# [OS X TeX] Single-stepping through TeX

Doug McKenna doug at mathemaesthetics.com
Fri Nov 18 19:49:29 EST 2011

```Ross Moore wrote -

>> Is there any way to single-step through a very simple TeX execution
>> (after inputing the plain format), in order to watch with a debugger how
>> it operates?
>
>Not stepping through with a debugger.
>But you can see how the macro-expansion functions,
>and more detailed results from other aspects of the processing.
>
>Just put  \tracingall  into you document source.
>
>Beware that it can produce masses of output.
>So to limit this to a specific portion of your source,
>use braces as delimiters:
>
>{\tracingall  ....  }

Thanks.  I understand how to trace the execution of a TeX input file.  I
didn't do a very good job of explaining what I was interested in:
watching the actual interpreter (the "tex" program) interpret that file.

>[snip]

>and/or another similar book by Don Knuth:  "TeX, The Program".

I've spent lots of time looking at the program, but unWEB-ing it in my
(programmer's) mind to follow an actual execution path is a huge effort.