Merge pull request #3189 from visr/julia1

[julia/en] update to run on julia 1.0

julia.html.markdown

@@ -2,17 +2,17 @@
 language: Julia
 contributors:
     - ["Leah Hanson", "http://leahhanson.us"]
-    - ["Pranit Bauva", "http://github.com/pranitbauva1997"]
+    - ["Pranit Bauva", "https://github.com/pranitbauva1997"]
-    - ["Daniel YC Lin", "http://github.com/dlintw"]
+    - ["Daniel YC Lin", "https://github.com/dlintw"]
 filename: learnjulia.jl
 ---
 
 Julia is a new homoiconic functional language focused on technical computing.
 While having the full power of homoiconic macros, first-class functions, and low-level control, Julia is as easy to learn and use as Python.
 
-This is based on Julia 0.6.4
+This is based on Julia 1.0.0
 
-```ruby
+```julia
 
 # Single line comments start with a hash (pound) symbol.
 #= Multiline comments can be written
@@ -27,38 +27,38 @@ This is based on Julia 0.6.4
 # Everything in Julia is an expression.
 
 # There are several basic types of numbers.
-3 # => 3 (Int64)
+3  # => 3 (Int64)
-3.2 # => 3.2 (Float64)
+3.2  # => 3.2 (Float64)
-2 + 1im # => 2 + 1im (Complex{Int64})
+2 + 1im  # => 2 + 1im (Complex{Int64})
-2//3 # => 2//3 (Rational{Int64})
+2 // 3  # => 2 // 3 (Rational{Int64})
 
 # All of the normal infix operators are available.
-1 + 1 # => 2
+1 + 1      # => 2
-8 - 1 # => 7
+8 - 1      # => 7
-10 * 2 # => 20
+10 * 2     # => 20
-35 / 5 # => 7.0
+35 / 5     # => 7.0
-5 / 2 # => 2.5 # dividing an Int by an Int always results in a Float
+5 / 2      # => 2.5  # dividing integers always results in a Float64
-div(5, 2) # => 2 # for a truncated result, use div
+div(5, 2)  # => 2    # for a truncated result, use div
-5 \ 35 # => 7.0
+5 \ 35     # => 7.0
-2 ^ 2 # => 4 # power, not bitwise xor
+2^2        # => 4    # power, not bitwise xor
-12 % 10 # => 2
+12 % 10    # => 2
 
 # Enforce precedence with parentheses
-(1 + 3) * 2 # => 8
+(1 + 3) * 2  # => 8
 
 # Bitwise Operators
-~2 # => -3   # bitwise not
+~2         # => -3 # bitwise not
-3 & 5 # => 1 # bitwise and
+3 & 5      # => 1  # bitwise and
-2 | 4 # => 6 # bitwise or
+2 | 4      # => 6  # bitwise or
-xor(2, 4) # => 6 # bitwise xor
+xor(2, 4)  # => 6  # bitwise xor
-2 >>> 1 # => 1 # logical shift right
+2 >>> 1    # => 1  # logical shift right
-2 >> 1  # => 1 # arithmetic shift right
+2 >> 1     # => 1  # arithmetic shift right
-2 << 1  # => 4 # logical/arithmetic shift left
+2 << 1     # => 4  # logical/arithmetic shift left
 
-# You can use the bits function to see the binary representation of a number.
+# Use the bitstring function to see the binary representation of a number.
-bits(12345)
+bitstring(12345)
 # => "0000000000000000000000000000000000000000000000000011000000111001"
-bits(12345.0)
+bitstring(12345.0)
 # => "0100000011001000000111001000000000000000000000000000000000000000"
 
 # Boolean values are primitives
@@ -66,48 +66,38 @@ true
 false
 
 # Boolean operators
-!true # => false
+!true   # => false
-!false # => true
+!false  # => true
-1 == 1 # => true
+1 == 1  # => true
-2 == 1 # => false
+2 == 1  # => false
-1 != 1 # => false
+1 != 1  # => false
-2 != 1 # => true
+2 != 1  # => true
-1 < 10 # => true
+1 < 10  # => true
-1 > 10 # => false
+1 > 10  # => false
-2 <= 2 # => true
+2 <= 2  # => true
-2 >= 2 # => true
+2 >= 2  # => true
 # Comparisons can be chained
-1 < 2 < 3 # => true
+1 < 2 < 3  # => true
-2 < 3 < 2 # => false
+2 < 3 < 2  # => false
 
 # Strings are created with "
-try
 "This is a string."
-catch ; end
-
-# Julia has several types of strings, including ASCIIString and UTF8String.
-# More on this in the Types section.
 
