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+---
+name: perl6
+category: language
+language: perl6
+filename: learnperl6.pl
+contributors:
+    - ["Nami-Doc", "http://github.com/Nami-Doc"]
+---
+
+Perl 6 is a highly capable, feature-rich programming language made for at
+least the next hundred years.
+
+The primary Perl 6 compiler is called [Rakudo](http://rakudo.org), which runs on
+the JVM and [the MoarVM](http://moarvm.com) and
+[prior to March 2015](http://pmthium.com/2015/02/suspending-rakudo-parrot/),
+[the Parrot VM](http://parrot.org/).
+
+Meta-note : the triple pound signs are here to denote headlines,
+double paragraphs, and single notes.
+
+`#=>` represents the output of a command.
+
+```perl
+# Single line comment start with a pound
+
+#`(
+  Multiline comments use #` and a quoting construct.
+  (), [], {}, 「」, etc, will work.
+)
+
+### Variables
+
+# In Perl 6, you declare a lexical variable using `my`
+my $variable;
+# Perl 6 has 4 kinds of variables:
+
+## * Scalars. They represent a single value. They start with a `$`
+
+my $str = 'String';
+# double quotes allow for interpolation (which we'll see later):
+my $str2 = "String";
+
+# variable names can contain but not end with simple quotes and dashes,
+#  and can contain (and end with) underscores :
+# my $weird'variable-name_ = 5; # works !
+
+my $bool = True; # `True` and `False` are Perl 6's boolean
+my $inverse = !$bool; # You can invert a bool with the prefix `!` operator
+my $forced-bool = so $str; # And you can use the prefix `so` operator
+                           # which turns its operand into a Bool
+
+## * Lists. They represent multiple values. Their name start with `@`.
+
+my @array = 'a', 'b', 'c';
+# equivalent to :
+my @letters = <a b c>; # array of words, delimited by space.
+                     # Similar to perl5's qw, or Ruby's %w.
+my @array = 1, 2, 3;
+
+say @array[2]; # Array indices start at 0 -- This is the third element
+
+say "Interpolate an array using [] : @array[]";
+#=> Interpolate an array using [] : 1 2 3
+
+@array[0] = -1; # Assign a new value to an array index
+@array[0, 1] = 5, 6; # Assign multiple values
+
+my @keys = 0, 2;
+@array[@keys] = @letters; # Assign using an array
+say @array; #=> a 6 b
+
+## * Hashes, or key-value Pairs.
+# Hashes are actually arrays of Pairs
+# (you can construct a Pair object using the syntax `Key => Value`),
+#  except they get "flattened" (hash context), removing duplicated keys.
+my %hash = 1 => 2,
+           3 => 4;
+my %hash = autoquoted => "key", # keys get auto-quoted
+            "some other" => "value", # trailing commas are okay
+            ;
+my %hash = <key1 value1 key2 value2>; # you can also create a hash
+                                      # from an even-numbered array
+my %hash = key1 => 'value1', key2 => 'value2'; # same as this
+
+# You can also use the "colon pair" syntax:
+# (especially handy for named parameters that you'll see later)
+my %hash = :w(1), # equivalent to `w => 1`
+           # this is useful for the `True` shortcut:
+           :truey, # equivalent to `:truey(True)`, or `truey => True`
+           # and for the `False` one:
+           :!falsey, # equivalent to `:falsey(False)`, or `falsey => False`
+           ;
+
+say %hash{'key1'}; # You can use {} to get the value from a key
+say %hash<key2>;   # If it's a string, you can actually use <>
+                   # (`{key1}` doesn't work, as Perl6 doesn't have barewords)
+
+## * Subs (subroutines, or functions in most other languages).
+# Stored in variable, they use `&`.
+sub say-hello { say "Hello, world" }
+
+sub say-hello-to(Str $name) { # You can provide the type of an argument
+                              # and it'll be checked at compile-time.
+
+    say "Hello, $name !";
+}
+
+## It can also have optional arguments:
+sub with-optional($arg?) { # the "?" marks the argument optional
+  say "I might return `(Any)` if I don't have an argument passed,
+      or I'll return my argument";
+  $arg;
+}
+with-optional; # returns Any
+with-optional(); # returns Any
+with-optional(1); # returns 1
+
+## You can also give them a default value when they're not passed:
+sub hello-to($name = "World") {
+  say "Hello, $name !";
+}
+hello-to; #=> Hello, World !
+hello-to(); #=> Hello, World !
+hello-to('You'); #=> Hello, You !
+
+## You can also, by using a syntax akin to the one of hashes (yay unified syntax !),
+##  pass *named* arguments to a `sub`.
+# They're optional, and will default to "Any" (Perl's "null"-like value).
+sub with-named($normal-arg, :$named) {
+  say $normal-arg + $named;
+}
+with-named(1, named => 6); #=> 7
+# There's one gotcha to be aware of, here:
+# If you quote your key, Perl 6 won't be able to see it at compile time,
+#  and you'll have a single Pair object as a positional paramater,
+#  which means this fails:
+with-named(1, 'named' => 6);
+
+with-named(2, :named(5)); #=> 7
+
+# To make a named argument mandatory, you can use `?`'s inverse, `!`
+sub with-mandatory-named(:$str!)  {
+  say "$str !";
+}
+with-mandatory-named(str => "My String"); #=> My String !
+with-mandatory-named; # run time error: "Required named parameter not passed"
+with-mandatory-named(3); # run time error: "Too many positional parameters passed"
+
+## If a sub takes a named boolean argument ...
