source: src/ResolvExpr/AlternativeFinder.cc @ 66f8528

//
// Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// AlternativeFinder.cc --
//
// Author           : Richard C. Bilson
// Created On       : Sat May 16 23:52:08 2015
// Last Modified By : Peter A. Buhr
// Last Modified On : Mon Jul  4 17:02:51 2016
// Update Count     : 29
//

#include <list>
#include <iterator>
#include <algorithm>
#include <functional>
#include <cassert>
#include <unordered_map>
#include <utility>
#include <vector>

#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 "Tuples/Tuples.h"
#include "Tuples/Explode.h"
#include "Common/utility.h"
#include "InitTweak/InitTweak.h"
#include "InitTweak/GenInit.h"
#include "ResolveTypeof.h"
#include "Resolver.h"

extern bool resolvep;
#define PRINT( text ) if ( resolvep ) { 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();
        }

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

        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() );
                        }
                }

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

                /// Prunes a list of alternatives down to those that have the minimum conversion cost for a given return type; skips ambiguous interpretations
                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;
                                {
                                        Type * newType = candidate->expr->get_result()->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::cerr << "cost " << candidate->cost << " beats " << mapPlace->second.candidate->cost << std::endl;
                                                )
                                                selected[ mangleName ] = current;
                                        } else if ( candidate->cost == mapPlace->second.candidate->cost ) {
                                                PRINT(
                                                        std::cerr << "marking ambiguous" << std::endl;
                                                )
                                                mapPlace->second.isAmbiguous = true;
                                        }
                                } else {
                                        selected[ mangleName ] = current;
                                }
                        }

                        PRINT(
                                std::cerr << "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;
                                        alt.env.applyFree( alt.expr->get_result() );
                                        *out++ = alt;
                                }
                        }
                }

                void renameTypes( Expression *expr ) {
                        expr->get_result()->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::cerr << "findSubExprs" << std::endl;
                                printAlts( finder.alternatives, std::cerr );
                        )
                        *out++ = finder;
                }
        }

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

        void AlternativeFinder::find( Expression *expr, bool adjust, bool prune ) {
                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 ) {
                                adjustExprType( i->expr->get_result(), i->env, indexer );
                        }
                }
                if ( prune ) {
                        PRINT(
                                std::cerr << "alternatives before prune:" << std::endl;
                                printAlts( alternatives, std::cerr );
                        )
                        AltList::iterator oldBegin = alternatives.begin();
                        pruneAlternatives( alternatives.begin(), alternatives.end(), front_inserter( alternatives ), indexer );
                        if ( alternatives.begin() == oldBegin ) {
                                std::ostringstream stream;
                                stream << "Can't choose between " << alternatives.size() << " 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( stream.str() );
                        }
                        alternatives.erase( oldBegin, alternatives.end() );
                        PRINT(
                                std::cerr << "there are " << alternatives.size() << " alternatives after elimination" << std::endl;
                        )
                }

                // Central location to handle gcc extension keyword for all expression types.
                for ( Alternative &iter: alternatives ) {
                        iter.expr->set_extension( expr->get_extension() );
                } // for
        }

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

        // std::unordered_map< Expression *, UniqueExpr * > ;

        template< typename StructOrUnionType >
        void AlternativeFinder::addAggMembers( StructOrUnionType *aggInst, Expression *expr, const Cost &newCost, const TypeEnvironment & env, Expression * member ) {
                // by this point, member must be a name expr
                NameExpr * nameExpr = safe_dynamic_cast< NameExpr * >( member );
                const std::string & name = nameExpr->get_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, expr->clone() ), env, newCost ) );
                                renameTypes( alternatives.back().expr );
                        } else {
                                assert( false );
                        }
                }
        }