 # Character literals are written with '
-try
 'a'
-catch ; end
 
-# Some strings can be indexed like an array of characters
+# Strings are UTF8 encoded. Only if they contain only ASCII characters can
-try
+# they be safely indexed.
-"This is a string"[1] # => 'T' # Julia indexes from 1
+ascii("This is a string")[1]  # => 'T' # Julia indexes from 1
-catch ; end
+# Otherwise, iterating over strings is recommended (map, for loops, etc).
-# However, this is will not work well for UTF8 strings,
-# so iterating over strings is recommended (map, for loops, etc).
 
 # $ can be used for string interpolation:
-try
 "2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
-catch ; end
 # You can put any Julia expression inside the parentheses.
 
-# Another way to format strings is the printf macro.
+# Another way to format strings is the printf macro from the stdlib Printf.
-@printf "%d is less than %f" 4.5 5.3 # 4 is less than 5.300000
+using Printf
+@printf "%d is less than %f\n" 4.5 5.3  # => 5 is less than 5.300000
 
 # Printing is easy
 println("I'm Julia. Nice to meet you!")
@@ -115,29 +105,29 @@ println("I'm Julia. Nice to meet you!")
 # String can be compared lexicographically
 "good" > "bye" # => true
 "good" == "good" # => true
-"1 + 2 = 3" == "1 + 2 = $(1+2)" # => true
+"1 + 2 = 3" == "1 + 2 = $(1 + 2)" # => true
 
 ####################################################
 ## 2. Variables and Collections
 ####################################################
 
 # You don't declare variables before assigning to them.
-some_var = 5 # => 5
+some_var = 5  # => 5
-some_var # => 5
+some_var  # => 5
 
 # Accessing a previously unassigned variable is an error
 try
-    some_other_var # => ERROR: some_other_var not defined
+    some_other_var  # => ERROR: UndefVarError: 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
+SomeOtherVar123! = 6  # => 6
 
 # You can also use certain unicode characters
-☃ = 8 # => 8
+☃ = 8  # => 8
 # These are especially handy for mathematical notation
 2 * π # => 6.283185307179586
 
@@ -156,165 +146,168 @@ SomeOtherVar123! = 6 # => 6
 #   functions are sometimes called mutating functions or in-place functions.
 
 # Arrays store a sequence of values indexed by integers 1 through n:
-a = Int64[] # => 0-element Int64 Array
+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 = [4, 5, 6]  # => 3-element Int64 Array: [4, 5, 6]
-b = [4; 5; 6] # => 3-element Int64 Array: [4, 5, 6]
+b = [4; 5; 6]  # => 3-element Int64 Array: [4, 5, 6]
-b[1] # => 4
+b[1]  # => 4
-b[end] # => 6
+b[end]  # => 6
 
 # 2-dimensional arrays use space-separated values and semicolon-separated rows.
-matrix = [1 2; 3 4] # => 2x2 Int64 Array: [1 2; 3 4]
+matrix = [1 2; 3 4]  # => 2x2 Int64 Array: [1 2; 3 4]
 
-# Arrays of a particular Type
+# Arrays of a particular type
-b = Int8[4, 5, 6] # => 3-element Int8 Array: [4, 5, 6]
+b = Int8[4, 5, 6]  # => 3-element Int8 Array: [4, 5, 6]
 
 # Add stuff to the end of a list with push! and append!
-push!(a,1)     # => [1]
+push!(a, 1)    # => [1]
-push!(a,2)     # => [1,2]
+push!(a, 2)    # => [1,2]
-push!(a,4)     # => [1,2,4]
+push!(a, 4)    # => [1,2,4]
-push!(a,3)     # => [1,2,4,3]
+push!(a, 3)    # => [1,2,4,3]
-append!(a,b) # => [1,2,4,3,4,5,6]
+append!(a, b)  # => [1,2,4,3,4,5,6]
 
 # Remove from the end with pop
-pop!(b)        # => 6 and b is now [4,5]
+pop!(b)  # => 6 and b is now [4,5]
 
 # Let's put it back
-push!(b,6)   # b is now [4,5,6] again.
+push!(b, 6)  # b is now [4,5,6] again.
 
-a[1] # => 1 # remember that Julia indexes from 1, not 0!
+a[1]  # => 1  # remember that Julia indexes from 1, not 0!
 
