How to decorate a function in Julia?

Question

As I'm programming a package in Julia, I've written several functions of the sort:

function scatterplot(data; x_col=:x, y_col=:y)

    data |> @vlplot(:circle, x=x_col, y=y_col)
end

Now the thing is, I'd actually like to implement kwargs in this function, something like:

function scatterplot(data; x_col=:x, y_col=:y; kwargs...)

    data |> @vlplot(:circle, x=x_col, y=y_col;kwargs...)
end

But since @vlplot is a macro, this doesn't actually work. So to I need to actually use metaprogramming as the following:

function example(data;xcol,ycol,kwargs...)
    x = kwargs
    expression = "@vlplot(data=$data,mark=:point, x=$xcol, y=$ycol,"
    for (k,v) in x
        add = string(k,"=",v,",")
        expression = expression*add
    end
    expression = expression[1:end-1]*")"
    return expression
end

The thing is, I want to avoid having to write this loop for each of mine functions if I want to use "kwargs", hence, how can one do this?

My idea was to somehow "decorate" each function such as @decorate_with_kwargs scatterplot. Is this possible?

Answer 1

Here is one possibility:

function debugger(f, params...)
    @show f, params
    res = f(params...)
    @show res
    res
end

And now testing:

julia> f(x,y) = x+y;

julia> debugger(f, 2,3)
(f, params) = (f, (2, 3))
res = 5
5

If your goal is handling kwargs in a macro here is how:

function gn(x, args...;kwargs...)
    println("I am called with x=$x args=$args kwargs=$kwargs")
end

macro fn(x, args...)
    aargs = []
    aakws = Pair{Symbol,Any}[]
    for el in args
        if Meta.isexpr(el, :(=))
            push!(aakws, Pair(el.args...))
        else
            push!(aargs, el)
        end
    end
    quote
        gn($x, $aargs...; $aakws...)
    end
end