unit Myc.Ast.Binding;

interface

uses
    System.SysUtils,
    System.Classes,
    System.Generics.Collections,
    Myc.Data.Scalar,
    Myc.Data.Value,
    Myc.Ast.Nodes,
    Myc.Ast.Visitor,
    Myc.Ast.Scope,
    Myc.Ast.Analyzer,
    Myc.Ast;

type
    IAstBinder = interface(IAstVisitor)
        function Execute(const RootNode: IAstNode; out Descriptor: IScopeDescriptor): IAstNode;
    end;

    TAstBinder = class; // Forward declaration

    TEvaluateProc = reference to function(const Node: IAstNode): TDataValue;

    // This visitor handles the expansion of a single macro body (` `...`).
    TExpansionVisitor = class(TAstTransformer)
    private
        FEvaluate: TEvaluateProc;
        FMacroScope: IExecutionScope;
        function TransformAndSpliceNodes(const ANodes: TArray<IAstNode>): TArray<IAstNode>;
    protected
        function VisitUnquote(const Node: IUnquoteNode): TDataValue; override;
        function VisitUnquoteSplicing(const Node: IUnquoteSplicingNode): TDataValue; override;
        function VisitFunctionCall(const Node: IFunctionCallNode): TDataValue; override;
        function VisitBlockExpression(const Node: IBlockExpressionNode): TDataValue; override;
    public
        constructor Create(const AMacroScope: IExecutionScope; const AEvaluate: TEvaluateProc);
        class function Expand(const MacroScope: IExecutionScope; const RootNode: IAstNode; const AEvaluate: TEvaluateProc): IAstNode;
    end;

    TAstBinder = class(TAstTransformer, IAstBinder)
    private
        type
            TUpvalueMapping = class
            public
                Map: TDictionary<TResolvedAddress, Integer>;
                constructor Create;
                destructor Destroy; override;
            end;
    private
        FInitialScope: IExecutionScope;
        FCurrentDescriptor: IScopeDescriptor;
        FUpvalueStack: TStack<TUpvalueMapping>;
        FNestedLambdaCount: Integer;
        FIsTailStack: TStack<Boolean>;
        FNextIsTail: Boolean;
        FBoxedDeclarations: THashSet<IVariableDeclarationNode>;
        FEvaluatorFactory: TEvaluatorFactory;
        // Operator folding maps
        FBinaryOperators: TDictionary<string, TScalar.TBinaryOp>;
        FUnaryOperators: TDictionary<string, TScalar.TUnaryOp>;

        procedure EnterScope;
        procedure ExitScope;
        function IsValidIdentifier(const Name: string): Boolean;

    protected
        function Accept(const Node: IAstNode): TDataValue; override;
        function VisitIdentifier(const Node: IIdentifierNode): TDataValue; override;
        function VisitVariableDeclaration(const Node: IVariableDeclarationNode): TDataValue; override;
        function VisitAssignment(const Node: IAssignmentNode): TDataValue; override;
        function VisitLambdaExpression(const Node: ILambdaExpressionNode): TDataValue; override;
        function VisitMacroDefinition(const Node: IMacroDefinitionNode): TDataValue; override;
        function VisitFunctionCall(const Node: IFunctionCallNode): TDataValue; override;
        function VisitMacroExpansionNode(const Node: IMacroExpansionNode): TDataValue; override;
        function VisitRecurNode(const Node: IRecurNode): TDataValue; override;
        function VisitBlockExpression(const Node: IBlockExpressionNode): TDataValue; override;
        function VisitIfExpression(const Node: IIfExpressionNode): TDataValue; override;
        function VisitTernaryExpression(const Node: ITernaryExpressionNode): TDataValue; override;
        function VisitBinaryExpression(const Node: IBinaryExpressionNode): TDataValue; override;
        function VisitUnaryExpression(const Node: IUnaryExpressionNode): TDataValue; override;

    public
        constructor Create(const AInitialScope: IExecutionScope; const AEvaluatorFactory: TEvaluatorFactory);
        destructor Destroy; override;
        function Execute(const RootNode: IAstNode; out Descriptor: IScopeDescriptor): IAstNode;

        class function Bind(
            const InitialScope: IExecutionScope;
            const RootNode: IAstNode;
            out Descriptor: IScopeDescriptor;
            const EvaluatorFactory: TEvaluatorFactory
        ): IAstNode; static;
    end;

