Workflow Tips

Here are some tips for working with Julia efficiently.

REPL-based workflow

As already elaborated in The Julia REPL, Julia's REPL provides rich functionality that facilitates an efficient interactive workflow. Here are some tips that might further enhance your experience at the command line.

A basic editor/REPL workflow

The most basic Julia workflows involve using a text editor in conjunction with the julia command line.

Create a file, say Tmp.jl, and include within it

module Tmp

say_hello() = println("Hello!")

# Your other definitions here

end # module

using .Tmp

Then, in the same directory, start the Julia REPL (using the julia command). Run the new file as follows:

julia> include("Tmp.jl")

julia> Tmp.say_hello()
Hello!

Explore ideas in the REPL. Save good ideas in Tmp.jl. To reload the file after it has been changed, just include it again.

The key in the above is that your code is encapsulated in a module. That allows you to edit struct definitions and remove methods, without restarting Julia.

(Explanation: structs cannot be edited after definition, nor can methods be deleted. But you can overwrite the definition of a module, which is what we do when we re-include("Tmp.jl")).

In addition, the encapsulation of code in a module protects it from being influenced by previous state in the REPL, protecting you from hard-to-detect errors.

Browser-based workflow

There are a few ways to interact with Julia in a browser:

Using Pluto notebooks through Pluto.jl
Using Jupyter notebooks through IJulia.jl

Revise-based workflows

Whether you're at the REPL or in IJulia, you can typically improve your development experience with Revise. It is common to configure Revise to start whenever julia is started, as per the instructions in the Revise documentation. Once configured, Revise will track changes to files in any loaded modules, and to any files loaded in to the REPL with includet (but not with plain include); you can then edit the files and the changes take effect without restarting your julia session. A standard workflow is similar to the REPL-based workflow above, with the following modifications:

Put your code in a module somewhere on your load path. There are several options for achieving this, of which two recommended choices are:
- For long-term projects, use PkgTemplates:
```
using PkgTemplates
t = Template()
t("MyPkg")
```
  This will create a blank package, "MyPkg", in your .julia/dev directory. Note that PkgTemplates allows you to control many different options through its Template constructor.
  In step 2 below, edit MyPkg/src/MyPkg.jl to change the source code, and MyPkg/test/runtests.jl for the tests.
- For "throw-away" projects, you can avoid any need for cleanup by doing your work in your temporary directory (e.g., /tmp).
  Navigate to your temporary directory and launch Julia, then do the following:
```
pkg> generate MyPkg            # type ] to enter pkg mode
julia> push!(LOAD_PATH, pwd())   # hit backspace to exit pkg mode
```
  If you restart your Julia session you'll have to re-issue that command modifying LOAD_PATH.
  In step 2 below, edit MyPkg/src/MyPkg.jl to change the source code, and create any test file of your choosing.
Develop your package
Before loading any code, make sure you're running Revise: say using Revise or follow its documentation on configuring it to run automatically.
Then navigate to the directory containing your test file (here assumed to be "runtests.jl") and do the following:
```
julia> using MyPkg

julia> include("runtests.jl")
```
You can iteratively modify the code in MyPkg in your editor and re-run the tests with include("runtests.jl"). You generally should not need to restart your Julia session to see the changes take effect (subject to a few limitations).