On Mar 17, 2011, at 1:49 PM, C.DeRykus wrote:
> On Mar 16, 9:58 am, c...@pobox.com (Chap Harrison) wrote:
>>
>> #!/usr/bin/perl
>>
>> use warnings;
>> use strict;
>> use feature ":5.10";
>>
>> #
>> # $line, unless empty, should contain one or more white-space-separated
>> # expressions of the form
>> # FOO
>> # or BAZ = BAR
>> #
>> # We need to parse them and set
>> # $param{FOO} = 1 # default if value is omitted
>> # $param{BAZ} = 'BAR'
>> #
>> # Valid input example:
>> # MIN=2 MAX = 12 WEIGHTED TOTAL= 20
>> # $param{MIN} = '2'
>> # $param{MAX} = '12'
>> # $param{WEIGHTED} = 1
>> # $param{TOTAL} = '20'
>> #
>>
>> my $line = 'min=2 max = 12 weighted total= 20';
>> $line = 'min=2 max, = 12 weighted total= 20';
>> say $line;
>> my %param;
>>
>> if ( $line and
>> ($line !~
>> s/
>> \G # Begin where prev. left off
>> (?: # Either a parameter...
>> (?: # Keyword clause:
>> (\w+) # KEYWORD (captured $1)
>> (?: # Value clause:
>> \s* #
>> = # equal sign
>> \s* #
>> (\w+) # VALUE (captured $2)
>> )? # Value clause is optional
>> )
>> \s* # eat up any trailing ws
>> ) ### <-- moved
>> | # ... or ...
>> $ # End of line.
>> / # use captured to set %param
>> $param{uc $1} = ( $2 ? $2 : 1 ) if defined $1;
>> /xeg
>> ) ) {
>> say "Syntax error: '$line'";
>> while (my ($x, $y) = each %param) {say "$x='$y'";}
>> exit;}
>>
>> while (my ($x, $y) = each %param) {say "$x='$y'";}
>
> I believe the problem is the "? # Value clause is optional"
> since, in the case of your badline with a ",", the regex will
> consume 'max' and then ignore the , since ? means 0 or 1
> instance. Therefore the regex will still succeed and $2 will
> be undefined. So the VALUE gets set to 1.
>
I agree - encountering the ',' causes the regex to think it's encountered a
keyword without a value. But why doesn't the *next* iteration of the global
substitution (which would begin at the ',') fail, causing the if-statement to
succeed and print "Syntax error"?
Perhaps I don't fully understand how the /g option works.... I thought it
would continue to "iterate" until either it reached the end of the string (in
which case the s/// would be considered to have succeeded) or it could not
match anything further (in which case it would be considered to have failed).
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