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Postings from October 2006
Larry (>):
> [...]
> The non-chaining precedence level is a bunch non-associative operators
> like .. and cmp. Historically, all operators of a particular precedence
> level have had the same associativity, so that when you analyze
>
> $a op1 $b op2 $c
>
> you only have to compare op1 with op2 if they're the same precedence, and
> given the prededence you don't actually have to look at the individual
> ops. What would it mean to have a left-associative op at the same precedence
> level as a right-associative op:
>
> $a lefty $b righty $c
>
> Who would win? So generally we try not to mix associativity within a
> precedence level.
Short question: what would happen if I as the user would try and
define two operators on the same precedence level, and then try to use
them in the above way? How far would I get?
In other words, I'd do something like this:
my sub infix:<lefty> is assoc('left') ($a, $b) { $a - $b; }
my sub infix:<righty> is assoc('right') ($a, $b) { $a - $b; }
say (1 lefty 2 righty 3); # a-ha! will this be -4 or 2 ?
Pugs currently dies on evaluating the last line, explaining to me that
an "ambiguous use of a right associative operator" occurred. This
might even be a fairly sane behavior. The only alternative I can think
of right now would be to disallow even _declaring_ two operators of
different associativity on the same precedence level... but that kind
of strictitude doesn't sound very perlish.
Kindly,
--
masak
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