函数定义 #

function name(parameters)
    body
    return value
end

function greet(name)
    println("Hello, $name!")
end

greet("Julia")

function add(a, b)
    a + b
end

result = add(1, 2)

function add(a, b)
    return a + b
end

add(a, b) = a + b
square(x) = x^2
greet(name) = println("Hello, $name!")

function power(base, exponent)
    base ^ exponent
end

power(2, 3)

function greet(name, greeting="Hello")
    println("$greeting, $name!")
end

greet("Julia")
greet("Julia", "Hi")

function create_point(x, y; color="red", size=1)
    println("Point at ($x, $y) with color=$color, size=$size")
end

create_point(1, 2)
create_point(1, 2; color="blue")
create_point(1, 2; color="blue", size=5)
create_point(1, 2, color="blue", size=5)

function sum_all(args...)
    total = 0
    for x in args
        total += x
    end
    return total
end

sum_all(1, 2, 3, 4, 5)

function process(; kwargs...)
    for (key, value) in kwargs
        println("$key = $value")
    end
end

process(a=1, b=2, c=3)

function add(a::Int, b::Int)::Int
    a + b
end

add(1, 2)
add(1.0, 2.0)

function divide(a::Float64, b::Float64)::Float64
    a / b
end

function process(x)::String
    string(x)
end

function process(x::Union{Int, Float64})
    x * 2
end

process(10)
process(10.5)

function foo(a, b, c)
    println("a=$a, b=$b, c=$c")
end

foo(1, 2, 3)

function bar(; a, b, c)
    println("a=$a, b=$b, c=$c")
end

bar(a=1, b=2, c=3)
bar(c=3, a=1, b=2)

function baz(a, b; c=3, d=4)
    println("a=$a, b=$b, c=$c, d=$d")
end

baz(1, 2)
baz(1, 2; c=10)
baz(1, 2, c=10, d=20)

function sum_three(a, b, c)
    a + b + c
end

args = [1, 2, 3]
sum_three(args...)

kwargs = (a=1, b=2, c=3)
bar(; kwargs...)

f = x -> x^2
f(5)

g = add
g(1, 2)

function apply(f, x)
    f(x)
end

apply(x -> x^2, 5)
apply(sqrt, 16)

function multiplier(n)
    x -> x * n
end

times_3 = multiplier(3)
times_3(5)

"""
    add(a, b)

Add two numbers together.

# Arguments
- `a`: First number
- `b`: Second number

# Returns
The sum of `a` and `b`

# Examples
```julia
julia> add(1, 2)
3

### 6.2 查看文档

```julia
?add

function calculator(a, op, b)
    if op == "+"
        a + b
    elseif op == "-"
        a - b
    elseif op == "*"
        a * b
    elseif op == "/"
        b == 0 ? error("Division by zero") : a / b
    else
        error("Unknown operator: $op")
    end
end

calculator(10, "+", 5)
calculator(10, "/", 2)

function fibonacci(n::Int)
    n <= 0 && return 0
    n == 1 && return 1
    fibonacci(n - 1) + fibonacci(n - 2)
end

fibonacci(10)

function statistics(arr::Vector{<:Number})
    (
        count = length(arr),
        sum = sum(arr),
        mean = sum(arr) / length(arr),
        min = minimum(arr),
        max = maximum(arr)
    )
end

statistics([1, 2, 3, 4, 5])

function compose(f, g)
    x -> f(g(x))
end

double = x -> 2x
increment = x -> x + 1

double_then_increment = compose(increment, double)
double_then_increment(5)