MycLib/Src/AST/Myc.Ast.pas

unit Myc.Ast;

interface

uses
    System.SysUtils,
    Myc.Data.Scalar,
    Myc.Ast.Nodes;

type
    // Record acting as a namespace for the factory functions.
    TAst = record
        // --- Existing factory functions ---
        class function Constant(AValue: TScalar): IConstantNode; static;
        class function Identifier(AName: string): IIdentifierNode; static;
        class function BinaryExpr(
            ALeft: IExpressionNode;
            AOperator: TBinaryOperator;
            ARight: IExpressionNode
        ): IBinaryExpressionNode; static;
        class function UnaryExpr(const AOperator: TUnaryOperator; const ARight: IExpressionNode): IUnaryExpressionNode; static;
        class function IfExpr(
            const ACondition: IExpressionNode;
            const AThenBranch, AElseBranch: IExpressionNode
        ): IIfExpressionNode; static;
        class function TernaryExpr(
            const ACondition: IExpressionNode;
            const AThenBranch, AElseBranch: IExpressionNode
        ): ITernaryExpressionNode; static;
        class function LambdaExpr(const AParameters: TArray<IIdentifierNode>; const ABody: IExpressionNode): ILambdaExpressionNode; static;
        class function FunctionCall(const ACallee: IExpressionNode; const AArguments: array of IExpressionNode): IFunctionCallNode; static;
        class function Block(const AExpressions: array of IExpressionNode): IBlockExpressionNode; static;
        class function VarDecl(const AIdentifier: IIdentifierNode; AInitializer: IExpressionNode): IVariableDeclarationNode; static;
        class function Assign(const AIdentifier: IIdentifierNode; const AValue: IExpressionNode): IAssignmentNode; static;
        class function AssignResult(const AValue: IExpressionNode): IAssignmentNode; static; deprecated;
        class function Indexer(const ABase: IExpressionNode; const AIndex: IExpressionNode): IIndexerNode; static;
        class function MemberAccess(const ABase: IExpressionNode; const AMember: IIdentifierNode): IMemberAccessNode; static;
        class function CreateSeries(const ADefinition: String): ICreateSeriesNode; static;
        class function AddSeriesItem(
            const ASeries: IIdentifierNode;
            const AValue: IExpressionNode;
            const ALookback: IExpressionNode = nil
        ): IAddSeriesItemNode; static;
        class function SeriesLength(const ASeries: IIdentifierNode): ISeriesLengthNode; static;

        // --- Static method to run the binder ---
        // Traverses the AST and resolves all identifiers. This must be called before evaluating the AST.
        class procedure Bind(const ARootNode: IExpressionNode); static;
    end;

    // TAstTraverser provides a default AST traversal implementation.
    TAstTraverser = class abstract(TInterfacedObject, IAstVisitor)
    public
        function VisitConstant(const Node: IConstantNode): TAstValue; virtual;
        function VisitIdentifier(const Node: IIdentifierNode): TAstValue; virtual;
        function VisitBinaryExpression(const Node: IBinaryExpressionNode): TAstValue; virtual;
        function VisitUnaryExpression(const Node: IUnaryExpressionNode): TAstValue; virtual;
        function VisitIfExpression(const Node: IIfExpressionNode): TAstValue; virtual;
        function VisitTernaryExpression(const Node: ITernaryExpressionNode): TAstValue; virtual;
        function VisitLambdaExpression(const Node: ILambdaExpressionNode): TAstValue; virtual;
        function VisitFunctionCall(const Node: IFunctionCallNode): TAstValue; virtual;
        function VisitBlockExpression(const Node: IBlockExpressionNode): TAstValue; virtual;
        function VisitVariableDeclaration(const Node: IVariableDeclarationNode): TAstValue; virtual;
        function VisitAssignment(const Node: IAssignmentNode): TAstValue; virtual;
        function VisitIndexer(const Node: IIndexerNode): TAstValue; virtual;
        function VisitMemberAccess(const Node: IMemberAccessNode): TAstValue; virtual;
        function VisitCreateSeries(const Node: ICreateSeriesNode): TAstValue; virtual;
        function VisitAddSeriesItem(const Node: IAddSeriesItemNode): TAstValue; virtual;
        function VisitSeriesLength(const Node: ISeriesLengthNode): TAstValue; virtual;
    end;