    TBoundIdentifierNode = class(TIdentifierNode)
    private
        FAddress: TResolvedAddress;
    public
        constructor Create(const AUnboundNode: IIdentifierNode; const AAddress: TResolvedAddress);
        property Address: TResolvedAddress read FAddress;
    end;

    TBoundVariableDeclarationNode = class(TVariableDeclarationNode)
    private
        FIsBoxed: Boolean;
    public
        constructor Create(const AIdentifier: IIdentifierNode; AInitializer: IAstNode; AIsBoxed: Boolean);
        property IsBoxed: Boolean read FIsBoxed;
    end;

    TBoundLambdaExpressionNode = class(TLambdaExpressionNode)
    private
        FScopeDescriptor: IScopeDescriptor;
        FUpvalues: TArray<TResolvedAddress>;
        FHasNestedLambdas: Boolean;
    public
        constructor Create(
            const AUnboundNode: ILambdaExpressionNode;
            const ABody: IAstNode;
            const AParameters: TArray<IIdentifierNode>;
            const AScopeDescriptor: IScopeDescriptor;
            const AUpvalues: TArray<TResolvedAddress>;
            AHasNestedLambdas: Boolean
        );
        property ScopeDescriptor: IScopeDescriptor read FScopeDescriptor;
        property Upvalues: TArray<TResolvedAddress> read FUpvalues;
        property HasNestedLambdas: Boolean read FHasNestedLambdas;
    end;

    TBoundFunctionCallNode = class(TFunctionCallNode)
    private
        FIsTailCall: Boolean;
    public
        constructor Create(
            const AUnboundNode: IFunctionCallNode;
            const ACallee: IAstNode;
            const AArguments: TArray<IAstNode>;
            AIsTailCall: Boolean
        );
        property IsTailCall: Boolean read FIsTailCall;
    end;

implementation

uses
    System.Generics.Defaults,
    System.Character;

type
    TResolvedAddressComparer = class(TEqualityComparer<TResolvedAddress>)
    public
        function Equals(const Left, Right: TResolvedAddress): Boolean; override;
        function GetHashCode(const Value: TResolvedAddress): Integer; override;
    end;

{ TExpansionVisitor }

constructor TExpansionVisitor.Create(const AMacroScope: IExecutionScope; const AEvaluate: TEvaluateProc);
begin
    inherited Create;
    FMacroScope := AMacroScope;
    FEvaluate := AEvaluate;
end;

class function TExpansionVisitor.Expand(
    const MacroScope: IExecutionScope;
    const RootNode: IAstNode;
    const AEvaluate: TEvaluateProc
): IAstNode;
begin
    var expander := TExpansionVisitor.Create(MacroScope, AEvaluate) as IAstTransformer;
    Result := expander.Execute(RootNode);
end;

function TExpansionVisitor.TransformAndSpliceNodes(const ANodes: TArray<IAstNode>): TArray<IAstNode>;
var
    newList: TList<IAstNode>;
    nodeToSplice: IAstNode;
begin
    newList := TList<IAstNode>.Create;
    try
        for var node in ANodes do
        begin
            if (node is TUnquoteSplicingNode) then
            begin
                var spliceExpr := (node as TUnquoteSplicingNode).Expression;
                var evaluatedSpliceValue := VisitUnquote(TAst.Unquote(spliceExpr));

                if (not evaluatedSpliceValue.IsVoid) and (evaluatedSpliceValue.Kind = vkInterface) then
                begin
                    nodeToSplice := evaluatedSpliceValue.AsIntf<IAstNode>;
                    if (nodeToSplice is TBlockExpressionNode) then
                        newList.AddRange((nodeToSplice as TBlockExpressionNode).Expressions)
                    else
                        raise Exception.Create('Expression inside unquote-splicing (`~@`) must be a list of nodes (a block).');
                end
                else
                    raise Exception.Create('Expression inside unquote-splicing (`~@`) must evaluate to a list of nodes (a block).');
            end
            else
            begin
                var transformedValue := node.Accept(self);
                if not transformedValue.IsVoid then
                    newList.Add(transformedValue.AsIntf<IAstNode>);
            end;
        end;
        Result := newList.ToArray;
    finally
        newList.Free;
    end;
end;

function TExpansionVisitor.VisitUnquote(const Node: IUnquoteNode): TDataValue;
var
    value: TDataValue;
    expr: IAstNode;
    addr: TResolvedAddress;
begin
    expr := Node.Expression;

    if (expr is TIdentifierNode) then
    begin
        addr := FMacroScope.CreateDescriptor.FindSymbol((expr as TIdentifierNode).Name);
        if (addr.Kind = akLocalOrParent) and (addr.ScopeDepth = 0) then
        begin
            var argValue := FMacroScope.Values[addr];
            if argValue.Kind = vkInterface then
            begin
                Result := argValue;
                exit;
            end;
        end;
    end;