 # end is a shorthand for the last index. It can be used in any
 # indexing expression
-a[end] # => 6
+a[end]  # => 6
 
-# we also have shift and unshift
+# we also have popfirst! and pushfirst!
-shift!(a) # => 1 and a is now [2,4,3,4,5,6]
+popfirst!(a)  # => 1 and a is now [2,4,3,4,5,6]
-unshift!(a,7) # => [7,2,4,3,4,5,6]
+pushfirst!(a, 7)  # => [7,2,4,3,4,5,6]
 
 # Function names that end in exclamations points indicate that they modify
 # their argument.
-arr = [5,4,6] # => 3-element Int64 Array: [5,4,6]
+arr = [5,4,6]  # => 3-element Int64 Array: [5,4,6]
-sort(arr) # => [4,5,6]; arr is still [5,4,6]
+sort(arr)  # => [4,5,6]; arr is still [5,4,6]
-sort!(arr) # => [4,5,6]; arr is now [4,5,6]
+sort!(arr)  # => [4,5,6]; arr is now [4,5,6]
 
 # Looking out of bounds is a BoundsError
 try
-    a[0] # => ERROR: BoundsError() in getindex at array.jl:270
+    a[0]
-    a[end+1] # => ERROR: BoundsError() in getindex at array.jl:270
+    # => BoundsError: attempt to access 7-element Array{Int64,1} at index [0]
+    a[end + 1]
+    # => BoundsError: attempt to access 7-element Array{Int64,1} at index [8]
 catch e
     println(e)
 end
 
 # Errors list the line and file they came from, even if it's in the standard
-# library. If you built Julia from source, you can look in the folder base
+# library. You can look in the folder share/julia inside the julia folder to
-# inside the julia folder to find these files.
+# find these files.
 
 # You can initialize arrays from ranges
-a = [1:5;] # => 5-element Int64 Array: [1,2,3,4,5]
+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[1:3]  # => [1, 2, 3]
-a[2:end] # => [2, 3, 4, 5]
+a[2:end]  # => [2, 3, 4, 5]
 
 # Remove elements from an array by index with splice!
 arr = [3,4,5]
-splice!(arr,2) # => 4 ; arr is now [3,5]
+splice!(arr, 2)  # => 4 ; arr is now [3,5]
 
 # Concatenate lists with append!
 b = [1,2,3]
-append!(a,b) # Now a is [1, 2, 3, 4, 5, 1, 2, 3]
+append!(a, b)  # Now a is [1, 2, 3, 4, 5, 1, 2, 3]
 
 # Check for existence in a list with in
-in(1, a) # => true
+in(1, a)  # => true
 
 # Examine the length with length
-length(a) # => 8
+length(a)  # => 8
 
 # Tuples are immutable.
-tup = (1, 2, 3) # => (1,2,3) # an (Int64,Int64,Int64) tuple.
+tup = (1, 2, 3)  # => (1,2,3)  # an (Int64,Int64,Int64) tuple.
-tup[1] # => 1
+tup[1]  # => 1
-try:
+try
-    tup[1] = 3 # => ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
+    tup[1] = 3  # => ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
 catch e
     println(e)
 end
 
-# Many list functions also work on tuples
+# Many array functions also work on tuples
-length(tup) # => 3
+length(tup)  # => 3
-tup[1:2] # => (1,2)
+tup[1:2]  # => (1,2)
-in(2, tup) # => true
+in(2, tup)  # => true
 
 # 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
+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)
+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  # => false
-(1) == 1 # => true
+(1) == 1  # => true
 
 # Look how easy it is to swap two values
-e, d = d, e  # => (5,4) # d is now 5 and e is now 4
+e, d = d, e  # => (5,4)  # d is now 5 and e is now 4
 
 
 # Dictionaries store mappings
-empty_dict = Dict() # => Dict{Any,Any}()
+empty_dict = Dict()  # => Dict{Any,Any}()
 
 # You can create a dictionary using a literal
-filled_dict = Dict("one"=> 1, "two"=> 2, "three"=> 3)
+filled_dict = Dict("one" => 1, "two" => 2, "three" => 3)
-# => Dict{ASCIIString,Int64}
+# => Dict{String,Int64}
 
 # Look up values with []
-filled_dict["one"] # => 1
+filled_dict["one"]  # => 1
 
 # Get all keys
 keys(filled_dict)
-# => KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
+# => Base.KeySet for a Dict{String,Int64} with 3 entries. Keys:
+# "two", "one", "three"
 # Note - dictionary keys are not sorted or in the order you inserted them.
 
 # Get all values
 values(filled_dict)
-# => ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
+# => Base.ValueIterator{Dict{String,Int64}} with 3 entries. Values: 2, 1, 3
 # Note - Same as above regarding key ordering.
 
