gistfile1.ex

iex> Monad.identity do
...>   IO.puts 1
...>   {:ok, a} = {:ok, 2}
...>   IO.puts a
...> end
1
2
:ok
iex> Monad.error do
...>   IO.puts "reading file..."
...>   {:ok, bin} = :file.read_file("/etc/passwd")
...>   IO.puts bin
...> end
reading file...
##
# User Database
# 
# Note that this file is consulted directly only when the system is running
# in single-user mode.  At other times this information is provided by
# Open Directory.
#
# See the opendirectoryd(8) man page for additional information about
# Open Directory.
##
nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false
root:*:0:0:System Administrator:/var/root:/bin/sh
daemon:*:1:1:System Services:/var/root:/usr/bin/false

######## ... SKIPPED... #########

:ok
iex> Monad.error do
...>   IO.puts "reading file..."
...>   {:ok, bin} = :file.read_file("/etc/passwd_wrong")
...>   IO.puts bin
...> end
reading file...
{:error,:enoent}