To Ralph, You quoted the following in your email:
> Stephanie wrote: > > However, Troff's ability to take values of a numerical register and > > use it as a name to another register (.nr my_\na_\nb) intrigues me > > very much. > > I do not know if that "feature" was an intentional design or an > accident, and I do not know either if it is considered a good practice > or an abuse to take advantage of it, but I find it very useful. Unfortunately, I've tried looking for the email to my inbox that was the reply to my writing about Troff's ability to .... . It seems to be a technical issue that I didn't receive that email. I was wondering if you could send it to me again, quoted, so I can follow from the context? Thanks. Stephanie On Thu, Dec 7, 2017 at 5:57 AM, Ralph Corderoy <ra...@inputplus.co.uk> wrote: > Hello you two, > > > Stephanie wrote: > > > However, Troff's ability to take values of a numerical register and > > > use it as a name to another register (.nr my_\na_\nb) intrigues me > > > very much. > > > > I do not know if that "feature" was an intentional design or an > > accident, and I do not know either if it is considered a good practice > > or an abuse to take advantage of it, but I find it very useful. > > I don't know if `intentional' is the right word, more likely `obvious' > for the time. If you've only ever been used to `macros' as seen in C's > cpp(1) then you haven't been exposed to the more powerful macros that > were common to aid the simpler languages of the time, e.g. assembler. > > Today, m4(1) is still around from that era, along with troff, and is > worth examining. https://en.wikipedia.org/wiki/M4_(computer_language) > autoconf and sendmail still use it. And some years ago now, I > supplemented a BCPL-like language that only offered the machine word. > It was used to add `probes' to executables without recompiling. Fine > for small things, but it was pushed into more complex tasks and chasing > through structs and pointers with nothing but arithmetic because tedious > for its users so I used m4 to provide `struct'-defining statements that > in turn defined more macros that would do the member accesses and > pointer dereferences given based addresses, all based on the identifiers > used in the executable's source. > > Lisp also takes macros to town. Both code and data are lists in Lisp, > and macros allow manipulating those lists during `parsing'. A skilled > Lisp zealot writes any non-trivial program in a unique dialect of Lisp, > having cajoled the language with macros to fit the domain. I don't say > this in praise, just as another data point. :-) > > -- > Cheers, Ralph. > https://plus.google.com/+RalphCorderoy >
