# Haskell analog of Sweave and Pweave

Sweave and Pweave are programs that let you embed R and Python code respectively into LaTeX files. You can display the source code, the result of running the code, or both.

lhs2TeX is roughly the Haskell analog of Sweave and Pweave.  This post takes the sample code I wrote for Sweave and Pweave before and gives a lhs2TeX counterpart.

\documentclass{article}
%include polycode.fmt
%options ghci
\long\def\ignore#1{}
\begin{document}

Invisible code that sets the value of the variable $a$.

\ignore{
\begin{code}
a = 3.14
\end{code}
}

Visible code that sets $b$ and squares it.

(There doesn't seem to be a way to display the result of a block of code directly.
Seems you have to save the result and display it explicitly in an eval statement.)

\begin{code}
b = 3.15
c = b*b
\end{code}

$b^2$ = \eval{c}

Calling Haskell inline: $\sqrt{2} = \eval{sqrt 2}$

Recalling the variable $a$ set above: $a$ = \eval{a}.

\end{document}


If you save this code to a file foo.lhs, you can run

lhs2TeX -o foo.tex foo.lhs

to create a LaTeX file foo.tex which you could then compile with pdflatex.

One gotcha that I ran into is that your .lhs file must contain at least one code block, though the code block may be empty. You cannot just have code in \eval statements.

Unlike R and Python, the Haskell language itself has a notion of literate programming. Haskell specifies a format for literate comments. lhs2TeX is a popular tool for processing literate Haskell files but not the only one.

# Commutative diagrams in LaTeX

There are numerous packages for creating commutative diagrams in LaTeX. My favorite, based on my limited experience, is Paul Taylor’s package. Another popular package is tikz-cd.

To install Paul Taylor’s package on Windows, I created a directory called localtexmf, set the environment variable TEXINPUTS to its location, and copied diagrams.sty file in that directory.

Here are a couple examples, diagrams used in the definition of product and coproduct.

And here’s the LaTeX to produce the diagrams.

\begin{diagram}
& & X & & \\
& \ldTo^{f_1} & \dDashto_f & \rdTo^{f_2} & \\
A & \lTo_{\pi_1} & A\times B & \rTo_{\pi_2} & B \\
\end{diagram}

\begin{diagram}
& & X & & \\
& \ruTo^{f_1} & \uDashto_f & \luTo^{f_2} & \\
A & \rTo_{i_1} & A\oplus B & \lTo_{i_2} & B \\
\end{diagram}



# Unicode to LaTeX

I’ve run across a couple web sites that let you enter a LaTeX symbol and get back its Unicode value. But I didn’t find a site that does the reverse, going from Unicode to LaTeX, so I wrote my own.

Unicode / LaTeX Conversion

If you enter Unicode, it will return LaTeX. If you enter LaTeX, it will return Unicode. It interprets a string starting with “U+” as a Unicode code point, and a string starting with a backslash as a LaTeX command.

For example, the screenshot above shows what happens if you enter U+221E and click “convert.” You could also enter infty and get back U+221E.

However, if you go from Unicode to LaTeX to Unicode, you won’t always end up where you started. There may be multiple Unicode values that map to a single LaTeX symbol. This is because Unicode is semantic and LaTeX is not. For example, Unicode distinguishes between the Greek letter Ω and the symbol Ω for ohms, the unit of electrical resistance, but LaTeX does not.

# Automatic delimiter sizes in LaTeX

I recently read a math book in which delimiters never adjusted to the size of their content or the level of nesting. This isn’t unusual in articles, but books usually pay more attention to typography.

Here’s a part of an equation from the book:

Larger outer parentheses make the equation much easier to read, especially as part of a complex equation. It’s clear at a glance that the function φ-1 applies to the result of the integral.

The first equation was typeset using

\varphi^{-1} ( \int \varphi(f+g) ,dmu )

The latter used left and right to tell LaTeX that the parentheses should grow to match the size of the content between them.

\varphi^{-1} \left( \int \varphi(f+g) ,d\mu \right)

You can use \left and \right with more delimiters than just parentheses: braces, brackets, ceiling, floor, etc. And the left and right delimiters do not need to match. You could make a half-open interval, for example, with \left( on one side and \right] on the other.

For every \left delimiter there must be a corresponding \right delimiter. However, you can make one of the pair empty by using a period as its mate. For example, you could start an expression with \left[ and end it with \right. which would create a left bracket as tall as the tallest thing between that bracket and the corresponding \right. command. Note that \right. causes nothing to be displayed, not even a period.

