Checks if there is a message matching the given clauses in the current process mailbox.

In case there is no such message, the current process hangs until a message arrives or waits until a given timeout value.

Examples

receive do
  {:selector, number, name} when is_integer(number) ->
    name
  name when is_atom(name) ->
    name
  _ ->
    IO.puts(:stderr, "Unexpected message received")
end

An optional after clause can be given in case the message was not received after the given timeout period, specified in milliseconds:

receive do
  {:selector, number, name} when is_integer(number) ->
    name
  name when is_atom(name) ->
    name
  _ ->
    IO.puts(:stderr, "Unexpected message received")
after
  5000 ->
    IO.puts(:stderr, "No message in 5 seconds")
end

The after clause can be specified even if there are no match clauses. The timeout value given to after can be any expression evaluating to one of the allowed values:

• :infinity - the process should wait indefinitely for a matching message, this is the same as not using the after clause

• 0 - if there is no matching message in the mailbox, the timeout will occur immediately

• positive integer smaller than or equal to 4_294_967_295 (0xFFFFFFFF in hexadecimal notation) - it should be possible to represent the timeout value as an unsigned 32-bit integer.

Variable handling

The receive/1 special form handles variables exactly as the case/2 special macro. For more information, check the docs for case/2.