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Edited julia code for line length and runnability
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@ -2,6 +2,7 @@
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language: julia
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author: Leah Hanson
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author_url: http://leahhanson.us
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filename: learnjulia.jl
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---
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Julia is a new homoiconic functional language focused on technical computing.
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@ -9,7 +10,8 @@ While having the full power of homoiconic macros, first-class functions, and low
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This is based on the current development version of Julia, as of June 29th, 2013.
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```julia
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```ruby
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# Single line comments start with a hash.
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####################################################
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@ -48,8 +50,10 @@ div(5, 2) #=> 2
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2 << 1 #=> 4 # logical/arithmetic shift left
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# You can use the bits function to see the binary representation of a number.
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bits(12345) #=> "0000000000000000000000000000000000000000000000000011000000111001"
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bits(12345.0) #=> "0100000011001000000111001000000000000000000000000000000000000000"
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bits(12345)
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#=> "0000000000000000000000000000000000000000000000000011000000111001"
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bits(12345.0)
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#=> "0100000011001000000111001000000000000000000000000000000000000000"
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# Boolean values are primitives
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true
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@ -96,25 +100,42 @@ println("I'm Julia. Nice to meet you!")
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# No need to declare variables before assigning to them.
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some_var = 5 #=> 5
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some_var #=> 5
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# Accessing a previously unassigned variable is an error
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some_other_var #=> ERROR: some_other_var not defined
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# Variable Names:
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SomeOtherVar123! = 6 #=> 6 # You can use uppercase letters, digits, and exclamation points as well after the initial alphabetic character.
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☃ = 8 #=> 8 # You can also use unicode characters
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# Accessing a previously unassigned variable is an error
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try
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some_other_var #=> ERROR: some_other_var not defined
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catch e
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println(e)
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end
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# Variable name start with a letter. You can use uppercase letters, digits,
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# and exclamation points as well after the initial alphabetic character.
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SomeOtherVar123! = 6 #=> 6
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# You can also use unicode characters
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☃ = 8 #=> 8
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# A note on naming conventions in Julia:
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# * Names of variables are in lower case, with word separation indicated by underscores ('\_').
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# * Names of Types begin with a capital letter and word separation is shown with CamelCase instead of underscores.
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#
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# * Names of variables are in lower case, with word separation indicated by
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# underscores ('\_').
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#
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# * Names of Types begin with a capital letter and word separation is shown
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# with CamelCase instead of underscores.
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#
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# * Names of functions and macros are in lower case, without underscores.
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# * Functions that modify their inputs have names that end in !. These functions are sometimes called mutating functions or in-place functions.
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#
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# * Functions that modify their inputs have names that end in !. These
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# functions are sometimes called mutating functions or in-place functions.
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# Arrays store a sequence of values indexed by integers 1 through n:
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a = Int64[] #=> 0-element Int64 Array
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# 1-dimensional array literals can be written with comma-separated values.
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b = [4, 5, 6] #=> 3-element Int64 Array: [4, 5, 6]
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b[1] #=> 4
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b[end] #=> 6
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# 2-dimentional arrays use space-separated values and semicolon-separated rows.
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matrix = [1 2; 3 4] #=> 2x2 Int64 Array: [1 2; 3 4]
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@ -124,42 +145,53 @@ push!(a,2) #=> [1,2]
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push!(a,4) #=> [1,2,4]
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push!(a,3) #=> [1,2,4,3]
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append!(a,b) #=> [1,2,4,3,4,5,6]
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# Remove from the end with pop
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pop!(a) #=> 6 and b is now [4,5]
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# Let's put it back
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push!(b,6) # b is now [4,5,6] again.
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a[1] #=> 1 # remember that Julia indexes from 1, not 0!
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a[end] #=> 6 # end is a shorthand for the last index; it can be used in any indexing expression.
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# Function names that end in exclamations points indicate that they modify their argument.
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# end is a shorthand for the last index. It can be used in any
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# indexing expression
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a[end] #=> 6
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# Function names that end in exclamations points indicate that they modify
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# their argument.
