learnxinyminutes-docs/zh-cn/julia-cn.html.markdown
2018-08-31 07:55:10 +08:00

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language filename contributors translators lang
Julia learn-julia-zh.jl
Leah Hanson
http://leahhanson.us
Pranit Bauva
https://github.com/pranitbauva1997
Daniel YC Lin
https://github.com/dlintw
Jichao Ouyang
http://oyanglul.us
woclass
https://github.com/inkydragon
zh-cn
# 单行注释只需要一个井号
#= 多行注释
   只需要以 '#=' 开始 '=#' 结束
   还可以嵌套.
=#

####################################################
## 1. 原始类型与操作符
####################################################

# Julia 中一切皆为表达式

# 这是一些基本数字类型
typeof(3)       # => Int64
typeof(3.2)     # => Float64
typeof(2 + 1im) # => Complex{Int64}
typeof(2 // 3)  # => Rational{Int64}

# 支持所有的普通中缀操作符
1 + 1      # => 2
8 - 1      # => 7
10 * 2     # => 20
35 / 5     # => 7.0
10 / 2     # => 5.0  # 整数除法总是返回浮点数
div(5, 2)  # => 2    # 使用 div 可以获得整除的结果
5 \ 35     # => 7.0
2^2        # => 4    # 幂运算,不是异或 (xor)
12 % 10    # => 2

# 用括号提高优先级
(1 + 3) * 2 # => 8

# 位操作符
~2         # => -3 # 按位非 (not)
3 & 5      # => 1  # 按位与 (and)
2 | 4      # => 6  # 按位或 (or)
xor(2, 4)  # => 6  # 按位异或 (xor)
2 >>> 1    # => 1  # 逻辑右移
2 >> 1     # => 1  # 算术右移
2 << 1     # => 4  # 逻辑/算术左移

# 可以用函数 bitstring 查看二进制数。
bitstring(12345)
# => "0000000000000000000000000000000000000000000000000011000000111001"
bitstring(12345.0)
# => "0100000011001000000111001000000000000000000000000000000000000000"

# 布尔值是原始类型
true
false

# 布尔操作符
!true   # => false
!false  # => true
1 == 1  # => true
2 == 1  # => false
1 != 1  # => false
2 != 1  # => true
1 < 10  # => true
1 > 10  # => false
2 <= 2  # => true
2 >= 2  # => true

# 链式比较
1 < 2 < 3 # => true
2 < 3 < 2 # => false

# 字符串可以由 " 创建
"This is a string."

# 字符字面量可用 ' 创建
'a'

# 可以像取数组取值一样用 index 取出对应字符
ascii("This is a string")[1]  # => 'T' 
# Julia 的 index 从 1 开始 :(
# 但是对 UTF-8 无效,
# 因此建议使用遍历器 (map, for loops, 等).

# $ 可用于字符插值:
"2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
# 可以将任何 Julia 表达式放入括号。

# 另一种输出格式化字符串的方法是使用标准库 Printf 中的 Printf 宏
using Printf
@printf "%d is less than %f\n" 4.5 5.3  # => 5 is less than 5.300000

# 打印字符串很容易
println("I'm Julia. Nice to meet you!")

# 字符串可以按字典序进行比较
"good" > "bye" # => true
"good" == "good" # => true
"1 + 2 = 3" == "1 + 2 = $(1 + 2)" # => true

####################################################
## 2. 变量与集合
####################################################

# 给变量赋值就是声明变量
some_var = 5 # => 5
some_var # => 5

# 访问未声明变量会抛出异常
try
    some_other_var # => ERROR: UndefVarError: some_other_var not defined
catch e
    println(e)
end

# 变量名必须以下划线或字母开头
# 之后任何字母,数字,下划线,叹号都是合法的。
SomeOtherVar123! = 6 # => 6

# 甚至可以用 unicode 字符
 = 8 # => 8
# 用数学符号非常方便
2 * π # => 6.283185307179586

# 注意 Julia 的命名规约:
#
# * 变量名为小写,单词之间以下划线连接 "_" 。
#
# * 类型名以大写字母开头,单词以 CamelCase 方式连接。
#
# * 函数与宏的名字小写,无下划线。
#
# * 会改变输入的函数名末位为 !。
#   这类函数有时被称为 mutating functions 或 in-place functions.

