[Tex/LaTex] the difference between a typesetting language and a markup language

markuptex-coretypography

I remember, I read some article in a technical journal where the author drew the attention on the reader on a lot of people confusing typesetting languages and markup languages.

How can I surely tell if a language is a typesetting language or a markup language?

As far as I understand TeX is a typesetting language and LaTeX implements a markup language atop TeX. Is this a correct way to put things?

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As far as I understand TeX is a typesetting language and LaTeX implements a markup language atop TeX. Is this a correct way to put things?

yes, this is accurate, as well as concise.

a typesetting language provides the tools to convert an input stream into what is output on a surface. among the tools are

access to fonts, and commands to select and/or switch between them
commands to move along the surface in various directions
a mechanism to break an input stream into lines or paragraphs, and the result into pages
commands to apply the "basic" commands in a more efficient manner

as an example of the last point, one very valuable feature in tex is the concept of grouping. this is not present in other typesetting software i've used. for example, in one such system, there was a command to raise a superscript to the proper height, and a "reverse" command to step back out of it by the same distance. (it didn't always put one back at exactly the original baseline.) tex, on the other hand, stores the original values when a new group starts, applies the local values for the group, then forgets the local values and restores the saved values.

a markup system, on the other hand, identifies material according to its function or structure, not how it should look on a surface. thus there are identifiers for "title", "author", "chapter", "section", "theorem", etc., and these are converted at processing time to use appropriate typesetting commands. this structural markup permits easy switching of output format, provided a common vocabulary and syntax are used. latex and xml are two examples of markup systems. neither can be used without "back end" support. in latex, this support is integral, while xml requires separate tools; however, what is identified in both cases are the structural elements, not the final appearance, hence "markup".

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[Tex/LaTex] the difference between TeX and LaTeX

TeX is both a program (which does the typesetting, tex-core) and format (a set of macros that the engine uses, plain-tex). Looked at in either way, TeX gives you the basics only. If you read the source for The TeXBook, you'll see that Knuth wrote more macros to be able to typeset the book, and made a format for that.

LaTeX is a generalised set of macros to let you do many things. Most people don't want to have to program TeX, especially to set up things like sections, title pages, bibliographies and so on. LaTeX provides all of that: these are the 'macros' that it is made up of.

[Tex/LaTex] the difference between \let and \def

The difference is in the time at which the ‘right hand side’ is evaluated.

Thus \let\foo\bar defines \foo to have the value that \bar had at the point of definition. On the other hand, \def\foo{\bar} in effect defines \foo to have the value that \bar has at the point of use.

Consider:

\def\bar{hello}
\let\fooi\bar
\def\fooii{\bar}
\fooi +\fooii

\def\bar{goodbye}
\fooi +\fooii

This produces

hello+hello
hello+goodbye

This is a simple process.

However it's also a subtle one, so it might be worth highlighting a few key points:

When TeX encounters control sequences such as \fooi, it evaluates them; if these are macros (that is, they have been defined by \def, or \let equal to something which was defined by \def), then the result is that they will expand to other tokens, which TeX will then examine in turn, and so on, recursively, until what's left is either ‘primitive’ control sequences or letters (I'm simplifying a little bit).
\fooi expands directly to the characters hello (because \bar initially did, and \fooi was defined to have the same value).
\fooii, in contrast, expands to \bar, which is then immediately reexamined and reexpanded. In the first case, \bar expands to hello and in the second case to goodbye. The definition of \fooii hasn't changed, but \bar has been redefined in between.
Getting a clear idea of the process of this recursive expansion is very helpful when learning how to develop and debug TeX macros.

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[Tex/LaTex] the difference between TeX and LaTeX

[Tex/LaTex] the difference between \let and \def

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