    // externally evaluate the expression using the injected evaluator
    value := FEvaluate(expr);

    if value.Kind in [vkScalar, vkText, vkVoid] then
        Result := TDataValue.FromIntf<IAstNode>(TAst.Constant(value))
    else
        raise Exception.CreateFmt('Cannot unquote complex value of type %s at compile time.', [value.Kind.ToString]);
end;

function TExpansionVisitor.VisitUnquoteSplicing(const Node: IUnquoteSplicingNode): TDataValue;
begin
    raise Exception.Create('Unquote-splicing (`~@`) can only appear inside a list form (e.g., a function call or a `do` block).');
end;

function TExpansionVisitor.VisitFunctionCall(const Node: IFunctionCallNode): TDataValue;
var
    newArgs: TArray<IAstNode>;
    transformedCallee: IAstNode;
begin
    transformedCallee := Self.Accept(Node.Callee).AsIntf<IAstNode>;
    newArgs := TransformAndSpliceNodes(Node.Arguments);
    Result := TDataValue.FromIntf<IFunctionCallNode>(TAst.FunctionCall(transformedCallee, newArgs));
end;

function TExpansionVisitor.VisitBlockExpression(const Node: IBlockExpressionNode): TDataValue;
var
    newExprs: TArray<IAstNode>;
begin
    newExprs := TransformAndSpliceNodes(Node.Expressions);
    Result := TDataValue.FromIntf<IBlockExpressionNode>(TAst.Block(newExprs));
end;

{ TBoundIdentifierNode }
constructor TBoundIdentifierNode.Create(const AUnboundNode: IIdentifierNode; const AAddress: TResolvedAddress);
begin
    inherited Create(AUnboundNode.Name);
    FAddress := AAddress;
end;

{ TBoundVariableDeclarationNode }
constructor TBoundVariableDeclarationNode.Create(const AIdentifier: IIdentifierNode; AInitializer: IAstNode; AIsBoxed: Boolean);
begin
    inherited Create(AIdentifier, AInitializer);
    FIsBoxed := AIsBoxed;
end;

{ TBoundLambdaExpressionNode }
constructor TBoundLambdaExpressionNode.Create(
    const AUnboundNode: ILambdaExpressionNode;
    const ABody: IAstNode;
    const AParameters: TArray<IIdentifierNode>;
    const AScopeDescriptor: IScopeDescriptor;
    const AUpvalues: TArray<TResolvedAddress>;
    AHasNestedLambdas: Boolean
);
begin
    inherited Create(AParameters, ABody);
    FScopeDescriptor := AScopeDescriptor;
    FUpvalues := AUpvalues;
    FHasNestedLambdas := AHasNestedLambdas;
end;

{ TBoundFunctionCallNode }
constructor TBoundFunctionCallNode.Create(
    const AUnboundNode: IFunctionCallNode;
    const ACallee: IAstNode;
    const AArguments: TArray<IAstNode>;
    AIsTailCall: Boolean
);
begin
    inherited Create(ACallee, AArguments);
    FIsTailCall := AIsTailCall;
end;

{ TResolvedAddressComparer }
function TResolvedAddressComparer.Equals(const Left, Right: TResolvedAddress): Boolean;
begin
    Result := (Left = Right);
end;

function TResolvedAddressComparer.GetHashCode(const Value: TResolvedAddress): Integer;
begin
    Result := 17;
    Result := Result * 23 + Ord(Value.Kind);
    Result := Result * 23 + Value.ScopeDepth;
    Result := Result * 23 + Value.SlotIndex;
end;

{ TAstBinder.TUpvalueMapping }
constructor TAstBinder.TUpvalueMapping.Create;
begin
    inherited Create;
    Map := TDictionary<TResolvedAddress, Integer>.Create(TResolvedAddressComparer.Create);
end;

destructor TAstBinder.TUpvalueMapping.Destroy;
begin
    Map.Free;
    inherited Destroy;
end;

