//
// 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.
//
// CandidateFinder.cpp --
//
// Author           : Aaron B. Moss
// Created On       : Wed Jun 5 14:30:00 2019
// Last Modified By : Aaron B. Moss
// Last Modified On : Wed Jun 5 14:30:00 2019
// Update Count     : 1
//

#include "CandidateFinder.hpp"

#include <deque>
#include <iterator>               // for back_inserter
#include <sstream>
#include <string>
#include <unordered_map>
#include <vector>

#include "Candidate.hpp"
#include "CompilationState.h"
#include "Cost.h"
#include "ExplodedArg.hpp"
#include "Resolver.h"
#include "SatisfyAssertions.hpp"
#include "typeops.h"              // for adjustExprType, conversionCost, polyCost, specCost
#include "Unify.h"
#include "AST/Expr.hpp"
#include "AST/Node.hpp"
#include "AST/Pass.hpp"
#include "AST/Print.hpp"
#include "AST/SymbolTable.hpp"
#include "AST/Type.hpp"
#include "SymTab/Mangler.h"
#include "Tuples/Tuples.h"        // for handleTupleAssignment

#define PRINT( text ) if ( resolvep ) { text }

namespace ResolvExpr {

using std::move;

/// partner to move that copies any copyable type
template<typename T>
T copy( const T & x ) { return x; }

const ast::Expr * referenceToRvalueConversion( const ast::Expr * expr, Cost & cost ) {
	if ( expr->result.as< ast::ReferenceType >() ) {
		// cast away reference from expr
		cost.incReference();
		return new ast::CastExpr{ expr->location, expr, expr->result->stripReferences() };
	}
	
	return expr;
}

/// Unique identifier for matching expression resolutions to their requesting expression
UniqueId globalResnSlot = 0;

namespace {
	/// First index is which argument, second is which alternative, third is which exploded element
	using ExplodedArgs_new = std::deque< std::vector< ExplodedArg > >;

	/// Returns a list of alternatives with the minimum cost in the given list
	CandidateList findMinCost( const CandidateList & candidates ) {
		CandidateList out;
		Cost minCost = Cost::infinity;
		for ( const CandidateRef & r : candidates ) {
			if ( r->cost < minCost ) {
				minCost = r->cost;
				out.clear();
				out.emplace_back( r );
			} else if ( r->cost == minCost ) {
				out.emplace_back( r );
			}
		}
		return out;
	}

	/// Computes conversion cost between two types
	Cost computeConversionCost( 
		const ast::Type * argType, const ast::Type * paramType, const ast::SymbolTable & symtab, 
		const ast::TypeEnvironment & env 
	) {
		PRINT(
			std::cerr << std::endl << "converting ";
			ast::print( std::cerr, argType, 2 );
			std::cerr << std::endl << " to ";
			ast::print( std::cerr, paramType, 2 );
			std::cerr << std::endl << "environment is: ";
			ast::print( std::cerr, env, 2 );
			std::cerr << std::endl;
		)
		Cost convCost = conversionCost( argType, paramType, symtab, env );
		PRINT(
			std::cerr << std::endl << "cost is " << convCost << std::endl;
		)
		if ( convCost == Cost::infinity ) return convCost;
		convCost.incPoly( polyCost( paramType, symtab, env ) + polyCost( argType, symtab, env ) );
		PRINT(
			std::cerr << "cost with polycost is " << convCost << std::endl;
		)
		return convCost;
	}

	/// Computes conversion cost for a given expression to a given type
	const ast::Expr * computeExpressionConversionCost( 
		const ast::Expr * arg, const ast::Type * paramType, const ast::SymbolTable & symtab, const ast::TypeEnvironment & env, Cost & outCost 
	) {
		Cost convCost = computeConversionCost( arg->result, paramType, symtab, env );
		outCost += convCost;

		// If there is a non-zero conversion cost, ignoring poly cost, then the expression requires 
		// conversion. Ignore poly cost for now, since this requires resolution of the cast to 
		// infer parameters and this does not currently work for the reason stated below
		Cost tmpCost = convCost;
		tmpCost.incPoly( -tmpCost.get_polyCost() );
		if ( tmpCost != Cost::zero ) {
			ast::ptr< ast::Type > newType = paramType;
			env.apply( newType );
			return new ast::CastExpr{ arg->location, arg, newType };

			// xxx - *should* be able to resolve this cast, but at the moment pointers are not 
			// castable to zero_t, but are implicitly convertible. This is clearly inconsistent, 
			// once this is fixed it should be possible to resolve the cast.
			// xxx - this isn't working, it appears because type1 (parameter) is seen as widenable, 
			// but it shouldn't be because this makes the conversion from DT* to DT* since 
			// commontype(zero_t, DT*) is DT*, rather than nothing

			// CandidateFinder finder{ symtab, env };
			// finder.find( arg, ResolvMode::withAdjustment() );
			// assertf( finder.candidates.size() > 0, 
			// 	"Somehow castable expression failed to find alternatives." );
			// assertf( finder.candidates.size() == 1, 
			// 	"Somehow got multiple alternatives for known cast expression." );
			// return finder.candidates.front()->expr;
		}

		return arg;
	}

	/// Computes conversion cost for a given candidate
	Cost computeApplicationConversionCost( 
		CandidateRef cand, const ast::SymbolTable & symtab 
	) {
		auto appExpr = cand->expr.strict_as< ast::ApplicationExpr >();
		auto pointer = appExpr->func->result.strict_as< ast::PointerType >();
		auto function = pointer->base.strict_as< ast::FunctionType >();

		Cost convCost = Cost::zero;
		const auto & params = function->params;
		auto param = params.begin();
		auto & args = appExpr->args;

		for ( unsigned i = 0; i < args.size(); ++i ) {
			const ast::Type * argType = args[i]->result;
			PRINT(
				std::cerr << "arg expression:" << std::endl;
				ast::print( std::cerr, args[i], 2 );
				std::cerr << "--- results are" << std::endl;
				ast::print( std::cerr, argType, 2 );
			)

			if ( param == params.end() ) {
				if ( function->isVarArgs ) {
					convCost.incUnsafe();
					PRINT( std::cerr << "end of params with varargs function: inc unsafe: " 
						<< convCost << std::endl; ; )
					// convert reference-typed expressions into value-typed expressions
					cand->expr = ast::mutate_field_index( 
						appExpr, &ast::ApplicationExpr::args, i, 
						referenceToRvalueConversion( args[i], convCost ) );
					continue;
				} else return Cost::infinity;
			}

			if ( auto def = args[i].as< ast::DefaultArgExpr >() ) {
				// Default arguments should be free - don't include conversion cost.
				// Unwrap them here because they are not relevant to the rest of the system
				cand->expr = ast::mutate_field_index( 
					appExpr, &ast::ApplicationExpr::args, i, def->expr );
				++param;
				continue;
			}

