diff options
Diffstat (limited to 'ja-jp/julia-jp.html.markdown')
| -rw-r--r-- | ja-jp/julia-jp.html.markdown | 747 |
1 files changed, 747 insertions, 0 deletions
diff --git a/ja-jp/julia-jp.html.markdown b/ja-jp/julia-jp.html.markdown new file mode 100644 index 00000000..3a52018c --- /dev/null +++ b/ja-jp/julia-jp.html.markdown @@ -0,0 +1,747 @@ +--- +language: Julia +contributors: + - ["Leah Hanson", "http://leahhanson.us"] +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 the current development version of Julia, as of October 18th, 2013. + +```ruby + +# 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. +=# + +#################################################### +## 1. Primitive Datatypes and Operators +#################################################### + +# Everything in Julia is a expression. + +# 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) +# => "0000000000000000000000000000000000000000000000000011000000111001" +bits(12345.0) +# => "0100000011001000000111001000000000000000000000000000000000000000" + +# 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 +# Comparisons can be chained +1 < 2 < 3 # => true +2 < 3 < 2 # => false + +# Strings are created with " +"This is a string." + +# Character literals are written with ' +'a' + +# A string can be indexed like an array of characters +"This is a string"[1] # => 'T' # Julia indexes from 1 +# 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: +"2 + 2 = $(2 + 2)" # => "2 + 2 = 4" +# You can put any Julia expression inside the parenthesis. + +# 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!") + +#################################################### +## 2. Variables and Collections +#################################################### + +# 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. +# After that, you can use letters, digits, underscores, and exclamation points. +SomeOtherVar123! = 6 # => 6 + +# You can also use unicode characters +☃ = 8 # => 8 +# These are especially handy for mathematical notation +2 * π # => 6.283185307179586 + +# A note on naming conventions in Julia: +# +# * Word separation can be indicated by underscores ('_'), but use of +# underscores is discouraged unless the name would be hard to read +# otherwise. +# +# * Names of Types begin with a capital letter and word separation is shown +# with CamelCase instead of underscores. +# +# * Names of functions and macros are in lower case, without underscores. +# +# * Functions that modify their inputs have names that end in !. These +# 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 + +# 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] +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] + +# Remove from the end with pop +pop!(b) # => 6 and b is now [4,5] + +# Let's put it back +push!(b,6) # b is now [4,5,6] again. + +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 + +# we also have shift and unshift +shift!(a) # => 1 and a is now [2,4,3,4,5,6] +unshift!(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] +sort(arr) # => [4,5,6]; arr is still [5,4,6] +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[end+1] # => ERROR: BoundsError() in getindex at array.jl:270 +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 +# inside the julia folder to find these files. + +# 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] + +# Remove elements from an array by index with splice! +arr = [3,4,5] +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] + +# Check for existence in a list with in +in(1, a) # => true + +# Examine the length with length +length(a) # => 8 + +# Tuples are immutable. +tup = (1, 2, 3) # => (1,2,3) # an (Int64,Int64,Int64) tuple. +tup[1] # => 1 +try: + tup[1] = 3 # => ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64) +catch e + println(e) +end + +# Many list functions also work on tuples +length(tup) # => 3 +tup[1:2] # => (1,2) +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 + +# 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 + +# Look how easy it is to swap two values +e, d = d, e # => (5,4) # d is now 5 and e is now 4 + + +# 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] +# => Dict{ASCIIString,Int64} + +# Look up values with [] +filled_dict["one"] # => 1 + +# Get all keys +keys(filled_dict) +# => KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2]) +# 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]) +# 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(("two", 3), filled_dict) # => false +haskey(filled_dict, "one") # => true +haskey(filled_dict, 1) # => false + +# Trying to look up a non-existant key will raise an error +try + filled_dict["four"] # => ERROR: key not found: four in getindex at dict.jl:489 +catch e + println(e) +end + +# Use the get method to avoid that error by providing a default value +# get(dictionary,key,default_value) +get(filled_dict,"one",4) # => 1 +get(filled_dict,"four",4) # => 4 + +# Use Sets to represent collections of unordered, unique values +empty_set = Set() # => Set{Any}() +# Initialize a set with values +filled_set = Set(1,2,2,3,4) # => Set{Int64}(1,2,3,4) + +# Add more values to a set +push!