 # Check for existence of keys in a dictionary with in, haskey
-in(("one" => 1), filled_dict) # => true
+in(("one" => 1), filled_dict)  # => true
-in(("two" => 3), filled_dict) # => false
+in(("two" => 3), filled_dict)  # => false
-haskey(filled_dict, "one") # => true
+haskey(filled_dict, "one")     # => true
-haskey(filled_dict, 1) # => false
+haskey(filled_dict, 1)         # => false
 
 # Trying to look up a non-existent key will raise an error
 try
-    filled_dict["four"] # => ERROR: key not found: four in getindex at dict.jl:489
+    filled_dict["four"]  # => KeyError: key "four" not found
 catch e
     println(e)
 end
 
 # Use the get method to avoid that error by providing a default value
-# get(dictionary,key,default_value)
+# get(dictionary, key, default_value)
-get(filled_dict,"one",4) # => 1
+get(filled_dict, "one", 4)   # => 1
-get(filled_dict,"four",4) # => 4
+get(filled_dict, "four", 4)  # => 4
 
 # Use Sets to represent collections of unordered, unique values
-empty_set = Set() # => Set{Any}()
+empty_set = Set()  # => Set{Any}()
 # Initialize a set with values
-filled_set = Set([1,2,2,3,4]) # => Set{Int64}(1,2,3,4)
+filled_set = Set([1, 2, 2, 3, 4])  # => Set([4, 2, 3, 1])
 
 # Add more values to a set
-push!(filled_set,5) # => Set{Int64}(5,4,2,3,1)
+push!(filled_set, 5)  # => Set([4, 2, 3, 5, 1])
 
 # Check if the values are in the set
-in(2, filled_set) # => true
+in(2, filled_set)  # => true
-in(10, filled_set) # => false
+in(10, filled_set)  # => false
 
 # There are functions for set intersection, union, and difference.
-other_set = Set([3, 4, 5, 6]) # => Set{Int64}(6,4,5,3)
+other_set = Set([3, 4, 5, 6])          # => Set([4, 3, 5, 6])
-intersect(filled_set, other_set) # => Set{Int64}(3,4,5)
+intersect(filled_set, other_set)       # => Set([4, 3, 5])
-union(filled_set, other_set) # => Set{Int64}(1,2,3,4,5,6)
+union(filled_set, other_set)           # => Set([4, 2, 3, 5, 6, 1])
-setdiff(Set([1,2,3,4]),Set([2,3,5])) # => Set{Int64}(1,4)
+setdiff(Set([1,2,3,4]), Set([2,3,5]))  # => Set([4, 1])
 
 
 ####################################################
@@ -337,7 +330,7 @@ end
 
 # For loops iterate over iterables.
 # Iterable types include Range, Array, Set, Dict, and AbstractString.
-for animal=["dog", "cat", "mouse"]
+for animal = ["dog", "cat", "mouse"]
     println("$animal is a mammal")
     # You can use $ to interpolate variables or expression into strings
 end
@@ -355,15 +348,16 @@ end
 #    cat is a mammal
 #    mouse is a mammal
 
-for a in Dict("dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal")
+for pair in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
-    println("$(a[1]) is a $(a[2])")
+    from, to = pair
+    println("$from is a $to")
 end
 # prints:
 #    dog is a mammal
 #    cat is a mammal
 #    mouse is a mammal
 
-for (k,v) in Dict("dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal")
+for (k, v) in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
     println("$k is a $v")
 end
 # prints:
@@ -372,10 +366,11 @@ end
 #    mouse is a mammal
 
 # While loops loop while a condition is true
-x = 0
+let x = 0
-while x < 4
+    while x < 4
-    println(x)
+        println(x)
-    x += 1  # Shorthand for x = x + 1
+        x += 1  # Shorthand for x = x + 1
+    end
 end
 # prints:
 #   0
@@ -385,9 +380,9 @@ end
 
 # Handle exceptions with a try/catch block
 try
-   error("help")
+    error("help")
 catch e
-   println("caught it $e")
+    println("caught it $e")
 end
 # => caught it ErrorException("help")
 
@@ -407,15 +402,15 @@ function add(x, y)
     x + y
 end
 
-add(5, 6) # => 11 after printing out "x is 5 and y is 6"
+add(5, 6)  # => 11 after printing out "x is 5 and y is 6"
 
 # Compact assignment of functions
-f_add(x, y) = x + y # => "f (generic function with 1 method)"
+f_add(x, y) = x + y  # => "f (generic function with 1 method)"
-f_add(3, 4) # => 7
+f_add(3, 4)  # => 7
 
 # Function can also return multiple values as tuple
 fn(x, y) = x + y, x - y
-fn(3, 4) # => (7, -1)
+fn(3, 4)  # => (7, -1)
 
 # You can define functions that take a variable number of
 # positional arguments
@@ -425,41 +420,41 @@ function varargs(args...)
 end
 # => varargs (generic function with 1 method)
 
-varargs(1,2,3) # => (1,2,3)
+varargs(1, 2, 3)  # => (1,2,3)
 