			// mark conversion cost and also specialization cost of param type
			const ast::Type * paramType = (*param)->get_type();
			cand->expr = ast::mutate_field_index( 
				appExpr, &ast::ApplicationExpr::args, i, 
				computeExpressionConversionCost( 
					args[i], paramType, symtab, cand->env, convCost ) );
			convCost.decSpec( specCost( paramType ) );
			++param;  // can't be in for-loop update because of the continue
		}

		if ( param != params.end() ) return Cost::infinity;

		// specialization cost of return types can't be accounted for directly, it disables 
		// otherwise-identical calls, like this example based on auto-newline in the I/O lib:
		//
		//   forall(otype OS) {
		//     void ?|?(OS&, int);  // with newline
		//     OS&  ?|?(OS&, int);  // no newline, always chosen due to more specialization
		//   }

		// mark type variable and specialization cost of forall clause
		convCost.incVar( function->forall.size() );
		for ( const ast::TypeDecl * td : function->forall ) {
			convCost.decSpec( td->assertions.size() );
		}

		return convCost;
	}

	void makeUnifiableVars( 
		const ast::ParameterizedType * type, ast::OpenVarSet & unifiableVars, 
		ast::AssertionSet & need 
	) {
		for ( const ast::TypeDecl * tyvar : type->forall ) {
			unifiableVars[ tyvar->name ] = ast::TypeDecl::Data{ tyvar };
			for ( const ast::DeclWithType * assn : tyvar->assertions ) {
				need[ assn ].isUsed = true;
			}
		}
	}

	/// Gets a default value from an initializer, nullptr if not present
	const ast::ConstantExpr * getDefaultValue( const ast::Init * init ) {
		if ( auto si = dynamic_cast< const ast::SingleInit * >( init ) ) {
			if ( auto ce = si->value.as< ast::CastExpr >() ) {
				return ce->arg.as< ast::ConstantExpr >();
			} else {
				return si->value.as< ast::ConstantExpr >();
			}
		}
		return nullptr;
	}

	/// State to iteratively build a match of parameter expressions to arguments
	struct ArgPack {
		std::size_t parent;          ///< Index of parent pack
		ast::ptr< ast::Expr > expr;  ///< The argument stored here
		Cost cost;                   ///< The cost of this argument
		ast::TypeEnvironment env;    ///< Environment for this pack
		ast::AssertionSet need;      ///< Assertions outstanding for this pack
		ast::AssertionSet have;      ///< Assertions found for this pack
		ast::OpenVarSet open;        ///< Open variables for this pack
		unsigned nextArg;            ///< Index of next argument in arguments list
		unsigned tupleStart;         ///< Number of tuples that start at this index
		unsigned nextExpl;           ///< Index of next exploded element
		unsigned explAlt;            ///< Index of alternative for nextExpl > 0

		ArgPack()
		: parent( 0 ), expr(), cost( Cost::zero ), env(), need(), have(), open(), nextArg( 0 ), 
		  tupleStart( 0 ), nextExpl( 0 ), explAlt( 0 ) {}
		
		ArgPack( 
			const ast::TypeEnvironment & env, const ast::AssertionSet & need, 
			const ast::AssertionSet & have, const ast::OpenVarSet & open )
		: parent( 0 ), expr(), cost( Cost::zero ), env( env ), need( need ), have( have ), 
		  open( open ), nextArg( 0 ), tupleStart( 0 ), nextExpl( 0 ), explAlt( 0 ) {}
		
		ArgPack(
			std::size_t parent, const ast::Expr * expr, ast::TypeEnvironment && env, 
			ast::AssertionSet && need, ast::AssertionSet && have, ast::OpenVarSet && open, 
			unsigned nextArg, unsigned tupleStart = 0, Cost cost = Cost::zero, 
			unsigned nextExpl = 0, unsigned explAlt = 0 )
		: parent(parent), expr( expr ), cost( cost ), env( move( env ) ), need( move( need ) ),
		  have( move( have ) ), open( move( open ) ), nextArg( nextArg ), tupleStart( tupleStart ),
		  nextExpl( nextExpl ), explAlt( explAlt ) {}
		
		ArgPack(
			const ArgPack & o, ast::TypeEnvironment && env, ast::AssertionSet && need, 
			ast::AssertionSet && have, ast::OpenVarSet && open, unsigned nextArg, Cost added )
		: parent( o.parent ), expr( o.expr ), cost( o.cost + added ), env( move( env ) ), 
		  need( move( need ) ), have( move( have ) ), open( move( open ) ), nextArg( nextArg ), 
		  tupleStart( o.tupleStart ), nextExpl( 0 ), explAlt( 0 ) {}
		
		/// true if this pack is in the middle of an exploded argument
		bool hasExpl() const { return nextExpl > 0; }

		/// Gets the list of exploded candidates for this pack
		const ExplodedArg & getExpl( const ExplodedArgs_new & args ) const {
			return args[ nextArg-1 ][ explAlt ];
		}
		
		/// Ends a tuple expression, consolidating the appropriate args
		void endTuple( const std::vector< ArgPack > & packs ) {
			// add all expressions in tuple to list, summing cost
			std::deque< const ast::Expr * > exprs;
			const ArgPack * pack = this;
			if ( expr ) { exprs.emplace_front( expr ); }
			while ( pack->tupleStart == 0 ) {
				pack = &packs[pack->parent];
				exprs.emplace_front( pack->expr );
				cost += pack->cost;
			}
			// reset pack to appropriate tuple
			std::vector< ast::ptr< ast::Expr > > exprv( exprs.begin(), exprs.end() );
			expr = new ast::TupleExpr{ expr->location, move( exprv ) };
			tupleStart = pack->tupleStart - 1;
			parent = pack->parent;
		}
	};