implementation

uses
    System.Classes,
    System.Generics.Collections;

type
    { TAstNode }
    // Common base class for AST nodes to reduce boilerplate.
    TAstNode = class(TInterfacedObject, IExpressionNode)
    public
        function Accept(const Visitor: IAstVisitor): TAstValue; virtual; abstract;
    end;

    { TConstantNode }
    TConstantNode = class(TAstNode, IConstantNode)
    private
        FValue: TScalar;
        function GetValue: TScalar;
    public
        constructor Create(AValue: TScalar);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TIdentifierNode }
    // TIdentifierNode now includes fields for binder annotations.
    TIdentifierNode = class(TAstNode, IIdentifierNode)
    private
        FName: string;
        // --- Annotation fields added for the binder ---
        FIsResolved: Boolean;
        FScopeDepth: Integer;
        FSlotIndex: Integer;
        function GetName: string;
    public
        constructor Create(AName: string);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;

        function Resolve(out ScopeDepth: Integer; out SlotIndex: Integer): Boolean;

        property Name: string read FName;
    end;

    { TBinaryExpressionNode }
    TBinaryExpressionNode = class(TAstNode, IBinaryExpressionNode)
    private
        FLeft: IExpressionNode;
        FOperator: TBinaryOperator;
        FRight: IExpressionNode;
        function GetLeft: IExpressionNode;
        function GetOperator: TBinaryOperator;
        function GetRight: IExpressionNode;
    public
        constructor Create(ALeft: IExpressionNode; AOperator: TBinaryOperator; ARight: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TUnaryExpressionNode }
    TUnaryExpressionNode = class(TAstNode, IUnaryExpressionNode)
    private
        FOperator: TUnaryOperator;
        FRight: IExpressionNode;
        function GetOperator: TUnaryOperator;
        function GetRight: IExpressionNode;
    public
        constructor Create(const AOperator: TUnaryOperator; const ARight: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TIfExpressionNode }
    TIfExpressionNode = class(TAstNode, IIfExpressionNode)
    private
        FCondition: IExpressionNode;
        FThenBranch: IExpressionNode;
        FElseBranch: IExpressionNode;
        function GetCondition: IExpressionNode;
        function GetThenBranch: IExpressionNode;
        function GetElseBranch: IExpressionNode;
    public
        constructor Create(const ACondition, AThenBranch, AElseBranch: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TTernaryExpressionNode }
    TTernaryExpressionNode = class(TAstNode, ITernaryExpressionNode)
    private
        FCondition: IExpressionNode;
        FThenBranch: IExpressionNode;
        FElseBranch: IExpressionNode;
        function GetCondition: IExpressionNode;
        function GetThenBranch: IExpressionNode;
        function GetElseBranch: IExpressionNode;
    public
        constructor Create(const ACondition, AThenBranch, AElseBranch: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TLambdaExpressionNode }
    TLambdaExpressionNode = class(TAstNode, ILambdaExpressionNode)
    private
        FParameters: TArray<IIdentifierNode>;
        FBody: IExpressionNode;
        function GetParameters: TArray<IIdentifierNode>;
        function GetBody: IExpressionNode;
    public
        constructor Create(const AParameters: TArray<IIdentifierNode>; const ABody: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TFunctionCallNode }
    TFunctionCallNode = class(TAstNode, IFunctionCallNode)
    private
        FCallee: IExpressionNode;
        FArguments: TList<IExpressionNode>;
        function GetCallee: IExpressionNode;
        function GetArguments: TList<IExpressionNode>;
    public
        constructor Create(const ACallee: IExpressionNode; const AArguments: array of IExpressionNode);
        destructor Destroy; override;
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TBlockExpressionNode }
    TBlockExpressionNode = class(TAstNode, IBlockExpressionNode)
    private
        FExpressions: TList<IExpressionNode>;
