Why finl? A manifestoSticky

In 1994, LaTeX2e was released as a transitional step towards LaTeX 3. 26 years later, there still isn’t a 1.0 release of LaTeX 3. In the interim, we’ve seen the rise of HTML and the web, the dominance of PDF as a format for representation of printed material (and now there is a plan to have PDF extended with “liquid mode” that allows reflowing of PDF text for smaller screens).

In the meantime, the TeX engine has been extended multiple times, the little-used TeX-XeT, some early efforts to support large Asian character sets, and we have in widish use pdfTeX, XeTeX, LuaTeX along with an assortment of abandoned engines. Worst of all, it seems that none of pdfTeX, XeTeX or LuaTeX can serve as the one TeX to rule them all, each with some limitations that can require users to switch engines depending on their needs.

As I’ve thought about it, the problem at its root is TeX itself. It’s what would be referred to in contemporary software engineering parlance, as a tightly-coupled monolith. Worse still, it’s a tightly-coupled monolith with numerous compromises baked in because of the limitations of 1970s computing hardware. It seems that the vast majority of what work has been done with LaTeX 3 has been geared towards dealing with the limitations of TeX as a programming language.

On top of that, there’s been an explosion of questionable, if not outright harmful practices from the greater LaTeX community. Ideally, a document should be translated from one document class to another structurally similar class (naming-wise, the choice of “class” to name document classes is unfortunate, but understandable) should not require changing anything after the preamble, better still, nothing but the \documentclass command itself. All the appearance should be handled through the document class and packages should be employed to provide document structure enhancements or new capabilities). There are numerous violations of this. The memoir class is a mess, claiming to be a replacement for article, report and book (this reminds me of the mess that’s PHP where the same data structure acts as an array and an associative array and as a consequence manages to merge the worst aspects of both in one inefficient construct) and at the same time, providing a number of bits of functionality that belong in packages rather than the document class. On the flipside, packages like geometry and fancyhdr fall into a category that LaTeX2e doesn’t really define, bits of common code that would be helpful to document class writers but shouldn’t really be exposed to document authors.

So what can be done? I believe a complete rethink of LaTeX is necessary. The macro-based language of LaTeX is intellectually satisfying in many of the same ways that solving a sudoku puzzle or playing chess can be. It is not, however, a straightforward programming model and does not conform to any popular paradigm (I don’t think any other programming language is of similar structure). It’s time to separate out the language for formatting the document from the language for writing the document, to make a clear break between extensions that modify appearance from extensions that provide new functionality.

While we’re at it, a number of other TeX limitations need to be done away with. TeX was written with the needs of typesetting The Art of Computer Programming and so doesn’t handle complicated page layouts well and for all its valiant efforts, this has impacted LaTeX. Multi-column layouts are painful, float handling is a mess, some things that designers expect to be able to do, like specifying baseline-to-baseline skips or forcing text onto grid lines are difficult if not impossible.

Unicode needs to be a first-class citizen. There’s no reason in 2020 for a document writer to have to type \’a instead of á in a document. UTF-8 is the new 7-bit ASCII.

The code of the engine should be decoupled. Why shouldn’t any application that is willing to interface with the code be able to directly access the parser or the paragraph layout engine or the math layout engine? Imagine if a user of Word could access a plugin that let her type \sum_{i=0}^{\infty} \frac{1}{2^{i}} or even ∑_{i=0}^{∞} \frac{1}{2^{i}} or selecting these symbols via GUI into a low-level token stream to get

sum from 0 to infinity of 1/2^i

in her document. Imagine if a document could be painlessly transformed into HTML or even (unicode) plain text because the page layout and formatting engines are decoupled enough to manage such things.

A current status on finl

This site got submitted to Hacker News (a lot sooner than I would have chosen), so a few notes on where things are and where they’re going.

I’m definitely writing in Rust. Much like I expect finl to remove pain points around LaTeX, Rust removes a lot of pain points around code that I would have otherwise written in C++. I’m currently focused on finishing up gftopdf, a replacement for gftodvi, as a tool to explore Rust, PDF creation and begin implementation of some sub-libraries of finl.

