Mailing List Archive: Re: Switch with refinements/hmmm!

[REBOL] Re: Switch with refinements/hmmm!

From: joel:neely:fedex at: 31-Oct-2001 21:01


Hi, Tim and all...

Just to recap the interesting variety of responses, there are multiple
design decisions to be addressed, depending on the minimum and maximum
number of switches/refinements that may be set:

0)  Is none an option?
    If so, is there to be a default behavior?
    If not, what (if any) error checking/handling is to be performed if
    none is set?
1)  Is one the only option?
    If so, what (if any) error checking/handling is to be performed if
    multiple refinements are set?
n)  Is more than one an option?
    If not (... error etc. as above...)?
    If so which action(s) is/are to be performed?
        The first one selected in textual order?
        All that are selected?
        Exactly one, randomly chosen?

Nenad Rakocevic wrote:
> If you need to set several refinement at the same time, here's my variant :
>
> refine-switch: func [/ref-one /ref-two /ref-three][
>     all [ref-one print "ref-one"]
>     all [ref-two print "ref-two"]
>     all [ref-three print "ref-three"]
> ]
>

Nice, and very REBOL-flavored, but only works under some circumstances:

    refine-switch: func [trace [logic!] /refa /refb /refc /local count] [
        count: 0
        all [refa if trace [print "ref A"] count: count + 1]
        all [refb if trace [print "ref B"] count: count + 2]
        all [refc if trace [print "ref C"] count: count + 4]
        count
    ]

Note the presence of an embedded expression that can evaluate to NONE,
which aborts each ALL statement prematurely, as in

    >> refine-switch false
    == 0
    >> refine-switch/refa false
    == 0
    >> refine-switch/refa true
    ref A
    == 1
    >> refine-switch/refa/refb true
    ref A
    ref B
    == 3
    >> refine-switch/refa/refb false
    == 0

Using ALL this way depends on all "brances" being made up of expressions
that will never return NONE or FALSE.  Of course, if that's the case for
your particular need, then it'll work just fine.

-jn-

--
; sub REBOL {}; sub head ($) {@_[0]}
REBOL []
# despam: func [e] [replace replace/all e ":" "." "#" "@"]
; sub despam {my ($e) = @_; $e =~ tr/:#/.@/; return "\n$e"}
print head reverse despam "moc:xedef#yleen:leoj" ;