[tex-k] Error in TeXbook: Trailing tabs don't typeset

Julian Gilbey julian at d-and-j.net
Fri Sep 1 10:17:06 CEST 2017

On Wed, Aug 30, 2017 at 07:55:55PM +0300, Evan Aad wrote:
> I think I found an error in the TeXbook. Please vet.
> Consider the following Plain TeX manuscript
> ---
> \catcode9=12\relax% ASCII 9 is tab
> .\ \ .\par%
> .
> .%
> \bye
> [...]
> Observe that there seem to be two spaces between the dots on the first
> line, but only one space between the dots on the second line.
> However, based on the TeXbook, I'd expect there two be two spaces
> between the dots on the second line too: one for the tab, and one for
> the carriage-return at the end of the line.

This is not correct: "Plain TeX makes <tab> act like a blank space."
says the TeXbook (page 45), so you have a blank space, and TeX enters
state S (skipping blanks).  It now reaches the end-of-line, and "if
TeX is in state S (skipping blanks), the end-of-line character is
simply dropped." (page 46).  So all that you end up with is a single
space character, as you observed.


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