Tbl and Troff

[Anw%maths.nottingham.ac.uk at UCL-CS.ARPA]

> My files consisted of a number of tables mixed with text.  I ran
> each table separately through tbl and that work out all right.
> However, when I combined several of this tables together I got the
> following error from tbl:  [...]

	A colleague here had a very-hard-to-find bug that sounds vaguely
similar.  His tables without the text ran through "tbl" and "nroff" with
no problems;  the text without the tables ran;  the first half of the file
was OK;  the second half was OK;  only when everything was put together
did garbled output appear.  This made it difficult to isolate the bug.
However, I eventually spotted a ".ds ed something-or-other" just above a
table;  this in itself is OK, but alarm bells rang, and sure enough there
was a ".ds ec ..." further up, which over-writes the built-in ".ec" request
which is output by "tbl".  You may have done something similar.

	We have now modded our "nroff"/"troff" to complain about attempts
to change built-ins, and picked up several bugs in macro packages as a
consequence.  I suppose it is too late to convince the world that it should
be an error to use or remove an undefined macro or string, or to define one
that already exists;  or that "," rather than "'" should be the default
second control character.

	-- Andy Walker, Maths Dept, Nottingham Univ
		anw at UK.AC.Nott.Maths