(filled_set,5) # => Set{Int64}(5,4,2,3,1) + +# Check if the values are in the set +in(2, filled_set) # => true +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) +intersect(filled_set, other_set) # => Set{Int64}(3,4,5) +union(filled_set, other_set) # => Set{Int64}(1,2,3,4,5,6) +setdiff(Set(1,2,3,4),Set(2,3,5)) # => Set{Int64}(1,4) + + +#################################################### +## 3. Control Flow +#################################################### + +# Let's make a variable +some_var = 5 + +# 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 +# => prints "some var is smaller than 10" + + +# For loops iterate over iterables. +# Iterable types include Range, Array, Set, Dict, and String. +for animal=["dog", "cat", "mouse"] + println("$animal is a mammal") + # You can use $ to interpolate variables or expression into strings +end +# prints: +# dog is a mammal +# cat is a mammal +# mouse is a mammal + +# You can use 'in' instead of '='. +for animal in ["dog", "cat", "mouse"] + println("$animal is a mammal") +end +# prints: +# dog is a mammal +# cat is a mammal +# mouse is a mammal + +for a in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"] + println("$(a[1]) is a $(a[2])") +end +# prints: +# dog is a mammal +# cat is a mammal +# mouse is a mammal + +for (k,v) in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"] + println("$k is a $v") +end +# prints: +# dog is a mammal +# cat is a mammal +# mouse is a mammal + +# While loops loop while a condition is true +x = 0 +while x < 4 + println(x) + x += 1 # Shorthand for x = x + 1 +end +# prints: +# 0 +# 1 +# 2 +# 3 + +# Handle exceptions with a try/catch block +try + error("help") +catch e + println("caught it $e") +end +# => caught it ErrorException("help") + + +#################################################### +## 4. Functions +#################################################### + +# The keyword 'function' creates new functions +#function name(arglist) +# body... +#end +function add(x, y) + println("x is $x and y is $y") + + # Functions return the value of their last statement + x + y +end + +add(5, 6) # => 11 after printing out "x is 5 and y is 6" + +# You can define functions that take a variable number of +# positional arguments +function varargs(args...) + return args + # use the keyword return to return anywhere in the function +end +# => varargs (generic function with 1 method) + +varargs(1,2,3) # => (1,2,3) + +# The ... is called a splat. +# We just used it in a function definition. +# It can also be used in a fuction call, +# where it will splat an Array or Tuple's contents into the argument list. +Set([1,2,3]) # => Set{Array{Int64,1}}([1,2,3]) # produces a Set of Arrays +Set([1,2,3]...) # => Set{Int64}(1,2,3) # this is equivalent to Set(1,2,3) + +x = (1,2,3) # => (1,2,3) +Set(x) # => Set{(Int64,Int64,Int64)}((1,2,3)) # a Set of Tuples +Set(x...) # => Set{Int64}(2,3,1) + + +# You can define functions with optional positional arguments +function defaults(a,b,x=5,y=6) + return "$a $b and $x $y" +end + +defaults('h','g') # => "h g and 5 6" +defaults('h','g','j') # => "h g and j 6" +defaults('h','g','j','k') # => "h g and j k" +try + defaults('h') # => ERROR: no method defaults(Char,) + 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 ; + return ["k1"=>k1,"name2"=>name2] +end + +keyword_args(name2="ness") # => ["name2"=>"ness","k1"=>4] +keyword_args(k1="mine") # => ["k1"=>"mine","name2"=>"hello"] +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") + println("normal arg: $normal_arg") + println("optional arg: $optional_positional_arg") + println("keyword arg: $keyword_arg") +end + +all_the_args(1, 3, keyword_arg=4) +# prints: +# normal arg: 1 +# optional arg: 3 +# keyword arg: 4 + +# Julia has first class functions +function create_adder(x) + adder = function (y) + return x + y + end + return adder +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 + adder +end + +add_10 = create_adder(10) +add_10(3) # => 13 + + +# 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] + +#################################################### +## 5. Types +#################################################### + +# 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 + +# Types are first-class values +typeof(Int64) # => DataType +typeof(DataType) # => DataType +# DataType is the type that represents types, including itself. + +# Types are used for documentation, optimizations, and dispatch. +# They are not statically checked. + +# Users can define types +# They are like records or structs in other languages. +# New types are defined using the `type` keyword. + +# type Name +# field::OptionalType +# ... +# end +type Tiger + taillength::Float64 + 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") + +# The type doubles as the constructor function for values of that type +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 Cat # just a name and point in the type hierarchy + +# Abstract types cannot be instantiated, but can have subtypes. +# For example, Number is an abstract type +subtypes(Number) # => 6-element Array{Any,1}: + # Complex{Float16} + # Complex{Float32} + # Complex{Float64} + # Complex{T<:Real} + # ImaginaryUnit + # Real +subtypes(Cat) # => 0-element Array{Any,1} + +# Every type has