27 March 2012

While brew install erlang sounds easy enough, it won't give us what we need for 2 reasons:

To tackle the first problem, let's find out which versions of Erlang are available:

$ brew versions erlang
R15B     git checkout 12b8d77 /usr/local/Library/Formula/erlang.rb
R14B04   git checkout 8560672 /usr/local/Library/Formula/erlang.rb
R14B03   git checkout 9332ca9 /usr/local/Library/Formula/erlang.rb
R14B02   git checkout b782d9d /usr/local/Library/Formula/erlang.rb

In order to select R14B04, we just need to execute the provided command:

$ cd $(brew --prefix)
$ git checkout 8560672 /usr/local/Library/Formula/erlang.rb

(In case brew complains about a missing git repository, just run brew update and try again. This should only happen with new brew installations.)

brew info erlang should now list R14B04 as the selected version, but trying to install via brew install erlang will fail with compiler errors. The solution is to instruct brew to use gcc for compilation (instead of llvm-gcc or clang).
Unfortunately, gcc isn't available in Lion or the standard Homebrew formula repository. We therefore have to install it from Homebrew's dupes repository:

$ brew install https://raw.github.com/Homebrew/homebrew-dupes/master/apple-gcc42.rb

Now it's time to actually install Erlang using gcc (this may take a while):

$ brew -v install --use-gcc erlang

If all goes well, the Erlang shell should now work and show us it's running on Erlang R14B04:

$ erl
Erlang R14B04 (erts-5.8.5) [source] [64-bit] [smp:4:4] [rq:4] [async-threads:0] [hipe] [kernel-poll:false]

Finally, we can now go on to install Rebar, an Erlang build tool. We need to provide the --HEAD option, since Rebar "is a head-only formula" (fortunately, brew is smart enough to tell you what to do about that in case you forgot):

$ brew -v install --HEAD rebar