>you can write
>
>RETURN @atoto
>
>VFP 6.0 doesn't want to save this syntaxe

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This is what hte helps says about it

Passing Parameters by Reference
See Also

You can pass parameters by reference every time or only in a specific instance.

To pass parameters by reference

Use the TO REFERENCE clause of the SET UDFPARMS command before calling the UDF:
-or-

Use the @ token to pass a variable or array by reference, as in the following example:
? "UDF value: " + STR(plusone(@nX))


I don't know at this moment what is wrong with it.