Edited julia code for line length and runnability

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Adam 2013-07-02 22:13:30 -07:00
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@ -2,6 +2,7 @@
language: julia
author: Leah Hanson
author_url: http://leahhanson.us
filename: learnjulia.jl
---
Julia is a new homoiconic functional language focused on technical computing.
@ -9,7 +10,8 @@ While having the full power of homoiconic macros, first-class functions, and low
This is based on the current development version of Julia, as of June 29th, 2013.
```julia
```ruby
# Single line comments start with a hash.
####################################################
@ -48,8 +50,10 @@ div(5, 2) #=> 2
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"
bits(12345)
#=> "0000000000000000000000000000000000000000000000000011000000111001"
bits(12345.0)
#=> "0100000011001000000111001000000000000000000000000000000000000000"
# Boolean values are primitives
true
@ -96,25 +100,42 @@ println("I'm Julia. Nice to meet you!")
# No need to declare variables before assigning to them.
some_var = 5 #=> 5
some_var #=> 5
# Accessing a previously unassigned variable is an error
some_other_var #=> ERROR: some_other_var not defined
# Variable Names:
SomeOtherVar123! = 6 #=> 6 # You can use uppercase letters, digits, and exclamation points as well after the initial alphabetic character.
☃ = 8 #=> 8 # You can also use unicode characters
# Accessing a previously unassigned variable is an error
try
some_other_var #=> ERROR: some_other_var not defined
catch e
println(e)
end
# Variable name start with a letter. You can use uppercase letters, digits,
# and exclamation points as well after the initial alphabetic character.
SomeOtherVar123! = 6 #=> 6
# You can also use unicode characters
☃ = 8 #=> 8
# A note on naming conventions in Julia:
# * Names of variables are in lower case, with word separation indicated by underscores ('\_').
# * Names of Types begin with a capital letter and word separation is shown with CamelCase instead of underscores.
#
# * Names of variables are in lower case, with word separation indicated by
# underscores ('\_').
#
# * 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.
#
# * 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]
@ -124,42 +145,53 @@ 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!(a) #=> 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!
a[end] #=> 6 # end is a shorthand for the last index; it can be used in any indexing expression.
# Function names that end in exclamations points indicate that they modify their argument.
# end is a shorthand for the last index. It can be used in any
# indexing expression
a[end] #=> 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
a[0] #=> ERROR: BoundsError() in getindex at array.jl:270
a[end+1] #=> ERROR: BoundsError() in getindex at array.jl:270
# 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.
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]
# Omit the beginning
a[2:] #=> [2, 3, 4, 5]
# Remove arbitrary elements from a list with splice!
arr = [3,4,5]
splice!(arr,2) #=> 4 ; arr is now [3,5]
# Concatenate lists with append!
# Concatenate lists with append!
b = [1,2,3]
append!(a,b) # Now a is [1, 3, 4, 5, 1, 2, 3]
# Check for existence in a list with contains
# Check for existence in a list with contains
contains(a,1) #=> true
# Examine the length with length
@ -168,7 +200,11 @@ length(a) #=> 7
# Tuples are immutable.
tup = (1, 2, 3) #=>(1,2,3) # an (Int64,Int64,Int64) tuple.
tup[1] #=> 1
tup[0] = 3 #=> ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
try:
tup[0] = 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
@ -177,36 +213,46 @@ contains(tup,2) #=> 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 by default if you leave out the parentheses
d, e, f = 4, 5, 6 #=> (4,5,6)
# Now 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}()
# Here is a prefilled dictionary
filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3] #=> ["one"=> 1, "two"=> 2, "three"=> 3] # Dict{ASCIIString,Int64}
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])
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(d) #=> ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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 contains, haskey
contains(filled_dict,("one",1)) #=> true
contains(filled_dict,("two",3)) #=> false
haskey(filled_dict,"one") #=> true
haskey(filled_dict,1) #=> false
contains(filled_dict, ("one", 1)) #=> true
contains(filled_dict, ("two", 3)) #=> false
haskey(filled_dict, "one") #=> true
haskey(filled_dict, 1) #=> false
# Trying to look up a non-existing key will raise an error
filled_dict["four"] #=> ERROR: key not found: four in getindex at dict.jl:489
try
filled_dict["four"] #=> ERROR: key not found: four in getindex at dict.jl:489
catch e
println(e)
end
# Use get method to avoid the error
# get(dictionary,key,default_value)
@ -250,16 +296,16 @@ else # The else clause is optional too.
end
# For loops iterate over iterable things, such as ranges, lists, sets, dicts, strings.
# prints:
# dog is a mammal
# cat is a mammal
# mouse is a mammal
# For loops iterate over iterables, such as ranges, lists, sets, dicts, strings.
for animal=["dog", "cat", "mouse"]
# You can use $ to interpolate into strings
println("$animal is a mammal")
end
# prints:
# dog is a mammal
# cat is a mammal
# mouse is a mammal
# You can use in instead of =, if you want.
for animal in ["dog", "cat", "mouse"]
@ -288,14 +334,11 @@ while x < 4
end
# Handle exceptions with a try/except block
error("help") # ERROR: help in error at error.jl:21
try
error("help")
catch e
println("caught it $e")
end
end
#=> caught it ErrorException("help")
@ -306,7 +349,9 @@ end
# Use the keyword function to create new functions
function add(x, y)
println("x is $x and y is $y")
x + y # or equivalently: return x + y
# Functions implicitly return the value of their last statement
x + y
end
add(5, 6) #=> 11 after printing out "x is 5 and y is 6"
@ -322,7 +367,7 @@ varargs(1,2,3) #=> (1,2,3)
# The ... is called a splat.
# It can also be used in a fuction call
# to splat a list or tuple out to be the arguments
Set([1,2,3]) #=> Set{Array{Int64,1}}([1,2,3]) # no ..., produces a Set of Arrays
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)
@ -338,8 +383,12 @@ 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"
defaults('h') #=> ERROR: no method defaults(Char,)
defaults() #=> ERROR: no methods defaults()
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 ;
@ -416,9 +465,13 @@ tigger = Tiger(3.5,"orange") # the type doubles as the constructor function
# Abtract Types
abstract Cat # just a name and point in the type hierarchy
# types defined with the type keyword are concrete types; they can be instantiated
# types defined with the abstract keyword are abstract types; they can have subtypes
# each type has one supertype; a supertype can have zero or more subtypes.
# * types defined with the type keyword are concrete types; they can be
# instantiated
#
# * types defined with the abstract keyword are abstract types; they can
# have subtypes.
#
# * each type has one supertype; a supertype can have zero or more subtypes.
type Lion <: Cat # Lion is a subtype of Cat
mane_color
@ -427,7 +480,8 @@ end
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.
Panther() = new("green")
# Panthers will only have this constructor, and no default constructor.
end
# Multiple Dispatch
@ -455,9 +509,15 @@ function pet_cat(cat::Cat)
println("The cat says $(meow(cat))")
end
pet_cat(tigger) #=> ERROR: no method pet_cat(Tiger,)
try
pet_cat(tigger) #=> ERROR: no method pet_cat(Tiger,)
catch e
println(e)
end
pet_cat(Lion(Panther(),"42")) #=> prints "The cat says 42"
```
## Further Reading