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>>I need to use the _GetExpr, because in the report writer, in the window that appears when you are adding a field (built in foxpro window) there is a [...] button that when pressed calls up either the built in expression builder or if you have set the _GetExpr to your own app, then it calls up yours. The problem is that when you set an expression in the built in expression builder and close it, the previous window has an expression text box that is updated, but this does not happen (or at least I cannot figure out how to make it happen) when you use your own expression builder.
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>OK, silly question: does your replacement expression builder return a string?

Yes it does...it actually works if you do the command:
GETEXPR to x
and x will contain the value I returned.

I think I have discovered a workaround (not a great one though). Just before I exit my custom expression builder I send the keyboard commands appropriate to the area of the report writer it was called from, that do a paste in the report expression textbox. For example in the report field builder I have to do a backtab and then a ctrl+v. I would love to not have to use be using the keyboard command so if you know of a better way that would be great.