My roadmap for the immediate future:

  1. gftopdf (along with finl-charsub)
  2. finl-parse (be able to parse a finl document into an internal token list)
  3. finl-math (math typesetting initial version)
  4. finl-html (output a document to HTML)

finl is not LaTeX not in the same way that GNU is not Unix. The latter is, with a few idiosyncrasies, a drop-in replacement for Unix tools. finl is not attempting to replicate TeX and LaTeX but to reimagine and replace it. It’s more like Java vs C++. The document markup language is going to be almost identical to LaTeX (although the tabular environment might well be very different). But there will not be a TeX-style macro language. There will be non-Turing complete macros available to document authors, but any more sophisticated handling will be done through extensions written in Python.

Document structure and style will be separate concepts. Style will be declarative. I’m leaning towards YAML for this, but I’ve not made any firm commitments in my mind on this.

Extension loading will be designed to work with artifact repositories and will have three-part naming similar to dependencies in mvn/groovy. 

A document preamble might look like the following (everything is subject to change):

\DocumentType{article}
\DocumentStyle{IEEE:transactions:1.0.0}

\LoadExtension{ams:commutative-diagrams:1.2.3}[\cd -> \CD, *]

\RenewDocumentCommand{\le}{\leqslant}

This shows specifying the document style, loading an extension (with a command name mapped to a different name for the document) and a user-level macro to have \le typeset ⩽ instead of ≤ . Where a namespace is not specified (like in the \DocumentType command), the default namespace of finl will be assumed. Likewise, a missing version will be assumed to be the special version of LATEST. I’m thinking that the first time a document is processed, a file foo.lock will be created which will have the versions applied for any unspecified (or range-based) versions. Extensions are allowed to have their own dependencies. I think (but I can’t commit to it), that it should be possible to have extensionA require version 2 of extensionC and extensionB require version 3 of extensionC without conflict.

Oh, one more thing: Right now, some formatting on the blog is off—in particular, you cannot click on an article title to get to the permalink for the article, and comments can only be accessed from the article’s page which is not readily accessible. I welcome comments at my email of don.hosek@gmail.com

First impressions on Rust

I really like the expressiveness of the language. I’m writing code to read GF files from Metafont right now and there’s the Knuthian 1–4 byte parameter reading. This ends up being rather elegant in Rust, particularly the 3-byte version:

pub fn read3<R: Read>(input: &mut R) -> io::Result<i32> {
let mut buf = [0u8; 4];
input.read(&mut buf[1..4])?;
Ok(i32::from_be_bytes(buf))
}

This initializes a 4-byte buffer with zeros, fills the last three bytes of that buffer with the next three bytes of the input file and then translates the 4-byte buffer into an integer with big-endian semantics. When I figured out how to do this, I got happy endorphins rushing through my brain. It’s just cleaner than the C++ equivalent 

std::int_fast32_t read3() {
stream->read(buffer, 3);
return static_cast<uint8_t>(buffer[0]) << 16
| static_cast<uint8_t>(buffer[1]) << 8
| static_cast<uint8_t>(buffer[2]);
}

where I had to assemble the data manually (I didn’t need to declare or initialize the buffer here since in my implementation it was a field in the enclosing class). 

I’m reading three Rust books simultaneously as I learn. My thoughts on the books: The Rust Programming Language by  Steve Klabnik and Carol Nichols is superb. I like reading paper and I got it from the library, but it’s also freely available online (and updated).

Beginning Rust: From Novice to Professional by Carlo Milanesi seems a bit of a hot mess. It introduces things earlier than necessary, especially given its avowed audience. I could have predicted that though, from the publisher. I have yet to see a good book from Apress.

I’ve only just started Programming Rust: Fast, Safe Systems Development by Jim Blandy and Jason Overdorff so I have no opinion on that one yet. 

I’m a bit disappointed with the Rust plugin for CLion. I’ve gotten spoiled by Jetbrains’s support for Java and C++ in their IDEs where the IDE provide a lot of input-time checking and suggesting for me. It made getting back into C++ a lot easier. With Rust, numerous errors don’t actually show up until a proper compilation is run, and the suggestions for resolving issues aren’t always present or useful, particularly around borrowing. IDEs have made me fat and lazy and now I have to work. I don’t like that.

I’ve had questions along the way and it seems like the two online support communities I’ve found aren’t all that great. Neither reddit nor Stack Overflow have seemed adequate. In many instances, the suggestions are completely wrong, but the language and documentation are such that I’ve managed to find my way despite this.

