# How to design LaTeX output?

**URL:** <https://discourse.julialang.org/t/how-to-design-latex-output/9451>\
**Category:** New to Julia\
**Created:** [March 2, 2018, 2:03pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451 "2018-03-02T14:03:10Z")\
**Posts on this page:** 20\
**Page:** 1

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 2:03pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/1 "2018-03-02T14:03:10Z")

</div>

I write this long message because I am perplexed about the output  
facilities in Julia, to the point that I have no idea how to proceed with  
my design.

I want to write facilities for outputting in TeX/LaTeX my objects. I am  
trying to port GAP code and my objects could be things like character  
tables, polynomials, matrix of polynomials, etc… The main purpose of  
LaTeX facilities would be to prepare presentations/papers from julia  
computations.

With the philosophy I know, I would design this as follows:

- a function `stringlatex` for each type, which would build the LaTeX output  
recursively — for instance a matrix of Laurent polynomials would give

- a function `latex` which would in jupyter display the LaTeX inline and in  
the Repl would call latex/xdvi or pdflatex/xpdf.

The main purpose of `latex` would be mainly to check the output from  
`stringlatex`, but it could also serve as a `display` function sometimes.

It seems in julia print functions are the primordial form for output and  
string functions are derived from them, which seems a little more  
complicated than the other way:

- from string you can derive print as `write(string(x))`

- but from `print` to derive `string` you need more complex code as you can  
see by looking at the source of `print_to_string`

_Note added later: I discovered that there is an `sprint` function which_  
_can derive a `string` function from any `print` function: why is not_  
_`string` defined as `sprint(print,...)`?_

Looking at the source, it seems that everything is derived at the bottom  
from `show` with some options — this is good: all formatting routines  
have the same recursive logic, so this way they can share code. Thus I  
explored how to pass options to `show` and I found two ways:

- build an `IOContext` with a specific option, like `LaTeX=>true`

- use a mime-type: `show(io,"application/x-latex",x)`

and here I got very confused: which I should use? What is the relationship  
between `IOContexts` and mime-types?

These questions started me on exploring further the output facilities of  
julia which left me even more confused.

From my background in the 15 programming languages I learned along the  
years (I am 67) I see 3 basic forms of `print/string` functions which are  
necessary in a language (of course there are other ones like  
“export-to-latex” which is my current interest, but you may want also  
“export-to-html” or “export-to-xxx” where xxx is anything you may think of:  
R, Mathlab, Maple, Mathematica, etc…)

1- default output at the repl. This could have a ‘compact’ mode and a  
‘verbose’ mode.

2- A way to print a representation which can be read back — in the  
context of julia this means deriving from an object x a string s such  
that `eval(parse(s))=x`

3- A ‘display’ function which would show an object in the most enlightening  
way possible. For example, for a character table it would be a big  
square matrix with labels on the rows and columns (perhaps several rows  
of labels on the columns for the class names, class sizes, powermap,  
etc…).

An for each of these modes there would be a string function and a print  
function.

There is a ‘display’ function in julia, which seems to fit my requirement  
3, but I could not find anything which fits items 1 or 2.

I think a facility for 2 is needed in the context of metaprogramming (even of the  
most naive sort: preparing text files containing data which can be read in  
julia – I found that this is not as trivial as it seems: matrices  
outputted by GAP as vectors of vectors can sometimes not be read in julia  
depending on what is the last token before a line break).

- I could not discover which function does the printing at the repl.

- The correspondence between string and print functions does not seem to  
fit any coherent naming scheme: I could discover that ‘string’ is the  
string function for ‘print’ and ‘repr’ the string function for showall, but  
I could not find what are the string functions for ‘show’ or ‘showcompact’.

- Also I was suprised that there is a ‘summary’ function which is a string  
function and not a print function contrary to the apparent philosophy of  
the other ones.

Excuse me for this long rant and if I do not use the proper terminology,  
but the point is that I am here to learn.

---

<div class="post-metadata">

**Author:** ![saschatimme](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/saschatimme/32/10313_2.png) [@saschatimme](https://discourse.julialang.org/u/saschatimme)\
**Post date:** [March 2, 2018, 4:09pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/2 "2018-03-02T16:09:07Z")

</div>

I only skimmed the post, sorry if I miss something, but  
couldn’t you do something like

```julia
show(::IO, x^2-3x+4y^4*x)
4y^4*x + x^2 - 3x # parseable by Julia
show(::IO, ::MIME"text/plain", x^2-3x+4y^4*x)
4y⁴x + x² - 3x # Most readable
show(::IO, ::MIME"text/latex", x^2-3x+4y^4)
4y^4x + x^2 - 3x # parseable by LaTeX

```

and use the [stringmime](https://docs.julialang.org/en/stable/stdlib/io-network/#Base.Multimedia.stringmime) function to obtain a string version?

