Custom pretty printing post-processing

General Usage
1

I want to modify a custom pretty printing function for a type defined by another package. However, I don’t want to override their printing function, I just want to post-process the string before it is printed.

In particular, I want to take their latex output, modify it somehow, then print it as a latex string again (in say IJulia).

Here’s what I’ve tried so far:

function Base.show(io::IO, ::MIME"text/latex", x::MyType) 
    ltx = repr("text/latex", x)
    ltx = replace(ltx, "abc" => "def")
    print(io, ltx)
end

This however leads to a StackOverflowError, as I believe repr must call Base.show somewhere, leading to an infinite loop. I’m not sure how else to get the output before it is printed.

Any idea on how I can do this?

2

I think you want invoke, which you can use to call the old method, despite defining a new and more specialised one. Something like this:

function Base.show(io::IO, m::MIME"text/latex", x::MyType)
  io = IOBuffer()
  invoke(show, Tuple{IO, MIME"text/latex", Any}, io, m, x)  # need the exact signature here
  ltx = String(take!(io))
  ltx = replace(ltx, "abc" => "def")
3

invoke does look useful, but I don’t think it does exactly what I need here.

If I understand this function right, it is calling the show function for latex for the generic Any type. What I really need is the specific call for the type (in this case ::Vector{Equation}), then do some extra changes before displaying the result.

In other words, I want to call the original version of the specialised show function, before it was overloaded by my new function. Is it possible to do that in Julia?

4

I ended up fixing my problem in a much more straightforward way. Rather than getting the output of the previous method, I could just as easily call latexify again in my new function, like so:

using Latexify
function Base.show(io::IO, m::MIME"text/latex", x::MyType) 
    ltx = latexify(x)
    ltx = replace(ltx, "abc" => "def")
    print(io, ltx)
end

Turns out the simplest solution is sometimes the best!

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