+sub takes-a-bool($name, :$bool) {
+  say "$name takes $bool";
+}
+# ... you can use the same "short boolean" hash syntax:
+takes-a-bool('config', :bool); # config takes True
+takes-a-bool('config', :!bool); # config takes False
+
+## You can also provide your named arguments with defaults:
+sub named-def(:$def = 5) {
+  say $def;
+}
+named-def; #=> 5
+named-def(def => 15); #=> 15
+
+# Since you can omit parenthesis to call a function with no arguments,
+#  you need "&" in the name to capture `say-hello`.
+my &s = &say-hello;
+my &other-s = sub { say "Anonymous function !" }
+
+# A sub can have a "slurpy" parameter, or "doesn't-matter-how-many"
+sub as-many($head, *@rest) { # `*@` (slurpy) will basically "take everything else".
+                             # Note: you can have parameters *before* (like here)
+                             # a slurpy one, but not *after*.
+  say @rest.join(' / ') ~ " !";
+}
+say as-many('Happy', 'Happy', 'Birthday'); #=> Happy / Birthday !
+                                           # Note that the splat did not consume
+                                           #  the parameter before.
+
+## You can call a function with an array using the
+# "argument list flattening" operator `|`
+# (it's not actually the only role of this operator, but it's one of them)
+sub concat3($a, $b, $c) {
+  say "$a, $b, $c";
+}
+concat3(|@array); #=> a, b, c
+                  # `@array` got "flattened" as a part of the argument list
+
+### Containers
+# In Perl 6, values are actually stored in "containers".
+# The assignment operator asks the container on the left to store the value on
+#  its right. When passed around, containers are marked as immutable.
+# Which means that, in a function, you'll get an error if you try to
+#  mutate one of your arguments.
+# If you really need to, you can ask for a mutable container using `is rw`:
+sub mutate($n is rw) {
+  $n++;
+  say "\$n is now $n !";
+}
+
+# If what you want is a copy instead, use `is copy`.
+
+# A sub itself returns a container, which means it can be marked as rw:
+my $x = 42;
+sub x-store() is rw { $x }
+x-store() = 52; # in this case, the parentheses are mandatory
+                # (else Perl 6 thinks `x-store` is an identifier)
+say $x; #=> 52
+
+
+### Control Flow Structures
+## Conditionals
+
+# - `if`
+# Before talking about `if`, we need to know which values are "Truthy"
+#  (represent True), and which are "Falsey" (or "Falsy") -- represent False.
+# Only these values are Falsey: 0, (), {}, "", Nil, A type (like `Str` or `Int`),
+#  and of course False itself.
+# Every other value is Truthy.
+if True {
+  say "It's true !";
+}
+
+unless False {
+  say "It's not false !";
+}
+
+# As you can see, you don't need parentheses around conditions.
+# However, you do need the brackets around the "body" block:
+# if (true) say; # This doesn't work !
+
+# You can also use their postfix versions, with the keyword after:
+say "Quite truthy" if True;
+
+# - Ternary conditional, "?? !!" (like `x ? y : z` in some other languages)
+my $a = $condition ?? $value-if-true !! $value-if-false;
+
+# - `given`-`when` looks like other languages `switch`, but much more
+# powerful thanks to smart matching and thanks to Perl 6's "topic variable", $_.
+#
+# This variable contains the default argument of a block,
+#  a loop's current iteration (unless explicitly named), etc.
+#
+# `given` simply puts its argument into `$_` (like a block would do),
+#  and `when` compares it using the "smart matching" (`~~`) operator.
+#
+# Since other Perl 6 constructs use this variable (as said before, like `for`,
+# blocks, etc), this means the powerful `when` is not only applicable along with
+# a `given`, but instead anywhere a `$_` exists.
+given "foo bar" {
+  say $_; #=> foo bar
+  when /foo/ { # Don't worry about smart matching yet – just know `when` uses it.
+               # This is equivalent to `if $_ ~~ /foo/`.
+    say "Yay !";
+  }
+  when $_.chars > 50 { # smart matching anything with True (`$a ~~ True`) is True,
+                       # so you can also put "normal" conditionals.
+                       # This when is equivalent to this `if`:
+                       #  if $_ ~~ ($_.chars > 50) {...}
+                       # Which means:
+                       #  if $_.chars > 50 {...}
+    say "Quite a long string !";
+  }
+  default { # same as `when *` (using the Whatever Star)
+    say "Something else"
+  }
+}
+
+## Looping constructs
+
+# - `loop` is an infinite loop if you don't pass it arguments,
+# but can also be a C-style `for` loop:
+loop {
+  say "This is an infinite loop !";
+  last; # last breaks out of the loop, like the `break` keyword in other languages
+}
+
+loop (my $i = 0; $i < 5; $i++) {
+  next if $i == 3; # `next` skips to the next iteration, like `continue`
+                   # in other languages. Note that you can also use postfix
+                   # conditionals, loops, etc.
+  say "This is a C-style for loop !";
+}
+
+# - `for` - Passes through an array
+for @array -> $variable {
+  say "I've got $variable !";
+}
+
+# As we saw with given, for's default "current iteration" variable is `$_`.
+# That means you can use `when` in a `for` just like you were in a `given`.
+for @array {
+  say "I've got $_";
+
+  .say; # This is also allowed.
+        # A dot call with no "topic" (receiver) is sent to `$_` by default
+  $_.say; # the above and this are equivalent.
+}
+
+for @array {
+  # You can...
