Julia: Modules

Modules are used to organize your code logically and resolve naming conflicts. Package is a collection of modules.

Use the command ‘Pkg.add("PackageName")’  to install new package. ‘Pkg.add("Winston")’ install the package Winston.

Load and use a package
‘using’ command is used to load a package.

julia>using Winston
julia>plot(rand(100))

Above statement draws following graph.

How to define a module

module ModuleName
 statement 1
 statement 2
  ….
  ….
 Statement N
end

julia> module Module1
           function processData(x)
               x^2
           end
       end
Module1

julia> module Module2
           function processData(x)
               x^3
           end
       end
Module2 

Above snippet define two modules Module1, Module2. Both the modules define the function processData. You can import the modules and use the functions define in them (By qualifying the function by the module name).

julia> import Module1

julia> import Module2

julia> Module1.processData(10)
100

julia> Module2.processData(10)
1000

Within a module, you can control what definitions, constants are visible outside of this module.

operations.jl

module Arithmetic
 export addition, subtraction
 function addition(x, y)
  x+y
 end

 function subtraction(x, y)
  x-y
 end

 function mul(x, y)
  x*y
 end

 function div(x, y)
  x/y
 end
end 

sample.jl

include("operations.jl")

using Arithmetic

res1 = addition(10, 20)
res2 = subtraction(10, 20)

println("Sum of 10, 20 is $res1")
println("Subtraction of 10, 20 is $res2")

Output

$ julia sample.jl 
Sum of 10, 20 is 30
Subtraction of 10, 20 is -10

Since I exported the functions addition and subtraction using export keyword (export addition, subtraction), I can able to access these function in sample.jl file, but you can’t access the functions mul, div.

Update sample.jl like below and re run the program.

sample.jl

include("operations.jl")

using Arithmetic

res1 = addition(10, 20)
res2 = subtraction(10, 20)
res3 = mul(10, 20)

println("Sum of 10, 20 is $res1")
println("Subtraction of 10, 20 is $res2")
println("Multiplication of 10, 20 is $res3")

Output

$ julia sample.jl 
ERROR: LoadError: UndefVarError: mul not defined
 in include at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
 in include_from_node1 at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
 in process_options at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
 in _start at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
while loading /Users/harikrishna_gurram/study1/Julia/examples/sample.jl, in expression starting on line 7

Since functions mul, div are private to the module Arithmetic, you can’t access the functions outside.

Note

1. The type of a module is Module

julia> typeof(Module1)
Module

julia> typeof(Module2)
Module

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