# Single line comments start with a hash (pound) symbol.
#= Multiline comments can be written
   by putting '#=' before the text  and '=#'
   after the text. They can also be nested.
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# There are several basic types of numbers.
3 # => 3 (Int64)
3.2 # => 3.2 (Float64)
2 + 1im # => 2 + 1im (Complex{Int64})
2//3 # => 2//3 (Rational{Int64})

# All of the normal infix operators are available.
1 + 1 # => 2
8 - 1 # => 7
10 * 2 # => 20
35 / 5 # => 7.0
5 / 2 # => 2.5 # dividing an Int by an Int always results in a Float
div(5, 2) # => 2 # for a truncated result, use div
5 \ 35 # => 7.0
2 ^ 2 # => 4 # power, not bitwise xor
12 % 10 # => 2

# Enforce precedence with parentheses
(1 + 3) * 2 # => 8

# Bitwise Operators
~2 # => -3   # bitwise not
3 & 5 # => 1 # bitwise and
2 | 4 # => 6 # bitwise or
2 $ 4 # => 6 # bitwise xor
2 >>> 1 # => 1 # logical shift right
2 >> 1  # => 1 # arithmetic shift right
2 << 1  # => 4 # logical/arithmetic shift left

# You can use the bits function to see the binary representation of a number.
bits(12345)
bits(12345.0)

# Boolean values are primitives
true
false

# Boolean operators
!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
1 < 2 < 3 # => true
2 < 3 < 2 # => false

# Strings are created with "
"This is a string."

# Character literals are written with '
'a'

# Some strings can be indexed like an array of characters
"This is a string"[1] # => 'T' # Julia indexes from 1

# $ can be used for string interpolation:
"2 + 2 = $(2 + 2)" # => "2 + 2 = 4"

# Another way to format strings is the printf macro.
@printf "%d is less than %f" 4.5 5.3 # 5 is less than 5.300000

# Printing is easy
println("I'm Julia. Nice to meet you!")

# You don't declare variables before assigning to them.
some_var = 5 # => 5
some_var # => 5

# Accessing a previously unassigned variable is an error
try
    some_other_var # => ERROR: some_other_var not defined
catch e
    println(e)
end

# Variable names start with a letter or underscore.
# After that, you can use letters, digits, underscores, and exclamation points.
SomeOtherVar123! = 6 # => 6

# You can also use certain unicode characters
☃ = 8 # => 8
2 * π # => 6.283185307179586

# Arrays store a sequence of values indexed by integers 1 through n:
a = Int64[] # => 0-element Int64 Array

# 1-dimensional array literals can be written with comma-separated values.
b = [4, 5, 6] # => 3-element Int64 Array: [4, 5, 6]
b[1] # => 4
b[end] # => 6

# 2-dimentional arrays use space-separated values and semicolon-separated rows.
matrix = [1 2; 3 4] # => 2x2 Int64 Array: [1 2; 3 4]

# Add stuff to the end of a list with push! and append!
push!(a,1)     # => [1]
append!(a,b) # => [1,2,4,3,4,5,6]

# Function names that end in exclamations points indicate that they modify
# their argument.
sort(arr) # => [4,5,6]; arr is still [5,4,6]
sort!(arr) # => [4,5,6]; arr is now [4,5,6]

# You can initialize arrays from ranges
a = [1:5;] # => 5-element Int64 Array: [1,2,3,4,5]

# You can look at ranges with slice syntax.
a[1:3] # => [1, 2, 3]
a[2:end] # => [2, 3, 4, 5]

# Tuples are immutable.
tup = (1, 2, 3) # => (1,2,3) # an (Int64,Int64,Int64) tuple.

# You can unpack tuples into variables
a, b, c = (1, 2, 3) # => (1,2,3)  # a is now 1, b is now 2 and c is now 3

# Tuples are created even if you leave out the parentheses
d, e, f = 4, 5, 6 # => (4,5,6)

# A 1-element tuple is distinct from the value it contains
(1,) == 1 # => false
(1) == 1 # => true

# Dictionaries store mappings
empty_dict = Dict() # => Dict{Any,Any}()

# You can create a dictionary using a literal
filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3]

# Look up values with []
filled_dict["one"] # => 1

# Check for existence of keys in a dictionary with in, haskey
in(("one", 1), filled_dict) # => true

# Initialize a set with values
filled_set = Set(1,2,2,3,4) # => Set{Int64}(1,2,3,4)
setdiff(Set(1,2,3,4),Set(2,3,5)) # => Set{Int64}(1,4)

