[R] Looking for a book/tutorial with the following context:

[alaios]

Hello everyone.
It is time to start writing more and more function and I want to read in a
good reference 
-book ( I can buy one, especially if it is second handed :P)
-online tutorial
-any other guide

-How functions really work in R
-How to write bigger R programs
-If there are local function variables.
-Global ones and how to treat them
-How to include function files in order to keep your all increasing code
into separate files
-How to debug an R program step by step.
-How to print debugging messages.

I would like to thank you in advance for your help

Best Regards
Alex
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