+  next if $_ == 3; # Skip to the next iteration (`continue` in C-like languages).
+  redo if $_ == 4; # Re-do the iteration, keeping the same topic variable (`$_`).
+  last if $_ == 5; # Or break out of a loop (like `break` in C-like languages).
+}
+
+# The "pointy block" syntax isn't specific to for.
+# It's just a way to express a block in Perl6.
+if long-computation() -> $result {
+  say "The result is $result";
+}
+
+### Operators
+
+## Since Perl languages are very much operator-based languages,
+## Perl 6 operators are actually just funny-looking subroutines, in syntactic
+##  categories, like infix:<+> (addition) or prefix:<!> (bool not).
+
+## The categories are:
+# - "prefix": before (like `!` in `!True`).
+# - "postfix": after (like `++` in `$a++`).
+# - "infix": in between (like `*` in `4 * 3`).
+# - "circumfix": around (like `[`-`]` in `[1, 2]`).
+# - "post-circumfix": around, after another term (like `{`-`}` in `%hash{'key'}`)
+
+## The associativity and precedence list are explained below.
+
+# Alright, you're set to go !
+
+## * Equality Checking
+
+# - `==` is numeric comparison
+3 == 4; # False
+3 != 4; # True
+
+# - `eq` is string comparison
+'a' eq 'b';
+'a' ne 'b'; # not equal
+'a' !eq 'b'; # same as above
+
+# - `eqv` is canonical equivalence (or "deep equality")
+(1, 2) eqv (1, 3);
+
+# - `~~` is smart matching
+# For a complete list of combinations, use this table:
+# http://perlcabal.org/syn/S03.html#Smart_matching
+'a' ~~ /a/; # true if matches regexp
+'key' ~~ %hash; # true if key exists in hash
+$arg ~~ &bool-returning-function; # `True` if the function, passed `$arg`
+                                  # as an argument, returns `True`.
+1 ~~ Int; # "has type" (check superclasses and roles)
+1 ~~ True; # smart-matching against a boolean always returns that boolean
+           # (and will warn).
+
+# You also, of course, have `<`, `<=`, `>`, `>=`.
+# Their string equivalent are also avaiable : `lt`, `le`, `gt`, `ge`.
+3 > 4;
+
+## * Range constructors
+3 .. 7; # 3 to 7, both included
+# `^` on either side them exclusive on that side :
+3 ^..^ 7; # 3 to 7, not included (basically `4 .. 6`)
+# This also works as a shortcut for `0..^N`:
+^10; # means 0..^10
+
+# This also allows us to demonstrate that Perl 6 has lazy/infinite arrays,
+#  using the Whatever Star:
+my @array = 1..*; # 1 to Infinite ! `1..Inf` is the same.
+say @array[^10]; # you can pass arrays as subscripts and it'll return
+                 #  an array of results. This will print
+                 # "1 2 3 4 5 6 7 8 9 10" (and not run out of memory !)
+# Note : when reading an infinite list, Perl 6 will "reify" the elements
+# it needs, then keep them in memory. They won't be calculated more than once.
+# It also will never calculate more elements that are needed.
+
+# An array subscript can also be a closure.
+# It'll be called with the length as the argument
+say join(' ', @array[15..*]); #=> 15 16 17 18 19
+# which is equivalent to:
+say join(' ', @array[-> $n { 15..$n }]);
+
+# You can use that in most places you'd expect, even assigning to an array
+my @numbers = ^20;
+my @seq =  3, 9 ... * > 95; # 3 9 15 21 27 [...] 81 87 93 99
+@numbers[5..*] = 3, 9 ... *; # even though the sequence is infinite,
+                             # only the 15 needed values will be calculated.
+say @numbers; #=> 0 1 2 3 4 3 9 15 21 [...] 81 87
+              # (only 20 values)
+
+## * And, Or
+3 && 4; # 4, which is Truthy. Calls `.Bool` on `4` and gets `True`.
+0 || False; # False. Calls `.Bool` on `0`
+
+## * Short-circuit (and tight) versions of the above
+$a && $b && $c; # Returns the first argument that evaluates to False,
+                # or the last argument.
+$a || $b;
+
+# And because you're going to want them,
+#  you also have compound assignment operators:
+$a *= 2; # multiply and assignment
+$b %%= 5; # divisible by and assignment
+@array .= sort; # calls the `sort` method and assigns the result back
+
+### More on subs !
+# As we said before, Perl 6 has *really* powerful subs. We're going to see
+# a few more key concepts that make them better than in any other language :-).
+
+## Unpacking !
+# It's the ability to "extract" arrays and keys (AKA "destructuring").
+# It'll work in `my`s and in parameter lists.
+my ($a, $b) = 1, 2;
+say $a; #=> 1
+my ($, $, $c) = 1, 2, 3; # keep the non-interesting anonymous
+say $c; #=> 3
+
+my ($head, *@tail) = 1, 2, 3; # Yes, it's the same as with "slurpy subs"
+my (*@small) = 1;
+
+sub foo(@array [$fst, $snd]) {
+  say "My first is $fst, my second is $snd ! All in all, I'm @array[].";
+  # (^ remember the `[]` to interpolate the array)
+}
+foo(@tail); #=> My first is 2, my second is 3 ! All in all, I'm 2 3
+
+
+# If you're not using the array itself, you can also keep it anonymous,
+#  much like a scalar:
+sub first-of-array(@ [$fst]) { $fst }
+first-of-array(@small); #=> 1
+first-of-array(@tail); # Throws an error "Too many positional parameters passed"
+                       # (which means the array is too big).