# Here is an if statement. Indentation is not meaningful in Julia.
if some_var > 10
    println("some_var is totally bigger than 10.")
elseif some_var < 10    # This elseif clause is optional.
    println("some_var is smaller than 10.")
else                    # The else clause is optional too.
    println("some_var is indeed 10.")
end

# For loops iterate over iterables.
for animal=["dog", "cat", "mouse"]
    println("$animal is a mammal")
end

for animal in ["dog", "cat", "mouse"]
    println("$animal is a mammal")
end

for a in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"]
    println("$(a[1]) is a $(a[2])")
end

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

# While loops loop while a condition is true
while x < 4
    x += 1  # Shorthand for x = x + 1
end

# The keyword 'function' creates new functions
function add(x, y)
    x + y
end

# You can define functions that take a variable number of
# positional arguments
function varargs(args...)
    return args
end

# The ... is called a splat.
Set([1,2,3]...) # => Set{Int64}(1,2,3) # this is equivalent to Set(1,2,3)

# You can define functions with optional positional arguments
function defaults(a,b,x=5,y=6)
    return "$a $b and $x $y"
end

# You can define functions that take keyword arguments
function keyword_args(;k1=4,name2="hello") # note the ;
    return ["k1"=>k1,"name2"=>name2]
end

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

# You can combine all kinds of arguments in the same function
function all_the_args(normal_arg, optional_positional_arg=2; keyword_arg="foo")
    println("normal arg: $normal_arg")
end

all_the_args(1, 3, keyword_arg=4)

# Julia has first class functions
function create_adder(x)
    adder = function (y)
        return x + y
    end
end

# This is "stabby lambda syntax" for creating anonymous functions
(x -> x > 2)(3) # => true

# This function is identical to create_adder implementation above.
function create_adder(x)
    y -> x + y
end

# You can also name the internal function, if you want
function create_adder(x)
    function adder(y)
        x + y
    end
end

# There are built-in higher order functions
map(add_10, [1,2,3]) # => [11, 12, 13]
filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]

# We can use list comprehensions for nicer maps
[add_10(i) for i=[1, 2, 3]] # => [11, 12, 13]
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]

# Julia has a type system.
typeof(5) # => Int64

# Types are first-class values
typeof(Int64) # => DataType
typeof(DataType) # => DataType

# Types are used for documentation, optimizations, and dispatch.
type Tiger
  taillength::Float64
  coatcolor # not including a type annotation is the same as `::Any`
end

# abstract Name
abstract Cat # just a name and point in the type hierarchy

super(Int64) # => Signed
super(super(Signed)) # => Number

# <: is the subtyping operator
type Lion <: Cat # Lion is a subtype of Cat
  mane_color
  roar::AbstractString
end

# You can define more constructors for your type
Lion(roar::AbstractString) = Lion("green",roar)

type Panther <: Cat # Panther is also a subtype of Cat
  eye_color
  Panther() = new("green")
end

# Definitions for Lion, Panther, Tiger
function meow(animal::Lion)
  animal.roar # access type properties using dot notation
end

mutable struct Foo
end

# Code samples adapted from "Learn Julia in Y Minutes".  "Learn Julia in Y
# Minutes" is copyright Leah Hanson, and the original can be found at
# http://learnxinyminutes.com/docs/files/learnjulia.jl or
# https://github.com/adambard/learnxinyminutes-docs/blob/master/julia.html.markdown
#
# The use of "Learn Julia in Y Minutes" here in no way denotes endorsement by
# the author.
#
# "Learn Julia in Y Minutes" is licensed under http://creativecommons.org/licenses/by-sa/3.0/legalcode

# Unicode example
mutable struct Œuvre end
⇵ = uppercase

function résumer_œuvre(书名::Œuvre="Les Misérables")
    语言 = "français"
    for ϕ ∈ 1:1
        ⇵(语言) # "FRANÇAIS"
    end
end