The most common example of a delimiter with no mate may be a curly brace on the left with no matching brace on the right. In that case you’d need to open with \left{. The backslash in front of the brace is necessary to tell LaTeX that you want a literal brace and that you’re not just using the brace for grouping.

# Basics of Sweave and Pweave

Sweave is a tool for embedding R code in a LaTeX file. Pweave is an analogous tool for Python. By putting your code in your document rather than the results of running your code somewhere else, results are automatically recomputed when inputs change. This is especially useful with graphs: rather than including an image into your document, you include the code to create the image. (more…)

# The paper is too big

In response to the question “Why are default LaTeX margins so big?” Paul Stanley answers

It’s not that the margins are too wide. It’s that the paper is too big!

This sounds flippant, but he gives a compelling argument that paper really is too big for how it is now used.

As is surely by now well-known, the real question is the size of the text block. That is a really important factor in legibility. As others have noted, the optimum line length is broadly somewhere between 60 characters and 75 characters.

Given reasonable sizes of font which are comfortable for reading at the distance we want to read at (roughly 9 to 12 point), there are only so many line lengths that make sense. If you take a book off your shelf, especially a book that you would actually read for a prolonged period of time, and compare it to a LaTeX document in one of the standard classes, you’ll probably notice that the line length is pretty similar.

The real problem is with paper size. As it happens, we have ended up with paper sizes that were never designed or adapted for printing with 10-12 point proportionally spaced type. They were designed for handwriting (which is usually much bigger) or for typewriters. Typewriters produced 10 or 12 characters per inch: so on (say) 8.5 inch wide paper, with 1 inch margins, you had 6.5 inches of type, giving … around 65 to 78 characters: in other words something pretty close to ideal. But if you type in a standard proportionally spaced font (worse, in Times — which is rather condensed because it was designed to be used in narrow columns) at 12 point, you will get about 90 to 100 characters in the line.

He then gives six suggestions for what to do about this. You can see his answer for a full explanation. Here I’ll just summarize his points.

1. Use smaller paper.
2. Use long lines of text but extra space between lines.
3. Use wide margins.
4. Use margins for notes and illustrations.
5. Use a two column format.
6. Use large type.

Given these options, wide margins (as in #3 and #4) sound reasonable.

# Separating presentation from content

In the late ’90s I went to a fair number of Microsoft presentations. One presentation would say “The problem with Technology X is that it mixes presentation and content. We’ve introduced Technology Y to make your code cleaner, separating presentation and content.” A few months later I’d be at another presentation that would announce “The problem with Technology Y is that it mixes presentation and content. We’ve introduced Technology Z …” (Does this remind anyone else of The Cat in the Hat Comes Back?)

When I first learned LaTeX, I was told that one of its strengths is that it separates presentation and content. Then a few years later I hear complaints that the problem with LaTeX is that it mingles presentation and content, unlike XHTML. A few years later, guess what? XHTML mixes presentation and content, so we need something else.

I shut down when I hear someone announce that everything before their product was bad because it mixed presentation and content, and now with their solution, presentation and content will be completely separate.

Sometimes one technology really does make a cleaner separation of presentation and content. But at best the separation is relative. LaTeX separates presentation and content more than Word, though not as much as well-written HTML and CSS, maybe. But presentation and content cannot be entirely separated. Nor is their unanimous agreement on what exactly the dividing line is between the two.

Many people don’t want to separate their presentation and content. They don’t understand why this would be desirable, and they’ll fight against anything designed to encourage separation. Maybe they need to learn the advantages, or maybe they’re just doing the best they can to get their job done and they can’t be bothered with long term advantages that may not materialize.

The principle of separating presentation and content is admirable. It really does have advantages, but it’s easier said than done.

# Typesetting “C#” in LaTeX

How do you refer to the C# programming language in LaTeX? Simply typing C# doesn’t work because # is a special character in LaTeX. You could type C#. That works, but it looks a little odd. The number sign is too big and too low. (more…)

# Bundled versus unbundled version history

The other day I said to a colleague that an advantage to LaTeX over Microsoft Word is that it’s easy to version LaTeX files because they’re just plain text. My colleague had the opposite view. He said that LaTeX was impossible to version because its files are just plain text. How could we interpret the same facts so differently?

I was thinking about checking files in and out of a version control system. With a text file, the version control system can tell you exactly how two versions differ. But with something like a Word document, the system will give an unhelpful message like “binary files differ.”

My colleague was thinking about using the change tracking features of Microsoft Word. He’s accustomed to seeing documents in isolation, such as a file attachment in an email. In that setting, a plain text file has no version history, but a Word document may.

I assumed version information would be external to the document. He assumed the version information would be bundled with the document. My view is typical of software developers. His is typical of everyone else.