+
+# You can also use a slurp ...
+sub slurp-in-array(@ [$fst, *@rest]) { # You could keep `*@rest` anonymous
+  say $fst + @rest.elems; # `.elems` returns a list's length.
+                          # Here, `@rest` is `(3,)`, since `$fst` holds the `2`.
+}
+slurp-in-array(@tail); #=> 3
+
+# You could even extract on a slurpy (but it's pretty useless ;-).)
+sub fst(*@ [$fst]) { # or simply : `sub fst($fst) { ... }`
+  say $fst;
+}
+fst(1); #=> 1
+fst(1, 2); # errors with "Too many positional parameters passed"
+
+# You can also destructure hashes (and classes, which you'll learn about later !)
+# The syntax is basically `%hash-name (:key($variable-to-store-value-in))`.
+# The hash can stay anonymous if you only need the values you extracted.
+sub key-of(% (:value($val), :qua($qua))) {
+  say "Got val $val, $qua times.";
+}
+
+# Then call it with a hash: (you need to keep the brackets for it to be a hash)
+key-of({value => 'foo', qua => 1});
+#key-of(%hash); # the same (for an equivalent `%hash`)
+
+## The last expression of a sub is returned automatically
+# (though you may use the `return` keyword, of course):
+sub next-index($n) {
+  $n + 1;
+}
+my $new-n = next-index(3); # $new-n is now 4
+
+# This is true for everything, except for the looping constructs
+# (due to performance reasons): there's reason to build a list
+#  if we're just going to discard all the results.
+# If you still want to build one, you can use the `do` statement prefix:
+#  (or the `gather` prefix, which we'll see later)
+sub list-of($n) {
+  do for ^$n { # note the use of the range-to prefix operator `^` (`0..^N`)
+    $_ # current loop iteration
+  }
+}
+my @list3 = list-of(3); #=> (0, 1, 2)
+
+## You can create a lambda with `-> {}` ("pointy block") or `{}` ("block")
+my &lambda = -> $argument { "The argument passed to this lambda is $argument" }
+# `-> {}` and `{}` are pretty much the same thing, except that the former can
+# take arguments, and that the latter can be mistaken as a hash by the parser.
+
+# We can, for example, add 3 to each value of an array using map:
+my @arrayplus3 = map({ $_ + 3 }, @array); # $_ is the implicit argument
+
+# A sub (`sub {}`) has different semantics than a block (`{}` or `-> {}`):
+# A block doesn't have a "function context" (though it can have arguments),
+#  which means that if you return from it,
+#  you're going to return from the parent function. Compare:
+sub is-in(@array, $elem) {
+  # this will `return` out of the `is-in` sub
+  # once the condition evaluated to True, the loop won't be run anymore
+  map({ return True if $_ == $elem }, @array);
+}
+sub truthy-array(@array) {
+  # this will produce an array of `True` and `False`:
+  # (you can also say `anon sub` for "anonymous subroutine")
+  map(sub ($i) { if $i { return True } else { return False } }, @array);
+  # ^ the `return` only returns from the anonymous `sub`
+}
+
+# You can also use the "whatever star" to create an anonymous function
+# (it'll stop at the furthest operator in the current expression)
+my @arrayplus3 = map(*+3, @array); # `*+3` is the same as `{ $_ + 3 }`
+my @arrayplus3 = map(*+*+3, @array); # Same as `-> $a, $b { $a + $b + 3 }`
+                                     # also `sub ($a, $b) { $a + $b + 3 }`
+say (*/2)(4); #=> 2
+              # Immediatly execute the function Whatever created.
+say ((*+3)/5)(5); #=> 1.6
+                  # works even in parens !
+
+# But if you need to have more than one argument (`$_`)
+#  in a block (without wanting to resort to `-> {}`),
+#  you can also use the implicit argument syntax, `$^` :
+map({ $^a + $^b + 3 }, @array); # equivalent to following:
+map(sub ($a, $b) { $a + $b + 3 }, @array); # (here with `sub`)
+
+# Note : those are sorted lexicographically.
+# `{ $^b / $^a }` is like `-> $a, $b { $b / $a }`
+
+## About types...
+# Perl6 is gradually typed. This means you can specify the type
+#  of your variables/arguments/return types, or you can omit them
+#  and they'll default to "Any".
+# You obviously get access to a few base types, like Int and Str.
+# The constructs for declaring types are "class", "role",
+#  which you'll see later.
+
+# For now, let us examinate "subset":
+# a "subset" is a "sub-type" with additional checks.
+# For example: "a very big integer is an Int that's greater than 500"
+# You can specify the type you're subtyping (by default, Any),
+#  and add additional checks with the "where" keyword:
+subset VeryBigInteger of Int where * > 500;
+
+## Multiple Dispatch
+# Perl 6 can decide which variant of a `sub` to call based on the type of the
+# arguments, or on arbitrary preconditions, like with a type or a `where`:
+
+# with types
+multi sub sayit(Int $n) { # note the `multi` keyword here
+  say "Number: $n";
+}
+multi sayit(Str $s) { # a multi is a `sub` by default
+  say "String: $s";
+}
+sayit("foo"); # prints "String: foo"
+sayit(True); # fails at *compile time* with
+             # "calling 'sayit' will never work with arguments of types ..."
+
+# with arbitrary precondition (remember subsets?):
+multi is-big(Int $n where * > 50) { "Yes !" } # using a closure
+multi is-big(Int $ where 10..50) { "Quite." } # Using smart-matching
+                                              # (could use a regexp, etc)
+multi is-big(Int $) { "No" }
+
+subset Even of Int where * %% 2;
+
+multi odd-or-even(Even) { "Even" } # The main case using the type.
