# pulldown-latex

A pull parser for $\LaTeX$ parsing and `mathml` rendering.

This project is inspired `Katex`, `Temml`, `MathJax`, etc. It is in its very early
stages of development, and works for a small subset of what `Katex` and the likes support.
It is _not_ production ready and is mostly untested.

## Goals

__Follow modern LaTeX principles:__
Ideally, this library should be mostly compatible with `latex2e` and `amsmath`. The term
_mostly_ is used here to refer to the mathematical commands exposed by these packages; typesetting prose
is out of scope for this crate. Another consequence of this goal is that some plain-TeX commands that
are deprecated (e.g., `\atop`, `\over`, etc.) are not supported by this crate.

__Closely resembling conventional LaTeX:__
It is a goal for this crate to make efforts in generating aesthetic equations. This means that
the `mathml` output may be tweaked to make it resemble what `pdflatex`, `Katex` or `MathJax` outputs.

## Miscellaneous References & Tools
Sources used during the development of this crate. Any reference in code comments refer to
these links specifically.

- [TeXBook](https://visualmatheditor.equatheque.net/doc/texbook.pdf)
- [latex2e unofficial Reference](https://tug.org/texinfohtml/latex2e.html)
- [amsmath docs](https://www.latex-project.org/help/documentation/amsldoc.pdf)
- [Comprehensive symbol list](https://mirror.its.dal.ca/ctan/info/symbols/comprehensive/symbols-letter.pdf)
- [Unicode-math symbol list](https://mirror.its.dal.ca/ctan/macros/unicodetex/latex/unicode-math/unimath-symbols.pdf)
- [Unicode-math package page](https://ctan.org/pkg/unicode-math)
- [Font tester](https://fred-wang.github.io/MathFonts/)
- [Math Variant Selection](https://milde.users.sourceforge.net/LUCR/Math/math-font-selection.xhtml#math-styles)

## TODOs
1. State Changes
    - [X] Styles (text, script, etc.)
    - [X] Colors
2. Quirky commands
    - [X] Moving suffixes: `\limits`, `\nolimits`.
    - [X] `\relax`
    - [X] `\char`
3. More complete renderer
4. Rigorous trim start of strings
5. Math environments
6. Even more quirky stuff
    - [ ] `\sideset` command (using `mmultiscripts`?)
    - [ ] things at the bottom of primitive file in comments

### To Test
- [ ] All the things temml and katex test
- [ ] Cargo Mutants
- [ ] Errors

## Unsupported Plain-TeX & LaTeX behavior

- Changing `catcode`s of characters
- `\if`* macros
- `^^_` & `^^[0-9a-f][0-9a-f]` as a way of specifying characters
- __Redefining active characters__
    This library currently only supports default active characters, and hence does not allow for the 
    definition of active characters.
- Implicit characters as whitespace tokens
    As in the TeXbook p. 265, Knuth specifies that a `space token` stands for an _explicit_ or _implicit_
    space. This library does not currently support _implicit_ space tokens when a `space token` is required.
- Use of internal values and parameters, such as registers, and things like `\tolerance`
    (See TeXbook p. 267 for a complete definition)
- `\magnification` parameter & `true` sizes
- Case insensitive keywords matching. 
    According to TeXbook p. 265, keywords such as `pt`, `em`, `true`, etc. are matched case insensitively (e.g.,
    `pT` would match `pt`). This library does not support this behavior, as keywords must match exactly (i.e., 
    `em`, `true`, `pt`, etc.).
- `fil` units
    TeX allows the use of `fil`(ll...) units, this library does not.
- `\outer` specifier on definitions
- `\csname` & `\endcsname`
- `\begingroup` and `{`, and `\endgroup` and `}` behave the same way; that is to say, 
    `\begingroup` and `\endgroup` do not have the property of "keeping the same mode" (TeXbook p. 275).
- All vertical list manipulation commands.
    Things like `\vskip`, `\vfil`, `\moveleft` etc.
- `\hfil`, `\hfill`
- `\eqno`, `\leqno`, and equation numbers in general.
- `\over`, `\atop`, and all deprecated "fraction like" control sequences.


### Things that should work but don't currently
Splitting groupings within user defined macros. E.g.,
```
\def\abc{\left(}
\abc 4 \right)
```
This currently does not work.


### Unsupported Katex/Temml Options

- Macros preamble
- Wrap
- Left equation numbers
- `colorIsTextColor`
- `ThrowOnError`
- `maxSize`
- `trust`
- `\toggle` groups