	/// Instantiates an argument to match a parameter, returns false if no matching results left
	bool instantiateArgument( 
		const ast::Type * paramType, const ast::Init * init, const ExplodedArgs_new & args, 
		std::vector< ArgPack > & results, std::size_t & genStart, const ast::SymbolTable & symtab, 
		unsigned nTuples = 0 
	) {
		if ( auto tupleType = dynamic_cast< const ast::TupleType * >( paramType ) ) {
			// paramType is a TupleType -- group args into a TupleExpr
			++nTuples;
			for ( const ast::Type * type : *tupleType ) {
				// xxx - dropping initializer changes behaviour from previous, but seems correct
				// ^^^ need to handle the case where a tuple has a default argument
				if ( ! instantiateArgument( 
					type, nullptr, args, results, genStart, symtab, nTuples ) ) return false;
				nTuples = 0;
			}
			// re-constitute tuples for final generation
			for ( auto i = genStart; i < results.size(); ++i ) {
				results[i].endTuple( results );
			}
			return true;
		} else if ( const ast::TypeInstType * ttype = Tuples::isTtype( paramType ) ) {
			// paramType is a ttype, consumes all remaining arguments
			
			// completed tuples; will be spliced to end of results to finish
			std::vector< ArgPack > finalResults{};

			// iterate until all results completed
			std::size_t genEnd;
			++nTuples;
			do {
				genEnd = results.size();

				// add another argument to results
				for ( std::size_t i = genStart; i < genEnd; ++i ) {
					unsigned nextArg = results[i].nextArg;
					
					// use next element of exploded tuple if present
					if ( results[i].hasExpl() ) {
						const ExplodedArg & expl = results[i].getExpl( args );

						unsigned nextExpl = results[i].nextExpl + 1;
						if ( nextExpl == expl.exprs.size() ) { nextExpl = 0; }

						results.emplace_back(
							i, expl.exprs[ results[i].nextExpl ], copy( results[i].env ),
							copy( results[i].need ), copy( results[i].have ), 
							copy( results[i].open ), nextArg, nTuples, Cost::zero, nextExpl,
							results[i].explAlt );

						continue;
					}

					// finish result when out of arguments
					if ( nextArg >= args.size() ) {
						ArgPack newResult{
							results[i].env, results[i].need, results[i].have, results[i].open };
						newResult.nextArg = nextArg;
						const ast::Type * argType = nullptr;

						if ( nTuples > 0 || ! results[i].expr ) {
							// first iteration or no expression to clone,
							// push empty tuple expression
							newResult.parent = i;
							std::vector< ast::ptr< ast::Expr > > emptyList;
							newResult.expr = 
								new ast::TupleExpr{ CodeLocation{}, move( emptyList ) };
							argType = newResult.expr->result;
						} else {
							// clone result to collect tuple
							newResult.parent = results[i].parent;
							newResult.cost = results[i].cost;
							newResult.tupleStart = results[i].tupleStart;
							newResult.expr = results[i].expr;
							argType = newResult.expr->result;

							if ( results[i].tupleStart > 0 && Tuples::isTtype( argType ) ) {
								// the case where a ttype value is passed directly is special,
								// e.g. for argument forwarding purposes
								// xxx - what if passing multiple arguments, last of which is
								//       ttype?
								// xxx - what would happen if unify was changed so that unifying
								//       tuple
								// types flattened both before unifying lists? then pass in
								// TupleType (ttype) below.
								--newResult.tupleStart;
							} else {
								// collapse leftover arguments into tuple
								newResult.endTuple( results );
								argType = newResult.expr->result;
							}
						}

						// check unification for ttype before adding to final
						if ( 
							unify( 
								ttype, argType, newResult.env, newResult.need, newResult.have,
								newResult.open, symtab ) 
						) {
							finalResults.emplace_back( move( newResult ) );
						}

						continue;
					}

					// add each possible next argument
					for ( std::size_t j = 0; j < args[nextArg].size(); ++j ) {
						const ExplodedArg & expl = args[nextArg][j];

						// fresh copies of parent parameters for this iteration
						ast::TypeEnvironment env = results[i].env;
						ast::OpenVarSet open = results[i].open;

						env.addActual( expl.env, open );

						// skip empty tuple arguments by (nearly) cloning parent into next gen
						if ( expl.exprs.empty() ) {
							results.emplace_back(
								results[i], move( env ), copy( results[i].need ), 
								copy( results[i].have ), move( open ), nextArg + 1, expl.cost );
							
							continue;
						}

						// add new result
						results.emplace_back(
							i, expl.exprs.front(), move( env ), copy( results[i].need ), 
							copy( results[i].have ), move( open ), nextArg + 1, nTuples, 
							expl.cost, expl.exprs.size() == 1 ? 0 : 1, j );
					}
				}

				// reset for next round
				genStart = genEnd;
				nTuples = 0;
			} while ( genEnd != results.size() );

			// splice final results onto results
			for ( std::size_t i = 0; i < finalResults.size(); ++i ) {
				results.emplace_back( move( finalResults[i] ) );
			}
			return ! finalResults.empty();
		}

		// iterate each current subresult
		std::size_t genEnd = results.size();
		for ( std::size_t i = genStart; i < genEnd; ++i ) {
			unsigned nextArg = results[i].nextArg;

			// use remainder of exploded tuple if present
			if ( results[i].hasExpl() ) {
				const ExplodedArg & expl = results[i].getExpl( args );
				const ast::Expr * expr = expl.exprs[ results[i].nextExpl ];

				ast::TypeEnvironment env = results[i].env;
				ast::AssertionSet need = results[i].need, have = results[i].have;
				ast::OpenVarSet open = results[i].open;

				const ast::Type * argType = expr->result;

				PRINT(
					std::cerr << "param type is ";
					ast::print( std::cerr, paramType );
					std::cerr << std::endl << "arg type is ";
					ast::print( std::cerr, argType );
					std::cerr << std::endl;
				)

				if ( unify( paramType, argType, env, need, have, open, symtab ) ) {
					unsigned nextExpl = results[i].nextExpl + 1;
					if ( nextExpl == expl.exprs.size() ) { nextExpl = 0; }

					results.emplace_back(
						i, expr, move( env ), move( need ), move( have ), move( open ), nextArg, 
						nTuples, Cost::zero, nextExpl, results[i].explAlt );
				}

				continue;
			}

			// use default initializers if out of arguments
			if ( nextArg >= args.size() ) {
				if ( const ast::ConstantExpr * cnst = getDefaultValue( init ) ) {
					ast::TypeEnvironment env = results[i].env;
					ast::AssertionSet need = results[i].need, have = results[i].have;
					ast::OpenVarSet open = results[i].open;

					if ( unify( paramType, cnst->result, env, need, have, open, symtab ) ) {
						results.emplace_back(
							i, new ast::DefaultArgExpr{ cnst->location, cnst }, move( env ), 
							move( need ), move( have ), move( open ), nextArg, nTuples );
					}
				}

				continue;
			}

			// Check each possible next argument
			for ( std::size_t j = 0; j < args[nextArg].size(); ++j ) {
				const ExplodedArg & expl = args[nextArg][j];

