Elixir 2. Modules, Functions, Pipeline Operator

• modules is like namespace in Elixir
• every elixir function must be defined inside a module ¹
• module -> collection of function

IO is a module present in the elixir standard library, which have .puts() function

iex(1)> IO.puts("Hello, World")
Hello, World
:ok
iex(2)> IO.puts "Hello, World"
Hello, World
:ok
iex(3)>

To define our own module, use the defmodule construct. Inside the module, we define functions using def construct.

iex(1)> defmodule Math do
...(1)>    def sum(a, b) do
...(1)>        a + b
...(1)>    end
...(1)> end
{:module, Math,
 <<70, 79, 82, 49, 0, 0, 5, 64, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 0, 168,
   0, 0, 0, 18, 11, 69, 108, 105, 120, 105, 114, 46, 77, 97, 116, 104, 8, 95,
   95, 105, 110, 102, 111, 95, 95, 10, 97, ...>>, {:sum, 2}}
iex(2)> Math.sum(10, 99)
109
iex(3)> Math.sum(-1, -2)
-3
iex(4)> Math.sum(0, 0)
0
iex(5)> Math.sum(5, -5)
0
iex(6)>

• extension are .ex or .exs
• module must be defined in single source file, many moduels can be defined in single source file,
• module name must be start with uppercase and usually it is CamelCase style. A module name can contain number, underscore, and . (dot)
• we can nest modules

Functions

As with variables, function names can end with the ? and ! characters. The ? character is often used to indicate a function that returns either true or false. Placing the character ! at the end of the name indicates a function that may raise a runtime error. Both of these are conventions, rather than rules, but it’s best to follow them and respect the community style.

• defmodule and def are macros, not keywords
• if function has no argument then we can omit the parentheses:

defmodule Data do
 
  def name do
    "Kunal Singh"
  end
 
end
 
IO.puts(Data.name)

The return value of a function is the return value of its last expression. There’s no explicit return in Elixir.

-> if function definition is small, we can use condense syntax, like

defmodule Data do
 
  def name, do: "Kunal Singh"
 
end
 
IO.puts(Data.name)

defmodule Geometry do
  def square_area(a), do: a * a
end
 
area = Geometry.square_area(10)
 
IO.puts(area)

To run all these file use elixir as

elixir geometry.ex

Parenthesis are optional in elixir,

defmodule Geometry do
  def square_area(a), do: a * a
end
 
area = Geometry.square_area 10
 
IO.puts area

mix the Build tool for Elixir (which must have installed along with elixir) has a formatter, which can format the code as. mix format file.ex

If function are in very same module , no need to prefix it with the module name

defmodule Person do
 
  def first_name do
    "Kunal"
  end
 
  def last_name do
    "Singh"
  end
 
  def full_name do
    f = first_name()
    l = last_name()
    f <> " " <> l
  end
 
end
 
IO.puts(Person.full_name)

Note: f <> " " <> l in line 14 is string concatination

Pipeline Operator

a = -2 |> abs() |> Integer.to_string()
 
IO.puts(a)

This pipeline operator is just syntax sugar which will compile in this construct at compile time

IO.puts(Integer.to_string(abs(-2)))

In general the |> puts the result of previous function to the first argument of the next function i.e

previous(a, b) |> next(c, d)

is same as

next(pervious(a, b), c, d)

Question?

What is the output of the following code

a = -2 |> abs() |> max(1) |> min(0)
IO.puts(a)

To be continued...