Tail call optimization

ASTPlayground/MainForm.pas

@@ -70,6 +70,7 @@ type
         InnerLambdaButton: TButton;
         DumpButton: TButton;
         FailingUpvalueButton: TButton;
+        TailCallButten: TButton;
         procedure InnerLambdaButtonClick(Sender: TObject);
         procedure ClearButtonClick(Sender: TObject);
         procedure FormCreate(Sender: TObject);
@@ -87,6 +88,7 @@ type
         procedure Test1ButtonClick(Sender: TObject);
         procedure Test2ButtonClick(Sender: TObject);
         procedure FromJSONButtonClick(Sender: TObject);
+        procedure TailCallButtenClick(Sender: TObject);
         procedure ToJSONButtonClick(Sender: TObject);
     private
         // Stores the last AST generated by Test1 or Test2 button clicks.
@@ -182,7 +184,10 @@ begin
 
     resultValue := ExecuteAst(mainBlock, FGScope);
 
-    Assert(TScalar.FromInteger(15) = resultValue.AsScalar, 'The final result should be 15.');
+    //TODO Dieses Assert löst aus:
+    // "The final result should be 15, but is 10 (T:\Myc\ASTPlayground\MainForm.pas, line 186)"
+
+    Assert(TScalar.FromInteger(15) = resultValue.AsScalar, 'The final result should be 15, but is ' + resultValue.AsScalar.ToString);
 end;
 
 procedure TForm1.ClearButtonClick(Sender: TObject);
@@ -201,7 +206,7 @@ begin
     // It binds the AST and then decides whether to run a debug session or a standard evaluation.
     var scriptScope := TAstBinder.Bind(ANode, AParentScope).CreateScope(AParentScope);
     var visitor := CreateVisitor(scriptScope);
-    Result := ANode.Accept(visitor);
+    Result := visitor.Execute(ANode);
 end;
 
 procedure TForm1.FormCreate(Sender: TObject);
@@ -263,7 +268,7 @@ begin
                     )
                 );
 
-            Scope.Define('CreateSMA', smaAst.Accept(TEvaluatorVisitor.Create(TAstBinder.Bind(smaAst, FGScope).CreateScope(FGScope))));
+            Scope.Define('CreateSMA', CreateVisitor(TAstBinder.Bind(smaAst, FGScope).CreateScope(FGScope)).Execute(smaAst));
         end
     );
 
@@ -331,7 +336,7 @@ begin
     end;
 
     visitor := TPrettyPrintVisitor.Create;
-    FLastAst.Accept(visitor);
+    visitor.Execute(FLastAst);
     Memo1.Lines.Add(visitor.GetResult);
 end;
 
@@ -635,7 +640,7 @@ begin
 
     // This is a temporary visitor just for the setup execution.
     var setupVisitor := CreateVisitor(scope);
-    setupAst.Accept(setupVisitor);
+    setupVisitor.Execute(setupAst);
 
     // 2. Prepare for the simulation loop by modifying the now-populated scope.
     scope.Define('current_series', TDataValue.Void);
@@ -685,7 +690,7 @@ begin
         if series.AsRecordSeries.TotalCount >= smaSlowLength then
         begin
             scope[seriesAddress] := series;
-            var resultValue := callAst.Accept(visitor);
+            var resultValue := visitor.Execute(callAst);
             if i mod 50 = 0 then
             begin
                 Memo1.Lines.Add(Format('Tick %d/%d: Close = %.2f, Signal = %s', [i, numRecs, ohlcvRec.Close, resultValue.ToString]));
@@ -726,7 +731,7 @@ begin
 
     // This case is simple enough to just inline the logic from ExecuteAst
     var visitor := CreateVisitor(TriggerScope);
-    blk.Accept(visitor);
+    visitor.Execute(blk);
 
     FLastAst := blk;
 
@@ -737,7 +742,7 @@ end;
 function TForm1.CreateVisitor(Scope: IExecutionScope): IAstVisitor;
 begin
     if DebugBox.IsChecked then
-        Result := TDebugEvaluatorVisitor.CreateVisitor(Scope, Memo1.Lines, ShowScopeBox.IsChecked)
+        Result := TDebugEvaluatorVisitor.Create(Scope, Memo1.Lines, ShowScopeBox.IsChecked)
     else
         Result := TEvaluatorVisitor.Create(Scope);
 end;
@@ -906,6 +911,54 @@ begin
     end;
 end;
 
+procedure TForm1.TailCallButtenClick(Sender: TObject);
+const
+    // A large number to prove TCO prevents stack overflow
+    RecursionDepth = 1000000;
+var
+    root: IAstNode;
+    result: TDataValue;
+    sw: TStopwatch;
+begin
+    Memo1.Lines.Clear;
+    Memo1.Lines.Add(Format('--- Testing TCO with recursion depth of %d ---', [RecursionDepth]));
+    Application.ProcessMessages;
+    sw := TStopwatch.StartNew;
+
+    root :=
+        TAst.Block(
+            [
+                // var countDown = lambda(n) { ... };
+                TAst.VarDecl(
+                    TAst.Identifier('countDown'),
+                    TAst.LambdaExpr(
+                        [TAst.Identifier('n')],
+                        // if (n > 0) then Self(n-1) else 'done'
+                        TAst.IfExpr(
+                            TAst.BinaryExpr(TAst.Identifier('n'), boGreater, TAst.Constant(TScalar.FromInt64(0))),
+                            // This is the tail call position.
+                            TAst.FunctionCall(
+                                TAst.Identifier('Self'),
+                                [TAst.BinaryExpr(TAst.Identifier('n'), boSubtract, TAst.Constant(TScalar.FromInt64(1)))]
+                            ),
+                            // Base case of the recursion
+                            TAst.Constant(TScalar.FromString('done'))
+                        )
+                    )
+                ),
+                // Initial call to start the recursion
+                TAst.FunctionCall(TAst.Identifier('countDown'), [TAst.Constant(TScalar.FromInt64(RecursionDepth))])
+            ]
+        );
+
+    FLastAst := root;
+    result := ExecuteAst(root, FGScope);
+    sw.Stop;
+
+    Memo1.Lines.Add(Format('Result: %s', [result.ToString]));
+    Memo1.Lines.Add(Format('Execution finished in %d ms without stack overflow.', [sw.ElapsedMilliseconds]));
+end;
+
 procedure TForm1.ToJSONButtonClick(Sender: TObject);
 var
     jsonString: string;