On Wed, Sep 28, 2016 at 6:14 PM, Richard A. O'Keefe <ok@cs.otago.ac.nz> wrote:
m% cabal install doctest
cabal: /usr/bin/ar: permission denied

https://github.com/haskell/cabal/issues/2653#issuecomment-121997407
You have a cabal-install built against an older version of the unix package, which was doing an access() call that runs afoul of System Integrity Protection.

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