elixir KERNEL 4

Question 1

defmodule Sum do

def add(pid, x, y) do

send(pid, x + y)

end

end

spawn(Sum, :add, [self(), 1, 2])

receive do val -> val end

Answer 1

=> 3

Question 2

pets = %{

“cat” => %{age: 1},

“dog” => %{age: 3}

}

pets[“cat”][:age] |> update_in(&(&1 + 1))

Answer 2

=> %{

“cat” => %{age: 2},

“dog” => %{age: 3}

}

Question 3

c = %{age: 5}

v = %{age: 20}

auto = %{“car” => c, “van” => v}

add1 = &(&1 + 1)

auto[“van”].age |> update_in(add1)

Answer 3

%{“car” => %{age:5}, “van” => %{age: 21}}

Question 4

e = %{age: 4}

m = %{age: 7}

dogs = %{ellie: e, max: m}

update_in(dogs.max.age, &(&1 + 1))

Answer 4

%{ellie: %{age:4}, max: %{age: 8}}

Question 5

b = %{age: 1}

c = %{age: 2}

toys = %{“bear” => b, “car” => c}

plus1 = &(&1 + 1)

toys |> update_in([“car”, :age], plus1)

Answer 5

%{“bear” => %{age: 1}, %{“car” => %{age: 3}}

Question 6

defmodule Add do

def inc(pid, x),

do: send(pid, x + 1)

end

spawn_link(Add, :inc, [self(), 1])

receive do

val -> val

end

Answer 6

=> 2

Question 7

b = %{age: 1}

a = %{age: 2}

bots = %{“bob” => b, “amy” => a}

bots[“bob”][:age] |> get_and_update_in(&{&1, &1+1})

Answer 7

=> %{“bob” => %{age: 2}, “amy” => %{age: 2}}

Question 8

abs(-1.11)

Answer 8

=> 1.11

Question 9

abs(28)

Answer 9

=> 28

Question 10

ceil(-1.25)

Answer 10

=> -1

Question 11

floor(3.55)

Answer 11

=> 3

Question 12

1 in {1, 2, 3}

Answer 12

** (Protocol.UndefinedError)

protocol Enumerable not implemented for {1, 2, 3}

*Note: Tuple is a basic type,

but in/2 expects an enumerable on the right side

Question 13

1 in [1, 2] == Enum.member?([1, 2], 1)

Answer 13

=> true

Question 14

x = 1

case x do

x when x in [2, 3] -> “boo”

x when x in 0..2 -> “foo”

_x => “whatevs”

end

Answer 14

=> “foo”

Question 15

c = %{age: 30}

n = %{age:20}

jobs = %{“cop” => c, “nun” => n}

jobs[“cop”].age |> get_and_update_in(&(&1, &1+1))

Answer 15

=> {30, “cop” => %{age: 31}, “nun” => %{age: 20}}

Question 16

is_map_key(%{a: 1}, :a)

Answer 16

=> true

Question 17

1 not in [1, 2, 3]

Answer 17

=> false

Question 18

defmodule Feeling do

def love, do: “love you!”

end

Feeling.love()

Answer 18

=> “love you!”

Question 19

is_map_key(:a, %{a: 1})

Answer 19

BadMapError

*Note: is_map_key/2 expects a map as a first argument

Question 20

pets = %{amy: %{age: 7}, mia: %{age: 8}}

pets.amy.age |> get_and_update_in(&(&1, &1 + 1))

Answer 20

=> {7, %{amy: %{age: 8}, mia: %{age: 8}}}

Question 21

is_struct(URI.parse(“/”))

Answer 21

=> true

eg: URI.parse(“https://hexdocs.pm/elixir/Kernel.html#content”) =>

%URI{
authority: “hexdocs.pm”,
fragment: “content”,
host: “hexdocs.pm”,
path: “/elixir/Kernel.html”,
port: 443,
query: nil,
scheme: “https”,
userinfo: nil
}

Question 22

is_struct(%{})

Answer 22

=> false

Question 23

defmodule Lang do

def desc(a, b) do

”#{a} #{b}”

end

end

Lang.desc(“elixir”, “cool”)

Answer 23

=> “elixir cool”

Question 24

throw “hello”

Answer 24

** (throw) “hello”

Question 25

defmodule Inc do

def add(x, inc_by \1) do

x + inc_by

end

end

Inc.add(1)

Answer 25

=> 2

*Note: Inc.add(3, 5) => 8

Question 26

defmodule Title do

def name(name, title \ “”)

def name(name, title) do

title <> name

end

end

Title.name(“Smith”, “Dr.”

Answer 26

=> “Dr.Smith”

*Note: if only 1 argument is provided, the first def is called and name and default title are fed into the second def because there is no instruction block defined by the first def.