{ TAstBinder }

constructor TAstBinder.Create(const AInitialScope: IExecutionScope; const AEvaluatorFactory: TEvaluatorFactory);
var
    op: TScalar.TBinaryOp;
begin
    inherited Create;
    Assert(Assigned(AInitialScope));
    Assert(Assigned(AEvaluatorFactory));

    FInitialScope := AInitialScope;
    FEvaluatorFactory := AEvaluatorFactory;
    FCurrentDescriptor := AInitialScope.CreateDescriptor;
    FUpvalueStack := TObjectStack<TUpvalueMapping>.Create(True);
    FNestedLambdaCount := 0;
    FIsTailStack := TStack<Boolean>.Create;
    FNextIsTail := True;
    FBoxedDeclarations := nil;

    // Initialize operator folding maps
    FBinaryOperators := TDictionary<string, TScalar.TBinaryOp>.Create;
    for op := Low(TScalar.TBinaryOp) to High(TScalar.TBinaryOp) do
        FBinaryOperators.Add(op.ToString, op);

    FUnaryOperators := TDictionary<string, TScalar.TUnaryOp>.Create;
    FUnaryOperators.Add('not', TScalar.TUnaryOp.Not);
    // Note: '-' is handled as a special case in VisitFunctionCall
end;

destructor TAstBinder.Destroy;
begin
    FUnaryOperators.Free;
    FBinaryOperators.Free;
    FIsTailStack.Free;
    FUpvalueStack.Free;
    FBoxedDeclarations.Free;
    inherited;
end;

function TAstBinder.Accept(const Node: IAstNode): TDataValue;
begin
    if (not Assigned(Node)) or Done then
        exit;

    FIsTailStack.Push(FNextIsTail);
    try
        Result := inherited Accept(Node);
    finally
        FNextIsTail := FIsTailStack.Pop;
    end;
end;

class function TAstBinder.Bind(
    const InitialScope: IExecutionScope;
    const RootNode: IAstNode;
    out Descriptor: IScopeDescriptor;
    const EvaluatorFactory: TEvaluatorFactory
): IAstNode;
begin
    var binder := TAstBinder.Create(InitialScope, EvaluatorFactory) as IAstBinder;
    Result := binder.Execute(RootNode, Descriptor);
end;

procedure TAstBinder.EnterScope;
begin
    FCurrentDescriptor := TScope.CreateDescriptor(FCurrentDescriptor);
end;

function TAstBinder.Execute(const RootNode: IAstNode; out Descriptor: IScopeDescriptor): IAstNode;
begin
    FBoxedDeclarations := TUpvalueAnalyzer.Analyze(RootNode, FCurrentDescriptor.Parent);
    try
        EnterScope;
        try
            var transformedValue := Accept(RootNode);
            if transformedValue.IsVoid then
                Result := TAst.Block([])
            else
                Result := transformedValue.AsIntf<IAstNode>;
            Descriptor := FCurrentDescriptor;
        finally
            ExitScope;
        end;
    finally
        // The binder now owns the hash set, which will be freed in the destructor.
    end;
end;

function TAstBinder.VisitMacroDefinition(const Node: IMacroDefinitionNode): TDataValue;
begin
    FCurrentDescriptor.DefineMacro(Node.Name.Name, Node);
    Result := TDataValue.Void;
end;

function TAstBinder.VisitFunctionCall(const Node: IFunctionCallNode): TDataValue;
var
    calleeIdentifier: TIdentifierNode;
    binaryOp: TScalar.TBinaryOp;
    unaryOp: TScalar.TUnaryOp;
    macroDef: IMacroDefinitionNode;
begin
    if (Node.Callee is TIdentifierNode) then
    begin
        calleeIdentifier := Node.Callee as TIdentifierNode;

        // --- Optimization: Operator Folding ---

        // Try to fold binary operators
        if Length(Node.Arguments) = 2 then
        begin
            if FBinaryOperators.TryGetValue(calleeIdentifier.Name, binaryOp) then
            begin
                FNextIsTail := False;
                var left := Accept(Node.Arguments[0]).AsIntf<IAstNode>;
                var right := Accept(Node.Arguments[1]).AsIntf<IAstNode>;
                Result := TDataValue.FromIntf<IAstNode>(TAst.BinaryExpr(left, binaryOp, right));
                exit;
            end;
        end;

