user-define function can be used in Calculated Measure?

[bashanwu]

such as:
==================================
s1='begin'+
+'var a; '
+'var b; '
+'func xy; '
+'a = "Summa"; '
+'b = "Count"; '
+'Result = xy(a,b); '
+'end '

TPivotMap.AddCalculatedMeasure(‘Summa percents’; s1);
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My question is "where can define func xy",would you give me a more detail example? thank you very much!

[AlexZencovich]

User may define function which will used in formulas by set event handler

procedure MapCalcMeasureGetFunction(const Map: IMap; MeasureIndex: Integer; Col: Integer;
Row: Integer; const FunctionName: WideString;
ParamCount: Integer; Params: OleVariant; var Value: Double); dispid 217;

where function name will name of user-defined function which receive set of parameters passed in variant array Params