        function GetExpressions: TList<IExpressionNode>;
    public
        constructor Create(const AExpressions: array of IExpressionNode);
        destructor Destroy; override;
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TVariableDeclarationNode }
    TVariableDeclarationNode = class(TAstNode, IVariableDeclarationNode)
    private
        FIdentifier: IIdentifierNode;
        FInitializer: IExpressionNode;
        function GetIdentifier: IIdentifierNode;
        function GetInitializer: IExpressionNode;
    public
        constructor Create(const AIdentifier: IIdentifierNode; AInitializer: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TAssignmentNode }
    TAssignmentNode = class(TAstNode, IAssignmentNode)
    private
        FIdentifier: IIdentifierNode;
        FValue: IExpressionNode;
        function GetIdentifier: IIdentifierNode;
        function GetValue: IExpressionNode;
    public
        constructor Create(const AIdentifier: IIdentifierNode; const AValue: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TIndexerNode }
    TIndexerNode = class(TAstNode, IIndexerNode)
    private
        FBase: IExpressionNode;
        FIndex: IExpressionNode;
        function GetBase: IExpressionNode;
        function GetIndex: IExpressionNode;
    public
        constructor Create(const ABase: IExpressionNode; const AIndex: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TMemberAccessNode }
    TMemberAccessNode = class(TAstNode, IMemberAccessNode)
    private
        FBase: IExpressionNode;
        FMember: IIdentifierNode;
        function GetBase: IExpressionNode;
        function GetMember: IIdentifierNode;
    public
        constructor Create(const ABase: IExpressionNode; const AMember: IIdentifierNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TCreateSeriesNode }
    TCreateSeriesNode = class(TAstNode, ICreateSeriesNode)
    private
        FDefinition: String;
        function GetDefinition: String;
    public
        constructor Create(const ADefinition: String);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TAddSeriesItemNode }
    TAddSeriesItemNode = class(TAstNode, IAddSeriesItemNode)
    private
        FSeries: IIdentifierNode;
        FValue: IExpressionNode;
        FLookback: IExpressionNode;
        function GetSeries: IIdentifierNode;
        function GetValue: IExpressionNode;
        function GetLookback: IExpressionNode;
    public
        constructor Create(const ASeries: IIdentifierNode; const AValue: IExpressionNode; const ALookback: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    { TSeriesLengthNode }
    TSeriesLengthNode = class(TAstNode, ISeriesLengthNode)
    private
        FSeries: IIdentifierNode;
        function GetSeries: IIdentifierNode;
    public
        constructor Create(const ASeries: IIdentifierNode);
        function Accept(const Visitor: IAstVisitor): TAstValue; override;
    end;

    // --- Binder Implementation ---

    TSymbol = record
        Name: string;
        SlotIndex: Integer;
    end;

    TSymbolTable = class
    private
        FParent: TSymbolTable;
        FSymbols: TDictionary<string, TSymbol>;
        FNextSlotIndex: Integer;
    public
        constructor Create(AParent: TSymbolTable);
        destructor Destroy; override;
        function Define(const Name: string): TSymbol;
        function Resolve(const Name: string; out Symbol: TSymbol; out Depth: Integer): Boolean;
    end;

    // TBinder inherits from the base traverser and overrides methods with specific binding logic.
    TBinder = class(TAstTraverser)
    private
        FCurrentScope: TSymbolTable;
        procedure EnterScope;
        procedure ExitScope;
    public
        constructor Create;
        destructor Destroy; override;
        function VisitIdentifier(const Node: IIdentifierNode): TAstValue; override;
        function VisitLambdaExpression(const Node: ILambdaExpressionNode): TAstValue; override;
        function VisitVariableDeclaration(const Node: IVariableDeclarationNode): TAstValue; override;
        function VisitBlockExpression(const Node: IBlockExpressionNode): TAstValue; override;
    end;

