Transform a tex source so that all macros are replaced by their definition

Question

Is it possible to see the output of the TeX ‘pre-processor’, i. e. the intermediate step before the actual output is done but with all user-defined macros replaced and only

Answer 1

TeX has a lot of difference tracing tools built in, including tracing macro expansion. This only traces live macros as they are actually expanded, but it's still quite useful. Full details in The TeXbook and probably elsewhere.

When I'm trying to debug a macro problem I generally just use the big hammer:

\tracingall\tracingonline

then I dig in the output or the .log file for what I want to know.