 # The ... is called a splat.
 # We just used it in a function definition.
 # It can also be used in a function call,
 # where it will splat an Array or Tuple's contents into the argument list.
-add([5,6]...) # this is equivalent to add(5,6)
+add([5,6]...)  # this is equivalent to add(5,6)
 
-x = (5,6)     # => (5,6)
+x = (5, 6)  # => (5,6)
-add(x...)     # this is equivalent to add(5,6)
+add(x...)  # this is equivalent to add(5,6)
 
 
 # You can define functions with optional positional arguments
-function defaults(a,b,x=5,y=6)
+function defaults(a, b, x=5, y=6)
     return "$a $b and $x $y"
 end
 
-defaults('h','g') # => "h g and 5 6"
+defaults('h', 'g')  # => "h g and 5 6"
-defaults('h','g','j') # => "h g and j 6"
+defaults('h', 'g', 'j')  # => "h g and j 6"
-defaults('h','g','j','k') # => "h g and j k"
+defaults('h', 'g', 'j', 'k')  # => "h g and j k"
 try
-    defaults('h') # => ERROR: no method defaults(Char,)
+    defaults('h')  # => ERROR: no method defaults(Char,)
-    defaults() # => ERROR: no methods defaults()
+    defaults()  # => ERROR: no methods defaults()
 catch e
     println(e)
 end
 
 # You can define functions that take keyword arguments
-function keyword_args(;k1=4,name2="hello") # note the ;
+function keyword_args(;k1=4, name2="hello")  # note the ;
-    return Dict("k1"=>k1,"name2"=>name2)
+    return Dict("k1" => k1, "name2" => name2)
 end
 
-keyword_args(name2="ness") # => ["name2"=>"ness","k1"=>4]
+keyword_args(name2="ness")  # => ["name2"=>"ness","k1"=>4]
-keyword_args(k1="mine") # => ["k1"=>"mine","name2"=>"hello"]
+keyword_args(k1="mine")  # => ["k1"=>"mine","name2"=>"hello"]
-keyword_args() # => ["name2"=>"hello","k1"=>4]
+keyword_args()  # => ["name2"=>"hello","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")
@@ -483,7 +478,7 @@ function create_adder(x)
 end
 
 # This is "stabby lambda syntax" for creating anonymous functions
-(x -> x > 2)(3) # => true
+(x -> x > 2)(3)  # => true
 
 # This function is identical to create_adder implementation above.
 function create_adder(x)
@@ -499,15 +494,15 @@ function create_adder(x)
 end
 
 add_10 = create_adder(10)
-add_10(3) # => 13
+add_10(3)  # => 13
 
 
 # There are built-in higher order functions
-map(add_10, [1,2,3]) # => [11, 12, 13]
+map(add_10, [1,2,3])  # => [11, 12, 13]
-filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
+filter(x -> x > 5, [3, 4, 5, 6, 7])  # => [6, 7]
 
 # We can use list comprehensions
-[add_10(i) for i=[1, 2, 3]] # => [11, 12, 13]
+[add_10(i) for i = [1, 2, 3]] # => [11, 12, 13]
 [add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
 [x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
 
@@ -518,11 +513,11 @@ filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
 # Julia has a type system.
 # Every value has a type; variables do not have types themselves.
 # You can use the `typeof` function to get the type of a value.
-typeof(5) # => Int64
+typeof(5)  # => Int64
 
 # Types are first-class values
-typeof(Int64) # => DataType
+typeof(Int64)  # => DataType
-typeof(DataType) # => DataType
+typeof(DataType)  # => DataType
 # DataType is the type that represents types, including itself.
 
 # Types are used for documentation, optimizations, and dispatch.
@@ -530,78 +525,77 @@ typeof(DataType) # => DataType
 
 # Users can define types
 # They are like records or structs in other languages.
-# New types are defined using the `type` keyword.
+# New types are defined using the `struct` keyword.
 
-# type Name
+# struct Name
 #   field::OptionalType
 #   ...
 # end
-type Tiger
+struct Tiger
-  taillength::Float64
+    taillength::Float64
-  coatcolor # not including a type annotation is the same as `::Any`
+    coatcolor  # not including a type annotation is the same as `::Any`
 end
 
 # The default constructor's arguments are the properties
 # of the type, in the order they are listed in the definition
-tigger = Tiger(3.5,"orange") # => Tiger(3.5,"orange")
+tigger = Tiger(3.5, "orange")  # => Tiger(3.5,"orange")
 
 # The type doubles as the constructor function for values of that type
-sherekhan = typeof(tigger)(5.6,"fire") # => Tiger(5.6,"fire")
+sherekhan = typeof(tigger)(5.6, "fire")  # => Tiger(5.6,"fire")
 
 # These struct-style types are called concrete types
 # They can be instantiated, but cannot have subtypes.
 # The other kind of types is abstract types.
 