{ TConstantNode }

constructor TConstantNode.Create(AValue: TScalar);
begin
    inherited Create;
    FValue := AValue;
end;

function TConstantNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitConstant(Self);
end;

function TConstantNode.GetValue: TScalar;
begin
    Result := FValue;
end;

{ TIdentifierNode }

constructor TIdentifierNode.Create(AName: string);
begin
    inherited Create;
    FName := AName;
    FIsResolved := False;
    FScopeDepth := -1;
    FSlotIndex := -1;
end;

function TIdentifierNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitIdentifier(Self);
end;

function TIdentifierNode.GetName: string;
begin
    Result := FName;
end;

function TIdentifierNode.Resolve(out ScopeDepth: Integer; out SlotIndex: Integer): Boolean;
begin
    Result := FIsResolved;
    if Result then
    begin
        ScopeDepth := FScopeDepth;
        SlotIndex := FSlotIndex;
    end;
end;

{ TBinaryExpressionNode }

constructor TBinaryExpressionNode.Create(ALeft: IExpressionNode; AOperator: TBinaryOperator; ARight: IExpressionNode);
begin
    inherited Create;
    FLeft := ALeft;
    FOperator := AOperator;
    FRight := ARight;
end;

function TBinaryExpressionNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitBinaryExpression(Self);
end;

function TBinaryExpressionNode.GetLeft: IExpressionNode;
begin
    Result := FLeft;
end;

function TBinaryExpressionNode.GetOperator: TBinaryOperator;
begin
    Result := FOperator;
end;

function TBinaryExpressionNode.GetRight: IExpressionNode;
begin
    Result := FRight;
end;

{ TUnaryExpressionNode }

constructor TUnaryExpressionNode.Create(const AOperator: TUnaryOperator; const ARight: IExpressionNode);
begin
    inherited Create;
    FOperator := AOperator;
    FRight := ARight;
end;

function TUnaryExpressionNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitUnaryExpression(Self);
end;

function TUnaryExpressionNode.GetOperator: TUnaryOperator;
begin
    Result := FOperator;
end;

function TUnaryExpressionNode.GetRight: IExpressionNode;
begin
    Result := FRight;
end;

{ TIfExpressionNode }

constructor TIfExpressionNode.Create(const ACondition, AThenBranch, AElseBranch: IExpressionNode);
begin
    inherited Create;
    FCondition := ACondition;
    FThenBranch := AThenBranch;
    FElseBranch := AElseBranch;
end;

function TIfExpressionNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitIfExpression(Self);
end;

function TIfExpressionNode.GetCondition: IExpressionNode;
begin
    Result := FCondition;
end;

function TIfExpressionNode.GetElseBranch: IExpressionNode;
begin
    Result := FElseBranch;
end;

function TIfExpressionNode.GetThenBranch: IExpressionNode;
begin
    Result := FThenBranch;
end;

{ TTernaryExpressionNode }

constructor TTernaryExpressionNode.Create(const ACondition, AThenBranch, AElseBranch: IExpressionNode);
begin
    inherited Create;
    FCondition := ACondition;
    FThenBranch := AThenBranch;
    FElseBranch := AElseBranch;
end;

function TTernaryExpressionNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitTernaryExpression(Self);
end;

function TTernaryExpressionNode.GetCondition: IExpressionNode;
begin
    Result := FCondition;
end;

function TTernaryExpressionNode.GetElseBranch: IExpressionNode;
begin
    Result := FElseBranch;
end;

function TTernaryExpressionNode.GetThenBranch: IExpressionNode;
begin
    Result := FThenBranch;
end;

{ TLambdaExpressionNode }

constructor TLambdaExpressionNode.Create(const AParameters: TArray<IIdentifierNode>; const ABody: IExpressionNode);
begin
    inherited Create;
    FBody := ABody;
    FParameters := AParameters;
end;

function TLambdaExpressionNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitLambdaExpression(Self);
end;

function TLambdaExpressionNode.GetBody: IExpressionNode;
begin
    Result := FBody;
end;

function TLambdaExpressionNode.GetParameters: TArray<IIdentifierNode>;
begin
    Result := FParameters;
end;