        // Try to fold unary operators
        if Length(Node.Arguments) = 1 then
        begin
            if FUnaryOperators.TryGetValue(calleeIdentifier.Name, unaryOp) then
            begin
                FNextIsTail := False;
                var right := Accept(Node.Arguments[0]).AsIntf<IAstNode>;
                Result := TDataValue.FromIntf<IAstNode>(TAst.UnaryExpr(unaryOp, right));
                exit;
            end;

            // Special case for negation '-'
            if (calleeIdentifier.Name = '-') then
            begin
                FNextIsTail := False;
                var right := Accept(Node.Arguments[0]).AsIntf<IAstNode>;
                Result := TDataValue.FromIntf<IAstNode>(TAst.UnaryExpr(TScalar.TUnaryOp.Negate, right));
                exit;
            end;
        end;

        // --- Macro Expansion ---

        macroDef := FCurrentDescriptor.FindMacro(calleeIdentifier.Name);
        if macroDef <> nil then
        begin
            var expansionScope := TAst.CreateScope(nil);
            var params := macroDef.Parameters;
            if Length(Node.Arguments) <> Length(params) then
                raise Exception.CreateFmt(
                    'Macro %s expects %d arguments, but got %d',
                    [calleeIdentifier.Name, Length(params), Length(Node.Arguments)]);

            for var i := 0 to High(params) do
                expansionScope.Define(params[i].Name, TDataValue.FromIntf<IAstNode>(Node.Arguments[i]));

            // expand
            var expandedBody :=
                TExpansionVisitor.Expand(
                    expansionScope,
                    macroDef.Body.Expression,
                    function(const Node: IAstNode): TDataValue
                    var
                        subDescriptor: IScopeDescriptor;
                    begin
                        // in place evaluator for expanded expressions
                        var tempInitScope := TScope.CreateScope(FInitialScope.Parent, FCurrentDescriptor, nil);
                        var boundSubAst := TAstBinder.Bind(tempInitScope, Node, subDescriptor, FEvaluatorFactory);
                        var evalScope := subDescriptor.CreateScope(tempInitScope);
                        var evaluator := FEvaluatorFactory(evalScope);
                        Result := evaluator.Execute(boundSubAst);
                    end
                );

            // bind expanded body
            var boundExpandedBody := Self.Accept(expandedBody).AsIntf<IAstNode>;

            // wrap in new expansion node
            var macroNode := TMacroExpansionNode.Create(Node, boundExpandedBody) as IMacroExpansionNode;

            // done
            exit(TDataValue.FromIntf<IMacroExpansionNode>(macroNode));
        end;
    end;

    // --- Default: Bind as a standard function call ---
    var isTailCall := FIsTailStack.Peek;
    FNextIsTail := False;
    var callee := Accept(Node.Callee).AsIntf<IAstNode>;
    var args := TransformNodes<IAstNode>(Node.Arguments);
    var boundCall := TBoundFunctionCallNode.Create(Node, callee, args, isTailCall);
    Result := TDataValue.FromIntf<IFunctionCallNode>(boundCall);
end;

function TAstBinder.VisitMacroExpansionNode(const Node: IMacroExpansionNode): TDataValue;
var
    boundCallee: IAstNode;
    boundArgs: TArray<IAstNode>;
    boundExpandedBody: IAstNode;
    boundOriginalCall: IFunctionCallNode;
begin
    boundCallee := Accept(Node.Callee).AsIntf<IAstNode>;
    boundArgs := TransformNodes<IAstNode>(Node.Arguments);
    boundExpandedBody := Accept(Node.ExpandedBody).AsIntf<IAstNode>;
    boundOriginalCall := TAst.FunctionCall(boundCallee, boundArgs);
    var newMacroNode := TMacroExpansionNode.Create(boundOriginalCall, boundExpandedBody);
    Result := TDataValue.FromIntf<IMacroExpansionNode>(newMacroNode);
end;

procedure TAstBinder.ExitScope;
begin
    FCurrentDescriptor := FCurrentDescriptor.Parent;
end;

function TAstBinder.IsValidIdentifier(const Name: string): Boolean;
var
    c: Char;
begin
    if Name.IsEmpty then
        exit(False);
    c := Name[1];
    if not (c.IsLetter or (c = '_')) then
        exit(False);
    for c in Name do
    begin
        if not (c.IsLetterOrDigit or (c = '_') or (c = '-')) then
            exit(False);
    end;
    Result := True;
end;