+                                   # We don't name the argument.
+multi odd-or-even($) { "Odd" } # "else"
+
+# You can even dispatch based on a positional's argument presence !
+multi with-or-without-you(:$with!) { # You need make it mandatory to
+                                     # be able to dispatch against it.
+  say "I can live ! Actually, I can't.";
+}
+multi with-or-without-you {
+  say "Definitely can't live.";
+}
+# This is very, very useful for many purposes, like `MAIN` subs (covered later),
+#  and even the language itself is using it in several places.
+#
+# - `is`, for example, is actually a `multi sub` named `trait_mod:<is>`,
+#  and it works off that.
+# - `is rw`, is simply a dispatch to a function with this signature:
+# sub trait_mod:<is>(Routine $r, :$rw!) {}
+#
+# (commented because running this would be a terrible idea !)
+
+
+### Scoping
+# In Perl 6, contrarily to many scripting languages (like Python, Ruby, PHP),
+#  you are to declare your variables before using them. You know `my`.
+# (there are other declarators, `our`, `state`, ..., which we'll see later).
+# This is called "lexical scoping", where in inner blocks,
+#  you can access variables from outer blocks.
+my $foo = 'Foo';
+sub foo {
+  my $bar = 'Bar';
+  sub bar {
+    say "$foo $bar";
+  }
+  &bar; # return the function
+}
+foo()(); #=> 'Foo Bar'
+
+# As you can see, `$foo` and `$bar` were captured.
+# But if we were to try and use `$bar` outside of `foo`,
+# the variable would be undefined (and you'd get a compile time error).
+
+# Perl 6 has another kind of scope : dynamic scope.
+# They use the twigil (composed sigil) `*` to mark dynamically-scoped variables:
+my $*a = 1;
+# Dyamically-scoped variables depend on the current call stack,
+#  instead of the current block depth.
+sub foo {
+  my $*foo = 1;
+  bar(); # call `bar` in-place
+}
+sub bar {
+  say $*foo; # `$*a` will be looked in the call stack, and find `foo`'s,
+             #  even though the blocks aren't nested (they're call-nested).
+             #=> 1
+}
+
+### Object Model
+
+## Perl 6 has a quite comprehensive object model
+# You declare a class with the keyword `class`, fields with `has`,
+# methods with `method`. Every field to private, and is named `$!attr`,
+# but you have `$.` to get a public (immutable) accessor along with it.
+# (using `$.` is like using `$!` plus a `method` with the same name)
+
+# (Perl 6's object model ("SixModel") is very flexible,
+# and allows you to dynamically add methods, change semantics, etc ...
+# (this will not be covered here, and you should refer to the Synopsis).
+
+class A {
+  has $.field; # `$.field` is immutable.
+               # From inside the class, use `$!field` to modify it.
+  has $.other-field is rw; # You can obviously mark a public field `rw`.
+  has Int $!private-field = 10;
+
+  method get-value {
+    $.field + $!private-field;
+  }
+
+  method set-value($n) {
+    # $.field = $n; # As stated before, you can't use the `$.` immutable version.
+    $!field = $n;   # This works, because `$!` is always mutable.
+
+    $.other-field = 5; # This works, because `$.other-field` is `rw`.
+  }
+
+  method !private-method {
+    say "This method is private to the class !";
+  }
+};
+
+# Create a new instance of A with $.field set to 5 :
+# Note: you can't set private-field from here (more later on).
+my $a = A.new(field => 5);
+$a.get-value; #=> 15
+#$a.field = 5; # This fails, because the `has $.field` is immutable
+$a.other-field = 10; # This, however, works, because the public field
+                     #  is mutable (`rw`).
+
+## Perl 6 also has inheritance (along with multiple inheritance)
+# (though considered a misfeature by many)
+
+class A {
+  has $.val;
+
+  submethod not-inherited {
+    say "This method won't be available on B.";
+    say "This is most useful for BUILD, which we'll see later";
+  }
+
+  method bar { $.val * 5 }
+}
+class B is A { # inheritance uses `is`
+  method foo {
+    say $.val;
+  }
+
+  method bar { $.val * 10 } # this shadows A's `bar`
+}
+
+# When you use `my T $var`, `$var` starts off with `T` itself in it,
+# so you can call `new` on it.
+# (`.=` is just the dot-call and the assignment operator:
+#  `$a .= b` is the same as `$a = $a.b`)
+# Also note that `BUILD` (the method called inside `new`)
+#  will set parent properties too, so you can pass `val => 5`.
+my B $b .= new(val => 5);
+
+# $b.not-inherited; # This won't work, for reasons explained above
+$b.foo; # prints 5
+$b.bar; #=> 50, since it calls B's `bar`
+
+## Roles are supported too (also called Mixins in other languages)
+role PrintableVal {
+  has $!counter = 0;
+  method print {
+    say $.val;
+  }
+}
+
+# you "import" a mixin (a "role") with "does":
+class Item does PrintableVal {
+  has $.val;
+
+  # When `does`-ed, a `role` literally "mixes in" the class:
+  #  the methods and fields are put together, which means a class can access
+  #  the private fields/methods of its roles (but not the inverse !):
+  method access {
+    say $!counter++;
+  }
+
+  # However, this:
+  # method print {}
+  # is ONLY valid when `print` isn't a `multi` with the same dispatch.
