diff options
| -rw-r--r-- | julia.html.markdown | 53 |
1 files changed, 33 insertions, 20 deletions
diff --git a/julia.html.markdown b/julia.html.markdown index cf3a464b..e824bfcf 100644 --- a/julia.html.markdown +++ b/julia.html.markdown @@ -20,20 +20,20 @@ This is based on the current development version of Julia, as of June 29th, 2013 # Everything in Julia is a expression. -# You have numbers +# 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}) -# Math is what you would expect +# 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 -5 / 2 #=> 2.5 -div(5, 2) #=> 2 2 ^ 2 #=> 4 # power, not bitwise xor 12 % 10 #=> 2 @@ -77,11 +77,13 @@ false # Strings are created with " "This is a string." -# Character literals written with ' +# Character literals are written with ' 'a' -# A string can be treated like a list of characters +# 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 reccommended (map, for loops, etc). # $ can be used for string interpolation: "2 + 2 = $(2 + 2)" #=> "2 + 2 = 4" @@ -94,10 +96,10 @@ false ## 2. Variables and Collections #################################################### -# Printing is pretty easy +# Printing is easy println("I'm Julia. Nice to meet you!") -# No need to declare variables before assigning to them. +# You don't declare variables before assigning to them. some_var = 5 #=> 5 some_var #=> 5 @@ -108,12 +110,14 @@ 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. +# 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: # @@ -158,6 +162,10 @@ a[1] #=> 1 # remember that Julia indexes from 1, not 0! # 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] @@ -182,23 +190,24 @@ 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:] #=> [2, 3, 4, 5] +a[2:end] #=> [2, 3, 4, 5] -# Remove arbitrary elements from a list with splice! +# 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, 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 contains contains(a,1) #=> true # Examine the length with length -length(a) #=> 7 +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 try: tup[0] = 3 #=> ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64) @@ -214,17 +223,21 @@ 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 +# Tuples are created even 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 +# 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}() -# Here is a prefilled dictionary +# You can create a dictionary using a literal filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3] # => Dict{ASCIIString,Int64} @@ -247,19 +260,19 @@ 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 +# 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 get method to avoid the error +# 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 -# Sets store sets +# Use Sets to represent collections of unordered, unique values empty_set = Set() #=> Set{Any}() # Initialize a set with a bunch of values filled_set = Set(1,2,2,3,4) #=> Set{Int64}(1,2,3,4) |