function TAstBinder.VisitAssignment(const Node: IAssignmentNode): TDataValue;
begin
    FNextIsTail := False;
    Result := inherited VisitAssignment(Node);
end;

function TAstBinder.VisitBinaryExpression(const Node: IBinaryExpressionNode): TDataValue;
begin
    FNextIsTail := False;
    Result := inherited VisitBinaryExpression(Node);
end;

function TAstBinder.VisitBlockExpression(const Node: IBlockExpressionNode): TDataValue;
var
    exprs: TArray<IAstNode>;
    i: Integer;
    isContextTail: Boolean;
    transformedValue: TDataValue;
    exprList: TList<IAstNode>;
begin
    isContextTail := FIsTailStack.Peek;
    exprList := TList<IAstNode>.Create;
    try
        for i := 0 to High(Node.Expressions) do
        begin
            FNextIsTail := isContextTail and (i = High(Node.Expressions));
            transformedValue := Accept(Node.Expressions[i]);
            if not transformedValue.IsVoid then
                exprList.Add(transformedValue.AsIntf<IAstNode>);
        end;
        exprs := exprList.ToArray;
    finally
        exprList.Free;
    end;

    if (Length(exprs) = Length(Node.Expressions)) then
    begin
        var same := True;
        for i := 0 to High(exprs) do
            if exprs[i] <> Node.Expressions[i] then
            begin
                same := False;
                break;
            end;
        if same then
        begin
            Result := TDataValue.FromIntf<IBlockExpressionNode>(Node);
            exit;
        end;
    end;

    Result := TDataValue.FromIntf<IBlockExpressionNode>(TAst.Block(exprs));
end;

function TAstBinder.VisitIfExpression(const Node: IIfExpressionNode): TDataValue;
var
    isContextTail: Boolean;
    condition, thenBranch, elseBranch: IAstNode;
begin
    isContextTail := FIsTailStack.Peek;
    FNextIsTail := False;
    condition := Accept(Node.Condition).AsIntf<IAstNode>;
    FNextIsTail := isContextTail;
    thenBranch := Accept(Node.ThenBranch).AsIntf<IAstNode>;
    elseBranch := Accept(Node.ElseBranch).AsIntf<IAstNode>;

    if (condition <> Node.Condition) or (thenBranch <> Node.ThenBranch) or (elseBranch <> Node.ElseBranch) then
        Result := TDataValue.FromIntf<IIfExpressionNode>(TAst.IfExpr(condition, thenBranch, elseBranch))
    else
        Result := TDataValue.FromIntf<IIfExpressionNode>(Node);
end;

function TAstBinder.VisitLambdaExpression(const Node: ILambdaExpressionNode): TDataValue;
var
    i: integer;
    boundParams: TArray<IIdentifierNode>;
    boundBody: IAstNode;
    lambdaScope: IScopeDescriptor;
    upvalues: TArray<TResolvedAddress>;
    hasNestedLambdas: Boolean;
    lastNestedLambdaCount: Integer;
    boundLambda: ILambdaExpressionNode;
begin
    FUpvalueStack.Push(TUpvalueMapping.Create);
    try
        EnterScope;
        try
            FCurrentDescriptor.Define('<self>');
            SetLength(boundParams, Length(Node.Parameters));
            for i := 0 to High(Node.Parameters) do
            begin
                var paramNode := Node.Parameters[i];
                var slotIndex := FCurrentDescriptor.Define(paramNode.Name);
                var address := TResolvedAddress.Create(akLocalOrParent, 0, slotIndex);
                boundParams[i] := TBoundIdentifierNode.Create(paramNode, address);
            end;

            lastNestedLambdaCount := FNestedLambdaCount;
            FNextIsTail := True;
            boundBody := Accept(Node.Body).AsIntf<IAstNode>;
            hasNestedLambdas := FNestedLambdaCount > lastNestedLambdaCount;
            lambdaScope := FCurrentDescriptor;
        finally
            ExitScope;
        end;

        var upvalueMapping := FUpvalueStack.Peek;
        var sortedPairs := upvalueMapping.Map.ToArray;
        TArray.Sort<TPair<TResolvedAddress, Integer>>(
            sortedPairs,
            TComparer<TPair<TResolvedAddress, Integer>>.Construct(
                function(const Left, Right: TPair<TResolvedAddress, Integer>): Integer begin Result := Left.Value - Right.Value; end
            )
        );
        SetLength(upvalues, Length(sortedPairs));
        for i := 0 to High(sortedPairs) do
            upvalues[i] := sortedPairs[i].Key;
    finally
        FUpvalueStack.Pop;
    end;