+  # (this means a parent class can shadow a child class's `multi print() {}`,
+  #  but it's an error if a role does)
+
+  # NOTE: You can use a role as a class (with `is ROLE`). In this case, methods
+  # will be shadowed, since the compiler will consider `ROLE` to be a class.
+}
+
+### Exceptions
+# Exceptions are built on top of classes, in the package `X` (like `X::IO`).
+# Unlike many other languages, in Perl 6, you put the `CATCH` block *within* the
+#  block to `try`. By default, a `try` has a `CATCH` block that catches
+#  any exception (`CATCH { default {} }`).
+# You can redefine it using `when`s (and `default`)
+#  to handle the exceptions you want:
+try {
+  open 'foo';
+  CATCH {
+    when X::AdHoc { say "unable to open file !" }
+    # Any other exception will be re-raised, since we don't have a `default`
+    # Basically, if a `when` matches (or there's a `default`) marks the exception as
+    #  "handled" so that it doesn't get re-thrown from the `CATCH`.
+    # You still can re-throw the exception (see below) by hand.
+  }
+}
+
+# You can throw an exception using `die`:
+die X::AdHoc.new(payload => 'Error !');
+
+# You can access the last exception with `$!` (usually used in a `CATCH` block)
+
+# There are also some subtelties to exceptions. Some Perl 6 subs return a `Failure`,
+#  which is a kind of "unthrown exception". They're not thrown until you tried to look
+#  at their content, unless you call `.Bool`/`.defined` on them - then they're handled.
+#  (the `.handled` method is `rw`, so you can mark it as `False` back yourself)
+#
+# You can throw a `Failure` using `fail`. Note that if the pragma `use fatal` is on,
+#  `fail` will throw an exception (like `die`).
+fail "foo"; # We're not trying to access the value, so no problem.
+try {
+  fail "foo";
+  CATCH {
+    default { say "It threw because we try to get the fail's value!" }
+  }
+}
+
+# There is also another kind of exception: Control exceptions.
+# Those are "good" exceptions, which happen when you change your program's flow,
+#  using operators like `return`, `next` or `last`.
+# You can "catch" those with `CONTROL` (not 100% working in Rakudo yet).
+
+### Packages
+# Packages are a way to reuse code. Packages are like "namespaces", and any
+#  element of the six model (`module`, `role`, `class`, `grammar`, `subset`
+#  and `enum`) are actually packages. (Packages are the lowest common denomitor)
+# Packages are important - especially as Perl is well-known for CPAN,
+#  the Comprehensive Perl Archive Network.
+# You usually don't use packages directly: you use `class Package::Name::Here;`,
+# or if you only want to export variables/subs, you can use `module`:
+module Hello::World { # Bracketed form
+                      # If `Hello` doesn't exist yet, it'll just be a "stub",
+                      #  that can be redeclared as something else later.
+  # ... declarations here ...
+}
+module Parse::Text; # file-scoped form
+grammar Parse::Text::Grammar { # A grammar is a package, which you could `use`
+}
+
+# NOTE for Perl 5 users: even though the `package` keyword exists,
+#  the braceless form is invalid (to catch a "perl5ism"). This will error out:
+# package Foo; # because Perl 6 will think the entire file is Perl 5
+# Just use `module` or the brace version of `package`.
+
+# You can use a module (bring its declarations into scope) with `use`
+use JSON::Tiny; # if you installed Rakudo* or Panda, you'll have this module
+say from-json('[1]').perl; #=> [1]
+
+# As said before, any part of the six model is also a package.
+# Since `JSON::Tiny` uses (its own) `JSON::Tiny::Actions` class, you can use it:
+my $actions = JSON::Tiny::Actions.new;
+
+# We'll see how to export variables and subs in the next part:
+
+### Declarators
+# In Perl 6, you get different behaviors based on how you declare a variable.
+# You've already seen `my` and `has`, we'll now explore the others.
+
+## * `our` (happens at `INIT` time -- see "Phasers" below)
+# Along with `my`, there are several others declarators you can use.
+# The first one you'll want for the previous part is `our`.
+# (All packagish things (`class`, `role`, etc) are `our` by default)
+# it's like `my`, but it also creates a package variable:
+module Foo::Bar {
+  our $n = 1; # note: you can't put a type constraint on an `our` variable
+  our sub inc {
+    our sub available { # If you try to make inner `sub`s `our`...
+                        # Better know what you're doing (Don't !).
+      say "Don't do that. Seriously. You'd get burned.";
+    }
+    my sub unavailable { # `my sub` is the default
+      say "Can't access me from outside, I'm my !";
+    }
+  }
+
+  say ++$n; # lexically-scoped variables are still available
+}
+say $Foo::Bar::n; #=> 1
+Foo::Bar::inc; #=> 2
+Foo::Bar::inc; #=> 3
+
+## * `constant` (happens at `BEGIN` time)
+# You can use the `constant` keyword to declare a compile-time variable/symbol:
+constant Pi = 3.14;
+constant $var = 1;
+
+# And if you're wondering, yes, it can also contain infinite lists.
+constant why-not = 5, 15 ... *;
+say why-not[^5]; #=> 5 15 25 35 45
+
+## * `state` (happens at run time, but only once)
+# State variables are only executed one time
+# (they exist in other langages such as C as `static`)
+sub fixed-rand {
+  state $val = rand;
+  say $rand;
+}
+fixed-rand for ^10; # will print the same number 10 times
+
+# Note, however, that they exist separately in different enclosing contexts.