{ TFunctionCallNode }

constructor TFunctionCallNode.Create(const ACallee: IExpressionNode; const AArguments: array of IExpressionNode);
var
    arg: IExpressionNode;
begin
    inherited Create;
    FCallee := ACallee;
    FArguments := TList<IExpressionNode>.Create;
    for arg in AArguments do
        FArguments.Add(arg);
end;

destructor TFunctionCallNode.Destroy;
begin
    FArguments.Free;
    inherited;
end;

function TFunctionCallNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitFunctionCall(Self);
end;

function TFunctionCallNode.GetArguments: TList<IExpressionNode>;
begin
    Result := FArguments;
end;

function TFunctionCallNode.GetCallee: IExpressionNode;
begin
    Result := FCallee;
end;

{ TBlockExpressionNode }

constructor TBlockExpressionNode.Create(const AExpressions: array of IExpressionNode);
var
    expr: IExpressionNode;
begin
    inherited Create;
    FExpressions := TList<IExpressionNode>.Create;
    for expr in AExpressions do
        FExpressions.Add(expr);
end;

destructor TBlockExpressionNode.Destroy;
begin
    FExpressions.Free;
    inherited;
end;

function TBlockExpressionNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitBlockExpression(Self);
end;

function TBlockExpressionNode.GetExpressions: TList<IExpressionNode>;
begin
    Result := FExpressions;
end;

{ TVariableDeclarationNode }

constructor TVariableDeclarationNode.Create(const AIdentifier: IIdentifierNode; AInitializer: IExpressionNode);
begin
    inherited Create;
    FIdentifier := AIdentifier;
    FInitializer := AInitializer;
end;

function TVariableDeclarationNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitVariableDeclaration(Self);
end;

function TVariableDeclarationNode.GetIdentifier: IIdentifierNode;
begin
    Result := FIdentifier;
end;

function TVariableDeclarationNode.GetInitializer: IExpressionNode;
begin
    Result := FInitializer;
end;

{ TAssignmentNode }

constructor TAssignmentNode.Create(const AIdentifier: IIdentifierNode; const AValue: IExpressionNode);
begin
    inherited Create;
    FIdentifier := AIdentifier;
    FValue := AValue;
end;

function TAssignmentNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitAssignment(Self);
end;

function TAssignmentNode.GetIdentifier: IIdentifierNode;
begin
    Result := FIdentifier;
end;

function TAssignmentNode.GetValue: IExpressionNode;
begin
    Result := FValue;
end;

{ TIndexerNode }

constructor TIndexerNode.Create(const ABase, AIndex: IExpressionNode);
begin
    inherited Create;
    FBase := ABase;
    FIndex := AIndex;
end;

function TIndexerNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitIndexer(Self);
end;

function TIndexerNode.GetBase: IExpressionNode;
begin
    Result := FBase;
end;

function TIndexerNode.GetIndex: IExpressionNode;
begin
    Result := FIndex;
end;

{ TMemberAccessNode }

constructor TMemberAccessNode.Create(const ABase: IExpressionNode; const AMember: IIdentifierNode);
begin
    inherited Create;
    FBase := ABase;
    FMember := AMember;
end;

function TMemberAccessNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitMemberAccess(Self);
end;

function TMemberAccessNode.GetBase: IExpressionNode;
begin
    Result := FBase;
end;

function TMemberAccessNode.GetMember: IIdentifierNode;
begin
    Result := FMember;
end;

{ TCreateSeriesNode }

constructor TCreateSeriesNode.Create(const ADefinition: String);
begin
    inherited Create;
    FDefinition := ADefinition;
end;

function TCreateSeriesNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitCreateSeries(Self);
end;

function TCreateSeriesNode.GetDefinition: String;
begin
    Result := FDefinition;
end;