a super type; use the `super` function to get it. +typeof(5) # => Int64 +super(Int64) # => Signed +super(Signed) # => Real +super(Real) # => Number +super(Number) # => Any +super(super(Signed)) # => Number +super(Any) # => Any +# All of these type, except for Int64, are abstract. + +# <: is the subtyping operator +type Lion <: Cat # Lion is a subtype of Cat + mane_color + roar::String +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::String) = 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 + eye_color + Panther() = new("green") + # 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. +# When possible, you should use outer constructors rather than inner ones. + +#################################################### +## 6. Multiple-Dispatch +#################################################### + +# In Julia, all named functions are generic functions +# This means that they are built up from many small methods +# Each constructor for Lion is a method of the generic function Lion. + +# For a non-constructor example, let's make a function meow: + +# Definitions for Lion, Panther, Tiger +function meow(animal::Lion) + animal.roar # access type properties using dot notation +end + +function meow(animal::Panther) + "grrr" +end + +function meow(animal::Tiger) + "rawwwr" +end + +# Testing the meow function +meow(tigger) # => "rawwr" +meow(Lion("brown","ROAAR")) # => "ROAAR" +meow(Panther()) # => "grrr" + +# Review the local type hierarchy +issubtype(Tiger,Cat) # => false +issubtype(Lion,Cat) # => true +issubtype(Panther,Cat) # => true + +# Defining a function that takes Cats +function pet_cat(cat::Cat) + println("The cat says $(meow(cat))") +end + +pet_cat(Lion("42")) # => prints "The cat says 42" +try + pet_cat(tigger) # => ERROR: no method pet_cat(Tiger,) +catch e + println(e) +end + +# In OO languages, single dispatch is common; +# this means that the method is picked based on the type of the first argument. +# 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) + println("The $(t.coatcolor) tiger wins!") +end +# => fight (generic function with 1 method) + +fight(tigger,Panther()) # => 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 (generic function with 2 methods) + +fight(tigger,Panther()) # => prints The orange tiger 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 (generic function with 3 methods) + +fight(Lion("balooga!"),Panther()) # => prints The victorious cat says grrr +try + fight(Panther(),Lion("RAWR")) # => ERROR: no method fight(Panther,Lion) +catch +end + +# Also let the cat go first +fight(c::Cat,l::Lion) = println("The cat beats the Lion") +# => Warning: New definition +# fight(Cat,Lion) at none:1 +# is ambiguous with +# fight(Lion,Cat) at none:2. +# Make sure +# fight(Lion,Lion) +# is defined first. +#fight (generic function with 4 methods) + +# This warning is because it's unclear which fight will be called in: +fight(Lion("RAR"),Lion("brown","rarrr")) # => prints The victorious cat says rarrr +# The result may be different in other versions of Julia + +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 + + +# 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(5) #25 + +# What happens when we feed square_area an integer? +code_native(square_area, (Int32,)) + # .section __TEXT,__text,regular,pure_instructions + # Filename: none + # Source line: 1 # Prologue + # push RBP + # mov RBP, RSP + # Source line: 1 + # movsxd RAX, EDI # Fetch l from memory? + # imul RAX, RAX # Square l and store the result in RAX + # pop RBP # Restore old base pointer + # ret # Result will still be in RAX + +code_native(square_area, (Float32,)) + # .section __TEXT,__text,regular,pure_instructions + # Filename: none + # Source line: 1 + # push RBP + # mov RBP, RSP + # Source line: 1 + # vmulss XMM0, XMM0, XMM0 # Scalar single precision multiply (AVX) + # pop RBP + # ret + +code_native(square_area, (Float64,)) + # .section __TEXT,__text,regular,pure_instructions + # Filename: none + # Source line: 1 + # push RBP + # mov RBP, RSP + # Source line: 1 + # vmulsd XMM0, XMM0, XMM0 # Scalar double precision multiply (AVX) + # pop RBP + # ret + # +# Note that julia will use floating point instructions if any of the +# arguements 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 + +code_native(circle_area, (Int32,)) + # .section __TEXT,__text,regular,pure_instructions + # Filename: none + # Source line: 1 + # push RBP + # mov RBP, RSP + # Source line: 1 + # vcvtsi2sd XMM0, XMM0, EDI # Load integer (r) from memory + # movabs RAX, 4593140240 # Load pi + # vmulsd XMM1, XMM0, QWORD PTR [RAX] # pi * r + # vmulsd XMM0, XMM0, XMM1 # (pi * r) * r + # pop RBP + # ret + # + +code_native(circle_area, (Float64,)) + # .section __TEXT,__text,regular,pure_instructions + # Filename: none + # Source line: 1 + # push RBP + # mov RBP, RSP + # movabs RAX, 4593140496 + # Source line: 1 + # vmulsd XMM1, XMM0, QWORD PTR [RAX] + # vmulsd XMM0, XMM1, XMM0 + # pop RBP + # ret + # +``` + +## Further Reading + +You can get a lot more detail from [The Julia Manual](http://docs.julialang.org/en/latest/manual/) + +The best place to get help with Julia is the (very friendly) [mailing list](https://groups.google.com/forum/#!forum/julia-users). |