Killer Elixir-Tips

Killer Elixir-Tips

Elixir Tips and Tricks from the Experience of Development. Each part consists of 10 Unique Tips and Tricks with a clear explanation with live examples and outputs. These tips will speed up your development and save you time in typing code as well.

You can read specific parts with following links...

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Checkout some cherry picked tips from the all Parts

Taste Before you Eat :)

iex Custom Configuration - iex Decoration

Copy the content into a file and save the file as .iex.exs in your ~ home directory and see the magic. You can also download the file HERE

# IEx.configure colors: [enabled: true]
# IEx.configure colors: [ eval_result: [ :cyan, :bright ] ]
IO.puts IO.ANSI.red_background() <> IO.ANSI.white() <> " ❄❄❄ Good Luck with Elixir ❄❄❄ " <> IO.ANSI.reset
Application.put_env(:elixir, :ansi_enabled, true)
IEx.configure(
 colors: [
   eval_result: [:green, :bright] ,
   eval_error: [[:red,:bright,"Bug Bug ..!!"]],
   eval_info: [:yellow, :bright ],
 ],
 default_prompt: [
   "\e[G",    # ANSI CHA, move cursor to column 1
    :white,
    "I",
    :red,
    "❤" ,       # plain string
    :green,
    "%prefix",:white,"|",
     :blue,
     "%counter",
     :white,
     "|",
    :red,
    "▶" ,         # plain string
    :white,
    "▶▶"  ,       # plain string
      # ❤ ❤-»" ,  # plain string
    :reset
  ] |> IO.ANSI.format |> IO.chardata_to_string

)

Creating Custom Sigils and Documenting

Each x sigil calls its respective sigil_x definition

Defining Custom Sigils

defmodule MySigils do
  #returns the downcasing string if option l is given then returns the list of downcase letters
  def sigil_l(string,[]), do: String.downcase(string)
  def sigil_l(string,[?l]), do: String.downcase(string) |> String.graphemes

  #returns the upcasing string if option l is given then returns the list of downcase letters
  def sigil_u(string,[]), do: String.upcase(string)
  def sigil_u(string,[?l]), do: String.upcase(string) |> String.graphemes
end

usage

Load the module into iex

iex> import MySigils
iex> ~l/HELLO/
"hello"
iex> ~l/HELLO/l
["h", "e", "l", "l", "o"]
iex> ~u/hello/
"HELLO"
iex> ~u/hello/l
["H", "E", "L", "L", "O"]

Custom Error Definitions

Define Custom Error

defmodule BugError do
   defexception message: "BUG BUG .." # message is the default
end

Usage

iex bug_error.ex

iex> raise BugError
** (BugError) BUG BUG ..
iex> raise BugError, message: "I am Bug.." #here passing the message dynamic
** (BugError) I am Bug..

Writing Protocols

Define a Protocol

A Protocol is a way to dispatch to a particular implementation of a function based on the type of the parameter. The macros defprotocol and defimpl are used to define Protocols and Protocol implementations respectively for different types in the following example.

defprotocol Triple do    
  def triple(input)  
end  

defimpl Triple, for: Integer do    
  def triple(int) do     
    int * 3   
  end  
end   

defimpl Triple, for: List do
  def triple(list) do
    list ++ list ++ list   
  end  
end

Usage

Load the code into iex and execute

iex> Triple.triple(3) 
9
Triple.triple([1, 2])
[1, 2, 1, 2, 1, 2]

Ternary Operator

There is no ternary operator like true ? "yes" : "no" . So, the following is suggested.

"no" = if 1 == 0, do: "yes", else: "no"

Advantage of Kernel.||

When using pipelines, sometimes we break the pipeline for or operation. For example:

result = :input
|> do_something
|> do_another_thing

# Bad
result = (result || :default_output)
|> do_something_else

Indeed, || is only a shortcut for Kernel.|| . We can use Kernel.|| in the pipeline instead to avoid breaking the pipeline.

The code above will be:

result = :input
|> do_something
|> do_another_thing
|> Kernel.||(:default_output)  #<-- This line
|> do_something_else

This above tip is from qhwa

Checking Out Code Grouping

Code grouping stands for something great. It shows you how your code is grouped when you write multiple lines of code in single line with out using braces. It will be more clear with the following example.

one 1 |> two()

If you want to see how this line of code is grouped into, you can check in the following format..

quote(do: one 1 |> two()) |> Macro.to_string |> IO.puts
one(1 |> two())

So, by using the quote and Macro.to_string you can see how our code was grouped into.

This tip came out in discussion with the creator of Ecto MichalMuskala in the Elixir forum.

Elixir Short Circuit Operators && — ||

These replaces the nested complicated conditions. These are my best friends in the situations dealing with more complex comparisons. Trust me you gonna love this.

