st: inspecting loaded variables and programs

["Pijus Virketis" <pvirketis@hbk.com>]

Dear all,

I am wondering what the stata-idiomatic way is to discover if a variable
"x" or a (non-.ado) program "p" is currently loaded. Sometimes in a .do
script I need to check if "x" and "p" already exist, and drop/replace
them if they do. 

Thank you!

Pijus

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