## 3.3 Obtaining function definitions

So, instead of passing a string which Books.jl will evaluate, Books.jl can also obtain the code for a method directly. (Thanks to CodeTracking.@code_string.) For example, inside our package, we can define the following method:

function my_data()
DataFrame(A = [1, 2], B = [3, 4], C = [5, 6], D = [7, 8])
end

To show code and output (sco) for this method, use the @sco macro. This macro is exported by Books, so ensure that you have using Books in your package.

jl
@sco M.my_data()


This gives

function my_data()
DataFrame(A = [1, 2], B = [3, 4], C = [5, 6], D = [7, 8])
end
my_data()
Table 6: My data.
A B C D
1 3 5 7
2 4 6 8

To only show the source code, use @sc:

jl
@sc M.my_data()


resulting in

function my_data()
DataFrame(A = [1, 2], B = [3, 4], C = [5, 6], D = [7, 8])
end

To override options for your output, use the pre keyword argument of @sco:

jl
let
caption = "This caption is set via the pre keyword."
pre(out) = Options(out; caption)
@sco pre=pre my_data()
end


which appears to the reader as:

function my_data()
DataFrame(A = [1, 2], B = [3, 4], C = [5, 6], D = [7, 8])
end
my_data()
This caption is set via the pre keyword.
A B C D
1 3 5 7
2 4 6 8

See ?sco for more information. Since we’re using methods as code blocks, we can use the code shown in one code block in another. For example, to determine the mean of column A:

jl
@sco M.my_data_mean(my_data())


shows as

function my_data_mean(df::DataFrame)
Statistics.mean(df.A)
end
my_data_mean(my_data())

1.5

Or, we can show the output inline, namely 1.5, by using

jl M.my_data_mean(my_data())

It is also possible to show methods with parameters. For example,

jl
@sc M.hello("" )


shows

hello(name) = "Hello, \$name"

Now, we can show

M.hello("World")
Hello, World

Here, the M can be a bit confusing for readers. If this is a problem, you can export the method hello to avoid it. If you are really sure, you can export all symbols in your module with something like this.

CC BY-NC-SA 4.0 Rik Huijzer, and contributors