{ TAddSeriesItemNode }

constructor TAddSeriesItemNode.Create(const ASeries: IIdentifierNode; const AValue, ALookback: IExpressionNode);
begin
    inherited Create;
    FSeries := ASeries;
    FValue := AValue;
    FLookback := ALookback;
end;

function TAddSeriesItemNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitAddSeriesItem(Self);
end;

function TAddSeriesItemNode.GetLookback: IExpressionNode;
begin
    Result := FLookback;
end;

function TAddSeriesItemNode.GetSeries: IIdentifierNode;
begin
    Result := FSeries;
end;

function TAddSeriesItemNode.GetValue: IExpressionNode;
begin
    Result := FValue;
end;

{ TSeriesLengthNode }

constructor TSeriesLengthNode.Create(const ASeries: IIdentifierNode);
begin
    inherited Create;
    FSeries := ASeries;
end;

function TSeriesLengthNode.Accept(const Visitor: IAstVisitor): TAstValue;
begin
    Result := Visitor.VisitSeriesLength(Self);
end;

function TSeriesLengthNode.GetSeries: IIdentifierNode;
begin
    Result := FSeries;
end;

{ TSymbolTable }

constructor TSymbolTable.Create(AParent: TSymbolTable);
begin
    inherited Create;
    FParent := AParent;
    FSymbols := TDictionary<string, TSymbol>.Create;
    FNextSlotIndex := 0;
end;

destructor TSymbolTable.Destroy;
begin
    FSymbols.Free;
    inherited;
end;

function TSymbolTable.Define(const Name: string): TSymbol;
begin
    Result.Name := Name;
    Result.SlotIndex := FNextSlotIndex;
    inc(FNextSlotIndex);
    FSymbols.Add(Name, Result);
end;

function TSymbolTable.Resolve(const Name: string; out Symbol: TSymbol; out Depth: Integer): Boolean;
var
    currentScope: TSymbolTable;
begin
    Depth := 0;
    currentScope := Self;
    while Assigned(currentScope) do
    begin
        if currentScope.FSymbols.TryGetValue(Name, Symbol) then
            Exit(True);

        inc(Depth);
        currentScope := currentScope.FParent;
    end;
    Result := False;
end;

{ TBinder }

constructor TBinder.Create;
begin
    inherited;
    FCurrentScope := TSymbolTable.Create(nil); // Start with a global scope
end;

destructor TBinder.Destroy;
begin
    Assert(not Assigned(FCurrentScope.FParent), 'Scope leak in binder.');
    FCurrentScope.Free;
    inherited;
end;

procedure TBinder.EnterScope;
begin
    FCurrentScope := TSymbolTable.Create(FCurrentScope);
end;

procedure TBinder.ExitScope;
var
    oldScope: TSymbolTable;
begin
    oldScope := FCurrentScope;
    FCurrentScope := FCurrentScope.FParent;
    oldScope.Free;
end;

function TBinder.VisitBlockExpression(const Node: IBlockExpressionNode): TAstValue;
begin
    EnterScope;
    try
        // Default traversal of all expressions in the block
        inherited VisitBlockExpression(Node);
    finally
        ExitScope;
    end;
end;

function TBinder.VisitIdentifier(const Node: IIdentifierNode): TAstValue;
var
    symbol: TSymbol;
    depth: Integer;
    identNode: TIdentifierNode;
begin
    identNode := Node as TIdentifierNode;
    if identNode.FIsResolved then
        Exit;

    if FCurrentScope.Resolve(identNode.Name, symbol, depth) then
    begin
        identNode.FIsResolved := True;
        identNode.FScopeDepth := depth;
        identNode.FSlotIndex := symbol.SlotIndex;
    end
    else
        raise Exception.CreateFmt('Undefined identifier: "%s"', [identNode.Name]);
end;

function TBinder.VisitLambdaExpression(const Node: ILambdaExpressionNode): TAstValue;
var
    param: IIdentifierNode;
begin
    EnterScope;
    try
        // 1. Define all parameters in the new scope.
        for param in Node.Parameters do
            FCurrentScope.Define(param.Name);