# 数组存储一列值index 从 1 开始
a = Int64[]  # => 0-element Array{Int64,1}

# 一维数组可以以逗号分隔值的方式声明
b = [4, 5, 6]  # => 3-element Array{Int64,1}: [4, 5, 6]
b = [4; 5; 6]  # => 3-element Array{Int64,1}: [4, 5, 6]
b[1]    # => 4
b[end]  # => 6

# 二维数组以分号分隔维度
matrix = [1 2; 3 4]  # => 2×2 Array{Int64,2}: [1 2; 3 4]

# 指定数组的类型
b = Int8[4, 5, 6]  # => 3-element Array{Int8,1}: [4, 5, 6]

# 使用 push! 和 append! 往数组末尾添加元素
push!(a, 1)    # => [1]
push!(a, 2)    # => [1,2]
push!(a, 4)    # => [1,2,4]
push!(a, 3)    # => [1,2,4,3]
append!(a, b)  # => [1,2,4,3,4,5,6]

# 用 pop 弹出尾部的元素
pop!(b)  # => 6
b # => [4,5]

# 再放回去
push!(b, 6)  # => [4,5,6]
b # => [4,5,6]

a[1] # => 1 #  永远记住 Julia 的引索从 1 开始!而不是 0

# 用 end 可以直接取到最后索引. 可用作任何索引表达式
a[end] # => 6

# 数组还支持 popfirst! 和 pushfirst!
popfirst!(a)  # => 1 
a # => [2,4,3,4,5,6]
pushfirst!(a, 7)  # => [7,2,4,3,4,5,6]
a # => [7,2,4,3,4,5,6]

# 以叹号结尾的函数名表示它会改变参数的值
arr = [5,4,6]  # => 3-element Array{Int64,1}: [5,4,6]
sort(arr)   # => [4,5,6]
arr         # => [5,4,6]
sort!(arr)  # => [4,5,6]
arr         # => [4,5,6]

# 数组越界会抛出 BoundsError
try
    a[0] 
    # => ERROR: BoundsError: attempt to access 7-element Array{Int64,1} at 
    # index [0]
    # => Stacktrace:
    # =>  [1] getindex(::Array{Int64,1}, ::Int64) at .\array.jl:731
    # =>  [2] top-level scope at none:0
    # =>  [3] ...
    # => in expression starting at ...\LearnJulia.jl:188
    a[end + 1] 
    # => ERROR: BoundsError: attempt to access 7-element Array{Int64,1} at 
    # index [8]
    # => Stacktrace:
    # =>  [1] getindex(::Array{Int64,1}, ::Int64) at .\array.jl:731
    # =>  [2] top-level scope at none:0
    # =>  [3] ...
    # => in expression starting at ...\LearnJulia.jl:196
catch e
    println(e)
end

# 报错时错误会指出出错的文件位置以及行号,标准库也一样
# 你可以在 Julia 安装目录下的 share/julia 文件夹里找到这些标准库

# 可以用 range 初始化数组
a = [1:5;]  # => 5-element Array{Int64,1}: [1,2,3,4,5]

# 可以切割数组
a[1:3] # => [1, 2, 3]
a[2:end] # => [2, 3, 4, 5]

# 用 splice! 切割原数组
arr = [3,4,5]
splice!(arr, 2) # => 4 
arr # => [3,5]

# 用 append! 连接数组
b = [1,2,3]
append!(a, b) # => [1, 2, 3, 4, 5, 1, 2, 3]
a # => [1, 2, 3, 4, 5, 1, 2, 3]

# 检查元素是否在数组中
in(1, a) # => true

# 用 length 获得数组长度
length(a) # => 8

# 元组(Tuples)是不可变的
tup = (1, 2, 3)  # => (1,2,3)
typeof(tup) # => Tuple{Int64,Int64,Int64}
tup[1] # => 1
try
    tup[1] = 3  
    # => ERROR: MethodError: no method matching 
    # setindex!(::Tuple{Int64,Int64,Int64}, ::Int64, ::Int64)
catch e
    println(e)
end