Therefore, Title.name(“Johnson”) => “Johnson”

Question 27

all = fn :get_and_update, data, next -> Enum.map(data, next) end

get_and_update_in(

[%{x: 1, y: 0}, %{x: 0, y: 0}],

[all, :x],

&{&1, &1 +1}

)

Answer 27

=> [

{1, %{x: 2, y: 0}},

{0, %{x: 1, y: 0}}

]

Question 28

try do

throw(:catch_this)

catch

:throw, :catch_this -> :it_was_caught

end

Answer 28

=> :it_was_caught

Question 29

defmodule Title do

def name(name, title \ “”)

def name(name, title) do

title <> name

end

end

Title.name(“Smith”)

Answer 29

=> “Smith”

Question 30

try do

throw(:tantrum)

catch

:throw, value -> value

after

IO.puts “Are you ok?”

end

Answer 30

=> :tantrum

*Note: “Are you ok?” would be printed

before returning the value of throw.

Question 31

defmodule End do

def perform(reason) do

exit reason

catch

:exit, _ -> “Or keep going?”

end

end

End.perform(“Give up”)

Answer 31

=> “Or keep going?”

Question 32

try do

throw(:ball)

catch

x -> x

end

Answer 32

:ball

Question 33

try do

throw(:tantrum)

catch

_value -> __STACKTRACE__

end

Answer 33

Returns a stacktrace

Example from my particular iex session:

[
{:erl_eval, :do_apply, 6, [file: ‘erl_eval.erl’, line: 680]},
{:erl_eval, :try_clauses, 8, [file: ‘erl_eval.erl’, line: 914]},
{:elixir, :recur_eval, 3, [file: ‘src/elixir.erl’, line: 278]},
{:elixir, :eval_forms, 3, [file: ‘src/elixir.erl’, line: 263]},
{IEx.Evaluator, :handle_eval, 5, [file: ‘lib/iex/evaluator.ex’, line: 258]},
{IEx.Evaluator, :do_eval, 3, [file: ‘lib/iex/evaluator.ex’, line: 239]},
{IEx.Evaluator, :eval, 3, [file: ‘lib/iex/evaluator.ex’, line: 217]},
{IEx.Evaluator, :loop, 1, [file: ‘lib/iex/evaluator.ex’, line: 103]}
]

Question 34

destructure([x, y], [1, 2, 3])

{x, y}

Answer 34

=> {1, 2}

Question 35

destructure([a, b], [“oy”])

“a is #{a} and b is #{b}”

Answer 35

=> “a is oy and b is “

Question 36

score = %{rob: %{win: 2}, ann: %{win: 3}}

get_and_update_in(score, [:rob, :win], &{&1, &1 + 1})

Answer 36

{2, %{ann: %{win: 3}, rob %{win: 3}}

Question 37

defstructure([x, y], [1])

{x, y}

Answer 37

=> {1, nil}

Question 38

a = “a”

destructure([^a, 1], [:a, 1])

Answer 38

** (MatchError) no match of right hand side value: [:a, 1]

Question 39

defmodule Car do

defstruct color: :red

end

struct(Car)

Answer 39

=> %Car{color: :red}

Question 40

defmodule Car do

defstruct color: :red

end

struct(Car, color: :blue)

Answer 40

=> %Car{color: :blue}

Question 41

defmodule Pet do

defstruct name: “Bob”

end

pet = struct(Pet, name: “Mia”)

struct(pet, age: 1)

Answer 41

=> %Pet{name: “Mia”}

Question 42

defmodule Lang do

defstruct name: “Eli” <> “xir”

end

struct(Lang, %{“name” => “ruby”})

Answer 42

=> %Lang{name: “Elixir”}

Question 43

defmodule Car do

defstruct make: :BMW

end

a = struct(Car)

b = %{make: :BMW, __struct__: Car}

a == b

Answer 43

=> true

Question 44

defmodule Car do

defstruct [:make]

end

struct(Car)

Answer 44

=> %Car{make: nil}

Question 45

defmodule Car do

@enforce_keys [:make]

defstruct [:make]

end

struct(Car)

Answer 45

=> %Car{make: nil}

*Note:

enforce_keys has no effect here.

Use struct!/2 or % to enforce keys

Question 46

defmodule Car do

@enforce_keys [:make]

defstruct [:make]

end

struct!(Car)

Answer 46

** (ArgumentError)

The following keys must also be given when building struct Car:

[:make]

Question 47

defmodule Car do

defstruct [:make]

end

struct!(Car)

Answer 47

=> %Car{make: nil}

Question 48

defmodule Car do

defstruct [:make]

end

struct!(Car, color: :red)

Answer 48

** (KeyError) key :color not found in: %Car{make: nil}

Question 49

defmodule Child do

defstruct name: “El”

end

a = struct!(%Child{})

struct!(a, age: 1)

Answer 49

** (KeyError) key :age not found in: %Child{name: “El”}

Question 50

~U[2020-03-01T20:00:07.001+00:00]

Answer 50

~U[2020-03-01 20:00:07.001Z]

Question 51

Define a type, t, for given module so its type can be referenced as User.t

defmodule User do

defstruct name: “Bob”, age: 18

end

Answer 51

@type t :: %__MODULE__{

name: String.t(),
age: non_neg_integer

}

Question 52

~U[2020-03-01 20:34:00Z]

Answer 52

=> ~U[2020-03-01 20:34:00Z]

Question 53

:a in [:”a”]

Answer 53

=> true

Question 54

pid = self()

fn -> send(pid, 1 + 1) end

|> spawn_link()

receive do

val -> val

end

Answer 54

=> 2