+# If you declare a function with a `state` within a loop, it'll re-create the
+#  variable for each iteration of the loop. See:
+for ^5 -> $a {
+  sub foo {
+    state $val = rand; # This will be a different value for every value of `$a`
+  }
+  for ^5 -> $b {
+    say foo; # This will print the same value 5 times, but only 5.
+             # Next iteration will re-run `rand`.
+  }
+}
+
+
+
+### Phasers
+# Phasers in Perl 6 are blocks that happen at determined points of time in your
+#  program. When the program is compiled, when a for loop runs, when you leave a
+#  block, when an exception gets thrown ... (`CATCH` is actually a phaser !)
+# Some of them can be used for their return values, some of them can't
+#  (those that can have a "[*]" in the beginning of their explanation text).
+# Let's have a look !
+
+## * Compile-time phasers
+BEGIN { say "[*] Runs at compile time, as soon as possible, only once" }
+CHECK { say "[*] Runs at compile time, instead as late as possible, only once" }
+
+## * Run-time phasers
+INIT { say "[*] Runs at run time, as soon as possible, only once" }
+END { say "Runs at run time, as late as possible, only once" }
+
+## * Block phasers
+ENTER { say "[*] Runs everytime you enter a block, repeats on loop blocks" }
+LEAVE { say "Runs everytime you leave a block, even when an exception happened. Repeats on loop blocks." }
+
+PRE { say "Asserts a precondition at every block entry, before ENTER (especially useful for loops)" }
+POST { say "Asserts a postcondition at every block exit, after LEAVE (especially useful for loops)" }
+
+## * Block/exceptions phasers
+sub {
+    KEEP { say "Runs when you exit a block successfully (without throwing an exception)" }
+    UNDO { say "Runs when you exit a block unsuccessfully (by throwing an exception)" }
+}
+
+## * Loop phasers
+for ^5 {
+  FIRST { say "[*] The first time the loop is run, before ENTER" }
+  NEXT { say "At loop continuation time, before LEAVE" }
+  LAST { say "At loop termination time, after LEAVE" }
+}
+
+## * Role/class phasers
+COMPOSE { "When a role is composed into a class. /!\ NOT YET IMPLEMENTED" }
+
+# They allow for cute trick or clever code ...:
+say "This code took " ~ (time - CHECK time) ~ "s to run";
+
+# ... or clever organization:
+sub do-db-stuff {
+  ENTER $db.start-transaction; # New transaction everytime we enter the sub
+  KEEP $db.commit; # commit the transaction if all went well
+  UNDO $db.rollback; # or rollback if all hell broke loose
+}
+
+### Statement prefixes
+# Those act a bit like phasers: they affect the behavior of the following code.
+# Though, they run in-line with the executable code, so they're in lowercase.
+# (`try` and `start` are theoretically in that list, but explained somewhere else)
+# Note: all of these (except start) don't need explicit brackets `{` and `}`.
+
+# - `do` (that you already saw) - runs a block or a statement as a term
+# You can't normally use a statement as a value (or "term"):
+#
+#    my $value = if True { 1 } # `if` is a statement - parse error
+#
+# This works:
+my $a = do if True { 5 } # with `do`, `if` is now a term.
+
+# - `once` - Makes sure a piece of code only runs once
+for ^5 { once say 1 }; #=> 1
+                       # Only prints ... once.
+# Like `state`, they're cloned per-scope
+for ^5 { sub { once say 1 }() } #=> 1 1 1 1 1
+                                # Prints once per lexical scope
+
+# - `gather` - Co-routine thread
+# Gather allows you to `take` several values in an array,
+#  much like `do`, but allows you to take any expression.
+say gather for ^5 {
+  take $_ * 3 - 1;
+  take $_ * 3 + 1;
+} #=> -1 1 2 4 5 7 8 10 11 13
+say join ',', gather if False {
+  take 1;
+  take 2;
+  take 3;
+} # Doesn't print anything.
+
+# - `eager` - Evaluate statement eagerly (forces eager context)
+# Don't try this at home:
+#
+#    eager 1..*; # this will probably hang for a while (and might crash ...).
+#
+# But consider:
+constant thrice = gather for ^3 { say take $_ }; # Doesn't print anything
+# versus:
+constant thrice = eager gather for ^3 { say take $_ }; #=> 0 1 2
+
+# - `lazy` - Defer actual evaluation until value is fetched (forces lazy context)
+# Not yet implemented !!
+
+# - `sink` - An `eager` that discards the results (forces sink context)
+constant nilthingie = sink for ^3 { .say } #=> 0 1 2
+say nilthingie.perl; #=> Nil
+
+# - `quietly` - Supresses warnings
+# Not yet implemented !
+
+# - `contend` - Attempts side effects under STM
+# Not yet implemented !
+
+### More operators thingies !
+
+## Everybody loves operators ! Let's get more of them
+
+# The precedence list can be found here:
+# http://perlcabal.org/syn/S03.html#Operator_precedence
+# But first, we need a little explanation about associativity:
+
+# * Binary operators:
+$a ! $b ! $c; # with a left-associative `!`, this is `($a ! $b) ! $c`
+$a ! $b ! $c; # with a right-associative `!`, this is `$a ! ($b ! $c)`
+$a ! $b ! $c; # with a non-associative `!`, this is illegal
+$a ! $b ! $c; # with a chain-associative `!`, this is `($a ! $b) and ($b ! $c)`
+$a ! $b ! $c; # with a list-associative `!`, this is `infix:<>`
+
+# * Unary operators:
+!$a! # with left-associative `!`, this is `(!$a)!`
+!$a! # with right-associative `!`, this is `!($a!)`
+!$a! # with non-associative `!`, this is illegal
+
+## Create your own operators !
