Re: [Groff] condition: OR of two string comparisons

[Ralph Corderoy]

Hi Steffen,

> I'm wondering a bit since your current interim and part-time
> favorite Python supports ask-me-the-name-for-it sequences:
> 
>         elif o in ('-h', '--help'):

Python's just a language I'm using for some of the examples.  :-)
(42, 'foo', 3.14) is a tuple in Python.  A read-only ordered
fixed-length list that can have elements of varying types.  Python's
`in' operator can accept various things as its right operand, including
tuples.  http://en.wikipedia.org/wiki/Tuple

Awk has an `in' operator too for its associative arrays, AKA hashes in
Perl or dicts in Python.  It checks if the left operand is a key.

>   . ie     'Ar'\$1' .
>   . el .ie 'Cm'\$1' .
>   . el .ie 'Dv'\$1' .
>   . el .ie 'Er'\$1' .
>   ...
>   . el \{\
>   .   ds doc-mx-arx\n[doc-mx-ard]
>   .   return
>   . \}
> 
> And this would be terrible and expensive even with || and &&:
> 
>   .if $ 'Ar'\$1' || 'Cm'\$1' || 'Dv'\$1' || 'Er'\$1' || ...

No more expensive than the existing method you give above, assuming `||'
would short-circuit, as it clearly should.

> But rather easy and cheap with a sequence:
> 
>   .if $'\$1'Ar'Cm'Dv'Er'...$
> 
>   .if $ ,'\$1', 'Ar', 'Cm', 'Dv', 'Er'...

That seems to bring two advantages;  '\$1' is evaluated once, perhaps
this is the expense you refer to, and the reader knows '\$1' is always
one of the operands for the compare without having to check each one.
But with a new expression syntax up for grabs, there's other
possibilities depending on what's available.

    .if '\$1' == 'Ar' || '\$1' == 'Cm' || '\$1' == 'Dv' || '\$1' == 'Er' {

    .if '\$1' in ('Ar', 'Cm', 'Dv', 'Er') {

    .if '\$1' =~ r'^(Ar|Cm|Dv|Er)$' {

    .if len('\$1') == 2 && index('\$1,', 'Ar,Cm,Dv,Er,') >= 0 {

The second would seem nicest, if such syntax existed.  But even the
first would be an advantage over now.

Cheers, Ralph.