				// fresh copies of parent parameters for this iteration
				ast::TypeEnvironment env = results[i].env;
				ast::AssertionSet need = results[i].need, have = results[i].have;
				ast::OpenVarSet open = results[i].open;

				env.addActual( expl.env, open );

				// skip empty tuple arguments by (nearly) cloning parent into next gen
				if ( expl.exprs.empty() ) {
					results.emplace_back(
						results[i], move( env ), move( need ), move( have ), move( open ), 
						nextArg + 1, expl.cost );
					
					continue;
				}

				// consider only first exploded arg
				const ast::Expr * expr = expl.exprs.front();
				const ast::Type * argType = expr->result;

				PRINT(
					std::cerr << "param type is ";
					ast::print( std::cerr, paramType );
					std::cerr << std::endl << "arg type is ";
					ast::print( std::cerr, argType );
					std::cerr << std::endl;
				)

				// attempt to unify types
				if ( unify( paramType, argType, env, need, have, open, symtab ) ) {
					// add new result
					results.emplace_back(
						i, expr, move( env ), move( need ), move( have ), move( open ), 
						nextArg + 1, nTuples, expl.cost, expl.exprs.size() == 1 ? 0 : 1, j );
				}
			}
		}

		// reset for next parameter
		genStart = genEnd;

		return genEnd != results.size();
	}

	/// Actually visits expressions to find their candidate interpretations
	struct Finder final : public ast::WithShortCircuiting {
		CandidateFinder & selfFinder;
		const ast::SymbolTable & symtab;
		CandidateList & candidates;
		const ast::TypeEnvironment & tenv;
		ast::ptr< ast::Type > & targetType;

		Finder( CandidateFinder & f )
		: selfFinder( f ), symtab( f.symtab ), candidates( f.candidates ), tenv( f.env ), 
		  targetType( f.targetType ) {}
		
		void previsit( const ast::Node * ) { visit_children = false; }

		/// Convenience to add candidate to list
		template<typename... Args>
		void addCandidate( Args &&... args ) {
			candidates.emplace_back( new Candidate{ std::forward<Args>( args )... } );
		}

		void postvisit( const ast::ApplicationExpr * applicationExpr ) {
			addCandidate( applicationExpr, tenv );
		}

		/// Set up candidate assertions for inference
		void inferParameters( CandidateRef & newCand, CandidateList & out ) {
			// Set need bindings for any unbound assertions
			UniqueId crntResnSlot = 0; // matching ID for this expression's assertions
			for ( auto & assn : newCand->need ) {
				// skip already-matched assertions
				if ( assn.second.resnSlot != 0 ) continue;
				// assign slot for expression if needed
				if ( crntResnSlot == 0 ) { crntResnSlot = ++globalResnSlot; }
				// fix slot to assertion
				assn.second.resnSlot = crntResnSlot;
			}
			// pair slot to expression
			if ( crntResnSlot != 0 ) {
				newCand->expr.get_and_mutate()->inferred.resnSlots().emplace_back( crntResnSlot );
			}

			// add to output list; assertion satisfaction will occur later
			out.emplace_back( newCand );
		}

		/// Completes a function candidate with arguments located
		void validateFunctionCandidate( 
			const CandidateRef & func, ArgPack & result, const std::vector< ArgPack > & results, 
			CandidateList & out 
		) {
			ast::ApplicationExpr * appExpr = 
				new ast::ApplicationExpr{ func->expr->location, func->expr };
			// sum cost and accumulate arguments
			std::deque< const ast::Expr * > args;
			Cost cost = func->cost;
			const ArgPack * pack = &result;
			while ( pack->expr ) {
				args.emplace_front( pack->expr );
				cost += pack->cost;
				pack = &results[pack->parent];
			}
			std::vector< ast::ptr< ast::Expr > > vargs( args.begin(), args.end() );
			appExpr->args = move( vargs );
			// build and validate new candidate
			auto newCand = 
				std::make_shared<Candidate>( appExpr, result.env, result.open, result.need, cost );
			PRINT(
				std::cerr << "instantiate function success: " << appExpr << std::endl;
				std::cerr << "need assertions:" << std::endl;
				ast::print( std::cerr, result.need, 2 );
			)
			inferParameters( newCand, out );
		}

		/// Builds a list of candidates for a function, storing them in out
		void makeFunctionCandidates(
			const CandidateRef & func, const ast::FunctionType * funcType, 
			const ExplodedArgs_new & args, CandidateList & out
		) {
			ast::OpenVarSet funcOpen;
			ast::AssertionSet funcNeed, funcHave;
			ast::TypeEnvironment funcEnv{ func->env };
			makeUnifiableVars( funcType, funcOpen, funcNeed );
			// add all type variables as open variables now so that those not used in the parameter 
			// list are still considered open
			funcEnv.add( funcType->forall );

			if ( targetType && ! targetType->isVoid() && ! funcType->returns.empty() ) {
				// attempt to narrow based on expected target type
				const ast::Type * returnType = funcType->returns.front()->get_type();
				if ( ! unify( 
					returnType, targetType, funcEnv, funcNeed, funcHave, funcOpen, symtab ) 
				) {
					// unification failed, do not pursue this candidate
					return;
				}
			}

			// iteratively build matches, one parameter at a time
			std::vector< ArgPack > results;
			results.emplace_back( funcEnv, funcNeed, funcHave, funcOpen );
			std::size_t genStart = 0;

			for ( const ast::DeclWithType * param : funcType->params ) {
				auto obj = strict_dynamic_cast< const ast::ObjectDecl * >( param );
				// Try adding the arguments corresponding to the current parameter to the existing 
				// matches
				if ( ! instantiateArgument( 
					obj->type, obj->init, args, results, genStart, symtab ) ) return;
			}

			if ( funcType->isVarArgs ) {
				// append any unused arguments to vararg pack
				std::size_t genEnd;
				do {
					genEnd = results.size();

