perl6 grammars
DESCRIPTION
TRANSCRIPT
Regexesand Grammars
in Perl 6
Preface
Synopsis 5
Synopsis 5Regexes and Rules
S05
Damian ConwayAllison RandalPatrick MichaudLarry WallMoritz Lenz
Created: 24 Jun 2002Last Modified: 30 Aug 2010Version: 132
54 pages
Part I
Regexes
Random factsand terminology
Regular expressionsin Perl 5 were not regular
Regular expressionsin Perl 5 were not regular
Regular expressionsin Perl 6 are called regexes
Regular expressionsin Perl 5 were not regular
Regular expressionsin Perl 6 are called regexes
Which means “kinda like a regular expression”
Match objectcontains result of matching
$/
Capture variable indexesstart with 0
$0
$0, $1, etc.are part of $/
my $q = "Hotels in Berlin";$q ~~ /in\s(.*)/;
say $0; # Berlinsay $/[0]; # Berlin
Metacharacters
are everything except Unicode letters or numbers or underscore
Quotes
may be used for creating atoms
'I will never use PHP again. '*
Repetition
(\d+ \s?) ** 3
(\d+ \s?) ** 5..10
\d+ ** ','
/x modifier gone
"ab" ~~ / a b /;say $/; # ab
/s, /m modifiers gone
"a1\nb2\nc3" ~~ /^^ .2 $$/;
"a1\nb2\nc3" ~~ /\N+/;
/e modifier gone
$str =~ s/pattern/{action()}/;
Modifier syntax
@names = $str =~ m:i/MiSteR \s (\w+)/;
Brackets
Capturing group
( . . . )
Non-capturing group
[ . . . ]
Character class
<[ . . . ]>
Embedded closure
{ . . . }
Embedded closure
{ . . . }
> "500" ~~ /(\d+) {$0 < 200 or fail}/===SORRY!===
Named rule or token
<. . .>
Part II
Grammars
Keywords
grammargrammarruletokenprotoTOP
grammar Grammar { rule TOP {...} rule some_rule {...} token some_token {...}}
grammar Grammar { rule TOP {...} rule some_rule {...} token some_token {...}}Syntax is similarto class definition
grammar Grammar { rule TOP {...} rule some_rule {...} token some_token {...}}Grammar.parse($string);
Example.Step by step
Executed by Rakudo
rakudo.org
Executed by Rakudo
rakudo.org
Sometimes it fails
City
grammar SearchQuery {
}
grammar SearchQuery { rule TOP { }}
grammar SearchQuery { rule TOP { ^ $ }}
grammar SearchQuery { rule TOP { ^ <query> $ }}
grammar SearchQuery { rule TOP { ^ <query> $ }}
Easy, isn't it?
Grammars are part of the language
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { }}
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { <city> }}
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { <city> } token city { }}
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { <city> } token city { }}
N. B.
rules
token
token is a "word"
rule is a "phrase"
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { <city> } token city { }}
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { <city> } token city { <capital> }}
grammar SearchQuery { rule TOP { ^ <query> $ } rule query { <city> } token city { <capital> } token capital { }}
my $result = SearchQuery.parse("Amsterdam");say $result.perl;
Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { city => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam", to => 9, ), }, ), }, ), },)
Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { city => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam", to => 9, ), }, ), }, ), },)
Matched text
Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { city => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam", to => 9, ), }, ), }, ), },)
rule query {}
Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { city => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam", to => 9, ), }, ), }, ), },)
token city {}
Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { city => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam", to => 9, ), }, ), }, ), },)
token capital {}
Country
rule query { <city> | <country>}
rule query { <city> | <country>}rule country { 'Afghanistan' | 'Akrotiri' | 'Albania' | 'Algeria' | 'American Samoa' | 'Andorra' . . .}
my $result = SearchQuery.parse("Amsterdam");say $result.perl;
$result = SearchQuery.parse("China");say $result.perl;
rule query { <city> ',' <ws>? <country> | <city> | <country>}
rule query { <city> ',' <ws>? <country> | <city> | <country>}
SearchQuery.parse("Tirana, Albania");
rule query { <city> ',' <ws>? <country> | <city> | <country>}
SearchQuery.parse("Tirana, Albania");
Capturing and accessing
Everything goesto Match object
$/
SearchQuery.parse("Tirana, Albania");say $<query><city>;say $<query><country>;
SearchQuery.parse("Tirana, Albania");say $<query><city>;say $<query><country>;
Tirana
Albania
SearchQuery.parse("Tirana, Albania");say $<query><city>;say $<query><country>;
say $/<query><city>;say $/<query><country>;
Shortcut
Full syntax
rule query { 'Hotels in'? [ <city> ',' <ws>? <country> | <city> | <country> ] }
SearchQuery.parse("Tirana, Albania");say $<query><city>;say $<query><country>;
SearchQuery.parse\ ("Hotels in Tirana, Albania");say $<query><city>;say $<query><country>;
rule date { <day> <month> } token day { \d+ ['st' | 'nd' | 'th']? } token month { 'January' | 'February' | 'March' | 'April' . . .
SearchQuery.parse("Hotels in Tirana, Albania from 25th December");
SearchQuery.parse("Hotels in Tirana, Albania from 25 December");
What will $<query><date>
print?
What will $<query><date>
print?
25th Decemberor
25 December
token day { (\d+) {$0 <= 31 or fail} }
How to check days
rule query { 'Hotels in '? [ <city> ',' <ws>? <country> | <city> | <country> ] [ 'from' <date> 'to' <date> ]? [ 'for' <guest_number> ]? }
token guest_number { \d | 'one' | 'two' | 'three' | 'four' | 'five' }
"Hotels in Tirana, Albania from25 December to 7 January for two"
rule date { 'today' | 'tomorrow' | [ <day> <month> ] }
$ perl6 10-all.pl Hotels in Amsterdam, Netherlands from 1 January to 5 February for three City: Amsterdam Country: Netherlands From: 1 January To: 5 February Guests: three