The || operator always returns the first expression which is true. Elixir doesn’t care about the remaining expressions, and won’t evaluate them after a match has been found.

||

false || nil || :blackode || :elixir || :jose

Here if you observe the first expression is false next nil is also false in elixir next :blackode which evaluates to true and its value is returned immediately with out evaluating the :elixir and :jose . Similarly if all the statements evaluates to false the last expression is returned.

&&

iex> true && :true && :elixir && 5
5
iex> nil && 100
nil
iex> salary = is_login && is_admin && is_staff && 100_000

This && returns the second expression if the first expression is true or else it returns the first expression with out evaluating the second expression. In the above examples the last one is the situation where we encounter to use the && operator.

Comparing two different data types

I have self experience with this. When I was a novice in elixir, I just compared "5" > 4 unknowingly by an accident and to my surprise it returned with true.

In Elixir every term can compare with every other term. So one has to be careful in comparisons.

iex> x = "I am x "
"I am x "
iex> x > 34
true
iex> x > [1,2,3]
true
iex> [1, 2, 3] < 1234567890
false

Order of Comparison

number < atom < reference < fun < port < pid < tuple < map < list < bitstring (binary)

Arithmetic Operators as Lambda functions

When I see this first time, I said to my self “Elixir is Crazy”. This tip really saves time and it resembles your smartness. In Elixir every operator is a macro. So, we can use them as lambda functions.

iex> Enum.reduce([1,2,3], 0, &+/2)
6
iex> Enum.reduce([1,2,3], 0, &*/2)
0
iex> Enum.reduce([1,2,3], 3, &*/2)
18
iex> Enum.reduce([1,2,3], 3, &-/2)
-1
iex> Enum.reduce([1,2,3], 3, &//2)
0.5

Binary Pattern Matching

This is my recent discovery. I always encounter a situation like converting "$34.56" which is a string and I suppose do arithmetic operations. I usually do something like this before binary pattern matching..

iex> value = "$34.56"
iex ...      |> String.split("$")
iex ...      |> tl
iex ...      |> List.first
iex ...      |> String.to_float
34.56

Tip Approach

This tip makes my day easy. I recently used this is in one of my projects.

iex> "$" <> value = "$34.56"
"$34.56"
iex> String.to_float value  
34.56

Must Know the Differences of Map keys as :atoms and binary(strings)

Before I let you to use this tip, I just want to remind you that :atoms are not garbage collected. Atom keys are great! If you have a defined atoms, you are in no danger. What you should not do is converting user supplied input into atoms without sanitizing them first because it can lead to out of memory. You should also be cautious if you create dynamic atoms in your code.

But, you can use the . to retrieve the data from the keys as map.key unlike the usual notation like map["key"] . That really saves on typing. But, I don’t encourage this because, as programmers we should really care about memory.

iex> map = %{name: "blackode", blog: "medium"}
%{blog: "medium", name: "blackode"}

iex> map.name
"blackode"

iex> map.blog
"medium"

Be sure that when you try to retrieve a key with . form which is not present in the map, it will raise a key error instead of returning the nil unlike the map["key"] which returns nil if key is not present in a map.

iex> map["age"]
nil

iex> map.age
Bug Bug ..!!** (KeyError) key :age not found in: %{blog: "medium", name: "blackode"}
Bug Bug ..!!

Add Some Color To Your Console Prints

Elixir >=1.4.0 has ANSI color printing option to console. You can have great fun with colors. You can also provide background colors.

iex> import IO.ANSI
iex> IO.puts red <> "red" <> green <> " green" <> yellow <> " yellow" <> reset <> " normal"
iex> IO.puts Enum.join [red, "red", green, " green", yellow, " yellow", reset, " normal"]
red green yellow normal

The red prints in red color, green in green color, yellow in yellow color and normal in white. Have fun with colors…

For more details on color printing check Printex module which I created for fun in Elixir.

Functional Macros as Guard Clauses

We cannot make use of the functions as guard clauses in elixir. It means, when cannot accept custom defined functions. Consider the following lines of code…

defmodule Hello do
  def hello(name, age) when is_kid(age) do
    IO.puts "Hello Kid #{name}"
  end
  
  def hello(name, age) when is_adult(age) do
    IO.puts "Hello Mister #{name}"
  end
  
  def is_kid age do
    age < 12
  end
  
  def is_adult age do
    age > 18
  end
end

Here we defined a module Hello and a function hello that takes two parameters of name and age. So, based on age I am trying IO.putsaccordingly. If you do so you will get an error saying….

