sub ScanDirectory my $workDir shift my files opendir DIRHND, $workDir or die "Unable to open $workDi

1
sub ScanDirectory my workDir shift my
_at_files opendir( DIRHND, workDir) or
die "Unable to open workDir !\n"
while( my file readdir( DIRHND ) )
next if( file eq "." file eq ".." )
if( -d workDir . file )
push( _at_files, ScanDirectory( workDir . file )
) next push( _at_files,
"file\n" ) closedir( DIRHND )
return _at_files my dir shiftmy
_at_dirContent ScanDirectory( dir )print
_at_dirContent
2
kw.pm

• Perl 6 Rules and Grammars

3
Introduction

• Talk in two parts
• A quick look and evaluation of what exists to use
  now.
• A quick look at what is proposed, and what is
  good about it.
• Then beer.

perl 6 rules and grammars
4
State of mi/Onion/

• Here is what exists currently in terms of
  implementation
• Perl6Rules a CPAN module that implements a
  subset of the spec.
• The Parrot/Perl6 implementation has 0 so far on
  Pattern matching. Pugs is in the same state.

perl 6 rules and grammars
5
Perl6Rules

• Perl6Rules was created and published to CPAN in
  April 2004 by Damian Conway.
• It was originally part of the Perl6 bootstrapping
  plan They would implement Ponie and Parrot, and
  then use Perl6Rules to compile the initial
  Perl6. Then Perl6 could be self-hosting.

perl 6 rules and grammars
6
Perl6Rules

• But Perl6Rules simply isnt very good. At
  least in my opinion.
• It is rich on Damian-esque Source-Filter magic,
  but a little low on the set of things not
  Source-Filter magic.
• First of all, getting it going on Cygwin took me
  some time

perl 6 rules and grammars
7
Perl6Rules

• I ended up with stuff like this
• Failed 12/41 test scripts, 70.73 okay.
  -124/2401 subtests failed, 105.16 okay.
• test program seems to have generated a core
• Fatal error in one or more Perl 6 rules panic
  regfree data code 'ÿ' during global destruction.

perl 6 rules and grammars
8
Perl6Rules

• I know cygwin is a less popular, less robust
  place to do business, but 6 cores seemed a little
  high. However, Testers shows that it also fails
  on Solaris, BSD and Linux.
• I also disliked that it depended on YAML, but not
  in a way that CPAN.pm understood.
• Lastly, it was slow. Deadly slow.

perl 6 rules and grammars
9
Perl6Rules

• The other-other issue was that it doesnt
  completely implement Rules, nor consistent with
  the current spec.
• All that said, I was able to play around with the
  module, and get a bit of a feel for Rules.
• My suspicion is that Perl6 will bootstrap with
  Pugs.

perl 6 rules and grammars
10
Working Example

• __DATA__
• id centre points (relative to 1x1 unit
  square)
• centre indicates squares that are
  rotationally
• symetrical
• ------------------------------------------------
  -
• 1 (centre) 0, 0 1, 0 1, 1 0, 1
• 2 0, 1 1, 1 1, 0
• 3 0, 0 0.5, 1 1, 0
• 4 (centre) 0, 0.5 0.5, 1 1, 0.5 0.5, 0
• 5 0.5, 0 0.5, 1 1, 1 1, 0
• 6 0, 0 0, 0.5 1, 1 0.5, 0
• 7 0.25, 0.5 0.5, 0 0, 0 0.5, 0.99
  \
• 1, 0 0.5, 0 0.75, 0.5 0.25, 0.5
• etc

perl 6 rules and grammars
11
Working Example

• grammar NineBlock
• meta bits
• rule continuation \\ \n
• rule blankline
• rule comment \ .?
• top level
• rule config
• rule line w ?
  
• line components
• rule idnum w ( \d ) \ 1 print
  "1\n"
• rule centre \( centre center \)
  
• rule points w
• rule pair w ,
• rule point \d \. \d ?

perl 6 rules and grammars
12
Working Example

• slurp
• my config do local /
• heal continuations, ditch blanks and comments
• config s
• g
• validate
• print "valid\n" if config m/
  /

perl 6 rules and grammars
13
Working Example

• And that was about as far as I got with my
  working example.
• I spent an awfully long time trying to get it to
  capture things automatically, but without much
  luck.
• The captured results are returned into a tied
  global called 0, which was quirky and
  unmanageable.

perl 6 rules and grammars
14
Interpolation and Closures

• Perl 5
• _at_cmd qw get put try find copy
• cmd join '', map quotemeta _ _at_cmd
• str / (?cmd) \( .? \) /x
• Perl 6
• _at_cmd qw get put try find copy
• str mw/ _at_cmd \( .? \) /
• Or
• my _at_cmds
• str mweach/ ( _at_cmd ) ( \( \N? \) )
  
