komplex expressions in statement modifiers

[Rainer Weikusat]

The perl grep operator can be used to determine if some condition holds
for some elements of a list. In scalar context, it returns the number of
times the condition was true. This means it's semantically a bad fit for
finding a single element in a list because it always processes the
complete list. But it can be used as test expression for a statement
modifier ... so far, so bad.

Upon spending a time thinking through this, it dawned to be that eval {
} is syntactically an expression, hence

------
@a = qw(a b c d e);

while ($l = <STDIN>) {
chomp($l);
print("found $l\n") if eval { $_ eq $l and return 1 for @a };
}
-------

is valid Perl (which works, obviously).

[George Bouras]

Post by Rainer Weikusat
The perl grep operator can be used to determine if some condition holds
for some elements of a list. In scalar context, it returns the number of
times the condition was true. This means it's semantically a bad fit for
finding a single element in a list because it always processes the
complete list. But it can be used as test expression for a statement
modifier ... so far, so bad.
Upon spending a time thinking through this, it dawned to be that eval {
} is syntactically an expression, hence
------
@a = qw(a b c d e);
while ($l = <STDIN>) {
chomp($l);
}
-------
is valid Perl (which works, obviously).

use the clever equal ~~

[Rainer Weikusat]

Post by George Bouras

Post by Rainer Weikusat
The perl grep operator can be used to determine if some condition holds
for some elements of a list. In scalar context, it returns the number of
times the condition was true. This means it's semantically a bad fit for
finding a single element in a list because it always processes the
complete list. But it can be used as test expression for a statement
modifier ... so far, so bad.
Upon spending a time thinking through this, it dawned to be that eval {
} is syntactically an expression, hence
------
@a = qw(a b c d e);
while ($l = <STDIN>) {
chomp($l);
}
-------
is valid Perl (which works, obviously).

use the clever equal ~~

I'm not interested in the smart alec operator :->, not the least because
it (presumably forever) prevents Perl from getting a non-experimental
multiway conditional construct (something I'm using frequently)

[Otto J. Makela]

Rainer Weikusat <***@talktalk.net> wrote:

[...]

Post by Rainer Weikusat
is valid Perl (which works, obviously).

Thanks for this bit of strangeness, it caused me to look up the Perl
"secret operators" page:

https://metacpan.org/pod/distribution/perlsecret/lib/perlsecret.pod

[Rainer Weikusat]

Post by Otto J. Makela
[...]

Post by Rainer Weikusat
is valid Perl (which works, obviously).

Thanks for this bit of strangeness, it caused me to look up the Perl
https://metacpan.org/pod/distribution/perlsecret/lib/perlsecret.pod

There's nothing particularly strange in this construct: Any operator
can (obviously) be used as test expression for a
conditional. And any operator with a &-prototype would do here:

---------
sub judge (&)
{
&{$_[0]}
}

@a = qw(a b c d e);

while ($l = <>) {
chomp($l);
print("found $l\n") if judge { $_ eq $l and return 1 for @a };
}
---------

eval is just one behaving in this way which is already available.

NB: The page is somewhat interesting. But I don't generally care for
"brevity" (for its own sake) or "obscurity" (at all).