[R] how to check if a library is loaded, from a function

[Nick Matzke]

Hi,

I've written a function which I load with a source command. 
  The function requires a certain library, phangorn, to work.

I would like the function to check if phangorn is loaded as 
a library before running.  For some reason, just putting 
require(phangorn) into the sourced function doesn't do anything.

This must be simple, but I can't figure it out!  Any help 
appreciated...

Cheers!
Nick

-- 
====================================================
Nicholas J. Matzke
Ph.D. Candidate, Graduate Student Researcher

Huelsenbeck Lab
Center for Theoretical Evolutionary Genomics
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When people thought the earth was spherical, they were 
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