        void AlternativeFinder::addTupleMembers( TupleType * tupleType, Expression *expr, const Cost &newCost, const TypeEnvironment & env, Expression * member ) {
                if ( ConstantExpr * constantExpr = dynamic_cast< ConstantExpr * >( member ) ) {
                        // get the value of the constant expression as an int, must be between 0 and the length of the tuple type to have meaning
                        // xxx - this should be improved by memoizing the value of constant exprs
                        // during parsing and reusing that information here.
                        std::stringstream ss( constantExpr->get_constant()->get_value() );
                        int val;
                        std::string tmp;
                        if ( ss >> val && ! (ss >> tmp) ) {
                                if ( val >= 0 && (unsigned int)val < tupleType->size() ) {
                                        alternatives.push_back( Alternative( new TupleIndexExpr( expr->clone(), val ), env, newCost ) );
                                } // if
                        } // if
                } else if ( NameExpr * nameExpr = dynamic_cast< NameExpr * >( member ) ) {
                        // xxx - temporary hack until 0/1 are int constants
                        if ( nameExpr->get_name() == "0" || nameExpr->get_name() == "1" ) {
                                std::stringstream ss( nameExpr->get_name() );
                                int val;
                                ss >> val;
                                alternatives.push_back( Alternative( new TupleIndexExpr( expr->clone(), val ), env, newCost ) );
                        }
                } // if
        }

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

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

                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();

                std::list< Type * > formalTypes;
                std::list< Type * >::iterator formalType = formalTypes.end();

                for ( std::list< Expression* >::iterator actualExpr = actuals.begin(); actualExpr != actuals.end(); ++actualExpr ) {

                        PRINT(
                                std::cerr << "actual expression:" << std::endl;
                                (*actualExpr)->print( std::cerr, 8 );
                                std::cerr << "--- results are" << std::endl;
                                (*actualExpr)->get_result()->print( std::cerr, 8 );
                        )
                        std::list< DeclarationWithType* >::iterator startFormal = formal;
                        Cost actualCost;
                        std::list< Type * > flatActualTypes;
                        flatten( (*actualExpr)->get_result(), back_inserter( flatActualTypes ) );
                        for ( std::list< Type* >::iterator actualType = flatActualTypes.begin(); actualType != flatActualTypes.end(); ++actualType ) {


                                // tuple handling code
                                if ( formalType == formalTypes.end() ) {
                                        // the type of the formal parameter may be a tuple type. To make this easier to work with,
                                        // flatten the tuple type and traverse the resulting list of types, incrementing the formal
                                        // iterator once its types have been extracted. Once a particular formal parameter's type has
                                        // been exhausted load the next formal parameter's type.
                                        if ( formal == formals.end() ) {
                                                if ( function->get_isVarArgs() ) {
                                                        convCost += Cost( 1, 0, 0 );
                                                        break;
                                                } else {
                                                        return Cost::infinity;
                                                }
                                        }
                                        formalTypes.clear();
                                        flatten( (*formal)->get_type(), back_inserter( formalTypes ) );
                                        formalType = formalTypes.begin();
                                        ++formal;
                                }

                                PRINT(
                                        std::cerr << std::endl << "converting ";
                                        (*actualType)->print( std::cerr, 8 );
                                        std::cerr << std::endl << " to ";
                                        (*formalType)->print( std::cerr, 8 );
                                )
                                Cost newCost = conversionCost( *actualType, *formalType, indexer, alt.env );
                                PRINT(
                                        std::cerr << std::endl << "cost is" << newCost << std::endl;
                                )

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

                                convCost += Cost( 0, polyCost( *formalType, alt.env, indexer ) + polyCost( *actualType, alt.env, indexer ), 0 );

                                formalType++;
                        }
                        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::cerr << std::endl << "converting ";
                                assert->second.actualType->print( std::cerr, 8 );
                                std::cerr << std::endl << " to ";
                                assert->second.formalType->print( std::cerr, 8 );
                        )
                        Cost newCost = conversionCost( assert->second.actualType, assert->second.formalType, indexer, alt.env );
                        PRINT(
                                std::cerr << 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;
        }

        /// Adds type variables to the open variable set and marks their assertions
        void makeUnifiableVars( Type *type, OpenVarSet &unifiableVars, AssertionSet &needAssertions ) {
                for ( Type::ForallList::const_iterator tyvar = type->get_forall().begin(); tyvar != type->get_forall().end(); ++tyvar ) {
                        unifiableVars[ (*tyvar)->get_name() ] = TypeDecl::Data{ *tyvar };
                        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() );
                }
        }

