~$ ruby -v                                                                                                 *[master]
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]
~$ pry                                                                                                     *[master]
[1] pry(main)> def plusone(x)
[1] pry(main)*   x + 1
[1] pry(main)* end
=> :plusone
[2] pry(main)>
[3] pry(main)> [1,2,3].map(&:plusone)
ArgumentError: wrong number of arguments (0 for 1)
from (pry):1:in `plusone'
[4] pry(main)>