Perl6 grammars

Regexes and Grammars in Perl 6

Preface

Synopsis 5

Synopsis 5 Regexes and Rules

Damian Conway Allison Randal Patrick Michaud Larry Wall Moritz Lenz

Created: 24 Jun 2002 Last Modified: 30 Aug 2010 Version: 132

54 pages

Part I Regexes

Random facts and terminology

Regular expressions in Perl 5 were not regular

Regular expressions in Perl 5 were not regular Regular expressions in Perl 6 are called regexes

Regular expressions in Perl 5 were not regular Regular expressions in Perl 6 are called regexes Which means “kinda like a regular expression”

Match object contains result of matching $/

Capture variable indexes start with 0 $0

$0, $1, etc. are part of $/

my $q = "Hotels in Berlin"; $q ~~ /ins(.*)/; say $0; # Berlin say $/[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 "a1nb2nc3" ~~ /N+/; "a1nb2nc3" ~~ /^^ .2 $$/;

/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

grammar rule token proto TOP

grammar Grammar { rule TOP {...} rule some_rule {...} token some_token {...} }

grammar Grammar { rule TOP {...} rule some_rule {...} token some_token {...} } Syntax is similar to 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

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 { N. B. rule TOP { ^ <query> $ rules } rule query { <city> } token token city { } }

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> } }

^ <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",

Match.new( from => 0, Matched text 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",

Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( rule query { from => 0, } orig => "Amsterdam", to => 9, named => { city => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam",

Match.new( from => 0, orig => "Amsterdam", to => 9, named => { query => Match.new( from => 0, orig => "Amsterdam", to => 9, named => { city => Match.new( token city { from => 0, } orig => "Amsterdam", to => 9, named => { capital => Match.new( from => 0, orig => "Amsterdam",

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( token capital { from => 0, } orig => "Amsterdam",

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");

Capturing and accessing

Everything goes to 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>; Shortcut say $<query><country>; say $/<query><city>; Full syntax say $/<query><country>;

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 December or 25 December

How to check days token day { (d+) {$0 <= 31 or fail} }

[ <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 from 25 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

__END__ Andrew Shitov talks.shitov.ru | andy@shitov.ru

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Perl6 grammars

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