        // 2. Now visit the parameter identifiers to resolve them to their new definitions,
        //    and visit the body to resolve its identifiers.
        inherited VisitLambdaExpression(Node);
    finally
        ExitScope;
    end;
end;

function TBinder.VisitVariableDeclaration(const Node: IVariableDeclarationNode): TAstValue;
begin
    // 1. First, visit the initializer expression to resolve its identifiers.
    if Assigned(Node.Initializer) then
        Node.Initializer.Accept(Self);

    // 2. Then, define the new variable in the current scope.
    FCurrentScope.Define(Node.Identifier.Name);

    // 3. Finally, visit the declaration's own identifier to resolve it.
    Node.Identifier.Accept(Self);
end;

{ TAst }

class procedure TAst.Bind(const ARootNode: IExpressionNode);
var
    binder: IAstVisitor;
begin
    binder := TBinder.Create;
    ARootNode.Accept(binder);
end;

class function TAst.AddSeriesItem(
    const ASeries: IIdentifierNode;
    const AValue: IExpressionNode;
    const ALookback: IExpressionNode
): IAddSeriesItemNode;
begin
    Result := TAddSeriesItemNode.Create(ASeries, AValue, ALookback);
end;

class function TAst.Assign(const AIdentifier: IIdentifierNode; const AValue: IExpressionNode): IAssignmentNode;
begin
    Result := TAssignmentNode.Create(AIdentifier, AValue);
end;

class function TAst.AssignResult(const AValue: IExpressionNode): IAssignmentNode;
begin
    Result := Assign(TAst.Identifier('Result'), AValue);
end;

class function TAst.Block(const AExpressions: array of IExpressionNode): IBlockExpressionNode;
begin
    Result := TBlockExpressionNode.Create(AExpressions);
end;

class function TAst.Constant(AValue: TScalar): IConstantNode;
begin
    Result := TConstantNode.Create(AValue);
end;

class function TAst.CreateSeries(const ADefinition: String): ICreateSeriesNode;
begin
    Result := TCreateSeriesNode.Create(ADefinition);
end;

class function TAst.BinaryExpr(ALeft: IExpressionNode; AOperator: TBinaryOperator; ARight: IExpressionNode): IBinaryExpressionNode;
begin
    Result := TBinaryExpressionNode.Create(ALeft, AOperator, ARight);
end;

class function TAst.FunctionCall(const ACallee: IExpressionNode; const AArguments: array of IExpressionNode): IFunctionCallNode;
begin
    Result := TFunctionCallNode.Create(ACallee, AArguments);
end;

class function TAst.Identifier(AName: string): IIdentifierNode;
begin
    Result := TIdentifierNode.Create(AName);
end;

class function TAst.IfExpr(const ACondition: IExpressionNode; const AThenBranch, AElseBranch: IExpressionNode): IIfExpressionNode;
begin
    Result := TIfExpressionNode.Create(ACondition, AThenBranch, AElseBranch);
end;

class function TAst.Indexer(const ABase, AIndex: IExpressionNode): IIndexerNode;
begin
    Result := TIndexerNode.Create(ABase, AIndex);
end;

class function TAst.MemberAccess(const ABase: IExpressionNode; const AMember: IIdentifierNode): IMemberAccessNode;
begin
    Result := TMemberAccessNode.Create(ABase, AMember);
end;

class function TAst.SeriesLength(const ASeries: IIdentifierNode): ISeriesLengthNode;
begin
    Result := TSeriesLengthNode.Create(ASeries);
end;

class function TAst.TernaryExpr(const ACondition: IExpressionNode; const AThenBranch, AElseBranch: IExpressionNode): ITernaryExpressionNode;
begin
    Result := TTernaryExpressionNode.Create(ACondition, AThenBranch, AElseBranch);
end;