        /// instantiate a single argument by matching actuals from [actualIt, actualEnd) against formalType,
        /// producing expression(s) in out and their total cost in cost.
        template< typename AltIterator, typename OutputIterator >
        bool instantiateArgument( Type * formalType, Initializer * defaultValue, AltIterator & actualIt, AltIterator actualEnd, OpenVarSet & openVars, TypeEnvironment & resultEnv, AssertionSet & resultNeed, AssertionSet & resultHave, const SymTab::Indexer & indexer, Cost & cost, OutputIterator out ) {
                if ( TupleType * tupleType = dynamic_cast< TupleType * >( formalType ) ) {
                        // formalType is a TupleType - group actuals into a TupleExpr whose type unifies with the TupleType
                        TupleExpr * tupleExpr = new TupleExpr();
                        for ( Type * type : *tupleType ) {
                                if ( ! instantiateArgument( type, defaultValue, actualIt, actualEnd, openVars, resultEnv, resultNeed, resultHave, indexer, cost, back_inserter( tupleExpr->get_exprs() ) ) ) {
                                        delete tupleExpr;
                                        return false;
                                }
                        }
                        tupleExpr->set_result( Tuples::makeTupleType( tupleExpr->get_exprs() ) );
                        *out++ = tupleExpr;
                } else if ( actualIt != actualEnd ) {
                        // both actualType and formalType are atomic (non-tuple) types - if they unify
                        // then accept actual as an argument, otherwise return false (fail to instantiate argument)
                        Expression * actual = actualIt->expr;
                        Type * actualType = actual->get_result();
                        PRINT(
                                std::cerr << "formal type is ";
                                formalType->print( std::cerr );
                                std::cerr << std::endl << "actual type is ";
                                actualType->print( std::cerr );
                                std::cerr << std::endl;
                        )
                        if ( ! unify( formalType, actualType, resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
                                return false;
                        }
                        // move the expression from the alternative to the output iterator
                        *out++ = actual;
                        actualIt->expr = nullptr;
                        cost += actualIt->cost;
                        ++actualIt;
                } else {
                        // End of actuals - Handle default values
                        if ( SingleInit *si = dynamic_cast<SingleInit *>( defaultValue )) {
                                // 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( formalType, cnst->get_type(), resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
                                                        // xxx - Don't know if this is right
                                                        *out++ = cnstexpr->clone();
                                                        return true;
                                                } // if
                                        } // if
                                } // if
                        } // if
                        return false;
                } // if
                return true;
        }

        bool AlternativeFinder::instantiateFunction( std::list< DeclarationWithType* >& formals, const AltList &actuals, bool isVarArgs, OpenVarSet& openVars, TypeEnvironment &resultEnv, AssertionSet &resultNeed, AssertionSet &resultHave, AltList & out ) {
                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 );

                // flatten actuals so that each actual has an atomic (non-tuple) type
                AltList exploded;
                Tuples::explode( actuals, indexer, back_inserter( exploded ) );

                AltList::iterator actualExpr = exploded.begin();
                AltList::iterator actualEnd = exploded.end();
                for ( DeclarationWithType * formal : formals ) {
                        // match flattened actuals with formal parameters - actuals will be grouped to match
                        // with formals as appropriate
                        Cost cost;
                        std::list< Expression * > newExprs;
                        ObjectDecl * obj = safe_dynamic_cast< ObjectDecl * >( formal );
                        if ( ! instantiateArgument( obj->get_type(), obj->get_init(), actualExpr, actualEnd, openVars, resultEnv, resultNeed, resultHave, indexer, cost, back_inserter( newExprs ) ) ) {
                                deleteAll( newExprs );
                                return false;
                        }
                        // success - produce argument as a new alternative
                        assert( newExprs.size() == 1 );
                        out.push_back( Alternative( newExprs.front(), resultEnv, cost ) );
                }
                if ( actualExpr != actualEnd ) {
                        // there are still actuals remaining, but we've run out of formal parameters to match against
                        // this is okay only if the function is variadic
                        if ( ! isVarArgs ) {
                                return false;
                        }
                        out.splice( out.end(), exploded, actualExpr, actualEnd );
                }
                return true;
        }

        // /// Map of declaration uniqueIds (intended to be the assertions in an AssertionSet) to their parents and the number of times they've been included
        //typedef std::unordered_map< UniqueId, std::unordered_map< UniqueId, unsigned > > AssertionParentSet;

        static const int recursionLimit = /*10*/ 4;  ///< Limit to depth of recursion satisfaction
        //static const unsigned recursionParentLimit = 1;  ///< Limit to the number of times an assertion can recursively use itself

