[WiX-users] correctly define preprocessor var in wxs?

[<jo...@ms...>]

I have been struggling to find one simple example of defining a
preprocessor variable in the wxs file.

Currently, If I Append this to my candle command line:
   -dMyVar='foo.exe'
then references to $(var.MyVar) in wxs work.
But no matter how I define MyVar in the main wxs, they are not found.

Why does this not work, defined in my main project wxs?
<WixVariable Id='MyVar' Value='foo.exe' />


Until that works, I can't hope to reach my goal of using an environment
variable (ExeName):
<?ifdef $(env.ExeName) ?>
<WixVariable Id='MyVar' Value="$(env.ExeName)" />
<?else?>
<WixVariable Id='MyVar' Value='foo.exe' />
<?endif?>


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