 # abstract Name
-abstract type Cat end # just a name and point in the type hierarchy
+abstract type Cat end  # just a name and point in the type hierarchy
 
 # Abstract types cannot be instantiated, but can have subtypes.
+using InteractiveUtils  # defines the subtype and supertype function
 # For example, Number is an abstract type
-subtypes(Number) # => 2-element Array{Any,1}:
+subtypes(Number)  # => 2-element Array{Any,1}:
                  #     Complex{T<:Real}
                  #     Real
-subtypes(Cat) # => 0-element Array{Any,1}
+subtypes(Cat)  # => 0-element Array{Any,1}
 
 # AbstractString, as the name implies, is also an abstract type
-subtypes(AbstractString)        # 6-element Array{Union{DataType, UnionAll},1}:
+subtypes(AbstractString)  # 4-element Array{Any,1}:
-				# Base.SubstitutionString
+                            #  String
-				# Base.Test.GenericString
+                            #  SubString
-				# DirectIndexString      
+                            #  SubstitutionString
-				# RevString              
+                            #  Test.GenericString
-				# String                 
-				# SubString
 
 # Every type has a super type; use the `supertype` function to get it.
-typeof(5) # => Int64
+typeof(5)  # => Int64
-supertype(Int64) # => Signed
+supertype(Int64)  # => Signed
-supertype(Signed) # => Integer
+supertype(Signed)  # => Integer
-supertype(Integer) # => Real
+supertype(Integer)  # => Real
-supertype(Real) # => Number
+supertype(Real)  # => Number
-supertype(Number) # => Any
+supertype(Number)  # => Any
-supertype(supertype(Signed)) # => Real
+supertype(supertype(Signed))  # => Real
-supertype(Any) # => Any
+supertype(Any)  # => Any
 # All of these type, except for Int64, are abstract.
-typeof("fire") # => String
+typeof("fire")  # => String
-supertype(String) # => AbstractString
+supertype(String)  # => AbstractString
 # Likewise here with String
-supertype(DirectIndexString) # => AbstractString
+supertype(SubString)  # => AbstractString
 
 # <: is the subtyping operator
-type Lion <: Cat # Lion is a subtype of Cat
+struct Lion <: Cat  # Lion is a subtype of Cat
-  mane_color
+    mane_color
-  roar::AbstractString
+    roar::AbstractString
 end
 
 # You can define more constructors for your type
 # Just define a function of the same name as the type
 # and call an existing constructor to get a value of the correct type
-Lion(roar::AbstractString) = Lion("green",roar)
+Lion(roar::AbstractString) = Lion("green", roar)
 # This is an outer constructor because it's outside the type definition
 
-type Panther <: Cat # Panther is also a subtype of Cat
+struct Panther <: Cat  # Panther is also a subtype of Cat
-  eye_color
+    eye_color
-  Panther() = new("green")
+    Panther() = new("green")
-  # Panthers will only have this constructor, and no default constructor.
+    # Panthers will only have this constructor, and no default constructor.
 end
 # Using inner constructors, like Panther does, gives you control
 # over how values of the type can be created.
@@ -619,35 +613,35 @@ end
 
 # Definitions for Lion, Panther, Tiger
 function meow(animal::Lion)
-  animal.roar # access type properties using dot notation
+    animal.roar  # access type properties using dot notation
 end
 
 function meow(animal::Panther)
-  "grrr"
+    "grrr"
 end
 
 function meow(animal::Tiger)
-  "rawwwr"
+    "rawwwr"
 end
 
 # Testing the meow function
-meow(tigger) # => "rawwr"
+meow(tigger)  # => "rawwr"
-meow(Lion("brown","ROAAR")) # => "ROAAR"
+meow(Lion("brown", "ROAAR"))  # => "ROAAR"
-meow(Panther()) # => "grrr"
+meow(Panther())  # => "grrr"
 
 # Review the local type hierarchy
-issubtype(Tiger,Cat) # => false
+Tiger <: Cat # => false
-issubtype(Lion,Cat) # => true
+Lion <: Cat # => true
-issubtype(Panther,Cat) # => true
+Panther <: Cat # => true
 
 # Defining a function that takes Cats
 function pet_cat(cat::Cat)
-  println("The cat says $(meow(cat))")
+    println("The cat says $(meow(cat))")
 end
 
-pet_cat(Lion("42")) # => prints "The cat says 42"
+pet_cat(Lion("42"))  # => prints "The cat says 42"
 try
-    pet_cat(tigger) # => ERROR: no method pet_cat(Tiger,)
+    pet_cat(tigger)  # => ERROR: no method pet_cat(Tiger,)
 catch e
     println(e)
 end
@@ -657,129 +651,132 @@ end
 # In Julia, all of the argument types contribute to selecting the best method.
 
