st: recommendation for learning to write Stata ado-files

[Andrea Bennett <mac.stata@gmail.com>]

Hi,

Does anyone have a good starting point for learning how to write ado- 
files (in case it is part of the Stata manuals, I don't have them!).  
Is there a book you would recommend? Or do you usually just learn by  
looking at existing ado-files?

Kind regards,

Andrea
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