					// iterate results
					for ( std::size_t i = genStart; i < genEnd; ++i ) {
						unsigned nextArg = results[i].nextArg;

						// use remainder of exploded tuple if present
						if ( results[i].hasExpl() ) {
							const ExplodedArg & expl = results[i].getExpl( args );

							unsigned nextExpl = results[i].nextExpl + 1;
							if ( nextExpl == expl.exprs.size() ) { nextExpl = 0; }

							results.emplace_back(
								i, expl.exprs[ results[i].nextExpl ], copy( results[i].env ),
								copy( results[i].need ), copy( results[i].have ),
								copy( results[i].open ), nextArg, 0, Cost::zero, nextExpl,
								results[i].explAlt );

							continue;
						}

						// finish result when out of arguments
						if ( nextArg >= args.size() ) {
							validateFunctionCandidate( func, results[i], results, out );

							continue;
						}

						// add each possible next argument
						for ( std::size_t j = 0; j < args[nextArg].size(); ++j ) {
							const ExplodedArg & expl = args[nextArg][j];

							// fresh copies of parent parameters for this iteration
							ast::TypeEnvironment env = results[i].env;
							ast::OpenVarSet open = results[i].open;

							env.addActual( expl.env, open );

							// skip empty tuple arguments by (nearly) cloning parent into next gen
							if ( expl.exprs.empty() ) {
								results.emplace_back(
									results[i], move( env ), copy( results[i].need ), 
									copy( results[i].have ), move( open ), nextArg + 1, 
									expl.cost );

								continue;
							}

							// add new result
							results.emplace_back(
								i, expl.exprs.front(), move( env ), copy( results[i].need ),
								copy( results[i].have ), move( open ), nextArg + 1, 0, expl.cost, 
								expl.exprs.size() == 1 ? 0 : 1, j );
						}
					}

					genStart = genEnd;
				} while( genEnd != results.size() );
			} else {
				// filter out the results that don't use all the arguments
				for ( std::size_t i = genStart; i < results.size(); ++i ) {
					ArgPack & result = results[i];
					if ( ! result.hasExpl() && result.nextArg >= args.size() ) {
						validateFunctionCandidate( func, result, results, out );
					}
				}
			}
		}

		/// Adds implicit struct-conversions to the alternative list
		void addAnonConversions( const CandidateRef & cand ) {
			#warning unimplemented
			(void)cand;
			assert(false);
		}

		void postvisit( const ast::UntypedExpr * untypedExpr ) {
			CandidateFinder funcFinder{ symtab, tenv };
			funcFinder.find( untypedExpr->func, ResolvMode::withAdjustment() );
			// short-circuit if no candidates
			if ( funcFinder.candidates.empty() ) return;

			std::vector< CandidateFinder > argCandidates = 
				selfFinder.findSubExprs( untypedExpr->args );
			
			// take care of possible tuple assignments
			// if not tuple assignment, handled as normal function call
			Tuples::handleTupleAssignment( selfFinder, untypedExpr, argCandidates );

			// find function operators
			ast::ptr< ast::Expr > opExpr = new ast::NameExpr{ untypedExpr->location, "?()" };
			CandidateFinder opFinder{ symtab, tenv };
			// okay if there aren't any function operations
			opFinder.find( opExpr, ResolvMode::withoutFailFast() );
			PRINT(
				std::cerr << "known function ops:" << std::endl;
				print( std::cerr, opFinder.candidates, 1 );
			)

			// pre-explode arguments
			ExplodedArgs_new argExpansions;
			for ( const CandidateFinder & args : argCandidates ) {
				argExpansions.emplace_back();
				auto & argE = argExpansions.back();
				for ( const CandidateRef & arg : args ) { argE.emplace_back( *arg, symtab ); }
			}

			// Find function matches
			CandidateList found;
			SemanticErrorException errors;
			for ( CandidateRef & func : funcFinder ) {
				try {
					PRINT(
						std::cerr << "working on alternative:" << std::endl;
						print( std::cerr, *func, 2 );
					)

					// check if the type is a pointer to function
					const ast::Type * funcResult = func->expr->result->stripReferences();
					if ( auto pointer = dynamic_cast< const ast::PointerType * >( funcResult ) ) {
						if ( auto function = pointer->base.as< ast::FunctionType >() ) {
							CandidateRef newFunc{ new Candidate{ *func } };
							newFunc->expr = 
								referenceToRvalueConversion( newFunc->expr, newFunc->cost );
							makeFunctionCandidates( newFunc, function, argExpansions, found );
						}
					} else if ( 
						auto inst = dynamic_cast< const ast::TypeInstType * >( funcResult ) 
					) {
						if ( const ast::EqvClass * clz = func->env.lookup( inst->name ) ) {
							if ( auto function = clz->bound.as< ast::FunctionType >() ) {
								CandidateRef newFunc{ new Candidate{ *func } };
								newFunc->expr = 
									referenceToRvalueConversion( newFunc->expr, newFunc->cost );
								makeFunctionCandidates( newFunc, function, argExpansions, found );
							}
						}
					}
				} catch ( SemanticErrorException & e ) { errors.append( e ); }
			}

			// Find matches on function operators `?()`
			if ( ! opFinder.candidates.empty() ) {
				// add exploded function alternatives to front of argument list
				std::vector< ExplodedArg > funcE;
				funcE.reserve( funcFinder.candidates.size() );
				for ( const CandidateRef & func : funcFinder ) { 
					funcE.emplace_back( *func, symtab );
				}
				argExpansions.emplace_front( move( funcE ) );

				for ( const CandidateRef & op : opFinder ) {
					try {
						// check if type is pointer-to-function
						const ast::Type * opResult = op->expr->result->stripReferences();
						if ( auto pointer = dynamic_cast< const ast::PointerType * >( opResult ) ) {
							if ( auto function = pointer->base.as< ast::FunctionType >() ) {
								CandidateRef newOp{ new Candidate{ *op} };
								newOp->expr = 
									referenceToRvalueConversion( newOp->expr, newOp->cost );
								makeFunctionCandidates( newOp, function, argExpansions, found );
							}
						}
					} catch ( SemanticErrorException & e ) { errors.append( e ); }
				}
			}

