.. operator and not including the condition of right operand

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

Replies are listed 'Best First'.
Re: .. operator and not including the condition of right operand by bart (Canon) on Apr 27, 2005 at 19:17 UTC
Inspect the result of the range operator a little closer... you'll find that it's not only usable as a boolean, but as a counter, and as an end indicator too. When the right hand evaluates to true, the value will contain an "E" (from exponent). This variation: `my @aap = qw( 0aap 0noot 1mies 2mies 0aap 0noot 1mies 6mies ); foreach (@aap) { if (my $test = ( /^1(.)/ .. /^0(.)/ )) { print "$test: $1\n"; } }` [download] Prints: 1: mies 2: mies 3E0: aap 1: mies 2: mies Spot the "E0"? Alternatively, you can set a flag in the right hand side. `my @aap = qw( 0aap 0noot 1mies 2mies 0aap 0noot 1mies 6mies ); foreach (@aap) { if (/^1(.)/ .. (my $last = /^0(.)/ )) { unless($last) { print "$1\n"; } } }` [download] Result: mies mies mies mies	[reply] [d/l] [select]
Re^2: .. operator and not including the condition of right operand by tlm (Prior) on Apr 28, 2005 at 02:16 UTC
In the "perverse" category: `use strict; use warnings; my @aap = qw( 0aap 0noot 1mies 2mies 0aap 0noot 1mies 6mies ); for (@aap) { print "$_\n" if - reverse '0' . (/^1(.)/ .. /^0(.)/); } __END__ 1mies 2mies 1mies 6mies` [download] I wonder what's more common, the situation described by the OP or the need to know the sequence number of the match? If the former is more common, then I think one could make the case for having the match of the right operand return a string of the form `'0En'` instead of the current `'nE0'`. Then, all that would be required to satisfy the OP's request would be to prepend `0+`, or better yet, a minus sign, in front of the `..` expression: `if ( -(/^1(.)/../^0(.)/) )` [download] whereas if one wanted to keep the line matching the right operand one would omit the `0+` or minus sign: `if ( (/^1(.)/../^0(.)/) )` [download] Those who actually wanted the match number, would have to scrape it off the return value: `if ( ( /^1(.)/../^0(.)/ ) =~ /(\d+)$/ ) { # $1 contains the sequence number of match` [download] I've tested this scheme a bit, and it seems to work; please let me know if I missed some corner (or not-so-corner) cases. the lowliest monk	[reply] [d/l] [select]
Re^3: .. operator and not including the condition of right operand by bart (Canon) on Apr 28, 2005 at 06:23 UTC
The reason for appending "E0" is that the value in numerical context is unchanged: "3E0" as an integer is 3 (just like "3E1" is 30; not because numification ignores everything from the "E" till the end). Your value would means zero. And I don't think `0+$count` is easier than `$count =~ /E/`. Nor faster, or much faster at least. Your `/(\d+)$/` definitely isn't easy, nor likely very fast. As you can guess from the generally unknown behaviour of what `..` actually returns, neither requirements are very common. That's why I'm most happy with the status, like it is.	[reply] [d/l] [select]
Re^4: .. operator and not including the condition of right operand by tlm (Prior) on Apr 28, 2005 at 12:18 UTC
Re: .. operator and not including the condition of right operand by dragonchild (Archbishop) on Apr 27, 2005 at 18:53 UTC
What should you do for `qw( 0aap 2mies 0aap 1mies 2mies 0aap );`? That will determine the best answer. The Perfect is the Enemy of the Good.	[reply] [d/l]
Re^2: .. operator and not including the condition of right operand by eXile (Priest) on Apr 27, 2005 at 18:57 UTC
1mies should start the match, so `mies mies` [download] should be printed in that case (updated the OP, to clarify)	[reply] [d/l]
Re^3: .. operator and not including the condition of right operand by dragonchild (Archbishop) on Apr 27, 2005 at 19:05 UTC
`my $good; for (@aap) { my ($type, $value) = /^(\d)(.*)/ or next; if ( $type == 0 ) { $good = 0; next; } elsif ($type == 1) { $good = 1; } next unless $good; print "$value\n"; }` [download] (Untested) The Perfect is the Enemy of the Good.	[reply] [d/l]
Re^4: .. operator and not including the condition of right operand by halley (Prior) on Apr 27, 2005 at 19:46 UTC
Re: .. operator and not including the condition of right operand by Fletch (Bishop) on Apr 27, 2005 at 19:18 UTC
Perhaps `...` which defers evaluating the right hand side until the next time the `...` is tested?	[reply] [d/l] [select]
Re: .. operator and not including the condition of right operand by ambrus (Abbot) on Apr 28, 2005 at 12:39 UTC
Try `?^1(.)?` instead of `/^1(.)/` on the left hand side of the flip-flop.	[reply] [d/l] [select]
Re: .. operator and not including the condition of right operand by sh1tn (Priest) on Apr 27, 2005 at 19:50 UTC
`foreach (@aap) { if( /^1/ ... !/^0/ ){ print "$_\n" } } __END__ 1mies 2mies 1mies 6mies` [download]	[reply] [d/l]
Re^2: .. operator and not including the condition of right operand by Roy Johnson (Monsignor) on Apr 27, 2005 at 20:00 UTC
Try that with `my @aap = qw(1one two three four 0stop done);` [download] The difference between the two-dot and three-dot forms is merely that the RHS will not be evaluated on the same pass as the LHS for the three-dot form. Your expression guarantees that a line beginning with 1 and any following lines beginning with 0 will be printed, plus one line that doesn't begin with 0. Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^3: .. operator and not including the condition of right operand by sh1tn (Priest) on Apr 27, 2005 at 20:09 UTC
`... if( /^1/ ... /^(0.*)/ ) { $1 and next; print "$_\n"; } ...` [download]	[reply] [d/l]
Re^4: .. operator and not including the condition of right operand by Roy Johnson (Monsignor) on Apr 27, 2005 at 20:22 UTC
Re^2: .. operator and not including the condition of right operand by tlm (Prior) on Apr 27, 2005 at 20:00 UTC
This fails with a different input: `% cat aap2 0aap 0noot 1mies 2mies 3mies 0aap 0noot 1mies 6mies % perl -nle 'print if (/^1/...!/^0/)' aap2 1mies 2mies 1mies 6mies` [download] Correct output should include `3mies`. the lowliest monk	[reply] [d/l] [select]