    inc(FNestedLambdaCount);
    boundLambda := TBoundLambdaExpressionNode.Create(Node, boundBody, boundParams, lambdaScope, upvalues, hasNestedLambdas);
    Result := TDataValue.FromIntf<ILambdaExpressionNode>(boundLambda);
end;

function TAstBinder.VisitRecurNode(const Node: IRecurNode): TDataValue;
begin
    if not FIsTailStack.Peek then
        raise Exception.Create('''recur'' can only be used in a tail position.');
    FNextIsTail := False;
    Result := inherited VisitRecurNode(Node);
end;

function TAstBinder.VisitTernaryExpression(const Node: ITernaryExpressionNode): TDataValue;
var
    isContextTail: Boolean;
    condition, thenBranch, elseBranch: IAstNode;
begin
    isContextTail := FIsTailStack.Peek;
    FNextIsTail := False;
    condition := Accept(Node.Condition).AsIntf<IAstNode>;
    FNextIsTail := isContextTail;
    thenBranch := Accept(Node.ThenBranch).AsIntf<IAstNode>;
    elseBranch := Accept(Node.ElseBranch).AsIntf<IAstNode>;

    if (condition <> Node.Condition) or (thenBranch <> Node.ThenBranch) or (elseBranch <> Node.ElseBranch) then
        Result := TDataValue.FromIntf<ITernaryExpressionNode>(TAst.TernaryExpr(condition, thenBranch, elseBranch))
    else
        Result := TDataValue.FromIntf<ITernaryExpressionNode>(Node);
end;

function TAstBinder.VisitUnaryExpression(const Node: IUnaryExpressionNode): TDataValue;
begin
    FNextIsTail := False;
    Result := inherited VisitUnaryExpression(Node);
end;

function TAstBinder.VisitIdentifier(const Node: IIdentifierNode): TDataValue;
var
    adr: TResolvedAddress;
    boundNode: IIdentifierNode;
begin
    adr := FCurrentDescriptor.FindSymbol(Node.Name);
    if adr.Kind = akLocalOrParent then
    begin
        if (adr.ScopeDepth > 0) and (FUpvalueStack.Count > 0) then
        begin
            var upvalue := FUpvalueStack.Peek;
            dec(adr.ScopeDepth);
            var upvalueIndex: Integer;
            if not upvalue.Map.TryGetValue(adr, upvalueIndex) then
            begin
                upvalueIndex := upvalue.Map.Count;
                upvalue.Map.Add(adr, upvalueIndex);
            end;
            boundNode := TBoundIdentifierNode.Create(Node, TResolvedAddress.Create(akUpvalue, 0, upvalueIndex));
        end
        else
            boundNode := TBoundIdentifierNode.Create(Node, adr);
        Result := TDataValue.FromIntf<IIdentifierNode>(boundNode);
    end
    else
        raise Exception.CreateFmt('Undefined identifier: "%s"', [Node.Name]);
end;

function TAstBinder.VisitVariableDeclaration(const Node: IVariableDeclarationNode): TDataValue;
var
    initializer: IAstNode;
    slotIndex: Integer;
    address: TResolvedAddress;
    boundIdentifier: IIdentifierNode;
    isBoxed: Boolean;
    boundDecl: IVariableDeclarationNode;
begin
    if not IsValidIdentifier(Node.Identifier.Name) then
        raise Exception.CreateFmt('Invalid identifier name: "%s".', [Node.Identifier.Name]);

    FNextIsTail := False;
    initializer := nil;
    if Node.Initializer <> nil then
        initializer := Accept(Node.Initializer).AsIntf<IAstNode>;

    slotIndex := FCurrentDescriptor.Define(Node.Identifier.Name);
    address := TResolvedAddress.Create(akLocalOrParent, 0, slotIndex);
    boundIdentifier := TBoundIdentifierNode.Create(Node.Identifier, address);
    isBoxed := (FBoxedDeclarations <> nil) and FBoxedDeclarations.Contains(Node);
    boundDecl := TBoundVariableDeclarationNode.Create(boundIdentifier, initializer, isBoxed);
    Result := TDataValue.FromIntf<IVariableDeclarationNode>(boundDecl);
end;

end.