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [March 2, 2018, 4:14pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/3 "2018-03-02T16:14:21Z")

</div>

Take a look at Latexify.jl.

> **[GitHub - korsbo/Latexify.jl: Convert julia objects to LaTeX equations, arrays...](https://github.com/korsbo/Latexify.jl)**
>
> Convert julia objects to LaTeX equations, arrays or other environments. - GitHub - korsbo/Latexify.jl: Convert julia objects to LaTeX equations, arrays or other environments.

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 4:16pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/4 "2018-03-02T16:16:06Z")

</div>

Ah! the output of `show` is parseable by julia? This then answers my point 2. Is this documented somewhere,  
so that implementers of various types follow this guideline?

And you suggest that I should use a mime type instead of an `IOContext`. I am also confused about mime types: I saw in the source a “application/x-latex” but you use “text/latex”. What is the difference?

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 4:20pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/5 "2018-03-02T16:20:03Z")

</div>

Excuse me, but it seems to me that Latexify.jl is designed the wrong way. There is a cornucopia of functions  
and it is not using options of `show`, precluding the possibility of sharing code with other output functions.

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [March 2, 2018, 4:29pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/6 "2018-03-02T16:29:17Z")

</div>

> [@Jean\_Michel](#):
>
> Excuse me, but it seems to me that Latexify.jl is designed the wrong way. There is a cornucopia of functions
> 
> and it is not using options of show, precluding the possibility of sharing code with other output functions.

Feel free to open an issue and share your expertise / what you’ve learned to improve it. MIME types have always confused me so some guidance to make this more widely applicable would be great. I’m sure it has at least a lot of tooling that could be used for the “right” design.

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 4:42pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/7 "2018-03-02T16:42:29Z")

</div>

By the way, is `show(::IO, ::MIME"text/plain",` your invention, or does it exist?  
I get

```
 julia> show(STDOUT,MIME"text/plain",1)
 ERROR: MethodError: no method matching show(::Base.TTY, ::Type{MIME{Symbol("text/plain")}}, ::Int64)
 Closest candidates are:
   show(::IO, ::DataType) at show.jl:211
   show(::IO, ::MIME{Symbol("text/csv")}, ::Any) at datafmt.jl:707
   show(::IO, ::MIME{Symbol("text/tab-separated-values")}, ::Any) at datafmt.jl:708
   ..

```

---

<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [March 2, 2018, 4:52pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/8 "2018-03-02T16:52:47Z")

</div>

You’re passing the `MIME{Symbol("text/plain")}` _type_, but the relevant methods are defined for the _instances_ of that (singleton) type. This isn’t something users will typically do by hand, but you can get the right behavior by actually instantiating that type:

```julia
julia> show(STDOUT, MIME"text/plain"(), 1)
1

```

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 5:08pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/9 "2018-03-02T17:08:50Z")

</div>

Thanks to you, I discovered (perhaps?) the function which does output to the Repl, which answers my  
point 1: it seems to be  
`show(STDOUT, MIME"text/plain"(), 1)`

thus I could construct the corresponding string function as

`sprint((x,y)->show(x,MIME"text/plain"(),y),obj)`

So for users to design a nice Repl display of their own type, one should add methods to this function. Is this documented somewhere? And you say it isn’t something to be done by hand: is there a shorter equivalent?

---

<div class="post-metadata">

**Author:** ![tkoolen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkoolen/32/1603_2.png) [@tkoolen](https://discourse.julialang.org/u/tkoolen)\
**Post date:** [March 2, 2018, 5:21pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/10 "2018-03-02T17:21:43Z")

</div>

Yep, relevant docs are:

- [https://docs.julialang.org/en/stable/manual/types/#Custom-pretty-printing-1](https://docs.julialang.org/en/stable/manual/types/#Custom-pretty-printing-1)
- [https://docs.julialang.org/en/stable/stdlib/io-network/#Multimedia-I/O-1](https://docs.julialang.org/en/stable/stdlib/io-network/#Multimedia-I/O-1)
- [https://docs.julialang.org/en/stable/stdlib/io-network/#Base.show-Tuple{Any,Any,Any}](https://docs.julialang.org/en/stable/stdlib/io-network/#Base.show-Tuple%7BAny,Any,Any%7D)

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 5:27pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/11 "2018-03-02T17:27:19Z")

</div>

I read that but could not find (missed?) the two crucial statements that  
`show(STDOUT, MIME"text/plain"(), x)` is what is used at the Repl,  
and that the output of `show(x)` is julia-parseable.