        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, /*const AssertionParentSet &needParents,*/
                                                 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, /*needParents,*/ level+1, indexer, out );
                                return;
                        }
                }

                ForwardIterator cur = begin++;
                if ( ! cur->second ) {
                        inferRecursive( begin, end, newAlt, openVars, decls, newNeed, /*needParents,*/ level, indexer, out );
                        return; // xxx - should this continue? previously this wasn't here, and it looks like it should be
                }
                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::cerr << "no candidates!" << std::endl; }
                for ( std::list< DeclarationWithType* >::const_iterator candidate = candidates.begin(); candidate != candidates.end(); ++candidate ) {
                        PRINT(
                                std::cerr << "inferRecursive: candidate is ";
                                (*candidate)->print( std::cerr );
                                std::cerr << 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() );
                                DeclarationWithType *candDecl = static_cast< DeclarationWithType* >( Declaration::declFromId( (*candidate)->get_uniqueId() ) );
                                //AssertionParentSet newNeedParents( needParents );
                                // skip repeatingly-self-recursive assertion satisfaction
                                // DOESN'T WORK: grandchild nodes conflict with their cousins
                                //if ( newNeedParents[ curDecl->get_uniqueId() ][ candDecl->get_uniqueId() ]++ > recursionParentLimit ) continue;
                                Expression *varExpr = new VariableExpr( candDecl );
                                delete varExpr->get_result();
                                varExpr->set_result( adjType->clone() );
                                PRINT(
                                        std::cerr << "satisfying assertion " << curDecl->get_uniqueId() << " ";
                                        curDecl->print( std::cerr );
                                        std::cerr << " with declaration " << (*candidate)->get_uniqueId() << " ";
                                        (*candidate)->print( std::cerr );
                                        std::cerr << 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, /*newNeedParents,*/ 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::cerr << "inferParameters: assertions needed are" << std::endl;
//          printAll( need, std::cerr, 8 );
//          )
                SymTab::Indexer decls( indexer );
                PRINT(
                        std::cerr << "============= original indexer" << std::endl;
                        indexer.print( std::cerr );
                        std::cerr << "============= new indexer" << std::endl;
                        decls.print( std::cerr );
                )
                addToIndexer( have, decls );
                AssertionSet newNeed;
                //AssertionParentSet needParents;
                inferRecursive( need.begin(), need.end(), newAlt, openVars, decls, newNeed, /*needParents,*/ 0, indexer, out );
//      PRINT(
//          std::cerr << "declaration 14 is ";
//          Declaration::declFromId
//          *out++ = newAlt;
//          )
        }

        template< typename OutputIterator >
        void AlternativeFinder::makeFunctionAlternatives( const Alternative &func, FunctionType *funcType, const AltList &actualAlt, OutputIterator out ) {
                OpenVarSet openVars;
                AssertionSet resultNeed, resultHave;
                TypeEnvironment resultEnv;
                makeUnifiableVars( funcType, openVars, resultNeed );
                AltList instantiatedActuals; // filled by instantiate function
                if ( targetType && ! targetType->isVoid() ) {
                        // attempt to narrow based on expected target type
                        Type * returnType = funcType->get_returnVals().front()->get_type();
                        if ( ! unify( returnType, targetType, resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
                                // unification failed, don't pursue this alternative
                                return;
                        }
                }

                if ( instantiateFunction( funcType->get_parameters(), actualAlt, funcType->get_isVarArgs(), openVars, resultEnv, resultNeed, resultHave, instantiatedActuals ) ) {
                        ApplicationExpr *appExpr = new ApplicationExpr( func.expr->clone() );
                        Alternative newAlt( appExpr, resultEnv, sumCost( instantiatedActuals ) );
                        makeExprList( instantiatedActuals, appExpr->get_args() );
                        PRINT(
                                std::cerr << "need assertions:" << std::endl;
                                printAssertionSet( resultNeed, std::cerr, 8 );
                        )
                        inferParameters( resultNeed, resultHave, newAlt, openVars, out );
                }
        }

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

                AlternativeFinder funcFinder( indexer, env );

