Elixir Language Anonymous Functions


In Elixir, a common practice is to use anonymous functions. Creating an anonymous function is simple:

iex(1)> my_func = fn x -> x * 2 end
#Function<6.52032458/1 in :erl_eval.expr/5>

The general syntax is:

fn args -> output end

For readability, you may put parenthesis around the arguments:

iex(2)> my_func = fn (x, y) -> x*y end
#Function<12.52032458/2 in :erl_eval.expr/5>

To invoke an anonymous function, call it by the assigned name and add . between the name and arguments.

iex(3)>my_func.(7, 5)

It is possible to declare anonymous functions without arguments:

iex(4)> my_func2 = fn -> IO.puts "hello there" end
iex(5)> my_func2.()
hello there

Using the capture operator

To make anonymous functions more concise you can use the capture operator &. For example, instead of:

iex(5)> my_func = fn (x) -> x*x*x end

You can write:

iex(6)> my_func = &(&1*&1*&1)

With multiple parameters, use the number corresponding to each argument, counting from 1:

iex(7)> my_func = fn (x, y) -> x + y end

iex(8)> my_func = &(&1 + &2)   # &1 stands for x and &2 stands for y

iex(9)> my_func.(4, 5)

Multiple bodies

An anonymous function can also have multiple bodies (as a result of pattern matching):

my_func = fn
  param1 -> do_this
  param2 -> do_that

When you call a function with multiple bodies Elixir attempts to match the parameters you have provided with the proper function body.