⚡ Writing and running code

How do I make my variables reactive?

All global variables are automatically reactive!

How do I write multiple expressions in one cell?

You can use a let ... end block or a begin ... end block to wrap multiple expressions into one. But you probably want to create multiple smaller cells instead! It makes reactivity much more useful.

I used print and display but nothing is happening! Help!

These functions will still write to the console where you started Pluto. To display things in Pluto.jl, you simply output the value you want to show.

For example, instead of

begin
    x = 25.0
    display(sqrt(x))
end

begin
    y = 0.1
    display(cos(y))
    display(sin(y))
end

you can write

begin
    x = 25.0
    sqrt(x)
end

begin
    y = 0.1
    cos(y), sin(y)
end

In Julia, the last subexpression in a block (begin, let, if, etc.) is the output value.

(If you need the plaintext result of print, take a look at PlutoUI.Print.)

How can I modify a variable in a different cell?

Variables can only be assigned and modified in a single cell. This is what makes reactivity possible:

For example, if you have four cells: "I have $(n) pets", n += 3, n *= 2 and n = 0, what is supposed to happen?

Try to write all assignments in one cell, using a begin ... end or a let ... end block, or try renaming your variables. The example above would become:

"I have $(n_today) pets"

begin
    n_today = n_yesterday
    n_today += 3
    n_today *= 2
end

n_yesterday = 0

That doesn't work for me!

Sometimes a mutable state makes the most sense for your problem.

In Pluto, assignments to values (e.g. a = 1) will 'trigger' reactivity, but assignments to properties (e.g. a.start = 2 or a[5] = 3) will not. This means that you can use a Ref (docs) to create 'non-reactive' variables.

How can I write different methods/specialisations for a function?

You need to put all definitions in one cell, using a begin ... end block.

Can I use @async to update values reactively on demand?

Unfortunately not. Pluto.jl uses static code analysis to determine which cells to run next — it does not use wrappers or a polling mechanism to watch variables in real-time. However, the @bind macro might be able to do what you want! Have a look at the Interactivity sample inside Pluto. Feel free to open a GitHub issue if this doesn't suit your needs.

How can I load startup.jl?

We want your notebooks to be reproducible, so our suggested method is that you copy and paste your personal setup script into a begin ... end block inside your notebook. This avoids implicit dependencies of your notebook. Alternatively, you could write include("path/to/startup.jl"), but this will only work on your computer.

How can I load a notebook upon launching Pluto?

You can pass the notebook keyword argument to Pluto.run, e.g. Pluto.run(notebook="/path/to/notebook.jl").

How can I use a sysimage inside Pluto?

Pluto.run() takes a keyword argument sysimage which can be used to add sysimage used by each notebook. To load the currently loaded sysimage, start pluto using:

Pluto.run(sysimage=unsafe_string(Base.JLOptions().image_file))