                {
                        std::string fname = InitTweak::getFunctionName( untypedExpr );
                        if ( fname == "&&" ) {
                                VoidType v = Type::Qualifiers();                // resolve to type void *
                                PointerType pt( Type::Qualifiers(), v.clone() );
                                UntypedExpr *vexpr = untypedExpr->clone();
                                vexpr->set_result( pt.clone() );
                                alternatives.push_back( Alternative( vexpr, 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 ) );

                // take care of possible tuple assignments
                // if not tuple assignment, assignment is taken care of as a normal function call
                Tuples::handleTupleAssignment( *this, untypedExpr, possibilities );

                AltList candidates;
                SemanticError errors;
                for ( AltList::const_iterator func = funcFinder.alternatives.begin(); func != funcFinder.alternatives.end(); ++func ) {
                        try {
                                PRINT(
                                        std::cerr << "working on alternative: " << std::endl;
                                        func->print( std::cerr, 8 );
                                )
                                // check if the type is pointer to function
                                PointerType *pointer;
                                if ( ( pointer = dynamic_cast< PointerType* >( func->expr->get_result() ) ) ) {
                                        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 ) );
                                                                } // for
                                                        } // if
                                                } // if
                                        } // if
                                } 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::cerr << "known function ops:" << std::endl;
                                                        printAlts( funcOpFinder.alternatives, std::cerr, 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 ( ( pointer = dynamic_cast< PointerType* >( funcOp->expr->get_result() ) ) ) {
                                                        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
                                                        } // if
                                                } // if
                                        } // for
                                } // if
                        } catch ( SemanticError &e ) {
                                errors.append( e );
                        }
                } // for

                // Implement SFINAE; resolution errors are only errors if there aren't any non-erroneous resolutions
                if ( candidates.empty() && ! errors.isEmpty() ) { throw errors; }

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

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

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

                if ( alternatives.empty() && targetType && ! targetType->isVoid() ) {
                        // xxx - this is a temporary hack. If resolution is unsuccessful with a target type, try again without a
                        // target type, since it will sometimes succeed when it wouldn't easily with target type binding. For example,
                        //   forall( otype T ) lvalue T ?[?]( T *, ptrdiff_t );
                        //   const char * x = "hello world";
                        //   unsigned char ch = x[0];
                        // Fails with simple return type binding. First, T is bound to unsigned char, then (x: const char *) is unified
                        // with unsigned char *, which fails because pointer base types must be unified exactly. The new resolver should
                        // fix this issue in a more robust way.
                        targetType = nullptr;
                        visit( untypedExpr );
                }
        }

        bool isLvalue( Expression *expr ) {
                // xxx - recurse into tuples?
                return expr->has_result() && expr->get_result()->get_isLvalue();
        }

        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 ) );
                        } // if
                } // for
        }

        void AlternativeFinder::visit( CastExpr *castExpr ) {
                Type *& toType = castExpr->get_result();
                assert( toType );
                toType = resolveTypeof( toType, indexer );
                SymTab::validateType( toType, &indexer );
                adjustExprType( toType, env, indexer );

                AlternativeFinder finder( indexer, env );
                finder.targetType = toType;
                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_result()->size() - castExpr->get_result()->size();
                        if ( discardedValues < 0 ) continue;
                        // xxx - may need to go into tuple types and extract relevant types and use unifyList. Note that currently, this does not
                        // allow casting a tuple to an atomic type (e.g. (int)([1, 2, 3]))
                        // unification run for side-effects
                        unify( castExpr->get_result(), (*i).expr->get_result(), i->env, needAssertions, haveAssertions, openVars, indexer );
                        Cost thisCost = castCost( (*i).expr->get_result(), castExpr->get_result(), indexer, i->env );
                        if ( thisCost != Cost::infinity ) {
                                // count one safe conversion for each value that is thrown away
                                thisCost += Cost( 0, 0, discardedValues );

