defmodule Closures do
  @moduledoc """
  A very simple example of closures in Elixir.  This example
  explicitly and intentionally mirrors closu1.go and closu2.go
  The important differnece in Elixir is that once the function
  is defined, the values in the closure are set. Changing the
  value stored with a variable has no effect on the closure.
  This is by language design and follows immediately from
  immutability

  Author: gtowell
  Created Aug 2022
  """

  @doc """
  Return a function that just add two numbers
  Realistically this only needs one line of code
  This is an example of currying.
  """
  def clos1(aa) do
    retfun = fn bb -> aa+bb end
    retfun
  end

  @doc """
  Return a function that just add two numbers
  Thanks to immutability the line aa=aa*2 is not relevant
  to the closure of the function defined on the previous line.
  """
  def clos2(aa) do
    retfun = fn bb -> aa+bb end
    aa = aa*2
    retfun
  end

  @doc """
  Testing code for the two previous functions
  """
  def main do
    fun17 = clos1(17)
    # Enum.each is weird in a function language.
    #           in that the function invoked is exectued
    #           for side effects ONLY
    Enum.each(1..5, fn v -> IO.puts("clos1 #{v} ==> #{fun17.(v)}" ) end)

    fun34 = clos2(17)
    Enum.each(1..5, fn v -> IO.puts("clos2 #{v} ==> #{fun34.(v)}") end )
  end
end

Closures.main