StructInstType* >( agg->expr->get_results().front() ) ) {
                    addAggMembers( structInst, agg->expr, agg->cost, memberExpr->get_member() );
                } else if ( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( agg->expr->get_results().front() ) ) {
                    addAggMembers( unionInst, agg->expr, agg->cost, memberExpr->get_member() );
                }
            }
        }
    }

    void AlternativeFinder::visit( MemberExpr *memberExpr ) {
        alternatives.push_back( Alternative( memberExpr->clone(), env, Cost::zero ) );
    }

    void AlternativeFinder::visit( NameExpr *nameExpr ) {
        std::list< DeclarationWithType* > declList;
        indexer.lookupId( nameExpr->get_name(), declList );
        PRINT(
            std::cerr << "nameExpr is " << nameExpr->get_name() << std::endl;
            )
        for ( std::list< DeclarationWithType* >::iterator i = declList.begin(); i != declList.end(); ++i ) {
            VariableExpr newExpr( *i, nameExpr->get_argName() );
            alternatives.push_back( Alternative( newExpr.clone(), env, Cost() ) );
            PRINT(
                std::cerr << "decl is ";
                (*i)->print( std::cerr );
                std::cerr << std::endl;
                std::cerr << "newExpr is ";
                newExpr.print( std::cerr );
                std::cerr << std::endl;
                )
            renameTypes( alternatives.back().expr );
            if ( StructInstType *structInst = dynamic_cast< StructInstType* >( (*i)->get_type() ) ) {
                addAggMembers( structInst, &newExpr, Cost( 0, 0, 1 ), "" );
            } else if ( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( (*i)->get_type() ) ) {
                addAggMembers( unionInst, &newExpr, Cost( 0, 0, 1 ), "" );
            }
        }
    }

    void AlternativeFinder::visit( VariableExpr *variableExpr ) {
        alternatives.push_back( Alternative( variableExpr->clone(), env, Cost::zero ) );
    }

    void AlternativeFinder::visit( ConstantExpr *constantExpr ) {
        alternatives.push_back( Alternative( constantExpr->clone(), env, Cost::zero ) );
    }

    void AlternativeFinder::visit( SizeofExpr *sizeofExpr ) {
        if ( sizeofExpr->get_isType() ) {
            alternatives.push_back( Alternative( sizeofExpr->clone(), env, Cost::zero ) );
        } else {
            AlternativeFinder finder( indexer, env );
            finder.find( sizeofExpr->get_expr() );
            if ( finder.alternatives.size() != 1 ) {
                throw SemanticError( "Ambiguous expression in sizeof operand: ", sizeofExpr->get_expr() );
            }
            Alternative &choice = finder.alternatives.front();
            alternatives.push_back( Alternative( new SizeofExpr( choice.expr->clone() ), choice.env, Cost::zero ) );
        }
    }

    void AlternativeFinder::resolveAttr( DeclarationWithType *funcDecl, FunctionType *function, Type *argType, const TypeEnvironment &env ) {
        // assume no polymorphism
        // assume no implicit conversions
        assert( function->get_parameters().size() == 1 );
        PRINT(
            std::cout << "resolvAttr: funcDecl is ";
            funcDecl->print( std::cout );
            std::cout << " argType is ";
            argType->print( std::cout );
            std::cout << std::endl;
            )
        if ( typesCompatibleIgnoreQualifiers( argType, function->get_parameters().front()->get_type(), indexer, env ) ) {
            alternatives.push_back( Alternative( new AttrExpr( new VariableExpr( funcDecl ), argType->clone() ), env, Cost::zero ) );
            for ( std::list< DeclarationWithType* >::iterator i = function->get_returnVals().begin(); i != function->get_returnVals().end(); ++i ) {
                alternatives.back().expr->get_results().push_back( (*i)->get_type()->clone() );
            }
        }
    }

    void AlternativeFinder::visit( AttrExpr *attrExpr ) {
        // assume no 'pointer-to-attribute'
        NameExpr *nameExpr = dynamic_cast< NameExpr* >( attrExpr->get_attr() );
        assert( nameExpr );
        std::list< DeclarationWithType* > attrList;
        indexer.lookupId( nameExpr->get_name(), attrList );
        if ( attrExpr->get_isType() || attrExpr->get_expr() ) {
            for ( std::list< DeclarationWithType* >::iterator i = attrList.begin(); i != attrList.end(); ++i ) {
                // check if the type is function
                if ( FunctionType *function = dynamic_cast< FunctionType* >( (*i)->get_type() ) ) {
                    // assume exactly one parameter
                    if ( function->get_parameters().size() == 1 ) {
                        if ( attrExpr->get_isType() ) {
                            resolveAttr( *i, function, attrExpr->get_type(), env );
                        } else {
                            AlternativeFinder finder( indexer, env );
                            finder.find( attrExpr->get_expr() );
                            for ( AltList::iterator choice = finder.alternatives.begin(); choice != finder.alternatives.end(); ++choice ) {
                                if ( choice->expr->get_results().size() == 1 ) {
                                    resolveAttr(*i, function, choice->expr->get_results().front(), choice->env );
                                }
                            }
                        }
                    }
                }
            }
        } else {
            for ( std::list< DeclarationWithType* >::iterator i = attrList.begin(); i != attrList.end(); ++i ) {
                VariableExpr newExpr( *i );
                alternatives.push_back( Alternative( newExpr.clone(), env, Cost() ) );
                renameTypes( alternatives.back().expr );
            }
        }
    }