These two approaches are analogous to functional programming versus object oriented programming. Version control systems have a functional view of files. The versioning functionality is unbundled from the file content, in part because the content (typically source code files) could be used by many different applications. Word provides a sort of object oriented versioning system, bundling versioning functionality with the data.

As with functional versus object oriented programming, there’s no “right” way to solve this problem, only approaches that work better in different contexts. I much prefer using a version control system to track changes to my files, but that approach won’t fly with people who don’t share a common version control system or don’t use version control at all.

Related posts:

# Typesetting chemistry in LaTeX

Yesterday I gave the following tip on TeXtip:

Set chemical formulas with math Roman. Example: sulfate is $mathrm{SO_4^{2-}}$

TorbjoernT and scmbradley let me know there’s a better way: use Martin Hansel’s package mhchem. The package is simpler to use and it correctly handles subtle typographical details.

Using the mhchem package, sulfate would be written ce{SO4^2-}. In addition to chemical compounds, mhchem has support for bonds, arrows, and related chemical notation.

Example:

Source:

\documentclass{article}
\usepackage[version=3]{mhchem}
\parskip=0.1in
\begin{document}

\ce{SO4^2-}

\ce{^{227}_{90}Th+}

\ce{A\bond{-}B\bond{=}C\bond{#}D}

\ce{CO2 + C -> 2CO}

\ce{SO4^2- + Ba^2+ -> BaSO4 v}

\end{document}

Related posts:

# Serious lessons from Knuth’s joke

On June 30, 2010 Donald Knuth announced iTeX, the successor to TeX. His announcement was an extended parody of much of what people recommend as the “right” way to develop software.

TeX has been extremely successful. The vast majority of math and computer science is published using TeX. And yet Knuth implies that TeX would have been an obscure failure if he had developed it using trendy software development techniques.

Here’s the video of Knuth’s presentation.

# Daily tip Twitter account FAQ

How many followers do you have?

About 2800 people are following at least one of these accounts at the time of writing, each following between 2 and 3 accounts on average for a total of about 5900 follows combining all accounts.

How do you schedule your posts?

I schedule the tips a week to a month in advance using HootSuite. Each account posts at the same time each week day starting with SansMouse at 9:30 AM and ending with AlgebraFact at 1:30 PM (US Central Time). Once in a while a tip will go out late due to a Twitter API failure. I occasionally sprinkle in a few unscheduled tweets but I keep the volume low.

What if I don’t use Twitter?

The SansMouse and RegexTip are in a cycle that starts with the most familiar tips and then moves on to less familiar ones. I mix elementary and advanced material in the mathematical accounts, though there’s a greater range in some accounts. If a tip is more elementary or more advanced than you’d like, you may find something more to your liking in a day or two.

Do you take suggestions? Questions?

I welcome corrections as well as suggestions for new tips. General suggestions are helpful, but I especially appreciate specific tweets.

I like to answer questions when I can, though I can’t respond to every question.

Any plans for new accounts?

I have a couple ideas I’m considering. If you have a suggestion for another daily tip account, let me know.

The following isn’t Q&A format, but it answers some common questions.

SansMouse is my oldest daily tip account. It gives one Windows keyboard shortcut each day. Most tips apply across all applications, but some tips are specific to popular software packages. Ben Jaffe has an analogous Twitter account commandtab for Mac OS.

RegexTip is currently the second most popular daily tip account with 1025 followers at the time of writing. This account gives tips for writing regular expressions as well as tips for how regular expressions are used in different environments. I mostly stick to the regular expression syntax supported by Perl 5, Microsoft’s .NET languages, JavaScript, etc.

TeXtip gives tips for typesetting in TeX and LaTeX. Topics include TeX commands, software for working with LaTeX, tips on typography, etc. I basically stick to LaTeX, though much applies to plain TeX. Also, I don’t say much about add-on packages but stick to the heart of LaTeX.

ProbFact is currently the most popular daily tip account with 1100 followers. This account gives one fact per day from probability. Probability and statistics are intimately related, but this account primarily sticks to probability proper, though some posts are more statistical. People have suggested I start a statistical counterpart to ProbFact, but I have no plans to do so.

AlgebraFact gives facts from linear algebra, number theory, group theory, etc. A few of the facts are advanced but most are not. I’ve gotten a few complaints for including number theory, but that’s been part of the charter from the beginning. The name AlgebraAndNumberTheoryFact would be more accurate, but too long.

TopologyFact gives theorems from topology (point-set topology, algebraic topology, etc.) and geometry. Point-set topology has a lot of theorems that can be condensed into 140 characters but I find other areas harder to tweet about. I could use some help here. I’d like to include more geometry: Euclidean geometry, differential geometry, etc. But I don’t want to include material so esoteric that not many will understand it.