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

			// Compute conversion costs
			for ( CandidateRef & withFunc : found ) {
				Cost cvtCost = computeApplicationConversionCost( withFunc, symtab );

				PRINT(
					auto appExpr = withFunc->expr.strict_as< ast::ApplicationExpr >();
					auto pointer = appExpr->func->result.strict_as< ast::PointerType >();
					auto function = pointer->base.strict_as< ast::FunctionType >();
					
					std::cerr << "Case +++++++++++++ " << appExpr->func << std::endl;
					std::cerr << "parameters are:" << std::endl;
					ast::printAll( std::cerr, function->params, 2 );
					std::cerr << "arguments are:" << std::endl;
					ast::printAll( std::cerr, appExpr->args, 2 );
					std::cerr << "bindings are:" << std::endl;
					ast::print( std::cerr, withFunc->env, 2 );
					std::cerr << "cost is: " << withFunc->cost << std::endl;
					std::cerr << "cost of conversion is:" << cvtCost << std::endl;
				)

				if ( cvtCost != Cost::infinity ) {
					withFunc->cvtCost = cvtCost;
					candidates.emplace_back( move( withFunc ) );
				}
			}
			found = move( candidates );

			// use a new list so that candidates are not examined by addAnonConversions twice
			CandidateList winners = findMinCost( found );
			promoteCvtCost( winners );

			// function may return a struct/union value, in which case we need to add candidates 
			// for implicit conversions to each of the anonymous members, which must happen after 
			// `findMinCost`, since anon conversions are never the cheapest
			for ( const CandidateRef & c : winners ) {
				addAnonConversions( c );
			}
			spliceBegin( candidates, winners );

			if ( candidates.empty() && targetType && ! targetType->isVoid() ) {
				// If resolution is unsuccessful with a target type, try again without, since it 
				// will sometimes succeed when it wouldn't with a target type binding.
				// For example:
				//   forall( otype T ) T & ?[]( T *, ptrdiff_t );
				//   const char * x = "hello world";
				//   unsigned char ch = x[0];
				// Fails with simple return type binding (xxx -- check this!) as follows:
				// * T is bound to unsigned char
				// * (x: const char *) is unified with unsigned char *, which fails
				// xxx -- fix this better
				targetType = nullptr;
				postvisit( untypedExpr );
			}
		}

		/// true if expression is an lvalue
		static bool isLvalue( const ast::Expr * x ) {
			return x->result && ( x->result->is_lvalue() || x->result.as< ast::ReferenceType >() );
		}

		void postvisit( const ast::AddressExpr * addressExpr ) {
			CandidateFinder finder{ symtab, tenv };
			finder.find( addressExpr->arg );
			for ( CandidateRef & r : finder.candidates ) {
				if ( ! isLvalue( r->expr ) ) continue;
				addCandidate( *r, new ast::AddressExpr{ addressExpr->location, r->expr } );
			}
		}

		void postvisit( const ast::LabelAddressExpr * labelExpr ) {
			addCandidate( labelExpr, tenv );
		}

		void postvisit( const ast::CastExpr * castExpr ) {
			#warning unimplemented
			(void)castExpr;
			assert(false);
		}

		void postvisit( const ast::VirtualCastExpr * castExpr ) {
			assertf( castExpr->result, "Implicit virtual cast targets not yet supported." );
			CandidateFinder finder{ symtab, tenv };
			// don't prune here, all alternatives guaranteed to have same type
			finder.find( castExpr->arg, ResolvMode::withoutPrune() );
			for ( CandidateRef & r : finder.candidates ) {
				addCandidate( 
					*r, new ast::VirtualCastExpr{ castExpr->location, r->expr, castExpr->result } );
			}
		}

		void postvisit( const ast::UntypedMemberExpr * memberExpr ) {
			#warning unimplemented
			(void)memberExpr;
			assert(false);
		}

		void postvisit( const ast::MemberExpr * memberExpr ) {
			addCandidate( memberExpr, tenv );
		}

		void postvisit( const ast::NameExpr * variableExpr ) {
			#warning unimplemented
			(void)variableExpr;
			assert(false);
		}

		void postvisit( const ast::VariableExpr * variableExpr ) {
			// not sufficient to just pass `variableExpr` here, type might have changed since
			// creation
			addCandidate( 
				new ast::VariableExpr{ variableExpr->location, variableExpr->var }, tenv );
		}

		void postvisit( const ast::ConstantExpr * constantExpr ) {
			addCandidate( constantExpr, tenv );
		}

		void postvisit( const ast::SizeofExpr * sizeofExpr ) {
			#warning unimplemented
			(void)sizeofExpr;
			assert(false);
		}

		void postvisit( const ast::AlignofExpr * alignofExpr ) {
			#warning unimplemented
			(void)alignofExpr;
			assert(false);
		}

		void postvisit( const ast::UntypedOffsetofExpr * offsetofExpr ) {
			#warning unimplemented
			(void)offsetofExpr;
			assert(false);
		}

		void postvisit( const ast::OffsetofExpr * offsetofExpr ) {
			addCandidate( offsetofExpr, tenv );
		}

		void postvisit( const ast::OffsetPackExpr * offsetPackExpr ) {
			addCandidate( offsetPackExpr, tenv );
		}

		void postvisit( const ast::LogicalExpr * logicalExpr ) {
			CandidateFinder finder1{ symtab, tenv };
			finder1.find( logicalExpr->arg1, ResolvMode::withAdjustment() );
			if ( finder1.candidates.empty() ) return;

			CandidateFinder finder2{ symtab, tenv };
			finder2.find( logicalExpr->arg2, ResolvMode::withAdjustment() );
			if ( finder2.candidates.empty() ) return;

			for ( const CandidateRef & r1 : finder1.candidates ) {
				for ( const CandidateRef & r2 : finder2.candidates ) {
					ast::TypeEnvironment env{ r1->env };
					env.simpleCombine( r2->env );
					ast::OpenVarSet open{ r1->open };
					mergeOpenVars( open, r2->open );
					ast::AssertionSet need;
					mergeAssertionSet( need, r1->need );
					mergeAssertionSet( need, r2->need );

					addCandidate(
						new ast::LogicalExpr{ 
							logicalExpr->location, r1->expr, r2->expr, logicalExpr->isAnd },
						move( env ), move( open ), move( need ), r1->cost + r2->cost );
				}
			}
		}

		void postvisit( const ast::ConditionalExpr * conditionalExpr ) {
			// candidates for condition
			CandidateFinder finder1{ symtab, tenv };
			finder1.find( conditionalExpr->arg1, ResolvMode::withAdjustment() );
			if ( finder1.candidates.empty() ) return;

