I've come to the point where some of the packages I want to use require me
to work from source.

ERROR: dependencies ‘Rcompression’ are not available for package ‘RKML’
* removing ‘/Users/mosher/Library/R/2.11/library/RKML’
* installing *source* package ‘Rcompression’ ...
Checking configuration for Rcompression to find libz and libbz2
checking for gcc... no
checking for cc... no
checking for cl.exe... no
configure: error: no acceptable C compiler found in $PATH
See `config.log' for more details.
ERROR: configuration failed for package ‘Rcompression’

So, It appears that I have to install a compiler. Looking at Xcode the
package that was available required an OS upgrade
is Xcode the only option or is there another option I can use..

also, where does the $PATH get set

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