class function TAst.LambdaExpr(const AParameters: TArray<IIdentifierNode>; const ABody: IExpressionNode): ILambdaExpressionNode;
begin
    Result := TLambdaExpressionNode.Create(AParameters, ABody);
end;

class function TAst.UnaryExpr(const AOperator: TUnaryOperator; const ARight: IExpressionNode): IUnaryExpressionNode;
begin
    Result := TUnaryExpressionNode.Create(AOperator, ARight);
end;

class function TAst.VarDecl(const AIdentifier: IIdentifierNode; AInitializer: IExpressionNode): IVariableDeclarationNode;
begin
    Result := TVariableDeclarationNode.Create(AIdentifier, AInitializer);
end;

{ TAstTraverser }

function TAstTraverser.VisitAddSeriesItem(const Node: IAddSeriesItemNode): TAstValue;
begin
    Node.Series.Accept(Self);
    Node.Value.Accept(Self);
    if Assigned(Node.Lookback) then
        Node.Lookback.Accept(Self);
end;

function TAstTraverser.VisitAssignment(const Node: IAssignmentNode): TAstValue;
begin
    Node.Value.Accept(Self);
    Node.Identifier.Accept(Self);
end;

function TAstTraverser.VisitBinaryExpression(const Node: IBinaryExpressionNode): TAstValue;
begin
    Node.Left.Accept(Self);
    Node.Right.Accept(Self);
end;

function TAstTraverser.VisitBlockExpression(const Node: IBlockExpressionNode): TAstValue;
var
    expr: IExpressionNode;
begin
    for expr in Node.Expressions do
        expr.Accept(Self);
end;

function TAstTraverser.VisitConstant(const Node: IConstantNode): TAstValue;
begin
end;

function TAstTraverser.VisitCreateSeries(const Node: ICreateSeriesNode): TAstValue;
begin
end;

function TAstTraverser.VisitFunctionCall(const Node: IFunctionCallNode): TAstValue;
var
    arg: IExpressionNode;
begin
    Node.Callee.Accept(Self);
    for arg in Node.Arguments do
        arg.Accept(Self);
end;

function TAstTraverser.VisitIdentifier(const Node: IIdentifierNode): TAstValue;
begin
end;

function TAstTraverser.VisitIfExpression(const Node: IIfExpressionNode): TAstValue;
begin
    Node.Condition.Accept(Self);
    Node.ThenBranch.Accept(Self);
    if Assigned(Node.ElseBranch) then
        Node.ElseBranch.Accept(Self);
end;

function TAstTraverser.VisitIndexer(const Node: IIndexerNode): TAstValue;
begin
    Node.Base.Accept(Self);
    Node.Index.Accept(Self);
end;

function TAstTraverser.VisitLambdaExpression(const Node: ILambdaExpressionNode): TAstValue;
var
    param: IIdentifierNode;
begin
    for param in Node.Parameters do
        param.Accept(Self);
    Node.Body.Accept(Self);
end;

function TAstTraverser.VisitMemberAccess(const Node: IMemberAccessNode): TAstValue;
begin
    // Do not visit the member identifier, as it's not a variable in the current scope.
    Node.Base.Accept(Self);
end;

function TAstTraverser.VisitSeriesLength(const Node: ISeriesLengthNode): TAstValue;
begin
    Node.Series.Accept(Self);
end;

function TAstTraverser.VisitTernaryExpression(const Node: ITernaryExpressionNode): TAstValue;
begin
    Node.Condition.Accept(Self);
    Node.ThenBranch.Accept(Self);
    Node.ElseBranch.Accept(Self);
end;

function TAstTraverser.VisitUnaryExpression(const Node: IUnaryExpressionNode): TAstValue;
begin
    Node.Right.Accept(Self);
end;

function TAstTraverser.VisitVariableDeclaration(const Node: IVariableDeclarationNode): TAstValue;
begin
    if Assigned(Node.Initializer) then
        Node.Initializer.Accept(Self);
    Node.Identifier.Accept(Self);
end;

end.