keys from expressions in pgf macro

[tpapp]

When constructing options it would occasionally be useful to define not only values, but also keys with expressions. Currently the only way to do this that I am aware of is

let o = @pgf{}
    push!(o, v => nothing)
    o
end

A possible syntax could be $ interpolation, as in

line_styles = [:solid, :dashed, :dotted]
[@pgf({ $l }) for l in line_styles] # hypothetical feature and syntax