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-rw-r--r--julia.html.markdown152
1 files changed, 106 insertions, 46 deletions
diff --git a/julia.html.markdown b/julia.html.markdown
index c31df752..6c719b5c 100644
--- a/julia.html.markdown
+++ b/julia.html.markdown
@@ -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
+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
-# 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
+# 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