AnalysisFact is the most advanced account on average. Some of the posts are elementary, but some fairly advanced. Topics include real and complex analysis, functional analysis, special functions, differential equations, etc.

I’m doing a drawing to give away either a coffee mug or T-shirt to someone who mentions these tips on Twitter. Tomorrow is the last day to enter.

I also have a personal Twitter account. I use this account to post links, interact with friends, etc. I try to keep the signal to noise ratio fairly high, though not as high as the tip accounts.

# Complexity of HTML and LaTeX

Sometime around 1994, my office mate introduced me to HTML by saying it was 10 times simpler than LaTeX. At the time I thought he was right. Now I’m not so sure. Maybe he was right in 1994 when the expectations for HTML were very low.

It is easier to bang out a simple, ugly HTML page than to write your first LaTeX document. When you compare the time required to make an attractive document, the effort becomes more comparable. The more sophisticated you get, the simpler LaTeX becomes by comparison.

Of course the two languages are not exactly comparable. HTML targets a web browser while LaTeX targets paper. HTML would be much simpler if people only used it to create documents to print out on their own printer. A major challenge with HTML is not knowing how someone else will use your document. You don’t know what browser they will view it with, at what resolution, etc. For that matter, you don’t know whether they’re even going to view it at all — they may use a screen reader to listen to the document.

Writing HTML is much more complicated than writing LaTeX if you take a broad view of all that is required to do it well: learning about accessibility and internationalization, keeping track of browser capabilities and market shares, adapting to evolving standards, etc. The closer you look into it, the less HTML has in common with LaTeX. The two languages are not simply two systems of markup; they address different problems.

# Top four LaTeX mistakes

Here are four of the most common typesetting errors I see in books and articles created with LaTeX.

1) Quotes

Quotation marks in LaTeX files begin with two back ticks, , and end with two single quotes, ''.

The first “Yes” was written as

Yes.''

in LaTeX while the one with the backward opening quote was written as

"Yes."

2) Differentials

Differentials, most commonly the dx at the end of an integer, should have a little space separating them from other elements. The “dx” is a unit and so it needs a little space to keep from looking like the product of “d” and “x.” You can do this in LaTeX by inserting , before and between differentials.

The first integral was written as

 \int_0^1 f(x) \, dx

while the second forgot the , and was written as

 \int_0^1 f(x)  dx

The need for a little extra space around differentials becomes more obvious in multiple integrals.

The first was written as

dx , dy = r , dr \, d\theta

while the second was written as

dx  dy = r  dr  d\theta

3) Multi-letter function names

The LaTeX commands for typesetting functions like sin, cos, log, max, etc. begin with a backslash. The command log keeps “log,” for example, from looking like the product of variables “l”, “o”, and “g.”

The first example above was written as

\log e^x = x

and the second as

log e^x = x

The double angle identity for sine is readable when properly typeset and a jumbled mess when the necessary backslashes are left out.

The first example was written

\sin 2u = 2 \sin u \cos u

and the second as

sin 2u = 2 sin u cos u

4) Failure to use math mode

LaTeX uses math mode to distinguish variables from ordinary letters. Variables are typeset in math italic, a special style that is not the same as ordinary italic prose.

The first sentence was written as

Given a matrix $A$ and vector $b$, solve $Ax = b$.

and the second as

Given a matrix A and vector b, solve Ax = b.

Related posts:

# Including LaTeX in an Inkscape drawing

My previous post described how to include an Inkscape drawing in a LaTeX document. This post describes how to use LaTeX in an Inkscape drawing, which is probably more useful. The LaTeX output is included not as bitmap but as a vector drawing that can then be manipulated with all the features of Inkscape.

The Inkscape book describes the InkLaTeX extension, but the web site for InkLaTeX recommends a newer extension textext. Once textext is installed, you can insert LaTeX into an Inkscape drawing by going to the Extensions menu and selecting “TeX Text”. This launches a window in which to type your LaTeX source.

Before I could install textext, I had to install pstoedit. The textext extension also requires LaTeX and Ghostscript, but these were already on my computer. pstoedit has several installation options; I chose the default basic option and that worked. Also, pstoedit says that it requires two Visual C++ runtime DLLs: msvcr70.dll and msvcp70.dll. I already had these, but the pstoedit site gives a link to where you can find these DLLs if you need them.

I had Inkscape running when installed textext and I had to restart Inkscape to see the “TeX Text” menu.

Related post:

Including an Inkscape drawing in LaTeX