Stupid Mac tricks

I recently switched from Dropbox to sync for my synchronized cloud folder needs. Along the way, I moved all the files that were in ~/Dropbox to ~/Sync  I had a terminal window open with a shell cd’d to ~/DropBox/PreppyLion for the book I’m working on. I expected to get an error about that directory being in use and I couldn’t move the directory along with the other files. No error. Then I look in the terminal window and type in pwd  It showed ~/Sync/PreppyLion  It’s little things like this that always make me happy with modern computing platforms. I don’t know if this would work on Linux or Windows, but I’m happy it does on MacOS.

Page references

I’ve been thinking about page references lately and how they translate to non-print presentations. At the moment, I’m reading The Rust Programming Language by Steve Klabnik and Carol Nichols and I noticed that there was a page reference when they wrote:

We’ll discuss this concept in detail in “Variables and Mutability” on page 32.

This, in itself is not notable, but what is, is that there is a freely available version of the book on the web. A chance to see how this got translated in practice. There, the sentence is 

We’ll be discussing this concept in detail in the “Variables and Mutability” section in Chapter 3.

(hyperlink preserved in my copy of the sentence). Two things: This is clearly a manual rewrite of the sentence (with some change to the tense of the verb from simple future to future progressive) and they avoid the page reference entirely. 

A bit disappointing, but I am curious about what to do with things like the equivalent of a LaTeX \pageref if the document is translated for a web or ebook presentation. I had hoped to get something usable as a model from this wasn’t it. Ideally I’d like to be able to automatically translate something like page~\pageref{foo} into either “page 32” for a print/PDF presentation or some alternate text for the HTML/ebook presentation, but I have no idea what that alternate text should be.

Looking at rust is already beneficial

In addition to programming, I’m also a minor writer of fiction. One thing that I often do while working on a novel is write a short story to develop some aspect of craft. For example, part of the motivation for writing my story, Saint Jude’s Medallion was to work out how to tell a story through a conversation between two characters so that I could employ what I learned in the novel that I was writing at the time (which served as my MFA thesis but has since been trunked). In an analogous mode, finl functions to me as a novel and along the way, I’ll end up writing some “short story” programs to try things out and learn how to solve problems in a way that will be useful for writing finl.

The first of these “short story” programs is a mostly useless program, gftopdf, which will serve as a drop-in replacement for Knuth’s gftodvi. I have little need for this myself. It’s been decades since I wrote Metafont code seriously. But as Knuth mentions in gftodvi.web, gftodvi is a mini-TeX, and similarly, I could see using gftopdf as a mini-finl.

My gf reading code was my chance to finally implement some ideas I had played with around 1995 using function pointers as a means for simplifying the reading of a Knuthian byte file (I was thinking in terms of dvi back then, but gf is similar in spirit if not detail). I ended up creating a complicated structure using functors to implement each of the thirteen possible commands implemented over 240+ opcodes along with the four possible argument readers (1–4 bytes of signed/unsigned data). Then, while writing a post to ask about how to idiomatically implement this in rust, I realized that all the functor infrastructure was completely unnecessary. I could instead just directly implement the functors as method calls since I was building an array of lambdas anyway¹. The rust version of the code is going to be far simpler than the C++ version and only part of that (if any of it) will be due to rust. As an added bonus, I had puzzled over how the original code would be extensible for use by other programs and using virtual functions in place of functors means that my gf reading class would be able to be subclassed to enable variations on the existing functionality in the unlikely event that anyone ever cared to reuse the code.

¹ The original idea was that it was going to be an array of Opcode functor/Argument functor pairs that would be composed during the file reading loop. A combination of scoping rules and C++ syntax made that less appealing once I wrote that loop and I ended up abandoning that original plan and going with an array of lambdas instead.