• push _at_cmds, cmd(1) arg(2) /

perl 6 rules and grammars
15
Qualifiers

• Other qualifiers
• my foo "fee fi fo feh far foo fum "
• foo seach2nd/ ( f \w ) /bar/
• foo now "fee bar fo bar far bar fum "
• my str "ahhh"
• _at_matches str m/ ah /
• returns "ahhh"
• _at_matches str many/ ah /
• returns "ahhh", "ahh", "ah", "a"

perl 6 rules and grammars
16
Flow control

• The backtracking controls are cleaner and way
  more powerful. But, they force you to think in a
  different way.
• dont retry previous atom
• fail out of current alternation
• fail out of current rule
• fail out of entire match
• uri m http\ftp\mailto\
• //

perl 6 rules and grammars
17
Flowcontrol

• Specifically, they cause you to think about your
  regex as a little program.
• Better examples
• m/ rm _at_options /
• mw/ if
• for
• loop ? /
• rule subname
• ( _ \w )
• fail if reserved1

perl 6 rules and grammars
18
Rules/Assertions

• Predefined Rules/Assertions
• ,,
• lookahead/behind
• (was (?pattern))
• ,

perl 6 rules and grammars
19
More Assertions

• m/ () /
• a closure that evaluates to a rule
• closure that runs at canonical time
• assertion that can be optimized away
• ie. m/ (.) bar /
• symbolic indirect
• short for
• same as p5 a-z_
• same
• negated a-z_
• -A-Za-z set ops

perl 6 rules and grammars
20
Yet More Assertions

• aggregate rules
• much like bare hash _at_array, but only
• evaluate to rules (string or ref).
• my _at_dog ( rxi Butch , rxi Duke ,
• rxi Teacup , )
• mw/Lets take for a walk./
• Literal assertions

perl 6 rules and grammars
21
Rules are Subs/Methods

• rule badline( Str errmsg )
• ( \N ) fail "errmsg 1"
• other rules
• given( lines )
• m
• line group
• _at_cmd
• command followed by etc.

perl 6 rules and grammars
22
Rules are Subs/Methods

• rule block
• \(
• stuff that isnt a block, or a block
• \)
• rule xblock(left, right)
• left
• right
• right

perl 6 rules and grammars
23
Readable 0-width assertions

• rule quoted_string (type)
• type
• type
• type
• rule string
• (
• )

perl 6 rules and grammars
24
Assertions and Binding

• rule quoted_string (type)
• type
• type
• type

perl 6 rules and grammars
25
Binding

• So, the part I like best about Perl6 Rules is the
  ease of reasonable capturing.
• In p5, I do this sort of junk all the time
• hash str m/(\w)(\w)/g
• Or, I see people doing stuff like this
• str m/Number\s(\d)/
• my num 1

perl 6 rules and grammars
26
Binding

• Or struggling with things like this
• m/(? attr(\w) )/xi
• or
• m/I ((dont)? know (howwhere)) to count from./
• In Perl6 rules, there are lots of nice, clean
  ways of binding your results to meaningful,
  lexical names.

perl 6 rules and grammars
27
Hypothetical Binding

• Starting from least cool, moving towards most
  cool
• normal lexical
• my num
• m/ (\d) let num 1 () /
• match lexical
• m/ (\d) let 1 () /
• In this case the variable lives in match
• variable / rather than the surrounding
• lexical pad. /num or /num.
• Also available as while / in scope.

perl 6 rules and grammars
28
Hypothetical Binding

• Alternations
• m/
• (\d) let 1
• () let 2
• (.) let 3
• /
• Shorthand for binding hypothetically
• m/
• (\d)
• ()
• (.)
• /

perl 6 rules and grammars
29
Hypothetical Binding

• hypo-bind n, if desired
• my (key, val) mw
• 1 (\w) \ 2 (.?)
• 2 (.?) \
• Repeated captures can be bound to arrays
• m/ _at_ (.?) , /
• Pairs of repeated captures can be bound to
  hashes
• m/ () (\N) /
• m/ (\N) /

perl 6 rules and grammars
30
Auto Hypothetical Binding

• captures to by default
• m/ ws \ ws
• hashkey value /
• suppresses autocapture
• What exactly happens in recursive-auto-hypo-bind
  cases is entirely hazy to me at this time. And I
  cant test it.
• In theory we are supposed to end up with a nice
  tree structure.

perl 6 rules and grammars
31
Auto Hypothetical Binding

• captures to by default
• m/ ws \ ws
• hashkey value /
• suppresses autocapture
• What exactly happens in recursive-auto-hypo-bind
  cases is entirely hazy to me at this time. And I
  cant test it.
• In theory we are supposed to end up with a nice
  tree structure.

perl 6 rules and grammars
32
Example

• grammar NineBlock
• meta bits
• rule continuation \\ \n
• rule blankline
• rule comment \ .?
• top level
• rule config
• rule line w ?
  
• line components
• rule idnum w ( \d ) \ 1 print
  "1\n"
• rule centre \( centre center \)
  
• rule points w
• rule pair w ,
• rule point \d \. \d ?

perl 6 rules and grammars
33
Ameliorated Example

• grammar NineBlock
• rule config
• push _at_,
• id ( )
• centre( ?
  10 )
• coord ( _at_ )
  
• 
  
• rule line w ?
  
• rule points w _at_ ()
• ?
• push _at_,
  ,
• 
  
• rule pair w ,
  
• rule point ( \d \.\d? )
• rule idnum w ( \d ) \
  
• rule centre \( centre center \)
  

perl 6 rules and grammars
34
Ameliorated Example

• slurp
• my conffile do local /
• Parse!
• my _at_nodes
• if ( conffile m/ / )
• _at_nodes _at_
• else
• die couldnt parse conffile!
• if ( _at_node0centre )
• etc

perl 6 rules and grammars
35
Conclusion

• In fact, I shouldnt have to do all that pushing
  and manual capturing. I should be able to let
  the grammar do it for me.
• But, I dont know how yet, and I suspect no one
  does.
• Questions?
• Beers?

perl 6 rules and grammars