Using ifs in conjunction with last and an anonymous block is just weird. An if/elsif cascade is clearer and more efficient:

sub count_separators {
    my $value = shift;
    my $delim = shift;
    my $set;

    if ($delim eq '{') { 
        $set = '{|}'; 
    }
    elsif ($delim eq '(') { 
        $set = '(|)'; 
    }
    elsif ($delim eq '"') {  
        $set = '"';
    }
    else {
        die; # Should never occur...
    }
    print 'sub { return shift =~ tr/' . $set . '//; }' . "\n";
  
    return eval 'sub { return shift =~ tr/' . $set . '//; }';
}
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If you really want to use the obscure fabricated switch statement, do it right :)

sub count_separators {
    my $value = shift;
    my $delim = shift;
    my $set;

    {
        $delim eq '{' and $set = '{|}' and last; 
        $delim eq '(' and $set = '(|)' and last; 
        $delim eq '"' and $set = '"'   and last;
        die; # Should never occur...
    }
    print 'sub { return shift =~ tr/' . $set . '//; }' . "\n";
  
    return eval 'sub { return shift =~ tr/' . $set . '//; }';
}
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But, given that you have only hardcoded sets, even though you have several of them, bringing eval into the equation is completely unnecessary.

This is far simpler and more efficient:

sub count_separators {
    my $value = shift;
    my $delim = shift;

    $delim eq '{' and return $value =~ tr[{|}][];
    $delim eq '(' and return $value =~ tr[(|)][]; 
    $delim eq '"' and return $value =~ tr["][]; #";
    die;
}
[download]