# 大多数组的函数同样支持元组
length(tup) # => 3
tup[1:2]    # => (1,2)
in(2, tup)  # => true

# 可以将元组的元素解包赋给变量
a, b, c = (1, 2, 3)  # => (1,2,3)  
a # => 1
b # => 2
c # => 3

# 不用括号也可以
d, e, f = 4, 5, 6  # => (4,5,6)
d # => 4
e # => 5
f # => 6

# 单元素 tuple 不等于其元素值
(1,) == 1 # => false
(1) == 1  # => true

# 交换值
e, d = d, e  # => (5,4) 
d # => 5
e # => 4


# 字典Dictionaries store mappings
empty_dict = Dict()  # => Dict{Any,Any} with 0 entries

# 也可以用字面量创建字典
filled_dict = Dict("one" => 1, "two" => 2, "three" => 3)
# => Dict{String,Int64} with 3 entries:
# =>  "two" => 2, "one" => 1, "three" => 3

# 用 [] 获得键值
filled_dict["one"] # => 1

# 获得所有键
keys(filled_dict)
# => Base.KeySet for a Dict{String,Int64} with 3 entries. Keys:
# =>  "two", "one", "three"
# 注意,键的顺序不是插入时的顺序

# 获得所有值
values(filled_dict)
# => Base.ValueIterator for a Dict{String,Int64} with 3 entries. Values: 
# =>  2, 1, 3
# 注意,值的顺序也一样

# 用 in 检查键值是否已存在,用 haskey 检查键是否存在
in(("one" => 1), filled_dict)  # => true
in(("two" => 3), filled_dict)  # => false
haskey(filled_dict, "one")     # => true
haskey(filled_dict, 1)         # => false

# 获取不存在的键的值会抛出异常
try
    filled_dict["four"]  # => ERROR: KeyError: key "four" not found
catch e
    println(e)
end

# 使用 get 可以提供默认值来避免异常
# get(dictionary,key,default_value)
get(filled_dict, "one", 4)   # => 1
get(filled_dict, "four", 4)  # => 4

# Sets 表示无序不可重复的值的集合
empty_set = Set()  # => Set(Any[])
# 初始化一个带初值的 Set
filled_set = Set([1, 2, 2, 3, 4])  # => Set([4, 2, 3, 1])

# 新增值
push!(filled_set, 5)  # => Set([4, 2, 3, 5, 1])

# 检查 Set 中是否存在某值
in(2, filled_set)   # => true
in(10, filled_set)  # => false

# 交集,并集,差集
other_set = Set([3, 4, 5, 6])         # => Set([4, 3, 5, 6])
intersect(filled_set, other_set)      # => Set([4, 3, 5])
union(filled_set, other_set)          # => Set([4, 2, 3, 5, 6, 1])
setdiff(Set([1,2,3,4]), Set([2,3,5])) # => Set([4, 1])

####################################################
## 3. 控制语句
####################################################

# 声明一个变量
some_var = 5

# 这是一个 if 语句块,其中的缩进不是必须的
if some_var > 10
    println("some_var is totally bigger than 10.")
elseif some_var < 10    # elseif 是可选的
    println("some_var is smaller than 10.")
else                    # else 也是可选的
    println("some_var is indeed 10.")
end
# => some_var is smaller than 10.


