MycLib/Src/AST/Myc.Ast.Compiler.Lowering.pas

unit Myc.Ast.Compiler.Lowering;

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.Types,
    Myc.Ast;

type
    IAstLowerer = interface(IAstVisitor)
        function Execute(const RootNode: IAstNode): IAstNode;
    end;

    // This transformer runs *after* TypeChecker (Phase 3).
    // It "lowers" the AST by rewriting complex nodes into simpler ones
    // that the evaluator can understand (e.g., operator folding).
    TAstLowerer = class(TAstTransformer, IAstLowerer)
    private
        FBinaryOperators: TDictionary<string, TScalar.TBinaryOp>;
        FUnaryOperators: TDictionary<string, TScalar.TUnaryOp>;
    protected
        // Override to find nodes to lower
        function VisitFunctionCall(const Node: IFunctionCallNode): IAstNode; override;
    public
        constructor Create;
        destructor Destroy; override;
        function Execute(const RootNode: IAstNode): IAstNode;

        class function Lower(const RootNode: IAstNode): IAstNode; static;
    end;

implementation

uses
    System.Generics.Defaults,
    Myc.Data.Keyword;

{ TAstLowerer }

constructor TAstLowerer.Create;
var
    op: TScalar.TBinaryOp;
    uOp: TScalar.TUnaryOp;
begin
    inherited Create;

    // Operator folding maps
    FBinaryOperators := TDictionary<string, TScalar.TBinaryOp>.Create;

    FBinaryOperators.Add('+', TScalar.TBinaryOp.Add);
    FBinaryOperators.Add('-', TScalar.TBinaryOp.Subtract);
    FBinaryOperators.Add('*', TScalar.TBinaryOp.Multiply);
    FBinaryOperators.Add('/', TScalar.TBinaryOp.Divide);
    FBinaryOperators.Add('=', TScalar.TBinaryOp.Equal);
    FBinaryOperators.Add('<>', TScalar.TBinaryOp.NotEqual);
    FBinaryOperators.Add('<', TScalar.TBinaryOp.Less);
    FBinaryOperators.Add('<=', TScalar.TBinaryOp.LessOrEqual);
    FBinaryOperators.Add('>', TScalar.TBinaryOp.Greater);
    FBinaryOperators.Add('>=', TScalar.TBinaryOp.GreaterOrEqual);

    FUnaryOperators := TDictionary<string, TScalar.TUnaryOp>.Create;

    FUnaryOperators.Add('not', TScalar.TUnaryOp.Not);
end;

destructor TAstLowerer.Destroy;
begin
    FUnaryOperators.Free;
    FBinaryOperators.Free;
    inherited;
end;

class function TAstLowerer.Lower(const RootNode: IAstNode): IAstNode;
begin
    var lowerer := TAstLowerer.Create as IAstLowerer;
    Result := lowerer.Execute(RootNode);
end;

function TAstLowerer.Execute(const RootNode: IAstNode): IAstNode;
begin
    Result := Accept(RootNode); // Use IAstNode-returning Accept
    if not Assigned(Result) then
        Result := TAst.Block([]);
end;

function TAstLowerer.VisitFunctionCall(const Node: IFunctionCallNode): IAstNode;
var
    calleeIdentifier: IIdentifierNode;
    binaryOp: TScalar.TBinaryOp;
    unaryOp: TScalar.TUnaryOp;
    left, right: IAstNode;
    nodeType: IStaticType;
begin
    // --- Optimization: Operator Folding ---
    if Node.Callee.Kind = akIdentifier then
    begin
        calleeIdentifier := Node.Callee.AsIdentifier;
        nodeType := Node.StaticType; // Get type from (un-lowered) node

        if (Length(Node.Arguments) = 2) then
        begin
            if FBinaryOperators.TryGetValue(calleeIdentifier.Name, binaryOp) then
            begin
                // Note: We MUST visit children *before* creating the new node
                left := Accept(Node.Arguments[0]);
                right := Accept(Node.Arguments[1]);

                // Call constructor directly, passing the inferred type
                Result := TAst.BinaryExpr(left, binaryOp, right, nodeType);
                exit;
            end;
        end;

        if (Length(Node.Arguments) = 1) then
        begin
            if FUnaryOperators.TryGetValue(calleeIdentifier.Name, unaryOp) then
            begin
                right := Accept(Node.Arguments[0]);
                // Call constructor directly, passing the inferred type
                Result := TAst.UnaryExpr(unaryOp, right, nodeType);
                exit;
            end;

            if (calleeIdentifier.Name = '-') then
            begin
                right := Accept(Node.Arguments[0]);
                // Call constructor directly, passing the inferred type
                Result := TAst.UnaryExpr(TScalar.TUnaryOp.Negate, right, nodeType);
                exit;
            end;
        end;
    end;

    // If no rewrite matched, continue traversal using the base implementation
    Result := inherited VisitFunctionCall(Node);
end;

end.