For Syntax Question

thrashbarg has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: For Syntax Question by pg (Canon) on Jul 19, 2004 at 16:39 UTC
Perlish! Just a style thing. That for is sort of modifier. It made you go through all elements of @a, and apply the operation to each of them. As if you are saying: `@e = (1,2,3,4); my $foo; for (@e) { $foo += $_ } print $foo;` [download]	[reply] [d/l]
Re: For Syntax Question by hardburn (Abbot) on Jul 19, 2004 at 16:40 UTC
Run it through B::Deparse to see how perl sees it: `$ perl -MO=Deparse -e '$foo += $_ for @e;' ; foreach $_ (@e) { $foo += $_; } -e syntax OK` [download] As the output shows, that line is exactly the same as if you had used `foreach $_ (@e) { . . .`. Taking the `for` to the end of the line just allows you to cram it into one statement, for better or worse. ---- send money to your kernel via the boot loader.. This and more wisdom available from Markov Hardburn.	[reply] [d/l] [select]
Re: For Syntax Question by borisz (Canon) on Jul 19, 2004 at 16:40 UTC
the code is the same as `foreach $_ (@e) { $foo += $_; }` [download] the syntax is for all kind of oneliners like this `$foo += $_ if $x < $foo;` [download] Boris	[reply] [d/l] [select]
Re: For Syntax Question by Limbic~Region (Chancellor) on Jul 19, 2004 at 16:43 UTC
threshbarg, Larry's formal training makes him a linguist. One of the main design goals of Perl is so that it is a "natural" language. Basically that means you can write your code the way you might speak it. The two main ways of doing this is: Do X for Y cases For Y cases do X to each case The latter takes a block {} and can be very complex. The former needs to pretty much be a single statement. You can use the low precendence operators like and/or to link a few but you strike out when you try and put conditionals like if in there. So to answer your question: In each iteration of the loop, $_ (see perldoc perlvar) is replaced with the value (actually it is an alias) of the index being iterated over in @e. That value is being added to the current value of $foo Cheers - L~R	[reply]
Re: For Syntax Question by pbeckingham (Parson) on Jul 19, 2004 at 17:29 UTC
The general form is: `<statement> <modifier>` [download] and it is roughly equivalent to: `<modifier> { <statement> }` [download] The modifiers can take the form of a conditional, or a looping construct: `<statement> if $a > 1; <statement> unless $true;` [download] `<statement> for @a; <statement> for 1..10; <statement> for keys %hash;` [download] The rule is that there can only be one modifier, so while there can be a complex logical condition, there cannot be two distinct conditions, or a mix of condition and loop. So the following are not valid: `<statement> <modifier> <modifier> <statement> for @a unless $true;` [download]	[reply] [d/l] [select]