---

<div class="post-metadata">

**Author:** ![tkoolen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkoolen/32/1603_2.png) [@tkoolen](https://discourse.julialang.org/u/tkoolen)\
**Post date:** [March 2, 2018, 6:11pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/12 "2018-03-02T18:11:22Z")

</div>

From the first link:

> Technically, the REPL calls `display(z)` to display the result of executing a line, which defaults to `show(STDOUT, MIME("text/plain"), z)`, which in turn defaults to `show(STDOUT, z)`

I don’t think the julia-parseable part is true in general (although generally an effort is made to make that be the case).

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 2, 2018, 7:06pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/13 "2018-03-02T19:06:33Z")

</div>

Do I understand correctly that “default to” in the above sentence means:

- If there is a method for `display(z)`, use it
- Otherwise if there is a method for `show(STDOUT, MIME("text/plain"), z)`, use it
- Otherwise use `show(STDOUT,z)`

---

<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [March 2, 2018, 10:32pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/14 "2018-03-02T22:32:51Z")

</div>

> [@Jean\_Michel](#):
>
> Do I understand correctly that “default to” in the above sentence means:

No. “Default to” is referring to what the fallback method does. For example, there is a fallback `show(io::IO, ::MIME"text/plain", x) = show(io, x)` method, which is why if you just define `show(io, x)` it will be called by `show(io, "text/plain", x)` unless you define a more specialized three-argument method.

Anyway, as explained in the docs, just overload `show` as needed.

---

<div class="post-metadata">

**Author:** ![chakravala](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chakravala/32/6832_2.png) [@chakravala](https://discourse.julialang.org/u/chakravala)\
**Post date:** [March 3, 2018, 11:36am UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/15 "2018-03-03T11:36:40Z")

</div>

I’m working on a new [package](https://github.com/chakravala/JuliaTeX.jl) that outputs LaTeX by compiling usng `latexmk` and display with `zathura` PDF viewer. It works well for people in the terminal with tiling window manager.

---

<div class="post-metadata">

**Author:** ![korsbo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/korsbo/32/15942_2.png) [@korsbo](https://discourse.julialang.org/u/korsbo)\
**Post date:** [March 6, 2018, 10:45am UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/16 "2018-03-06T10:45:37Z")

</div>

Latexify.jl does not implement the output formatting itself. That is taken care of by using the LatexString type from [LatexStrings.jl](https://github.com/stevengj/LaTeXStrings.jl) (and in the latest version it uses some Base.Markdown.MD). These types both have overloads to Base.show with nice defaults for rendering/printing.

I find that to work pretty well, although it becomes somewhat problematic that Juno does not support MIME"text/latex".

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 6, 2018, 10:54am UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/17 "2018-03-06T10:54:06Z")

</div>

Thank you for explaining that and pointing to `LatexStrings` which is what I should have looked at for my design. And sorry for criticizing `Latexify’ – though I still think there are too many functions…

---

<div class="post-metadata">

**Author:** ![korsbo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/korsbo/32/15942_2.png) [@korsbo](https://discourse.julialang.org/u/korsbo)\
**Post date:** [March 6, 2018, 1:14pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/18 "2018-03-06T13:14:45Z")

</div>

No problems. Do you mean that Latexify.jl has too many functions internally, or too many presented to the user? Do you have ideas for improvements?

---

<div class="post-metadata">

**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [March 6, 2018, 3:01pm UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/19 "2018-03-06T15:01:58Z")

</div>

I mean too many presented to the user. Some functionalities should be options, and the advantage of options is that you can pass them recursively to subroutines which gives great flexibility and allows to reuse more code. But to be honest I have not looked at your code in any detail so do not take my opinion too seriously.

---

<div class="post-metadata">

**Author:** ![korsbo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/korsbo/32/15942_2.png) [@korsbo](https://discourse.julialang.org/u/korsbo)\
**Post date:** [March 7, 2018, 10:30am UTC](https://discourse.julialang.org/t/how-to-design-latex-output/9451/20 "2018-03-07T10:30:04Z")

</div>

I have taken your critisism under advisment and opened an [issue](https://github.com/korsbo/Latexify.jl/issues/13) to gather opinions/advise before I move forward. Please feed free to weigh in (you and anyone who reads this).

[Next page](https://discourse.julialang.org/t/how-to-design-latex-output/9451.md?page=2)