# For 循环遍历
# 可迭代的类型包括Range, Array, Set, Dict 和 AbstractString
for animal = ["dog", "cat", "mouse"]
    println("$animal is a mammal")
    # 你可以用 $ 将变量或表达式插入字符串中 
end
# => dog is a mammal
# => cat is a mammal
# => mouse is a mammal

# 你也可以不用 '=' 而使用 'in'
for animal in ["dog", "cat", "mouse"]
    println("$animal is a mammal")
end
# => dog is a mammal
# => cat is a mammal
# => mouse is a mammal

for pair in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
    from, to = pair
    println("$from is a $to")
end
# => mouse is a mammal
# => cat is a mammal
# => dog is a mammal
# 注意!这里的输出顺序和上面的不同

for (k, v) in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
    println("$k is a $v")
end
# => mouse is a mammal
# => cat is a mammal
# => dog is a mammal

# While 循环
let x = 0
    while x < 4
        println(x)
        x += 1  # x = x + 1 的缩写
    end
end
# => 0
# => 1
# => 2
# => 3

# 用 try/catch 处理异常
try
    error("help")
catch e
    println("caught it $e")
end
# => caught it ErrorException("help")

####################################################
## 4. 函数
####################################################

# 关键字 'function' 用于定义函数
# function name(arglist)
#   body...
# end
function add(x, y)
    println("x is $x and y is $y")

    # 函数会返回最后一行的值
    x + y
end

add(5, 6)
# => x is 5 and y is 6
# => 11

# 更紧凑的定义函数
f_add(x, y) = x + y  # => f_add (generic function with 1 method)
f_add(3, 4)  # => 7

# 函数可以将多个值作为元组返回
fn(x, y) = x + y, x - y # => fn (generic function with 1 method)
fn(3, 4)  # => (7, -1)

# 还可以定义接收可变长参数的函数
function varargs(args...)
    return args
    # 使用 return 可以在函数内的任何地方返回
end
# => varargs (generic function with 1 method)

varargs(1,2,3) # => (1,2,3)

# 省略号 ... 称为 splat
# 刚刚用在了函数定义中
# 在调用函数时也可以使用它,此时它会把数组或元组解包为参数列表
add([5,6]...)  # 等价于 add(5,6)

x = (5, 6)  # => (5,6)
add(x...)  # 等价于 add(5,6)

# 可定义带可选参数的函数
function defaults(a, b, x=5, y=6)
    return "$a $b and $x $y"
end
# => defaults (generic function with 3 methods)

defaults('h', 'g')  # => "h g and 5 6"
defaults('h', 'g', 'j')  # => "h g and j 6"
defaults('h', 'g', 'j', 'k')  # => "h g and j k"
try
    defaults('h')  # => ERROR: MethodError: no method matching defaults(::Char)
    defaults()  # => ERROR: MethodError: no method matching defaults()
catch e
    println(e)
end

# 还可以定义带关键字参数的函数
function keyword_args(;k1=4, name2="hello")  # 注意分号 ';'
    return Dict("k1" => k1, "name2" => name2)
end
# => keyword_args (generic function with 1 method)

keyword_args(name2="ness")  # => ["name2"=>"ness", "k1"=>4]
keyword_args(k1="mine")     # => ["name2"=>"hello", "k1"=>"mine"]
keyword_args()              # => ["name2"=>"hello", "k1"=>4]

# 可以在一个函数中组合各种类型的参数
function all_the_args(normal_arg, optional_positional_arg=2; keyword_arg="foo")
    println("normal arg: $normal_arg")
    println("optional arg: $optional_positional_arg")
    println("keyword arg: $keyword_arg")
end
# => all_the_args (generic function with 2 methods)

all_the_args(1, 3, keyword_arg=4)
# => normal arg: 1
# => optional arg: 3
# => keyword arg: 4

# Julia 有一等函数
function create_adder(x)
    adder = function (y)
        return x + y
    end
    return adder
end
# => create_adder (generic function with 1 method)

