grep, cmp, and hashes: A weird syntax error in which perl apparently refuses to pick one of an ambiguous pair.

syntax-grep-cmp-hashes

use strict;
use warnings;

my @comparanda;
my @similar;
my $opts = {};

@similar = grep {  0 == ($a->{$opts->{'name'}}  cmp $b->{$opts->{'name'}}) } @comparanda; # case 1 - this is what I mean
@similar = grep { (0 ==  $a->{$opts->{'name'}}) cmp $b->{$opts->{'name'}}  } @comparanda; # case 2 - I can see why perl might think this
@similar = grep {  0 ==  $a->{$opts->{'name'}}  cmp $b->{$opts->{'name'}}  } @comparanda; # case 3 is either 1 or 2
# syntax error at parse-error.pl line 10, near "} cmp"
# Is this because it is ambiguous, or because it thinks the grep ends at "} cmp"?
# NB that cmp and == have same associativity
# Testing with other operators indicates that associativity seems to be the problem. 
# So why does perl not indicate this? Syntax error seems to be an unhelpful way of saying "I can't determine the order of operations here".