			// candidates for true result
			CandidateFinder finder2{ symtab, tenv };
			finder2.find( conditionalExpr->arg2, ResolvMode::withAdjustment() );
			if ( finder2.candidates.empty() ) return;

			// candidates for false result
			CandidateFinder finder3{ symtab, tenv };
			finder3.find( conditionalExpr->arg3, ResolvMode::withAdjustment() );
			if ( finder3.candidates.empty() ) return;

			for ( const CandidateRef & r1 : finder1.candidates ) {
				for ( const CandidateRef & r2 : finder2.candidates ) {
					for ( const CandidateRef & r3 : finder3.candidates ) {
						ast::TypeEnvironment env{ r1->env };
						env.simpleCombine( r2->env );
						env.simpleCombine( r3->env );
						ast::OpenVarSet open{ r1->open };
						mergeOpenVars( open, r2->open );
						mergeOpenVars( open, r3->open );
						ast::AssertionSet need;
						mergeAssertionSet( need, r1->need );
						mergeAssertionSet( need, r2->need );
						mergeAssertionSet( need, r3->need );
						ast::AssertionSet have;

						// unify true and false results, then infer parameters to produce new 
						// candidates
						ast::ptr< ast::Type > common;
						if ( 
							unify( 
								r2->expr->result, r3->expr->result, env, need, have, open, symtab, 
								common ) 
						) {
							#warning unimplemented
							assert(false);
						}
					}
				}
			}
		}

		void postvisit( const ast::CommaExpr * commaExpr ) {
			ast::TypeEnvironment env{ tenv };
			ast::ptr< ast::Expr > arg1 = resolveInVoidContext( commaExpr->arg1, symtab, env );
			
			CandidateFinder finder2{ symtab, env };
			finder2.find( commaExpr->arg2, ResolvMode::withAdjustment() );

			for ( const CandidateRef & r2 : finder2.candidates ) {
				addCandidate( *r2, new ast::CommaExpr{ commaExpr->location, arg1, r2->expr } );
			}
		}

		void postvisit( const ast::ImplicitCopyCtorExpr * ctorExpr ) {
			addCandidate( ctorExpr, tenv );
		}

		void postvisit( const ast::ConstructorExpr * ctorExpr ) {
			CandidateFinder finder{ symtab, tenv };
			finder.find( ctorExpr->callExpr, ResolvMode::withoutPrune() );
			for ( CandidateRef & r : finder.candidates ) {
				addCandidate( *r, new ast::ConstructorExpr{ ctorExpr->location, r->expr } );
			}
		}

		void postvisit( const ast::RangeExpr * rangeExpr ) {
			// resolve low and high, accept candidates where low and high types unify
			CandidateFinder finder1{ symtab, tenv };
			finder1.find( rangeExpr->low, ResolvMode::withAdjustment() );
			if ( finder1.candidates.empty() ) return;

			CandidateFinder finder2{ symtab, tenv };
			finder2.find( rangeExpr->high, ResolvMode::withAdjustment() );
			if ( finder2.candidates.empty() ) return;

			for ( const CandidateRef & r1 : finder1.candidates ) {
				for ( const CandidateRef & r2 : finder2.candidates ) {
					ast::TypeEnvironment env{ r1->env };
					env.simpleCombine( r2->env );
					ast::OpenVarSet open{ r1->open };
					mergeOpenVars( open, r2->open );
					ast::AssertionSet need;
					mergeAssertionSet( need, r1->need );
					mergeAssertionSet( need, r2->need );
					ast::AssertionSet have;

					ast::ptr< ast::Type > common;
					if ( 
						unify( 
							r1->expr->result, r2->expr->result, env, need, have, open, symtab, 
							common ) 
					) {
						ast::RangeExpr * newExpr = 
							new ast::RangeExpr{ rangeExpr->location, r1->expr, r2->expr };
						newExpr->result = common ? common : r1->expr->result;
						
						#warning unimplemented
						assert(false);
					}
				}
			}
		}

		void postvisit( const ast::UntypedTupleExpr * tupleExpr ) {
			std::vector< CandidateFinder > subCandidates = 
				selfFinder.findSubExprs( tupleExpr->exprs );
			std::vector< CandidateList > possibilities;
			combos( subCandidates.begin(), subCandidates.end(), back_inserter( possibilities ) );

			for ( const CandidateList & subs : possibilities ) {
				std::vector< ast::ptr< ast::Expr > > exprs;
				exprs.reserve( subs.size() );
				for ( const CandidateRef & sub : subs ) { exprs.emplace_back( sub->expr ); }

				ast::TypeEnvironment env;
				ast::OpenVarSet open;
				ast::AssertionSet need;
				for ( const CandidateRef & sub : subs ) {
					env.simpleCombine( sub->env );
					mergeOpenVars( open, sub->open );
					mergeAssertionSet( need, sub->need );
				}

				addCandidate(
					new ast::TupleExpr{ tupleExpr->location, move( exprs ) }, 
					move( env ), move( open ), move( need ), sumCost( subs ) );
			}
		}

		void postvisit( const ast::TupleExpr * tupleExpr ) {
			addCandidate( tupleExpr, tenv );
		}

		void postvisit( const ast::TupleIndexExpr * tupleExpr ) {
			addCandidate( tupleExpr, tenv );
		}

		void postvisit( const ast::TupleAssignExpr * tupleExpr ) {
			addCandidate( tupleExpr, tenv );
		}

		void postvisit( const ast::UniqueExpr * unqExpr ) {
			CandidateFinder finder{ symtab, tenv };
			finder.find( unqExpr->expr, ResolvMode::withAdjustment() );
			for ( CandidateRef & r : finder.candidates ) {
				// ensure that the the id is passed on so that the expressions are "linked"
				addCandidate( *r, new ast::UniqueExpr{ unqExpr->location, r->expr, unqExpr->id } );
			}
		}

		void postvisit( const ast::StmtExpr * stmtExpr ) {
			#warning unimplemented
			(void)stmtExpr;
			assert(false);
		}

		void postvisit( const ast::UntypedInitExpr * initExpr ) {
			#warning unimplemented
			(void)initExpr;
			assert(false);
		}

		void postvisit( const ast::InitExpr * ) {
			assertf( false, "CandidateFinder should never see a resolved InitExpr." );
		}

		void postvisit( const ast::DeletedExpr * ) {
			assertf( false, "CandidateFinder should never see a DeletedExpr." );
		}

		void postvisit( const ast::GenericExpr * ) {
			assertf( false, "_Generic is not yet supported." );
		}
	};

