DEV Community: bbronek

Beginning my journey with elixir Part III. Time, Mix Tasks, IEx, Errors, Executables.

bbronek — Sat, 20 Feb 2021 03:42:50 +0000

As I wrote in the last part, this article will be about dates and times, custom mix tasks, more about iex, error handling, and executable files. In the next part, I will focus on the practical use of basic knowledge, but for now, I encourage you to familiarize yourself with the problems contained in my presentation 😉

1.Dates and times

-Time
Examples of how to use the module :

Get a current time:

iex> Time.utc_now
~T[00:57:02.826573]

Take a look, that ~T is a sigil which I explained in Part II.

So maybe let's use our knowledge about sigils and create a Time struct.

iex> time = ~T[20:34:23.754335]
~T[20:34:23.754335]
iex> time.hour
20
iex> time.second
23

-Date

Get actual date:

iex> Date.utc_today
~D[2021-02-20]

So let's create a date structure and use it in practice

iex> {:ok, date} = Date.new(1023,5,24)
{:ok, ~D[1023-05-24]}
iex > Date.leap_year? date
false

-NaiveDateTime

The NaiveDateTime struct contains the fields year, month, day, hour, minute, second, microsecond and calendar. You can read more about this here.

Examples :

iex> NaiveDateTime.utc_now
~N[2021-02-20 01:18:10.218303]
iex> NaiveDateTime.diff(~N[2018-04-17 14:00:00], ~N[1970-01-01 00:00:00])
1523973600 <- result in seconds

-DateTime

The module supports date and timezones.

Example:

iex> DateTime.from_naive(~N[2013-04-21 11:25:02.0034], "Etc/UTC")
{:ok, ~U[2013-04-21 11:25:02.0034Z]}

More: link1, link2

2.Custom Mix Tasks

1.Create a new app by - 'mix new app'
2.Create a new directory newTask/lib/mix/tasks/task.ex
3.In task.ex create module
4.Use it by 'mix task'

3.IEx

You can by h before the module gets documentation about it, by i information about data type, r - recompile a particular module, t- information about types available in a given module.

iex> h Enum
Provides a set of algorithms to work with enumerables.

In Elixir, an enumerable is any data type that implements the Enumerable
protocol. Lists ([1, 2, 3]), Maps (%{foo: 1, bar: 2}) and Ranges (1..3) are
common data types used as enumerables: ...
iex> i Map
Term
  Map
Data type
  Atom ...
iex> t Map
@type key() :: any()
@type value() :: any()

4.Error Handling

When an error occurs Elixir returns the tuple {: error, reason}. The simplest way to make an error is by use raise:

iex> raise "Error"
** (RuntimeError) Error

It is set by default to raise a RuntimeError but if you want to change it you can by the simple way: raise typeoferror, message: "lorem ipsum", example:

raise ArithmeticError, message: "bad argument in arithmetic expression"

try-rescue-after
It is simple construction to handling errors, I hope that you understand it by reading this example:

iex> try do
...>   raise "err"
...> rescue
...>   e in RunTimeError -> IO.puts("Msg:" <> e.message)
...> after
...>   IO.puts "End"

Create own Error

defmodule NewError do
  defexception message: "an error has occurred"
end

5.Executable Files

You can make a file executable in Elixir by _File.chmod(pat_file,0o755) (755 is a permission for a file)_.

If you want to build executables projects, you can use escript.

See you 👋

Beginning my journey with elixir Part II. Modules, Enum, Loops, Strings, Recursion, Tests.

bbronek — Fri, 19 Feb 2021 00:00:26 +0000

So it's time for the second part of my journey with elixir.
I will try to explain in a clear way things I have lastly learned and also show you how to use the newly acquired knowledge to write some simple programs.
That being said, I encourage you to read and learn something really interesting 😃

1.Modules

Modules are used to organize functions in their own namespace, it is useful to allocate functions to modules in relation to their functionality.
Example :

defmodule Greetings do
 @moduledoc """
  Provides a function `greet/1` to greet a human
  """
  @doc """
  Prints a hello message

  ## Parameters

    - name: String 

  ## Examples

      iex> Greeter.greet("user324")
      "Good morning! user324"

      iex> Greeter.greet("Peter")
      "Good morning! Peter"

  """
  @greeting "Good morning!"

  def greet(name) do
    ~s(#{@greeting} #{name}.)
  end
end

defmodule Greetings2 do
  alias Greetings, as: Hi

  def main do
    Hi.greet("John")
  end
end

As you can see I used the @greeting attribute to use it as a greeting in the greet function. The ~s is a sigil. What is it? Here is an answer: Sigils are special syntax to working with literals, you can read more about this here. I also used the alias to use functions from another module in a different one.