# 这是用 "stabby lambda syntax" 创建的匿名函数
(x -> x > 2)(3) # => true

# 这个函数和上面的 create_adder 是等价的
function create_adder(x)
    y -> x + y
end
# => create_adder (generic function with 1 method)

# 你也可以给内部函数起个名字
function create_adder(x)
    function adder(y)
        x + y
    end
    adder
end
# => create_adder (generic function with 1 method)

add_10 = create_adder(10) # => (::getfield(Main, Symbol("#adder#11")){Int64}) 
                          # (generic function with 1 method)
add_10(3)  # => 13

# 内置的高阶函数有
map(add_10, [1,2,3])  # => [11, 12, 13]
filter(x -> x > 5, [3, 4, 5, 6, 7])  # => [6, 7]

# 还可以使用 list comprehensions 让 map 更美观
[add_10(i) for i = [1, 2, 3]]   # => [11, 12, 13]
[add_10(i) for i in [1, 2, 3]]  # => [11, 12, 13]

####################################################
## 5.  类型
####################################################

# Julia 有类型系统
# 所有的值都有类型;但变量本身没有类型
# 你可以用 `typeof` 函数获得值的类型
typeof(5) # => Int64

# 类型是一等值
typeof(Int64)     # => DataType
typeof(DataType)  # => DataType
# DataType 是代表类型的类型,也代表他自己的类型

# 类型可用于文档化代码、执行优化以及多重派分(dispatch)
# Julia 并不只是静态的检查类型

# 用户还可以自定义类型
# 就跟其它语言的 records 或 structs 一样
# 用 `struct` 关键字定义新的类型

# struct Name
#   field::OptionalType
#   ...
# end
struct Tiger
    taillength::Float64
    coatcolor  # 不带类型标注相当于 `::Any`
end

# 默认构造函数的参数是类型的属性,按类型定义中的顺序排列
tigger = Tiger(3.5, "orange")  # => Tiger(3.5, "orange")

# 用新类型作为构造函数还会创建一个类型
sherekhan = typeof(tigger)(5.6, "fire")  # => Tiger(5.6, "fire")

# 类似 struct 的类型被称为具体类型
# 它们可被实例化,但不能有子类型
# 另一种类型是抽象类型

# 抽象类型名
abstract type Cat end  # 仅仅是指向类型结构层次的一个名称

# 抽象类型不能被实例化,但可以有子类型
# 例如Number 就是抽象类型
subtypes(Number)  # => 2-element Array{Any,1}:
                  # =>  Complex
                  # =>  Real
subtypes(Cat)  # => 0-element Array{Any,1}

# AbstractString类如其名也是一个抽象类型
subtypes(AbstractString)  # => 4-element Array{Any,1}:
                          # =>  String
                          # =>  SubString
                          # =>  SubstitutionString
                          # =>  Test.GenericString

# 所有的类型都有父类型。可以用函数 `supertype` 得到父类型
typeof(5) # => Int64
supertype(Int64)    # => Signed
supertype(Signed)   # => Integer
supertype(Integer)  # => Real
supertype(Real)     # => Number
supertype(Number)   # => Any
supertype(supertype(Signed))  # => Real
supertype(Any)      # => Any
# 除了 Int64 外,其余的类型都是抽象类型
typeof("fire")      # => String
supertype(String)   # => AbstractString
supertype(AbstractString) # => Any
supertype(SubString)  # => AbstractString

# <: 是子类型化操作符
struct Lion <: Cat  # Lion 是 Cat 的子类型
    mane_color
    roar::AbstractString
end

# 可以继续为你的类型定义构造函数
# 只需要定义一个与类型同名的函数,并调用已有的构造函数得到正确的类型
Lion(roar::AbstractString) = Lion("green", roar)  # => Lion
# 这是一个外部构造函数,因为它在类型定义之外

struct Panther <: Cat # Panther 也是 Cat 的子类型
    eye_color
    Panther() = new("green")
    # Panthers 只有这个构造函数,没有默认构造函数
end
# 像 Panther 一样使用内置构造函数,让你可以控制如何构建类型的值
# 应该尽量使用外部构造函数,而不是内部构造函数