 # Let's define a function with more arguments, so we can see the difference
-function fight(t::Tiger,c::Cat)
+function fight(t::Tiger, c::Cat)
-  println("The $(t.coatcolor) tiger wins!")
+    println("The $(t.coatcolor) tiger wins!")
 end
 # => fight (generic function with 1 method)
 
-fight(tigger,Panther()) # => prints The orange tiger wins!
+fight(tigger, Panther())  # => prints The orange tiger wins!
-fight(tigger,Lion("ROAR")) # => prints The orange tiger wins!
+fight(tigger, Lion("ROAR"))  # => prints The orange tiger wins!
 
 # Let's change the behavior when the Cat is specifically a Lion
-fight(t::Tiger,l::Lion) = println("The $(l.mane_color)-maned lion wins!")
+fight(t::Tiger, l::Lion) = println("The $(l.mane_color)-maned lion wins!")
 # => fight (generic function with 2 methods)
 
-fight(tigger,Panther()) # => prints The orange tiger wins!
+fight(tigger, Panther())  # => prints The orange tiger wins!
-fight(tigger,Lion("ROAR")) # => prints The green-maned lion wins!
+fight(tigger, Lion("ROAR"))  # => prints The green-maned lion wins!
 
 # We don't need a Tiger in order to fight
-fight(l::Lion,c::Cat) = println("The victorious cat says $(meow(c))")
+fight(l::Lion, c::Cat) = println("The victorious cat says $(meow(c))")
 # => fight (generic function with 3 methods)
 
-fight(Lion("balooga!"),Panther()) # => prints The victorious cat says grrr
+fight(Lion("balooga!"), Panther())  # => prints The victorious cat says grrr
 try
-  fight(Panther(),Lion("RAWR"))
+    fight(Panther(), Lion("RAWR"))
 catch e
-  println(e) 
+    println(e)
-  # => MethodError(fight, (Panther("green"), Lion("green", "RAWR")), 0x000000000000557b)
+    # => MethodError(fight, (Panther("green"), Lion("green", "RAWR")),
+    #                0x000000000000557b)
 end
 
 # Also let the cat go first
-fight(c::Cat,l::Lion) = println("The cat beats the Lion")
+fight(c::Cat, l::Lion) = println("The cat beats the Lion")
 
 # This warning is because it's unclear which fight will be called in:
 try
-  fight(Lion("RAR"),Lion("brown","rarrr")) # => prints The victorious cat says rarrr
+    fight(Lion("RAR"), Lion("brown", "rarrr"))
+    # => prints The victorious cat says rarrr
 catch e
-  println(e)
+    println(e)
-  # => MethodError(fight, (Lion("green", "RAR"), Lion("brown", "rarrr")), 0x000000000000557c)
+  # => MethodError(fight, (Lion("green", "RAR"), Lion("brown", "rarrr")),
+  #                0x000000000000557c)
 end
 # The result may be different in other versions of Julia
 
-fight(l::Lion,l2::Lion) = println("The lions come to a tie")
+fight(l::Lion, l2::Lion) = println("The lions come to a tie")
-fight(Lion("RAR"),Lion("brown","rarrr")) # => prints The lions come to a tie
+fight(Lion("RAR"), Lion("brown", "rarrr"))  # => prints The lions come to a tie
 
 
 # Under the hood
 # You can take a look at the llvm  and the assembly code generated.
 
-square_area(l) = l * l      # square_area (generic function with 1 method)
+square_area(l) = l * l  # square_area (generic function with 1 method)
 
-square_area(5) #25
+square_area(5)  # => 25
 
 # What happens when we feed square_area an integer?
 code_native(square_area, (Int32,))
-	#	    .section    __TEXT,__text,regular,pure_instructions
+    #        .section    __TEXT,__text,regular,pure_instructions
-	#	Filename: none
+    #    Filename: none
-	#	Source line: 1              # Prologue
+    #    Source line: 1              # Prologue
-	#	    push    RBP
+    #        push    RBP
-	#	    mov RBP, RSP
+    #        mov RBP, RSP
-	#	Source line: 1
+    #    Source line: 1
-	#	    movsxd  RAX, EDI        # Fetch l from memory?
+    #        movsxd  RAX, EDI        # Fetch l from memory?
-	#	    imul    RAX, RAX        # Square l and store the result in RAX
+    #        imul    RAX, RAX        # Square l and store the result in RAX
-	#	    pop RBP                 # Restore old base pointer
+    #        pop RBP                 # Restore old base pointer
-	#	    ret                     # Result will still be in RAX
+    #        ret                     # Result will still be in RAX
 
