Thursday, February 25, 2010

Coding styles that make me twitch, part 7

Parentheses and precedence

This week, I will strive to be better at explaining the problem scope, while heroically and miraculously maintaining brevity.

I used to be annoyed at seeing extraneous parentheses with the ternary conditional operator pair ? :, but then I discovered that the PHP language designers decided to break precedence (see example #3). So I have stopped twitching as much as I used to when seeing parentheses galore in that context.

In Perl Best Practices, Damian Conway notes that even though the low-precedence logic operators and, not and or may seem nicer, they can confuse the reader regarding the intended meaning of the code. But he does not — as far as I can recall or find — address how these relates to parentheses and precedence (I suppose that should be "parentheses && precedence").

I start twitching when someone insists on using parentheses like this (imagine that the example was more convoluted):
if (expr1 ||
(expr2 && expr3) ||
That does not help understanding. It confuses me, as the read, regarding your intentions. Is there a piece of code missing, perhaps a little bit of || expr2b or || expr3b?

Sometimes, I even see misguidedly mixed-in letter-literal operators:
if (expr1 or
(expr2 && expr3) or

I much prefer seeing
if (expr1 ||
expr2 && expr3 ||
if (expr1
|| expr2 && expr3
|| expr4
depending on what floats your boat in the most stylish way imaginable.

I would have thought that the logical and/or/not part of operator precedence would be easy to understand. It is essentially the same in most programming languages: Ruby, Python, Perl, Java, C, ... and not even PHP managed to mess this one up.

The chance that anyone is going to be confused by your code because of these parentheses not being there is far, far smaller than the chance that they are going to be confused by their presence.

I have heard the defense "but the code is so non-obvious that I had to add them!" Well, make your code obvious instead.

Thursday, February 18, 2010

Coding styles that make me twitch, part 6

Edit: There are, apparently, strong feelings that I should not post my personal preferences. Reader discretion advised: this post expresses my personal opinions regarding a limited use case for file handling and filehandles, and must not be read as general advise on how to deal with filehandles in Perl, and so on.

Today's theme is: unnecessary variable clutter.
my $fh = new Filehandle("/usr/bin/somecmd someargs |");
while (my $l=<$fh>) {
if ($l=~m/foo bar zot/) {
# lots of code that does not depend on
# a variable file handle, nor creative
# usage of $l where $_ could not be used
# implicitly just as easily

Sure, there are situations where it makes sense to assign filehandles to variables, or using $l instead of $_, but the above example is not one of them. I found no particular reason why the original programmer had used new Filehandle, either.

Perl 5 has, on purpose, made this easier for us than in the above example:
open my $FH, '-|', '/usr/bin/somecmd someargs'
or croak "OMG\n";
while (<$FH>) {
if (/foo bar zot/) {
# lots of code

Thursday, February 11, 2010

Missing feature

A few hours ago, I suddenly had a bright(?) idea, or desire if you will:

Proper (Unicode) exponents in Perl.

That is, I want to be able to write 22, 4137, 3-9, etc. and have Perl understand them.

For Perl 5, I suspect someone would use a source filter to implement it.

For Perl 6, PerlJam++ suggested introducing each of the exponents as postfix operators, using this example for squaring:
our &postfix:<2> := &infix:<**>.assuming(b => 2);
But then a negative exponent would complicate things a bit.

It's a thought, anyway, and not one that I'd want to distract more pressing implementation concerns.

And ifwhen someone decides that this is a good idea to have in the language core, I'll start nagging about Knuth's up-arrow notation. Not that I'd want anyone attempt calculating 4↑↑↑↑4.

Thursday, February 4, 2010


This is just a small anecdote.

Tonight, I finished a small Perl 5 script that I've been wanting to complete for a while, but where I was a bit nervous that I'd fsck it up right and good.

It was a script designed to handle two tab-separated text sources; one a list of tournament IDs and tournament names, the other a list of player results, one line per result with the player ID, tournament name, position and score achieved.

I achieved this by creating a hash of hashes for each file, referencing the first while parsing the other, and bravely inserting the data into a single database table.

I tested my code piece for piece while building it, which is sensible in itself, but what spooked me was this:

There was not a single bug. The script did what it was supposed to do, all along.

That's not supposed to happen.

I need a drink.