	/// Prunes a list of candidates down to those that have the minimum conversion cost for a given 
	/// return type. Skips ambiguous candidates.
	CandidateList pruneCandidates( CandidateList & candidates ) {
		struct PruneStruct {
			CandidateRef candidate;
			bool ambiguous;

			PruneStruct() = default;
			PruneStruct( const CandidateRef & c ) : candidate( c ), ambiguous( false ) {}
		};

		// find lowest-cost candidate for each type
		std::unordered_map< std::string, PruneStruct > selected;
		for ( CandidateRef & candidate : candidates ) {
			std::string mangleName;
			{
				ast::ptr< ast::Type > newType = candidate->expr->result;
				candidate->env.apply( newType );
				mangleName = Mangle::mangle( newType );
			}

			auto found = selected.find( mangleName );
			if ( found != selected.end() ) {
				if ( candidate->cost < found->second.candidate->cost ) {
					PRINT(
						std::cerr << "cost " << candidate->cost << " beats " 
							<< found->second.candidate->cost << std::endl;
					)

					found->second = PruneStruct{ candidate };
				} else if ( candidate->cost == found->second.candidate->cost ) {
					// if one of the candidates contains a deleted identifier, can pick the other, 
					// since deleted expressions should not be ambiguous if there is another option 
					// that is at least as good
					if ( findDeletedExpr( candidate->expr ) ) {
						// do nothing
						PRINT( std::cerr << "candidate is deleted" << std::endl; )
					} else if ( findDeletedExpr( found->second.candidate->expr ) ) {
						PRINT( std::cerr << "current is deleted" << std::endl; )
						found->second = PruneStruct{ candidate };
					} else {
						PRINT( std::cerr << "marking ambiguous" << std::endl; )
						found->second.ambiguous = true;
					}
				} else {
					PRINT(
						std::cerr << "cost " << candidate->cost << " loses to " 
							<< found->second.candidate->cost << std::endl;
					)
				}
			} else {
				selected.emplace_hint( found, mangleName, candidate );
			}
		}

		// report unambiguous min-cost candidates
		CandidateList out;
		for ( auto & target : selected ) {
			if ( target.second.ambiguous ) continue;

			CandidateRef cand = target.second.candidate;
			
			ast::ptr< ast::Type > newResult = cand->expr->result;
			cand->env.applyFree( newResult );
			cand->expr = ast::mutate_field(
				cand->expr.get(), &ast::Expr::result, move( newResult ) );
			
			out.emplace_back( cand );
		}
		return out;
	}

} // anonymous namespace

void CandidateFinder::find( const ast::Expr * expr, ResolvMode mode ) {
	// Find alternatives for expression
	ast::Pass<Finder> finder{ *this };
	expr->accept( finder );

	if ( mode.failFast && candidates.empty() ) {
		SemanticError( expr, "No reasonable alternatives for expression " );
	}

	if ( mode.satisfyAssns || mode.prune ) {
		// trim candidates to just those where the assertions are satisfiable
		// - necessary pre-requisite to pruning
		CandidateList satisfied;
		std::vector< std::string > errors;
		for ( auto & candidate : candidates ) {
			satisfyAssertions( *candidate, symtab, satisfied, errors );
		}

		// fail early if none such
		if ( mode.failFast && satisfied.empty() ) {
			std::ostringstream stream;
			stream << "No alternatives with satisfiable assertions for " << expr << "\n";
			for ( const auto& err : errors ) {
				stream << err;
			}
			SemanticError( expr->location, stream.str() );
		}

		// reset candidates
		candidates = move( satisfied );
	}

	if ( mode.prune ) {
		// trim candidates to single best one
		PRINT(
			std::cerr << "alternatives before prune:" << std::endl;
			print( std::cerr, candidates );
		)

		CandidateList pruned = pruneCandidates( candidates );
		
		if ( mode.failFast && pruned.empty() ) {
			std::ostringstream stream;
			CandidateList winners = findMinCost( candidates );
			stream << "Cannot choose between " << winners.size() << " alternatives for "
				"expression\n";
			ast::print( stream, expr );
			stream << " Alternatives are:\n";
			print( stream, winners, 1 );
			SemanticError( expr->location, stream.str() );
		}

		auto oldsize = candidates.size();
		candidates = move( pruned );

		PRINT(
			std::cerr << "there are " << oldsize << " alternatives before elimination" << std::endl;
		)
		PRINT(
			std::cerr << "there are " << candidates.size() << " alternatives after elimination" 
				<< std::endl;
		)
	}

	// adjust types after pruning so that types substituted by pruneAlternatives are correctly 
	// adjusted
	if ( mode.adjust ) {
		for ( CandidateRef & r : candidates ) {
			r->expr = ast::mutate_field( 
				r->expr.get(), &ast::Expr::result, 
				adjustExprType( r->expr->result, r->env, symtab ) );
		}
	}

	// Central location to handle gcc extension keyword, etc. for all expressions
	for ( CandidateRef & r : candidates ) {
		if ( r->expr->extension != expr->extension ) {
			r->expr.get_and_mutate()->extension = expr->extension;
		}
	}
}

std::vector< CandidateFinder > CandidateFinder::findSubExprs( 
	const std::vector< ast::ptr< ast::Expr > > & xs 
) {
	std::vector< CandidateFinder > out;

	for ( const auto & x : xs ) {
		out.emplace_back( symtab, env );
		out.back().find( x, ResolvMode::withAdjustment() );
		
		PRINT(
			std::cerr << "findSubExprs" << std::endl;
			print( std::cerr, out.back().candidates );
		)
	}

	return out;
}

} // namespace ResolvExpr

// Local Variables: //
// tab-width: 4 //
// mode: c++ //
// compile-command: "make install" //
// End: //