Perl6 grammars

Regexes
and Grammars
in Perl 6

Damian Conway
Allison Randal
Patrick Michaud
Larry Wall
Moritz Lenz

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

Regular expressions
in Perl 5 were not regular

Regular expressions

Regular expressions
in Perl 6 are called regexes

Regular expressions

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

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+)/;

Capturing group

(...)

Non-capturing group

[...]

Character class

<[ . . . ]>

Embedded closure

{...}

Embedded closure

{...}

> "500" ~~ /(d+) {$0 < 200 or fail}/
===SORRY!===

Named rule or token

<. . .>

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

grammar Grammar {
rule TOP {...}
}
Syntax is similar
to class deﬁnition

grammar Grammar {
rule TOP {...}
}
Grammar.parse($string);

Executed by Rakudo

rakudo.org

Executed by Rakudo

rakudo.org

Sometimes it fails

grammar SearchQuery {
rule TOP {

}
}

rule TOP {
^
$
}
}

rule TOP {
^
<query>
$
}
}

rule TOP {
^
<query>
$
}
}

Easy, isn't it?

Grammars are part
of the language

rule TOP {
^
<query>
$
}
rule query {
}
}

rule TOP {
^
<query>
$
}
rule query {
<city>
}
}

rule TOP {
^
<query>
$
}
rule query {
<city>
}
token city {
}
}

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

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,
to => 9,
named => {
city => Match.new(
from => 0,
to => 9,
named => {
capital => Match.new(
from => 0,

Match.new(
from => 0, Matched text
to => 9,
named => {
query => Match.new(
from => 0,
to => 9,
named => {
city => Match.new(
from => 0,
to => 9,
named => {
from => 0,

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

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

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

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>
| <country>
}

SearchQuery.parse("Tirana, Albania");

Everything goes
to Match object

$/

say $<query><city>;
say $<query><country>;

say $<query><city>;

Tirana
Albania

say $<query><city>; Shortcut

say $/<query><city>; Full syntax
say $/<query><country>;

rule query {
'Hotels in'?
[
| <city>
| <country>
]
}

say $<query><city>;

SearchQuery.parse
("Hotels in Tirana, Albania");
say $<query><city>;

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>
| <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

Perl6 grammars

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