####################################################
## 6. 多分派
####################################################

# Julia 中所有的函数都是通用函数,或者叫做泛型函数(generic functions)
# 也就是说这些函数都是由许多小方法组合而成的
# Lion 的每一种构造函数都是通用函数 Lion 的一个方法

# 我们来看一个非构造函数的例子
# 首先,让我们定义一个函数 meow

# Lion, Panther, Tiger 的 meow 定义分别为
function meow(animal::Lion)
    animal.roar # 使用点记号 '.' 访问属性
end

function meow(animal::Panther)
    "grrr"
end

function meow(animal::Tiger)
    "rawwwr"
end

# 试试 meow 函数
meow(tigger)  # => "rawwwr"
meow(Lion("brown", "ROAAR"))  # => "ROAAR"
meow(Panther()) # => "grrr"

# 回顾类型的层次结构
Tiger <: Cat    # => false
Lion <: Cat     # => true
Panther <: Cat  # => true

# 定义一个接收 Cat 类型的函数
function pet_cat(cat::Cat)
    println("The cat says $(meow(cat))")
end
# => pet_cat (generic function with 1 method)

pet_cat(Lion("42"))  # => The cat says 42
try
    pet_cat(tigger)  # => ERROR: MethodError: no method matching pet_cat(::Tiger)
catch e
    println(e)
end

# 在面向对象语言中,通常都是单分派
# 这意味着使用的方法取决于第一个参数的类型
# 而 Julia 中选择方法时会考虑到所有参数的类型

# 让我们定义一个有更多参数的函数,这样我们就能看出区别
function fight(t::Tiger, c::Cat)
    println("The $(t.coatcolor) tiger wins!")
end
# => fight (generic function with 1 method)

fight(tigger, Panther())  # => The orange tiger wins!
fight(tigger, Lion("ROAR")) # => fight(tigger, Lion("ROAR"))

# 让我们修改一下传入 Lion 类型时的行为
fight(t::Tiger, l::Lion) = println("The $(l.mane_color)-maned lion wins!")
# => fight (generic function with 2 methods)

fight(tigger, Panther())  # => The orange tiger wins!
fight(tigger, Lion("ROAR"))  # => The green-maned lion wins!

# 我们不需要一只老虎参与战斗
fight(l::Lion, c::Cat) = println("The victorious cat says $(meow(c))")
# => fight (generic function with 3 methods)

fight(Lion("balooga!"), Panther())  # => The victorious cat says grrr
try
    fight(Panther(), Lion("RAWR"))  
    # => ERROR: MethodError: no method matching fight(::Panther, ::Lion)
    # => Closest candidates are:
    # =>   fight(::Tiger, ::Lion) at ...
    # =>   fight(::Tiger, ::Cat) at ...
    # =>   fight(::Lion, ::Cat) at ...
    # => ...
catch e
    println(e)
end

# 试试把 Cat 放在前面
fight(c::Cat, l::Lion) = println("The cat beats the Lion")
# => fight (generic function with 4 methods)

# 由于无法判断该使用哪个 fight 方法,而产生了错误
try
    fight(Lion("RAR"), Lion("brown", "rarrr"))
    # => ERROR: MethodError: fight(::Lion, ::Lion) is ambiguous. Candidates:
    # =>   fight(c::Cat, l::Lion) in Main at ...
    # =>   fight(l::Lion, c::Cat) in Main at ...
    # => Possible fix, define
    # =>   fight(::Lion, ::Lion)
    # => ...
catch e
    println(e)
end
# 在不同版本的 Julia 中错误信息可能有所不同

fight(l::Lion, l2::Lion) = println("The lions come to a tie") 
# => fight (generic function with 5 methods)
fight(Lion("RAR"), Lion("brown", "rarrr"))  # => The lions come to a tie


