Fizzbuzz

Pattern Matching

The match and pin operators

x = 1 >> 1

2 = x >> ** (MatchError) no match of right hand side value: 1

^x = 2 >> ** (MatchError) no match of right hand side value: 1

Assignment

{a, b, c} = {:hello, "world", 42}

{:ok, result} = {:ok, 13} >> {:ok, 13}

{:ok, result} = {:error, :oops} >> ** (MatchError)

list = [1, 2, 3] >> [1, 2, 3]

[head | tail] = list >> [1, 2, 3]

head >> 1

tail >> [2, 3]

[0 | list] >> [0, 1, 2, 3]

Case

case {1, 2, 3} do
    {4, 5, 6} ->
        "This clause won't match"
    {1, x, 3} ->
        "This clause will match and bind x to 2 in this clause"
    _ ->
        "This clause would match any value"
end

Guards

Allowed expressions

• Comparison operators (==, !=, ===, !==, >, >=, <, <=)
• Strictly boolean operators (and, or, not)
• Arithmetic unary and binary operators (+, -, +, -, *, /)
• in and not int
• Type-check functions (is_list, is_number), etc
• Functions that work on built-in datatypes (abs/1, map_size/1), etc

Case

case {1, 2, 3} do
    {1, x, 3} when x > 0 ->
        "Will match"
    _ ->
        "Would match, if guard condition were not satisfied"
end

Anonymous functions

f = fn
    x, y when x > 0 -> x + y
    x, y -> x * y
end

f.(1, 3) >> 4

f.(-1, 3) >> -3

Function Clauses

def foo(x) when is_integer(x), do: x
def foo(x) when is_float(x), do: round(x)
def foo(_), do: raise ArgumentError, message: "NAN"

Macros

"Macros in Elixir lets you perform syntactic extensions, which are expanded to before a program executes. We use macros to transform our internal program structure by treating code as data, and thus metaprogram."

Quote

The internal representation of any expression.

quote do: sum(1, 2, 3) >> {:sum, [], [1, 2, 3]}

The first element is the function name, the second is a keyword list containing metadata and the third is the arguments list.

quote do: 1 + 2 >> {:+, [context: Elixir, import: Kernel], [1, 2]}

Unquote

Inject some other particular chunk of code inside the representation we want to retrieve

number = 13

Macro.to_string(quote do: 11 + number) >> "11 + number"

Macro.to_string(quote do: 11 + unquote(number)) >> "11 + 13"