Elixirの対話モードで制御構造の動作を確認してみた

# 概要
Elixirの対話モードで制御構造の動作を確認してみました。以下のページを参考にしました。

https://elixirschool.com/ja/lessons/basics/control_structures

# 対話モードで実行
以下のコマンドを実行しました。
```
$ iex
Erlang/OTP 24 [erts-12.2.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [jit]

Interactive Elixir (1.12.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> if String.valid?("Hello") do
...(1)> "Valid string!"
...(1)> else
...(1)> "Invalid string."
...(1)> end
"Valid string!"
iex(2)> if "a string value" do
...(2)> "Truthy"
...(2)> end
"Truthy"
iex(3)> unless is_integer("hello") do
...(3)> "Not an Int"
...(3)> end
"Not an Int"
iex(4)> case {:ok, "Hello World"} do
...(4)> {:ok, result} -> result
...(4)> {:error} -> "Uh oh!"
...(4)> _ -> "Catch all"
...(4)> end
"Hello World"
iex(5)> case :even do
...(5)> :odd -> "Odd"
...(5)> end    
** (CaseClauseError) no case clause matching: :even

iex(5)> case :even do
...(5)> :odd -> "Odd"
...(5)> _ -> "Not Odd"
...(5)> end
"Not Odd"
iex(6)> pie = 3.14
3.14
iex(7)> case "cherry pie" do
...(7)> ^pie -> "Not so tasty"
...(7)> pie -> "I bet #{pie} is tasty"
...(7)> end
"I bet cherry pie is tasty"
iex(8)> case {1, 2, 3} do
...(8)> {1, x, 3} when x > 0 ->
...(8)> "Will match"
...(8)> _ ->
...(8)> "Won't match"
...(8)> end
"Will match"
iex(9)> cond do
...(9)> 2 + 2 == 5 ->
...(9)> "This will not be true"
...(9)> 2 * 2 == 3 ->
...(9)> "Nor this"
...(9)> 1 + 1 == 2 ->
...(9)> "But this will"
...(9)> end
"But this will"
iex(10)> cond do
...(10)> 7 + 1 == 0 -> "Incorrect"
...(10)> true -> "Catch all"
...(10)> end
"Catch all"
iex(11)> user = %{first: "Sean", last: "Callan"}
%{first: "Sean", last: "Callan"}
iex(12)> with {:ok, first} <- Map.fetch(user, :first),
...(12)> {:ok, last} <- Map.fetch(user, :last),
...(12)> do: last <> ", " <> first
"Callan, Sean"
iex(13)> user = %{first: "doomspork"}
%{first: "doomspork"}
iex(14)> with {:ok, first} <- Map.fetch(user, :first),
...(14)> {:ok, last} <- Map.fetch(user, :last),
...(14)> do: last <> ", " <> first
:error
iex(15)> case Repo.insert(changeset) do
...(15)> {:ok, user} ->
...(15)> case Guardian.encode_and_sign(user, :token, claims) do
...(15)> {:ok, jwt, full_claims} ->
...(15)> important_stuff(jwt, full_claims)
...(15)> error ->
...(15)> error
...(15)> end
...(15)> error ->
...(15)> error
...(15)> end
** (CompileError) iex:15: undefined function changeset/0
    (stdlib 3.17) lists.erl:1358: :lists.mapfoldl/3
iex(15)> with {:ok, user} <- Repo.insert(changeset),
...(15)> {:ok, jwt, full_claims} <- Guardian.encode_and_sign(user, :token, claims),
...(15)> do: important_stuff(jwt, full_claims)
** (CompileError) iex:15: undefined function changeset/0
    (stdlib 3.17) lists.erl:1358: :lists.mapfoldl/3
    (stdlib 3.17) lists.erl:1358: :lists.mapfoldl/3
iex(15)> import Integer
Integer
iex(16)> m = %{a: 1, c: 3}
%{a: 1, c: 3}
iex(17)> a =
...(17)> with {:ok, number} <- Map.fetch(m, :a),
...(17)> true <- is_even(number) do
...(17)> IO.puts "#{number} divided by 2 is #{div(number, 2)}"
...(17)> :even
...(17)> else
...(17)> :error ->
...(17)> IO.puts("We don't have this item in map")
...(17)> :error
...(17)> _ -> 
...(17)> IO.puts("It is odd")
...(17)> :odd
...(17)> end
It is odd
:odd
iex(18)> 
```

# まとめ
何かの役に立てばと。