2.Enum

The Enum is a module to work with enumerables.
I will only show a few functions from this module because it contains over 70 functions. It will be all?, any?, chunk_every, chunk_by, each, map, min, filter, reduce, sort and uniq

-all?

iex>Enum.all?(["one","two","three"], fn(x) -> String.length(x) == 4 end)
false
Enum.all?(["one","two","thre"], fn(x) -> String.length(x) == 3 end)
true

-any?

iex>Enum.any?(["one","two","three"], fn(x) -> String.length(x) == 4 end)
true
Enum.any?(["one","two","thre"], fn(x) -> String.length(x) == 5 end)
false

-chunk_every

iex>Enum.chunk_every(["one","two","three"], 2) 
[["one", "two"], ["three"]]

-chunk_by

iex>Enum.chunk_by(["world","universe","hi"], fn(x) -> String.length(x) end) 
[["world"], ["universe"], ["hi"]]

-each

iex>Enum.each(["How","are","you","?"], fn(x) -> IO.puts(x) end) 
How
are
you
?
:ok

-map

iex> Enum.map([0, 1, 2, 3], fn(x) -> x * x end)
[0, 1, 4, 9]

-min

iex> Enum.min([1, 32, 42, -10])
-10

-filter

iex> Enum.filter([1, 2, 3, 4], fn(x) -> rem(x, 2) == 0 end)
[2, 4]

-reduce

iex> Enum.reduce(["a","b","c"], fn(x,acc)-> x <> acc end)
"cba"

Explanation: acc is the first element of the list.
This how it works:

1. x = 'b' acc = 'a' -> out: "ba"
2. x = 'c' acc = "ba" -> out: "cba"
"cba"

-sort

iex> Enum.sort([%{:val => 4}, %{:val => 1}], fn(x, y) -> x[:val] > y[:val] end)
[%{val: 4}, %{val: 1}]

-uniq

iex>  Enum.uniq([1, 2, 3, 2, 1, 1, 1, 1, 1])
[1, 2, 3]

3.Loops

-for loop


iex>for {_key, val} <- [one: 1, two: 2, three: 3], do: IO.puts _key

one
two
three

iex> import Integer
Integer
iex> for x <- 1..20, is_even(x), do: IO.puts x
2
4
6
8
10
12
14
16
18
20

-functional approach source


defmodule Loop do
   def print_multiple_times(msg, n) when n <= 1 do
      IO.puts msg
   end

   def print_multiple_times(msg, n) do
      IO.puts msg
      print_multiple_times(msg, n - 1)
   end
end

Results :

iex> c("file.ex")
[Loop]
iex> Loop.print_multiple_times("HI",3)
HI
HI
HI
:ok

4.Strings

-You can use ASCII to assign a string value.

iex> string = <<104,101,108,108,111>>
"Hello"

-Easy for returning an ASCII value of a char :

iex>?a
97

Anagram program :

defmodule Anagram do
  def anagrams?(a, b) when is_binary(a) and is_binary(b) do
    sort_string(a) == sort_string(b)
  end

  def sort_string(string) do
    string
    |> String.downcase()
    |> String.graphemes()
    |> Enum.sort()
  end
end

Useful link grapheme.