Choosing a programming language revisited

A comment from someone on Hacker News who happened to stumble across this site, inspired me to give another look at rust as a programming language. Having spent a few months digging into C++, my initial thoughts are that as pros:

  • ICU for Unicode support
  • harfbuzz for text rendering
  • within the limits of compiler support for bleeding edge features, code should be widely portable by sticking to standard C++

and cons

  • library support is painful. I’ve been spoiled writing for the JVM over the last 13 years. I can easily add a library to a Java project by just adding a dependency to my pom.xml and I’m done. Since there is no real standard for C++ object/library files, adding a library often means downloading and compiling from source. It’s not uncommon to deal with dependencies by creating a git submodule and if you’re lucky, it will have a CMake configuration that allows it to be used as a subproject.
  • Lack of a standard project structure means that there’s a lot of mental labor involved in just figuring out where to put files.
  • PDF creation seems to have only a couple of options, but they seem to not be actively maintained. libharu has a post on its homepage asking for a volunteer maintainer to take over and the mailing list has at least one volunteer who has offered only to receive silence. And libharu’s CMake configuration is a bit broken so it requires (a) some unmerged changes to build as a subproject and (2) some non-standard declarations in the master project to integrate it.
  • C++20 is still not quite all here yet. I had hoped to use some features including modules and ranges in my coding, but it appears that these are not yet supported by clang. I have an irrational resistance to gcc and a rational resistance to msvc but both of those compilers don’t fully support C++20 either. Again, Java world has spoiled me. It’s only inertia that keeps me from setting my compile level higher than Java 11 on stuff I’m working on right now.

So what about rust? Some digging reveals that people have used it as a development language for iOS. It’s still in its infancy, but it should be much better by the time I need to care. Since it’s really a single development system rather than an undefined galaxy of compilers implementing a common standard like with C++, they’re able to wrap up library dependencies using the crate mechanism. ICU and harfbuzz both have rust crates and there’s an actively maintained PDF creation crate.

And as an added bonus, I can use the rust plugin for IntelliJ (or CLion, although I may drop my use of that if rust works out).

The big negative is that rust is a completely new language to me, but then again, C++ has changed enough since I was actively using it in the 90s that so is C++.

The things we forget

Looking at a post on tex.stackexchange.com I found myself digging into man pages to find out about some (comparatively) new options on the modern TeX engines and not remembering what virTeX was (it’s TeX with no format preloaded). Along the way of refreshing my memory, I stumbled upon this post from thirty years ago (almost exactly, in fact), which reveals that (a) once upon a time, this was part of my basic knowledge and (2) my recollections that during my maintenance on the VAX/VMS port of TeX I did, in fact, create the first TeX executable with iniTeX built in to the same executable as TeX and accessed via a command-line switch. 

Character substitutions in text

TeX handles some character sequence substitutions by (ab)using the ligature mechanism, e.g., ``→“. This works reasonably well for Computer Modern which defines these in its ligature table, but falls apart once we start trying to use non-TeX fonts. Furthermore, there’s the added complication that most fonts put the characters ' and ` in character positions 39 and 126 while TeX is expecting those characters to typeset ’ and ‘.

 

I’m thinking that a solution to this would be to have a character sequence substitution that’s run-time configurable as part of the text-input pipeline. This would happen after commands have been interpreted but before the text stream is processed for ligatures and line breaks. The standard route would be to import a tab-delimited table of input and output sequences of Unicode characters. The standard TeX input would look like:

 

`
``
'
''
--
---
!` ¡
?` ¿
~ \u00a0

 

Note that we no longer have an active character concept to allow using ~ for non-breaking spaces. Also, the timing of when the substitutions take place mean that we cannot use this mechanism to insert commands into the input stream. doing a mapping like TeX\TeX will not typeset the TeX logo but will typeset the sequence \TeX instead including the backslash (Actually, given the use of \ to open a Unicode hex sequence it might produce something like a tab followed by eX depending on what other escape sequences are employed.

 

Other TeX conventions, like the AMS Cyrillic transliteration where ligatures are used to map sequences like yu→ю can easily be managed. Similarly Silvio Levy’s ASCII input scheme for polytonic Greek can also be easily managed. These would allow for easy input of non-Latin alphabets for users who primarily write in Latin alphabets and work on operating systems where switching keyboard layouts to allow input of non-Latin scrips are difficult.

