pandoc-unicode-math

If you prefer Markdown to Latex because of its readability, then why not improve the readability of math expressions as well? Just use the power of Unicode!

What does this filter do?

This Pandoc filter replaces Unicode math symbols and greek letters like ∀, ∈, →, λ, or Ω in math environments (i.e., between single or double dollar signs for inline or display math, respectively) by equivalent Latex commands like \forall, \in, \rightarrow, \lambda, or \Omega. That means you can write expressions like these in Markdown and still get Latex's superior math typesetting when converting to PDF:

$$α → β ≡ ¬α ∨ β ≡ ¬(α ∧ ¬β)$$

$$∀ x ∈ \{ 2, 4, … \}, ∀ y ∈ ℕ : (x ⋅ y) mod 2 = 0$$

$$ℕ ⊂ ℤ ⊂ ℝ$$

Now compare them to the same expressions written with Latex commands:

$$\alpha \rightarrow \beta \equiv \neg \alpha \lor \beta \equiv \neg (\alpha \land \neg \beta)$$

$$\forall x \in \{ 2, 4, \dots \}, \forall y \in \mathbb{N} : (x \cdot y) mod 2 = 0$$

$$\mathbb{N} \subset \mathbb{Z} \subset \mathbb{R}$$

If you prefer the Unicode variant, this filter is for you!

A complete list of symbols that are replaced by this filter can be found in the src/Symbols.hs file.

Usage

1. Get binaries here and put them in your PATH. Be careful to choose a release that matches your Pandoc version (otherwise you'll get an error like Incompatible API versions: encoded with [1,20] but attempted to decode with [1,21].). If necessary, you can build from source (see below).

2. Write a Markdown document containing Unicode characters in a math environment like the provided example file.

3. Invoke Pandoc to convert the Markdown document to PDF and apply the filter along the way:

   $ pandoc example.md --filter pandoc-unicode-math -o example.pdf
   

But my keyboard has no "α" and "∃" keys!

The pandoc-unicode-math filter will not make writing math expressions easier. It only makes reading them easier. How to input Unicode symbols depends on your editor. In Vim, digraphs and the characterize plugin are very useful for working with Unicode.

However, to help you get started with existing documents a second filter called pandoc-unicode-math-from-latex is provided that replaces "regular" Latex math commands like \forall or \alpha by equivalent Unicode symbols like ∀ or α. Yes, that means it's the inverse of the pandoc-unicode-math filter, except that pandoc-unicode-math replaces characters like Α (greek Alpha) by A (latin A) but pandoc-unicode-math-from-latex does not do the reverse since this would be ambiguous. This filter can be used like this:

$ pandoc latex-math.md --filter pandoc-unicode-math-from-latex -o unicode-math.md

Limitations

For more complex math containing fractions like \frac{2}{3+5} or lots of subscripts and superscripts like k_{n+1}^2 you still need raw Latex because these things cannot be expressed by single Unicode characters. However, Unicode symbols and Latex commands can be used together in the same expression:

∃ x ∈ ℕ : \frac{x}{2} = 21

Alternatives

Instead of writing Unicode symbols in your source file and applying this filter, you can write regular Latex math commands and use an editor that displays them in a more readable way. For example, using Vim and the Markdown plugin, these settings have the desired effect:

let g:vim_markdown_math=1
set conceallevel=2

Building from source

These filters are written in Haskell, so you need GHC (compiler) and Cabal (build tool), best installed with ghcup. Clone the Git repository, change to its top level directory and run the following command:

$ cabal install --constraint 'pandoc-types ^>= 1.23'

On Linux, this will build and install two filters, pandoc-unicode-math and pandoc-unicode-math-from-latex to ~/.cabal/bin/ and on Windows, well, I don't know but surely somewhere sensible.

In the above command you have to choose a version of the pandoc-types library that matches your Pandoc release. (If you run cabal build in a separate step the --constraint option should be included there as well.) For reference, here is a compatibility list:

pandoc-types	pandoc	GHC
1.23	≥ 3.0	8.8.4, 8.10.7, 9.4.2
1.22	2.11-2.19	8.8.4, 8.10.7, 9.4.2
1.21	2.10	8.8.4, 8.10.7
1.20	2.8-2.9	8.8.4, 8.10.7

The GHC column records compiler versions I successfully built with. Other versions may or may not work.

Contributing

Pull Requests are welcome. It's easy to add new symbols to the src/Symbols.hs file.