# dateregex - a regular expression expression to find dates in text,
# taken from Regular Expressions for Language Engineering, 
# Karttunen, Chanod, Grefenstette, 1997, Rank Xerox Research Center, France
# Perl can handle it.


$n1to9 = '[1-9]';
$n0to9 = '[0-9]';
$SP   = ',\s+';
$day   = '(Monday|Tuesday|Wednesday|Thursday|Friday|Saturday|Sunday)';
$month = '(January|February|March|April|May|June|July|August|September|October|November|December)';
$date  = '([12][0-9]|[1-9]|3[01])';
$year  = '([1-9][0-9][0-9][0-9])';  
$date_expression = '($day|(($day$SP)?$month $date($SP$year)?))';
$long_date = '(($day$SP)?$month\s+$date($SP$year)?)';

@text = <DATA>;
$text = join(" ",@text);
print $text;

#$no text =~ s/$long_date/\[$1\]/g;
$text =~ s/((($day$SP)?$month\s+$date($SP$year)?)|$day)/\[$1\]/g; # yes

#no $text =~ s/($date_expression)/\[$1\]/g;
# yes $text =~ s/($year|$date)/\[$1\]/g;
print "text: ", $text;


# regular expression symbols: 
# 0 - epsilon, empty string, 
# ? - any
# # - boundary marker, refers to either the beginning or end of a string
# % - the escape character


__DATA__
Sunday
August 11
Sunday, August 11
August 11, 1996
Sunday, August 11, 1996
1
2
Tuesday
3
Monday