** (CompileError) hello.ex:2: cannot invoke local is_kid/1 inside guard
    hello.ex:2: (module)

This is because when cannot accept functions as guards. We need to convert them to macros Lets do that…

defmodule MyGuards do

  defmacro is_kid age do
    quote do: unquote(age) < 12
  end

  defmacro is_adult age do
    quote do: unquote(age) > 18
  end

end
# order of module matters here.....
defmodule Hello do

  import MyGuards

  def hello(name, age) when is_kid(age) do
    IO.puts "Hello Kid #{name}"
  end

  def hello(name, age) when is_adult(age) do
    IO.puts "Hello Mister #{name}"
  end

   def hello(name, age) do
    IO.puts "Hello Youth #{name}"
  end

end

In the above lines of code, we wrapped all our guards inside a module MyGuards and make sure the module is top of the module Hello so, the macros first gets compiled. Now compile and execute you will see the following output..

iex> Hello.hello "blackode", 21
Hello Mister blackode
:ok
iex> Hello.hello "blackode", 11
Hello Kid blackode
:ok

Starting on Elixir v1.6, you can use defguard/1.

The defguard is also a macro. You can also create private guards with defguardp. Hope, you got the point here. Consider the following example.

NOTE: The defguard and defguardp should reside inside the module like other macros. It raises a compile time error, if some thing that don't fit in the guard clause section when.

Suppose, you want to check the given number is either three or five, you can define the guard as following.

defmodule Number.Guards do
  defguard is_three_or_five(number) when (number===3) or (number===5)
end

Usage

import Number.Guards
defmodule Hello do
  def check_favorite_number(num) when is_three_or_five(num) do
    IO.puts "The given #{num} is on of my favourite numbers"
  end
  def check_favorite_number(_num), do: IO.puts "Not my favorite number"
end

You can also use them inside your code logic as they results boolean value.

iex> import Number.Guards
Number.Guards

iex> is_three_or_five(5)
true

iex> is_three_or_five(3)
true

iex> is_three_or_five(1)
false

Check the following execution screen shot.

Finding whether Module was loaded or not

Sometimes, we have to make sure that certain module is loaded before making a call to the function. We are supposed to ensure the module is loaded.

Code.ensure_loaded? <Module>

iex> Code.ensure_loaded? :kernel
true
iex> Code.ensure_loaded :kernel
{:module, :kernel}

Similarly we are having ensure_compile to check whether the module is compiled or not…

Converting Binary to Capital Atom

Elixir provides a special syntax which is usually used for module names. What is called a module name is an uppercase ASCII letter followed by any number of lowercase or uppercase ASCII letters, numbers, or underscores.

This identifier is equivalent to an atom prefixed by Elixir. So in the defmodule Blackode example Blackode is equivalent to :"Elixir.Blackode"

When we use String.to_atom "Blackode" it converts it into :Blackode But actually we need something like “Blackode” to Blackode. To do that we need to use Module.concat

iex(2)> String.to_atom "Blackode"
:Blackode
iex(3)> Module.concat Elixir,"Blackode"
Blackode

In Command line applications whatever you pass they convert it into binary. So, again you suppose to do some casting operations …

Pattern match [ vs ] destructure.

We all know that = does the pattern match for left and right side. We cannot do [a, b, c] = [1, 2, 3, 4] this raise a MatchError

iex(11)> [a, b, c] = [1, 2, 3, 4]
** (MatchError) no match of right hand side value: [1, 2, 3, 4]

We can use destructure/2 to do the job.

iex(1)> destructure [a, b, c], [1, 2, 3, 4]
[1, 2, 3]
iex(2)> {a, b, c}
{1, 2, 3}

If the left side is having more entries than in right side, it assigns the nil value for remaining entries..

iex> destructure([a, b, c], [1])
iex> {a, b, c} 
{1, nil, nil}

The Goodness of Data decoration [ inspect with :label ] option

We can decorate our output with inspect and label option. The string of label is added at the beginning of the data we are inspecting.

iex(1)> IO.inspect [1, 2, 3], label: "the list "
the list : [1, 2, 3]
[1, 2, 3]

If you closely observe this it again returns the inspected data. So, we can use them as intermediate results in |> pipe operations like following……

[1, 2, 3] 
|> IO.inspect(label: "before change") 
|> Enum.map(&(&1 * 2)) 
|> IO.inspect(label: "after change") 
|> length

You will see the following output

before change: [1, 2, 3]
after change: [2, 4, 6]
3

Piping Anonymous functions

We can pass the anonymous functions in two ways. One is directly using &like following..

[1, 2, 3, 4, 5]
|> length()
|> (&(&1*&1)).()

This is the most weirdest approach. How ever, we can use the reference of the anonymous function by giving its name.

square = & &1 * &1
[1, 2, 3, 4, 5]
|> length()
|> square.()

The above style is much better than previous . You can also use fn to define anonymous functions.

Or use Kernel.then/2 function since 1.12.0

[1, 2, 3, 4, 5]
|> length()
|> then