                                Expression * argExpr = i->expr->clone();
                                if ( argExpr->get_result()->size() > 1 && ! castExpr->get_result()->isVoid() ) {
                                        // Argument expression is a tuple and the target type is not void. Cast each member of the tuple
                                        // to its corresponding target type, producing the tuple of those cast expressions. If there are
                                        // more components of the tuple than components in the target type, then excess components do not
                                        // come out in the result expression (but UniqueExprs ensure that side effects will still be done).
                                        if ( Tuples::maybeImpure( argExpr ) && ! dynamic_cast< UniqueExpr * >( argExpr ) ) {
                                                // expressions which may contain side effects require a single unique instance of the expression.
                                                argExpr = new UniqueExpr( argExpr );
                                        }
                                        std::list< Expression * > componentExprs;
                                        for ( unsigned int i = 0; i < castExpr->get_result()->size(); i++ ) {
                                                // cast each component
                                                TupleIndexExpr * idx = new TupleIndexExpr( argExpr->clone(), i );
                                                componentExprs.push_back( new CastExpr( idx, castExpr->get_result()->getComponent( i )->clone() ) );
                                        }
                                        delete argExpr;
                                        assert( componentExprs.size() > 0 );
                                        // produce the tuple of casts
                                        candidates.push_back( Alternative( new TupleExpr( componentExprs ), i->env, i->cost, thisCost ) );
                                } else {
                                        // handle normally
                                        candidates.push_back( Alternative( new CastExpr( argExpr->clone(), toType->clone() ), i->env, i->cost, thisCost ) );
                                }
                        } // if
                } // for

                // 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 ( StructInstType *structInst = dynamic_cast< StructInstType* >( agg->expr->get_result() ) ) {
                                addAggMembers( structInst, agg->expr, agg->cost, agg->env, memberExpr->get_member() );
                        } else if ( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( agg->expr->get_result() ) ) {
                                addAggMembers( unionInst, agg->expr, agg->cost, agg->env, memberExpr->get_member() );
                        } else if ( TupleType * tupleType = dynamic_cast< TupleType * >( agg->expr->get_result() ) ) {
                                addTupleMembers( tupleType, agg->expr, agg->cost, agg->env, memberExpr->get_member() );
                        } // if
                } // for
        }

        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() ) ) {
                                NameExpr nameExpr( "" );
                                addAggMembers( structInst, &newExpr, Cost( 0, 0, 1 ), env, &nameExpr );
                        } else if ( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( (*i)->get_type() ) ) {
                                NameExpr nameExpr( "" );
                                addAggMembers( unionInst, &newExpr, Cost( 0, 0, 1 ), env, &nameExpr );
                        } // if
                } // for
        }

        void AlternativeFinder::visit( VariableExpr *variableExpr ) {
                // not sufficient to clone here, because variable's type may have changed
                // since the VariableExpr was originally created.
                alternatives.push_back( Alternative( new VariableExpr( variableExpr->get_var() ), 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() ) {
                        // xxx - resolveTypeof?
                        alternatives.push_back( Alternative( sizeofExpr->clone(), env, Cost::zero ) );
                } else {
                        // find all alternatives for the argument to sizeof
                        AlternativeFinder finder( indexer, env );
                        finder.find( sizeofExpr->get_expr() );
                        // find the lowest cost alternative among the alternatives, otherwise ambiguous
                        AltList winners;
                        findMinCost( finder.alternatives.begin(), finder.alternatives.end(), back_inserter( winners ) );
                        if ( winners.size() != 1 ) {
                                throw SemanticError( "Ambiguous expression in sizeof operand: ", sizeofExpr->get_expr() );
                        } // if
                        // return the lowest cost alternative for the argument
                        Alternative &choice = winners.front();
                        alternatives.push_back( Alternative( new SizeofExpr( choice.expr->clone() ), choice.env, Cost::zero ) );
                } // if
        }

        void AlternativeFinder::visit( AlignofExpr *alignofExpr ) {
                if ( alignofExpr->get_isType() ) {
                        // xxx - resolveTypeof?
                        alternatives.push_back( Alternative( alignofExpr->clone(), env, Cost::zero ) );
                } else {
                        // find all alternatives for the argument to sizeof
                        AlternativeFinder finder( indexer, env );
                        finder.find( alignofExpr->get_expr() );
                        // find the lowest cost alternative among the alternatives, otherwise ambiguous
                        AltList winners;
                        findMinCost( finder.alternatives.begin(), finder.alternatives.end(), back_inserter( winners ) );
                        if ( winners.size() != 1 ) {
                                throw SemanticError( "Ambiguous expression in alignof operand: ", alignofExpr->get_expr() );
                        } // if
                        // return the lowest cost alternative for the argument
                        Alternative &choice = winners.front();
                        alternatives.push_back( Alternative( new AlignofExpr( choice.expr->clone() ), choice.env, Cost::zero ) );
                } // if
        }

