Re^4: hangman game

Hello QM,

I assume you’re referring to the comma operator in scalar context, which “evaluates its left argument, throws that value away, then evaluates its right argument and returns that value.” (perlop#Comma-Operator).

A quick Google search found this 2010 discussion: http://stackoverflow.com/questions/2200759/when-is-perls-scalar-comma-operator-useful, in which Jonathan Feinberg suggests that the scalar context comma operator is provided for two reasons:

As a hangover from C, because Perl was originally derived from C.
Because it’s useful in cases where you want to execute two or more statements in a syntactic context that allows only a single statement.

Here’s a contrived example:

19:49 >perl -wE "for (my ($i, $j) = (1, 5); $i <= 5; ++$i, --$j) { say
+ abs($i - $j); }"
4
2
0
2
4

19:49 >
[download]

Of course, it is quite possible to re-structure that loop without resorting to use of the comma operator in scalar context. But in Perl’s spirit of TMTOWTDI, the ++$i, --$j syntax is provided for convenience. That’s my take on it, anyway.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^5: hangman game by QM (Parson) on May 19, 2015 at 10:18 UTC
`++$i, --$j` Yes, that's a good example. However, it seems that as long as the sub-expressions are evaluated, it would work the same way: `for (my ($i, $j) = (1, 5); $i <= 5; ++$i + --$j) { say abs($i - $j); } 4 2 0 2 4` [download] Which is a bit more unobvious, and not what I was after. A `do { block; }` also works, as would almost anything that evaluated the sub-expressions, and throw the result away. A more complicated variable update would look odd though. Probably better to just use a `while` loop in that case. Are there any other examples that are more difficult to rewrite without the comma operator? -QM -- Quantum Mechanics: The dreams stuff is made of	[reply] [d/l] [select]

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Re^5: hangman game
by QM (Parson) on May 19, 2015 at 10:18 UTC

++$i, --$j

However, it seems that as long as the sub-expressions are evaluated, it would work the same way:

for (my ($i, $j) = (1, 5); $i <= 5; ++$i + --$j) {
    say abs($i - $j); 
}

4
2
0
2
4
[download]

Which is a bit more unobvious, and not what I was after.

A do { block; } also works, as would almost anything that evaluated the sub-expressions, and throw the result away. A more complicated variable update would look odd though. Probably better to just use a while loop in that case.

Are there any other examples that are more difficult to rewrite without the comma operator?

-QM
--
Quantum Mechanics: The dreams stuff is made of

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