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arr = [5,4,6] #=> 3-element Int64 Array: [5,4,6]
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sort(arr) #=> [4,5,6]; arr is still [5,4,6]
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sort!(arr) #=> [4,5,6]; arr is now [4,5,6]
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# Looking out of bounds is a BoundsError
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a[0] #=> ERROR: BoundsError() in getindex at array.jl:270
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a[end+1] #=> ERROR: BoundsError() in getindex at array.jl:270
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# Errors list the line and file they came from, even if it's in the standard library.
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# If you built Julia from source, you can look in the folder base inside the julia folder to find these files.
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try
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a[0] #=> ERROR: BoundsError() in getindex at array.jl:270
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a[end+1] #=> ERROR: BoundsError() in getindex at array.jl:270
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catch e
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println(e)
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end
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# Errors list the line and file they came from, even if it's in the standard
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# library. If you built Julia from source, you can look in the folder base
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# inside the julia folder to find these files.
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# You can initialize arrays from ranges
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a = [1:5] #=> 5-element Int64 Array: [1,2,3,4,5]
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# You can look at ranges with slice syntax.
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a[1:3] #=> [1, 2, 3]
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# Omit the beginning
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a[2:] #=> [2, 3, 4, 5]
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# Remove arbitrary elements from a list with splice!
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arr = [3,4,5]
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splice!(arr,2) #=> 4 ; arr is now [3,5]
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# Concatenate lists with append!
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# Concatenate lists with append!
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b = [1,2,3]
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append!(a,b) # Now a is [1, 3, 4, 5, 1, 2, 3]
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# Check for existence in a list with contains
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# Check for existence in a list with contains
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contains(a,1) #=> true
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# Examine the length with length
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@ -168,7 +200,11 @@ length(a) #=> 7
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# Tuples are immutable.
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tup = (1, 2, 3) #=>(1,2,3) # an (Int64,Int64,Int64) tuple.
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tup[1] #=> 1
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tup[0] = 3 #=> ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
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try:
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tup[0] = 3 #=> ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
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catch e
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println(e)
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end
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# Many list functions also work on tuples
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length(tup) #=> 3
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@ -177,36 +213,46 @@ contains(tup,2) #=> true
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# You can unpack tuples into variables
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a, b, c = (1, 2, 3) #=> (1,2,3) # a is now 1, b is now 2 and c is now 3
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# Tuples are created by default if you leave out the parentheses
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d, e, f = 4, 5, 6 #=> (4,5,6)
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# Now look how easy it is to swap two values
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e, d = d, e #=> (5,4) # d is now 5 and e is now 4
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# Dictionaries store mappings
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empty_dict = Dict() #=> Dict{Any,Any}()
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# Here is a prefilled dictionary
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filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3] #=> ["one"=> 1, "two"=> 2, "three"=> 3] # Dict{ASCIIString,Int64}
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filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3]
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# => Dict{ASCIIString,Int64}
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# Look up values with []
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filled_dict["one"] #=> 1
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# Get all keys
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keys(filled_dict) #=> KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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keys(filled_dict)
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#=> KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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# Note - dictionary keys are not sorted or in the order you inserted them.
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# Get all values
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values(d) #=> ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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values(filled_dict)
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#=> ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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# Note - Same as above regarding key ordering.
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# Check for existence of keys in a dictionary with contains, haskey
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contains(filled_dict,("one",1)) #=> true
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contains(filled_dict,("two",3)) #=> false
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haskey(filled_dict,"one") #=> true
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haskey(filled_dict,1) #=> false
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contains(filled_dict, ("one", 1)) #=> true
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contains(filled_dict, ("two", 3)) #=> false
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haskey(filled_dict, "one") #=> true
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haskey(filled_dict, 1) #=> false
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# Trying to look up a non-existing key will raise an error
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filled_dict["four"] #=> ERROR: key not found: four in getindex at dict.jl:489
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try
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filled_dict["four"] #=> ERROR: key not found: four in getindex at dict.jl:489
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catch e
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println(e)
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end
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# Use get method to avoid the error
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# get(dictionary,key,default_value)
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@ -250,16 +296,16 @@ else # The else clause is optional too.