Mistakes of LaTeX: the tabular environment

One constant annoyance that I’ve encountered when people learn LaTeX is the default behavior of the tabular environment. Rather than presenting itself as a separate paragraph block, it is instead automatically in TeX’s horizontal mode. This means that if, for example, a user writes:

some text

\begin{tabular}{...}
...
\end{tabular}

more text

the tabular will be presented left-ish aligned (actually, indented by \parindent). This is never what the user intended. Worse still is the result if the blank line before or after the tabular is omitted. My solution to this was to encourage users to create an aroundtbl environment which usually was just a \begin{center}\end{center} but the correct solution would have been to not require this in the first case. Instances where a user wants a tabular to be in horizontal mode are rare and if they really were important, wrapping the tabular in a minipage would be a better solution (or having a variant of the tabular environment).

It’s long past time for this to be able to be fixed in LaTeX proper, but it makes sense to do it with the tabular replacement in finl.

Defining a document markup language for finl

The markup language for finl will be based on LaTeX, but many of the pain points of LaTeX come from the macro-expansion approach that Knuth’s TeX takes towards parsing the document. I can remember being a teenager reading The TeXbook and puzzling over the whole mouth-gullet-stomach description and finding that challenging to follow. 

LaTeX attempts to impose a sense of order on some of the randomness of TeX’s syntax (albeit with the price of occasional verbosity and losing some of the natural language sense of plain TeX, cf., the difference between typing {a \over b} vs \frac{a}{b}). Still, LaTeX’s basic markup language is a good starting point. This gives us commands and environments as the basic markup for a document. There’s something to be said for different modes of parsing as well. Parsing rules for math would differ from parsing rules for text, and there should be an option to be able to take a chunk of input completely unparsed, e.g., for \verb or the verbatim environment. Changing the timing of how things are parsed would enable us to do things like \footnote{This footnote has \verb+some_verbatim+ text}.

Commands

We retain the basic definition of how commands are parsed. A command begins with \ and is followed by a single non-letter or a string of letters until we come to a non-letter. Letters are defined as those Unicode characters that are marked as alphabetic, which means that not only is \bird a valid command, but so is \pták and also \طائر and \鳥

Commands can take any number of arguments. Arguments can be of the following forms:

  • Required argument. This will be either a single token (a unicode character, a command with its arguments or an environment) or a delimited token list (usually enclosed in braces but see below). 
    Note that this varies from existing LaTeX syntax in that a user could write, e.g., \frac 1\sqrt{2} rather than \frac 1{\sqrt{2}}. I may change my mind on this later.
  • Optional argument.  This must be delimited by square brackets. Inside an optional argument, if a closing square bracket is desired, it must appear inside braces, or, can be escaped as \]. \[ will also be treated as a square bracket within an optional argument.
  • Ordered pair. Two floating-point numbers, separated with a comma enclosed in parentheses. Any white space inside the parentheses will be ignored. This would be used for, e.g., graphics environments.

A command can have a single * immediately after the command which indicates an alternate form of the command.

Arguments can have types as well. These can be:

  • Parsed text. This will be parsed as normal, including any enclosed macros.
  • Mathematics. Spaces will be ignored. Math-only commands will be defined. ^ will indicate a superscript, _ will indicate a subscript (note that outside of math mode, ^ and _ will simply typeset those characters).
  • Unparsed text. This will be treated as a straight unparsed character stream. The command will be responsible for parsing this stream. The argument can either be enclosed in braces or the character at the beginning of the unparsed character stream will be used to indicate the closing of the character stream.
  • Key-value pair list. This will be a list of key-value pairs separated by ->  Any white space at the beginning or end of the list will be ignored as well as any white space surrounding the arrows. If a value contains ->  the whole value should be enclosed in braces.
  • No space mode. Parsed as normal except all spaces are ignored.

As an aside, unparsed text can be re-submitted for parsing, potentially after manipulation of the text by the command definition.

Environments

Environments are marked with \begin{X} and \end{X} where X is the environment name.

Environment names can consist of any characters except {} or *. A single * at the end of the environment name indicates that this is an alternate form of the command, as with commands above.

The \begin environment command can take any number of arguments as above.

The contents of the environment can be any of the types for command arguments as above. Unparsed text, however, can only be concluded with the appropriate \end environment command.

There will be some special shortcuts for environments. \(…\) and $…$ shall be equivalent to \begin{math}…\end{math} \[…\] and $$…$$ shall be equivalent to \begin{displaymath}…\end{displaymath}

Updates

26 Feb 2021 Minor formatting change, indicate that key-value pairs are separated by ->.

27 May 2021 Oh my, the key-value language was crud. Fixed that.