 code_native(square_area, (Float32,))
-	#	    .section    __TEXT,__text,regular,pure_instructions
+    #        .section    __TEXT,__text,regular,pure_instructions
-	#	Filename: none
+    #    Filename: none
-	#	Source line: 1
+    #    Source line: 1
-	#	    push    RBP
+    #        push    RBP
-	#	    mov RBP, RSP
+    #        mov RBP, RSP
-	#	Source line: 1
+    #    Source line: 1
-	#	    vmulss  XMM0, XMM0, XMM0  # Scalar single precision multiply (AVX)
+    #        vmulss  XMM0, XMM0, XMM0  # Scalar single precision multiply (AVX)
-	#	    pop RBP
+    #        pop RBP
-	#	    ret
+    #        ret
 
 code_native(square_area, (Float64,))
-	#	    .section    __TEXT,__text,regular,pure_instructions
+    #        .section    __TEXT,__text,regular,pure_instructions
-	#	Filename: none
+    #    Filename: none
-	#	Source line: 1
+    #    Source line: 1
-	#	    push    RBP
+    #        push    RBP
-	#	    mov RBP, RSP
+    #        mov RBP, RSP
-	#	Source line: 1
+    #    Source line: 1
-	#	    vmulsd  XMM0, XMM0, XMM0 # Scalar double precision multiply (AVX)
+    #        vmulsd  XMM0, XMM0, XMM0  # Scalar double precision multiply (AVX)
-	#	    pop RBP
+    #        pop RBP
-	#	    ret
+    #        ret
-	#
+    #
 # Note that julia will use floating point instructions if any of the
 # arguments are floats.
 # Let's calculate the area of a circle
 circle_area(r) = pi * r * r     # circle_area (generic function with 1 method)
-circle_area(5)                  # 78.53981633974483
+circle_area(5)  # 78.53981633974483
 
 code_native(circle_area, (Int32,))
-	#	    .section    __TEXT,__text,regular,pure_instructions
+    #        .section    __TEXT,__text,regular,pure_instructions
-	#	Filename: none
+    #    Filename: none
-	#	Source line: 1
+    #    Source line: 1
-	#	    push    RBP
+    #        push    RBP
-	#	    mov RBP, RSP
+    #        mov RBP, RSP
-	#	Source line: 1
+    #    Source line: 1
-	#	    vcvtsi2sd   XMM0, XMM0, EDI          # Load integer (r) from memory
+    #        vcvtsi2sd   XMM0, XMM0, EDI          # Load integer (r) from memory
-	#	    movabs  RAX, 4593140240              # Load pi
+    #        movabs  RAX, 4593140240              # Load pi
-	#	    vmulsd  XMM1, XMM0, QWORD PTR [RAX]  # pi * r
+    #        vmulsd  XMM1, XMM0, QWORD PTR [RAX]  # pi * r
-	#	    vmulsd  XMM0, XMM0, XMM1             # (pi * r) * r
+    #        vmulsd  XMM0, XMM0, XMM1             # (pi * r) * r
-	#	    pop RBP
+    #        pop RBP
-	#	    ret
+    #        ret
-	#
+    #
 
 code_native(circle_area, (Float64,))
-	#	    .section    __TEXT,__text,regular,pure_instructions
+    #        .section    __TEXT,__text,regular,pure_instructions
-	#	Filename: none
+    #    Filename: none
-	#	Source line: 1
+    #    Source line: 1
-	#	    push    RBP
+    #        push    RBP
-	#	    mov RBP, RSP
+    #        mov RBP, RSP
-	#	    movabs  RAX, 4593140496
+    #        movabs  RAX, 4593140496
-	#	Source line: 1
+    #    Source line: 1
-	#	    vmulsd  XMM1, XMM0, QWORD PTR [RAX]
+    #        vmulsd  XMM1, XMM0, QWORD PTR [RAX]
-	#	    vmulsd  XMM0, XMM1, XMM0
+    #        vmulsd  XMM0, XMM1, XMM0
-	#	    pop RBP
+    #        pop RBP
-	#	    ret
+    #        ret
-	#
+    #
 ```
 
 ## Further Reading
 
-You can get a lot more detail from [The Julia Manual](http://docs.julialang.org/en/latest/#Manual-1)
+You can get a lot more detail from the [Julia Documentation](https://docs.julialang.org/)
 
 The best place to get help with Julia is the (very friendly) [Discourse forum](https://discourse.julialang.org/).