Why can't I assign this perl sub to a variable?
I'm trying to understand the convoluted execution path of the imap routine on p.158 of HOP.
This code works
# code from rng-iterator.pl
sub make_rand {
my $seed = shift || (time & 0x7fff);
print "nin make_rand, at6: seed=$seed";
return sub
{ $seed = (29*$seed+11111) & 0x7fff;
print "nin make_rand sub, at9: seed=$seed";
return $seed;
}
}
# code adapted from HOP p.158, to make an iterator version of map
sub imap {
my ($transform, $it) = @_;
print "nin imap, at17";
return sub
{ my $next = $it->();
print "nin imap sub, at20, next=$next";
return unless defined $next;
$newVal = $transform->($next);
print "nin imap sub, at23, newVal=$newVal";
return $newVal;
}
}
# to return random number 0 .. 1
$rng = imap(sub {$_[0] / 37268}, make_rand(1)); # set seed
print "nin main at30, rng=$rng";
while (<>) {
my $random = $rng->();
print "nin main, at 32: random=$random";
}
There seems to be no problem returning a reference to a sub (imap) to a string $rng, and using that to point to imap's sub .
I wanted to assign the sub to a string INSIDE of imap, and return the string, as here:
$imapSub = sub
{ my $next = $it->();
print "nin imap sub, at20, next=$next";
return unless defined $next;
$newVal = $transform->($next);
print "nin imap sub, at23, newVal=$newVal";
return $newVal;
}
return $imapSub;
Perl reported a Syntax Error when I tried to return or print $imapSub, or even use it as an argument to ref(). It didn't complain when I assigned the sub to the variable.
It does the same even if I explicitly cast a reference the subroutine as $&sub.
Why do I get a syntax error when I attempt to use the reference?
您在语句$imapSub = sub { ... }括号后面缺少分号，因此无论您在此之后放置的是何种意外，都会导致语法错误。
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