Re: [Groff] Conditional problem: "!" operator after "&"

[Ralph Corderoy]

Hi Larry,

> I'm seeing this in both the release and this morning's CVS versions. A
> test file that illustrates the issue:

I think this matches Kernighan's CSTR 54.

> mac-lkollar:/tmp lkollar$ cat -n test.t
>      1  .nr NCS 1
>      2  .nr SIP 1
>      3  .LP
>      4  This is a test,
>      5  .if \n[NCS]&!\n[SIP] .nop NCS only.
>      6  .if !\n[NCS]&\n[SIP] .nop SIP only.
>      7  .if \n[NCS]&\n[SIP] .nop NCS and SIP.
>      8  .if !\n[NCS]&!\n[SIP] .nop actually it isn't because nothing is 
> defined!
> mac-lkollar:/tmp lkollar$
> 
> Running groff on this file produces the warnings:
> 
> test.t:5: warning: numeric expression expected (got `!')
> test.t:8: warning: numeric expression expected (got `!')

The `!' for logical not is part of .if, not an operator in general
expressions.  It is only allowed immediately after the `if' and negates
the whole of the following expression.

This may help.  Note the parenthesis are required.

    $ cat test.t
    .if (\na=0)&(\nb=0) .tm x 0
    .if (\na=0)&(\nb=1) .tm x 1
    .if (\na=1)&(\nb=0) .tm x 2
    .if (\na=1)&(\nb=1) .tm x 3
    .
    .if !\na .if !\nb .tm y 0
    .if !\na .if \nb .tm y 1
    .if \na .if !\nb .tm y 2
    .if \na .if \nb .tm y 3
    .
    .if !\na&\nb .tm z 012
    .if \na&\nb .tm z 3
    $
    $ for a in 0 1; do
    >     for b in 0 1; do
    >         echo = $a $b
    >         troff -ra=$a -rb=$b <test.t >/dev/null
    >     done
    > done
    = 0 0
    x 0
    y 0
    z 012
    = 0 1
    x 1
    y 1
    z 012
    = 1 0
    x 2
    y 2
    z 012
    = 1 1
    x 3
    y 3
    z 3
    $ 

Cheers,
Ralph.