gistfile1.erl

% Example of Erlang guards
-module(double).
-export([double/1]).

%% If guard expressions are separated by a comma, it means AND.
%% If guard expressions are separated by a semi-colon, it means OR.
double(X) when X > 0; X < 0 -> X * 2;
% If a function has multiple lines, each line (except the last), must be 
% terminated by a comma
double(X) when X =:= 0 -> io:format("Trying to double a zero homie?~n"),
          0.