On Jun 11, 9:10 am, [EMAIL PROTECTED] (Jonathan Lang) wrote: > Rereading A03, I ran across the original reasoning behind why Perl 5's > '?:' trinary operator became '?? ::' first, and then '?? !!'. Three > reasons were given: > > * the '?' and ':' tokens are far too broadly useful to be gobbled up > by the trinary operator. > > * the doubled symbols bring to mind the short-circuiting operators > (e.g., '&&' and '||'), suggesting a similar short-circuiting behavior > here. > > * the '!!' brings to mind "evaluate this when the condition fails". > > IMHO, the first point was always more about the ':' than it was about > the '?'; if you were to replace ':' with '!', I suspect that this > concern would largely go away. That is, I don't see any infix:<?> or > infix:<!> operators in the current draft. A case could be made that a > trinary '... ? ... ! ...' operator could work within the current state > of things without conflict. Also, the whitespace disambiguation rules > that were later implemented go a long way to resolving the original > problem of ':' trying to do too much. > > That said, the latter two points are still valid. '... ? ... : ...' > might be perfectly workable; but so is '... ?? ... !! ...'. > > However, there still may be room for improvement. Consider the > following possibility: > > Instead of being a single, inflexible trinary operator, break this > into a pair of binary operators: infix:<??> and infix:<!!>. Each can > be used on its own, returning the right side if the condition > evaluates as expected (i.e., true for ?? and false for !!), and > otherwise returns 'undef'. A variation of chaining associativity gets > used, with the "chaining rule" being '$v1 op1 $v2 // $v1 op2 $v3' > instead of '$v1 op1 $v2 && $v2 op2 $v3', as is the case for comparison > chaining. So all of the following would be valid syntax: > > $test ?? $a !! $b # true: $a; false: $b > $test !! $a ?? $b # true: $b; false: $a > $test ?? $a # true: $a; false: undef > $test !! $b # true: undef; false: $a > > I suggest this mainly because it's potentially more extensible than > the current model. I could see someone devising a "fuzzy logic" > module which could allow for such things as: > > $test ?? $a !! $b maybe $c likely $d unlikely $e > > -- > Jonathan "Dataweaver" Lang
Surely if you defined !! to return "undef but true" and both operators to be left associative then it all works. 1==0 ?? "True" !! "False" -> (undef) !! "False" which seems right to me. 1==1 !! "False" ?? "True" -> (undef but true) ?? "True" also good. TTFN, Struan