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end
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# For loops iterate over iterable things, such as ranges, lists, sets, dicts, strings.
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# prints:
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# dog is a mammal
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# cat is a mammal
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# mouse is a mammal
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# For loops iterate over iterables, such as ranges, lists, sets, dicts, strings.
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for animal=["dog", "cat", "mouse"]
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# You can use $ to interpolate into strings
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println("$animal is a mammal")
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end
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# prints:
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# dog is a mammal
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# cat is a mammal
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# mouse is a mammal
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# You can use in instead of =, if you want.
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for animal in ["dog", "cat", "mouse"]
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@ -288,14 +334,11 @@ while x < 4
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end
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# Handle exceptions with a try/except block
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error("help") # ERROR: help in error at error.jl:21
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try
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error("help")
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catch e
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println("caught it $e")
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end
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end
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#=> caught it ErrorException("help")
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@ -306,7 +349,9 @@ end
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# Use the keyword function to create new functions
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function add(x, y)
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println("x is $x and y is $y")
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x + y # or equivalently: return x + y
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# Functions implicitly return the value of their last statement
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x + y
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end
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add(5, 6) #=> 11 after printing out "x is 5 and y is 6"
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@ -322,7 +367,7 @@ varargs(1,2,3) #=> (1,2,3)
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# The ... is called a splat.
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# It can also be used in a fuction call
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# to splat a list or tuple out to be the arguments
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Set([1,2,3]) #=> Set{Array{Int64,1}}([1,2,3]) # no ..., produces a Set of Arrays
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Set([1,2,3]) #=> Set{Array{Int64,1}}([1,2,3]) # produces a Set of Arrays
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Set([1,2,3]...) #=> Set{Int64}(1,2,3) # this is equivalent to Set(1,2,3)
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x = (1,2,3) #=> (1,2,3)
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@ -338,8 +383,12 @@ end
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defaults('h','g') #=> "h g and 5 6"
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defaults('h','g','j') #=> "h g and j 6"
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defaults('h','g','j','k') #=> "h g and j k"
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defaults('h') #=> ERROR: no method defaults(Char,)
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defaults() #=> ERROR: no methods defaults()
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try
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defaults('h') #=> ERROR: no method defaults(Char,)
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defaults() #=> ERROR: no methods defaults()
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catch e
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println(e)
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end
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# You can define functions that take keyword arguments
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function keyword_args(;k1=4,name2="hello") # note the ;
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@ -416,9 +465,13 @@ tigger = Tiger(3.5,"orange") # the type doubles as the constructor function
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# Abtract Types
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abstract Cat # just a name and point in the type hierarchy
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# types defined with the type keyword are concrete types; they can be instantiated
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# types defined with the abstract keyword are abstract types; they can have subtypes
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# each type has one supertype; a supertype can have zero or more subtypes.
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# * types defined with the type keyword are concrete types; they can be
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# instantiated
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#
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# * types defined with the abstract keyword are abstract types; they can
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# have subtypes.
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#
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# * each type has one supertype; a supertype can have zero or more subtypes.
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type Lion <: Cat # Lion is a subtype of Cat
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mane_color
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@ -427,7 +480,8 @@ end
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type Panther <: Cat # Panther is also a subtype of Cat
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eye_color
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Panther() = new("green") # Panthers will only have this constructor, and no default constructor.
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Panther() = new("green")
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# Panthers will only have this constructor, and no default constructor.
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end
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# Multiple Dispatch
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@ -455,9 +509,15 @@ function pet_cat(cat::Cat)
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println("The cat says $(meow(cat))")
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end
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pet_cat(tigger) #=> ERROR: no method pet_cat(Tiger,)
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try
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pet_cat(tigger) #=> ERROR: no method pet_cat(Tiger,)
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catch e
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println(e)
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end
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pet_cat(Lion(Panther(),"42")) #=> prints "The cat says 42"
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```
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## Further Reading
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