5.Short view of recursion.

defmodule Rec do
  def rec(a,b) do
    if a<=b do
      IO.puts "Hi #{a}"
      a = a + 1
      rec(a,b)
    end
  end
end

Results:

[Rec]
iex> Rec.rec(2,7)
Hi 2
Hi 3
Hi 4
Hi 5
Hi 6
Hi 7
nil

6. Tests

I wrote a simple program and I hope that it will be useful in understanding the methods of testing.

defmodule App do

    def get_name do
      IO.gets("What is yout name? ")
      |>String.trim
    end

    def get_number do
      IO.getn("Give a number: [0-9] ",1)
    end

    def main() do
      name = get_name()
      IO.puts("Hello #{name}")
      number = get_number()
      name
    end

end

ExUnit.start

defmodule Tests do
  alias App
  use ExUnit.Case

  test "check if name is valid" do
    refute String.match?(App.main,~r/[0-9]/)
  end
end

Explanation: IO.getn(string,size) , ~r/[0-9]/ (regex);

Before testing, you have to launch it by ExUnit.start,
to use the test condition I had to write before it use ExUnit.Case. ' refute String.match?(App.main,~r/[0-9]/) '
refute it is the same as unless, you can also use assert in testing which means 'should' or 'expect to be' .

Result:

What is your name? qwer45
Hello qwer45
Give a number: [0-9] 5

1) test check if name is valid (Tests)
     tests.exs:27
     Expected false or nil, got true
     code: refute String.match?(App.main, ~r"[0-9]")
     arguments:

         # 1
         "qwer45"

         # 2
         ~r/[0-9]/

     stacktrace:
       tests.exs:28: (test)



Finished in 4.8 seconds (0.07s on load, 4.7s on tests)
1 test, 1 failure

This all for part II in the next part I plan to write about using dates and times, custom mix tasks, more about iex, error handling, and executable files. Have a nice day ✋

Beginning my journey with elixir Part I - problem with mix and 5 most interesting things I learned so far.

bbronek — Wed, 03 Feb 2021 01:33:01 +0000

Currently, I am a student of computer science and I am dedicated to programming, I tried different technologies such as node, python but elixir excites me the most and with this technology I bind my professional future. In this series, I would like to share my adventure, successes, and problems I encountered. Hope you will enjoy this series 😀

I started from learning basics from Elixir school and Elixir webpage. Everything was going well with learning until I got an error when I had to use mix. I installed elixir with instructions. I am using Linux Mint and the error I got when trying to create a new app was:

╰─❯ mix new app
** (Mix) Application name must start with a letter and have only lowercase letters, numbers, and underscore, got: "app". The application name is inferred from the path, if you'd like to explicitly name the application then use the "--app APP" option.

I couldn't find an answer on StackOverflow so I decided to ask on the elixir channel on discord and good people advised me to install elixir via asdf. It is an extendable version manager that can be used to install elixir properly link.

I removed elixir and erlang then installed the latest versions of them using asdf:

1) asdf plugin add erlang && asdf plugin add the elixir
2) asdf install erlang latest
3) asdf global erlang <version>
4) asdf install elixir latest
5) asdf global elixir <version>

Thankfully, I can now enjoy the functionality of the mix.

I will now move on to the most interesting things I learned.

1.Pin operator it makes assignment when the left side if the match includes variables. Example:

iex> x = 42
42
iex> ^x = 44
** (MatchError) no match of right-hand side value: 44

As you can see when I tried to match x with 44 I got an error above.

2.Cond is used to match conditions similar to if-else or else in other languages. Example:

iex> cond do
...>   "apple" == "banana" -> "Incorrect"
...>   true -> "Catched all"
...> end
"Catched all"

3.Pipe operator it takes the result of one function and passes it on as the first parameter of another expressions. Example:

iex> "HEllo WoRld" |> String.downcase() |> String.split()
["hello", "world"]

4.Documentation of Modules and functions Example:

defmodule Calculator do
  @moduledoc """
Provides a function `add/2` to add two numbers and print them out
  """

  def add(x,y) do
   IO.puts x+y
  end
end

You can access Calculator documentation by using the h helper function:

iex>c("file.ex") 
[Module]
...> Calculator.function(5,4)
9
:ok

iex> h Calculator

                Calculator

Provides a function add/2 to add two numbers

5.Start new project using mix Example:

$ mix new app

Output:

* creating README.md
* creating .formatter.exs
* creating .gitignore
* creating mix.exs
* creating lib
* creating lib/app.ex
* creating test
* creating test/test_helper.exselse
* creating test/app_test.exs

Your Mix project was created successfully.
You can use "mix" to compile it, test it, and more:

    cd app
    mix test

Run "mix help" for more commands.