# Under the hood
# 你还可以看看 llvm 以及它生成的汇编代码

square_area(l) = l * l  # => square_area (generic function with 1 method)
square_area(5)  # => 25

# 当我们喂给 square_area 一个整数时会发生什么?
code_native(square_area, (Int32,))
    #         .text
    # ; Function square_area {
    # ; Location: REPL[49]:1
    #         pushq   %rbp
    #         movq    %rsp, %rbp
    # ; Function *; {
    # ; Location: int.jl:54
    #         imull   %ecx, %ecx
    # ;}
    #         movl    %ecx, %eax
    #         popq    %rbp
    #         retq
    #         nopl    (%rax,%rax)
    # ;}

code_native(square_area, (Float32,))
    #         .text
    # ; Function square_area {
    # ; Location: REPL[49]:1
    #         pushq   %rbp
    #         movq    %rsp, %rbp
    # ; Function *; {
    # ; Location: float.jl:398
    #         vmulss  %xmm0, %xmm0, %xmm0
    # ;}
    #         popq    %rbp
    #         retq
    #         nopw    (%rax,%rax)
    # ;}

code_native(square_area, (Float64,))
    #         .text
    # ; Function square_area {
    # ; Location: REPL[49]:1
    #         pushq   %rbp
    #         movq    %rsp, %rbp
    # ; Function *; {
    # ; Location: float.jl:399
    #         vmulsd  %xmm0, %xmm0, %xmm0
    # ;}
    #         popq    %rbp
    #         retq
    #         nopw    (%rax,%rax)
    # ;}

# 注意只要参数中有浮点数Julia 就会使用浮点指令
# 让我们计算一下圆的面积
circle_area(r) = pi * r * r # => circle_area (generic function with 1 method)
circle_area(5)  # => 78.53981633974483

code_native(circle_area, (Int32,))
    #         .text
    # ; Function circle_area {
    # ; Location: REPL[53]:1
    #         pushq   %rbp
    #         movq    %rsp, %rbp
    # ; Function *; {
    # ; Location: operators.jl:502
    # ; Function *; {
    # ; Location: promotion.jl:314
    # ; Function promote; {
    # ; Location: promotion.jl:284
    # ; Function _promote; {
    # ; Location: promotion.jl:261
    # ; Function convert; {
    # ; Location: number.jl:7
    # ; Function Type; {
    # ; Location: float.jl:60
    #         vcvtsi2sdl      %ecx, %xmm0, %xmm0
    #         movabsq $532051920, %rax        # imm = 0x1FB677D0
    # ;}}}}}
    # ; Function *; {
    # ; Location: float.jl:399
    #         vmulsd  (%rax), %xmm0, %xmm1
    #         vmulsd  %xmm0, %xmm1, %xmm0
    # ;}}
    #         popq    %rbp
    #         retq
    #         nopl    (%rax)
    # ;}

code_native(circle_area, (Float64,))
    #         .text
    # ; Function circle_area {
    # ; Location: REPL[53]:1
    #         pushq   %rbp
    #         movq    %rsp, %rbp
    #         movabsq $532052040, %rax        # imm = 0x1FB67848
    # ; Function *; {
    # ; Location: operators.jl:502
    # ; Function *; {
    # ; Location: promotion.jl:314
    # ; Function *; {
    # ; Location: float.jl:399
    #         vmulsd  (%rax), %xmm0, %xmm1
    # ;}}}
    # ; Function *; {
    # ; Location: float.jl:399
    #         vmulsd  %xmm0, %xmm1, %xmm0
    # ;}
    #         popq    %rbp
    #         retq
    #         nopl    (%rax,%rax)
    # ;}