J is very crazy programming language, it can solve many problems in one liner. Also, it is one of the hardest language to read. Here are good thing about J J is very easy to install. J has package manager and you can just one click to install package. J is very fast language matrix computation and statistic. J is array language, so list and matrix are very common Here are the code for J and other languages for doing the same thing.

c =. 3  NB. c is local variable
c =: 3  NB. c is global variable


!3      NB. 3 factorial 
-- Haskell
fac n | n == 0 = 1
      | n > 0 = n * (fac (n-1))

l =. i. 2  NB. create a list = [0, 1, 2]
l = [0..2] NB. Haskell

{. list    NB. head list
}. list    NB. tail list

l =. i:2 NB. list = [-2, -1, 0, 1, 2]
l = [-2..2]

APL symbols is used by the computer language called APL. Here's a complete list of APL symbols in Unicode.