Erlang at Yun is missing, I compiled it.
Down load Erlang:
cd /mnt/sda1
wget -O erlang.tar.gz https://www.dropbox.com/s/5d2ce7acevb81t2/erlang.tar.gz?dl=0 --no-check-certificate
tar -zxvf erlang.tar.gz
Install Erlang:
cd erlang
opkg update
opkg install erlang_R15B01-4_ar71xx.ipk
Test " hello world":
erl -noshell -eval 'io:fwrite("Hello, World!\n"), init:stop().'
Hello, World!