anon_functions.ex

defmodule MyModule do
  # this is valid sytax. However, you can't access x and my_function inside `def`
  x = 2
  my_function = fn (x) -> x * 2 end
  
  # this is valid syntax. It will replace @my_variable with 2 anywehre inside the module at compile time.
  @my_variable 2
  
  # the following line will not compile
  # because only the following values are supported here:
  # lists, tuples, maps, atoms, numbers, bitstrings, PIDs and remote functions in the format &Mod.fun/arity
  @my_function fn (x) -> x * 2 end # compile error
  
  # now for the good code that will do what you intend:
  
  def first() do
    # this function will return an anonymous function
    fn (a) -> a * 2 end
  end
  
  def second() do
    double = first() # now 'double' is the anonymous function which we defined inside of first()
    IO.puts double.(4) # this will print 8
    third(double)
  end
  
  def third(f) do
    IO.puts f.(10) # we passed the anonymous function as a parameter, so f is like double, this will print 20
  end
end