    void AlternativeFinder::visit( LogicalExpr *logicalExpr ) {
        AlternativeFinder firstFinder( indexer, env );
        firstFinder.findWithAdjustment( logicalExpr->get_arg1() );
        for ( AltList::const_iterator first = firstFinder.alternatives.begin(); first != firstFinder.alternatives.end(); ++first ) {
            AlternativeFinder secondFinder( indexer, first->env );
            secondFinder.findWithAdjustment( logicalExpr->get_arg2() );
            for ( AltList::const_iterator second = secondFinder.alternatives.begin(); second != secondFinder.alternatives.end(); ++second ) {
                LogicalExpr *newExpr = new LogicalExpr( first->expr->clone(), second->expr->clone(), logicalExpr->get_isAnd() );
                alternatives.push_back( Alternative( newExpr, second->env, first->cost + second->cost ) );
            }
        }
    }

    void AlternativeFinder::visit( ConditionalExpr *conditionalExpr ) {
        AlternativeFinder firstFinder( indexer, env );
        firstFinder.findWithAdjustment( conditionalExpr->get_arg1() );
        for ( AltList::const_iterator first = firstFinder.alternatives.begin(); first != firstFinder.alternatives.end(); ++first ) {
            AlternativeFinder secondFinder( indexer, first->env );
            secondFinder.findWithAdjustment( conditionalExpr->get_arg2() );
            for ( AltList::const_iterator second = secondFinder.alternatives.begin(); second != secondFinder.alternatives.end(); ++second ) {
                AlternativeFinder thirdFinder( indexer, second->env );
                thirdFinder.findWithAdjustment( conditionalExpr->get_arg3() );
                for ( AltList::const_iterator third = thirdFinder.alternatives.begin(); third != thirdFinder.alternatives.end(); ++third ) {
                    OpenVarSet openVars;
                    AssertionSet needAssertions, haveAssertions;
                    Alternative newAlt( 0, third->env, first->cost + second->cost + third->cost );
                    std::list< Type* > commonTypes;
                    if ( unifyList( second->expr->get_results().begin(), second->expr->get_results().end(), third->expr->get_results().begin(), third->expr->get_results().end(), newAlt.env, needAssertions, haveAssertions, openVars, indexer, commonTypes ) ) {
                        ConditionalExpr *newExpr = new ConditionalExpr( first->expr->clone(), second->expr->clone(), third->expr->clone() );
                        std::list< Type* >::const_iterator original = second->expr->get_results().begin();
                        std::list< Type* >::const_iterator commonType = commonTypes.begin();
                        for ( ; original != second->expr->get_results().end() && commonType != commonTypes.end(); ++original, ++commonType ) {
                            if ( *commonType ) {
                                newExpr->get_results().push_back( *commonType );
                            } else {
                                newExpr->get_results().push_back( (*original)->clone() );
                            }
                        }
                        newAlt.expr = newExpr;
                        inferParameters( needAssertions, haveAssertions, newAlt, openVars, back_inserter( alternatives ) );
                    }
                }
            }
        }
    }

    void AlternativeFinder::visit( CommaExpr *commaExpr ) {
        TypeEnvironment newEnv( env );
        Expression *newFirstArg = resolveInVoidContext( commaExpr->get_arg1(), indexer, newEnv );
        AlternativeFinder secondFinder( indexer, newEnv );
        secondFinder.findWithAdjustment( commaExpr->get_arg2() );
        for ( AltList::const_iterator alt = secondFinder.alternatives.begin(); alt != secondFinder.alternatives.end(); ++alt ) {
            alternatives.push_back( Alternative( new CommaExpr( newFirstArg->clone(), alt->expr->clone() ), alt->env, alt->cost ) );
        }
        delete newFirstArg;
    }

    void AlternativeFinder::visit( TupleExpr *tupleExpr ) {
        std::list< AlternativeFinder > subExprAlternatives;
        findSubExprs( tupleExpr->get_exprs().begin(), tupleExpr->get_exprs().end(), back_inserter( subExprAlternatives ) );
        std::list< AltList > possibilities;
        combos( subExprAlternatives.begin(), subExprAlternatives.end(), back_inserter( possibilities ) );
        for ( std::list< AltList >::const_iterator i = possibilities.begin(); i != possibilities.end(); ++i ) {
            TupleExpr *newExpr = new TupleExpr;
            makeExprList( *i, newExpr->get_exprs() );
            for ( std::list< Expression* >::const_iterator resultExpr = newExpr->get_exprs().begin(); resultExpr != newExpr->get_exprs().end(); ++resultExpr ) {
                for ( std::list< Type* >::const_iterator resultType = (*resultExpr)->get_results().begin(); resultType != (*resultExpr)->get_results().end(); ++resultType ) {
                    newExpr->get_results().push_back( (*resultType)->clone() );
                }
            }

            TypeEnvironment compositeEnv;
            simpleCombineEnvironments( i->begin(), i->end(), compositeEnv );
            alternatives.push_back( Alternative( newExpr, compositeEnv, sumCost( *i ) ) );
        }
    }
} // namespace ResolvExpr