        template< typename StructOrUnionType >
        void AlternativeFinder::addOffsetof( StructOrUnionType *aggInst, 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 OffsetofExpr( aggInst->clone(), dwt ), env, Cost::zero ) );
                                renameTypes( alternatives.back().expr );
                        } else {
                                assert( false );
                        }
                }
        }

        void AlternativeFinder::visit( UntypedOffsetofExpr *offsetofExpr ) {
                AlternativeFinder funcFinder( indexer, env );
                // xxx - resolveTypeof?
                if ( StructInstType *structInst = dynamic_cast< StructInstType* >( offsetofExpr->get_type() ) ) {
                        addOffsetof( structInst, offsetofExpr->get_member() );
                } else if ( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( offsetofExpr->get_type() ) ) {
                        addOffsetof( unionInst, offsetofExpr->get_member() );
                }
        }

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

        void AlternativeFinder::visit( OffsetPackExpr *offsetPackExpr ) {
                alternatives.push_back( Alternative( offsetPackExpr->clone(), 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::cerr << "resolvAttr: funcDecl is ";
                        funcDecl->print( std::cerr );
                        std::cerr << " argType is ";
                        argType->print( std::cerr );
                        std::cerr << 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->set_result( (*i)->get_type()->clone() );
                        } // for
                } // if
        }

        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_result()->size() == 1 ) {
                                                                        resolveAttr(*i, function, choice->expr->get_result(), choice->env );
                                                                } // fi
                                                        } // for
                                                } // if
                                        } // if
                                } // if
                        } // for
                } 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 );
                        } // for
                } // if
        }

        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 );
                                        Type* commonType = nullptr;
                                        if ( unify( second->expr->get_result(), third->expr->get_result(), newAlt.env, needAssertions, haveAssertions, openVars, indexer, commonType ) ) {
                                                ConditionalExpr *newExpr = new ConditionalExpr( first->expr->clone(), second->expr->clone(), third->expr->clone() );
                                                newExpr->set_result( commonType ? commonType : second->expr->get_result()->clone() );
                                                newAlt.expr = newExpr;
                                                inferParameters( needAssertions, haveAssertions, newAlt, openVars, back_inserter( alternatives ) );
                                        } // if
                                } // for
                        } // for
                } // for
        }

        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 ) );
                } // for
                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() );
                        newExpr->set_result( Tuples::makeTupleType( newExpr->get_exprs() ) );

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

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

        void AlternativeFinder::visit( ConstructorExpr * ctorExpr ) {
                AlternativeFinder finder( indexer, env );
                // don't prune here, since it's guaranteed all alternatives will have the same type
                // (giving the alternatives different types is half of the point of ConstructorExpr nodes)
                finder.findWithAdjustment( ctorExpr->get_callExpr(), false );
                for ( Alternative & alt : finder.alternatives ) {
                        alternatives.push_back( Alternative( new ConstructorExpr( alt.expr->clone() ), alt.env, alt.cost ) );
                }
        }

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

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

        void AlternativeFinder::visit( UniqueExpr *unqExpr ) {
                AlternativeFinder finder( indexer, env );
                finder.findWithAdjustment( unqExpr->get_expr() );
                for ( Alternative & alt : finder.alternatives ) {
                        // ensure that the id is passed on to the UniqueExpr alternative so that the expressions are "linked"
                        UniqueExpr * newUnqExpr = new UniqueExpr( alt.expr->clone(), unqExpr->get_id() );
                        alternatives.push_back( Alternative( newUnqExpr, alt.env, alt.cost ) );
                }
        }

        void AlternativeFinder::visit( StmtExpr *stmtExpr ) {
                StmtExpr * newStmtExpr = stmtExpr->clone();
                ResolvExpr::resolveStmtExpr( newStmtExpr, indexer );
                // xxx - this env is almost certainly wrong, and needs to somehow contain the combined environments from all of the statements in the stmtExpr...
                alternatives.push_back( Alternative( newStmtExpr, env, Cost::zero ) );
        }

} // namespace ResolvExpr

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