+# Okay, you've been reading all of that, so I guess I should try
+#  to show you something exciting.
+# I'll tell you a little secret (or not-so-secret):
+# In Perl 6, all operators are actually just funny-looking subroutines.
+
+# You can declare an operator just like you declare a sub:
+sub prefix:<win>($winner) { # refer to the operator categories
+                            # (yes, it's the "words operator" `<>`)
+  say "$winner Won !";
+}
+win "The King"; #=> The King Won !
+                # (prefix is before)
+
+# you can still call the sub with its "full name"
+say prefix:<!>(True); #=> False
+
+sub postfix:<!>(Int $n) {
+  [*] 2..$n; # using the reduce meta-operator ... See below ;-) !
+}
+say 5!; #=> 120
+        # Postfix operators (after) have to come *directly* after the term.
+        # No whitespace. You can use parentheses to disambiguate, i.e. `(5!)!`
+
+
+sub infix:<times>(Int $n, Block $r) { # infix in the middle
+  for ^$n {
+    $r(); # You need the explicit parentheses to call the function in `$r`,
+          #  else you'd be referring at the variable itself, like with `&r`.
+  }
+}
+3 times -> { say "hello" }; #=> hello
+                            #=> hello
+                            #=> hello
+                            # You're very recommended to put spaces
+                            # around your infix operator calls.
+
+# For circumfix and post-circumfix ones
+sub circumfix:<[ ]>(Int $n) {
+  $n ** $n
+}
+say [5]; #=> 3125
+         # circumfix is around. Again, not whitespace.
+
+sub postcircumfix:<{ }>(Str $s, Int $idx) {
+  # post-circumfix is
+  # "after a term, around something"
+  $s.substr($idx, 1);
+}
+say "abc"{1}; #=> b
+              # after the term `"abc"`, and around the index (1)
+
+# This really means a lot -- because everything in Perl 6 uses this.
+# For example, to delete a key from a hash, you use the `:delete` adverb
+#  (a simple named argument underneath):
+%h{$key}:delete;
+# equivalent to:
+postcircumfix:<{ }>(%h, $key, :delete); # (you can call operators like that)
+# It's *all* using the same building blocks!
+# Syntactic categories (prefix infix ...), named arguments (adverbs), ...,
+#  - used to build the language - are available to you.
+
+# (you are, obviously, recommended against making an operator out of
+# *everything* -- with great power comes great responsibility)
+
+## Meta operators !
+# Oh boy, get ready. Get ready, because we're delving deep
+#  into the rabbit's hole, and you probably won't want to go
+#  back to other languages after reading that.
+#  (I'm guessing you don't want to already at that point).
+# Meta-operators, as their name suggests, are *composed* operators.
+# Basically, they're operators that apply another operator.
+
+## * Reduce meta-operator
+# It's a prefix meta-operator that takes a binary functions and
+#  one or many lists. If it doesn't get passed any argument,
+#  it either return a "default value" for this operator
+#  (a meaningless value) or `Any` if there's none (examples below).
+#
+# Otherwise, it pops an element from the list(s) one at a time, and applies
+#  the binary function to the last result (or the list's first element)
+#  and the popped element.
+#
+# To sum a list, you could use the reduce meta-operator with `+`, i.e.:
+say [+] 1, 2, 3; #=> 6
+# equivalent to `(1+2)+3`
+say [*] 1..5; #=> 120
+# equivalent to `((((1*2)*3)*4)*5)`.
+
+# You can reduce with any operator, not just with mathematical ones.
+# For example, you could reduce with `//` to get
+#  the first defined element of a list:
+say [//] Nil, Any, False, 1, 5; #=> False
+                                # (Falsey, but still defined)
+
+
+# Default value examples:
+say [*] (); #=> 1
+say [+] (); #=> 0
+            # meaningless values, since N*1=N and N+0=N.
+say [//];   #=> (Any)
+            # There's no "default value" for `//`.
+
+# You can also call it with a function you made up, using double brackets:
+sub add($a, $b) { $a + $b }
+say [[&add]] 1, 2, 3; #=> 6
+
+## * Zip meta-operator
+# This one is an infix meta-operator than also can be used as a "normal" operator.
+# It takes an optional binary function (by default, it just creates a pair),
+#  and will pop one value off of each array and call its binary function on these
+#  until it runs out of elements. It runs the an array with all these new elements.
+(1, 2) Z (3, 4); # ((1, 3), (2, 4)), since by default, the function makes an array
+1..3 Z+ 4..6; # (5, 7, 9), using the custom infix:<+> function
+
+# Since `Z` is list-associative (see the list above),
+#  you can use it on more than one list
+(True, False) Z|| (False, False) Z|| (False, False); # (True, False)
+
+# And, as it turns out, you can also use the reduce meta-operator with it:
+[Z||] (True, False), (False, False), (False, False); # (True, False)
+
+
+## And to end the operator list:
+
+## * Sequence operator
+# The sequence operator is one of Perl 6's most powerful features:
+# it's composed of first, on the left, the list you want Perl 6 to deduce from
+#  (and might include a closure), and on the right, a value or the predicate
+#  that says when to stop (or Whatever for a lazy infinite list).
+my @list = 1, 2, 3 ... 10; # basic deducing
+#my @list = 1, 3, 6 ... 10; # this throws you into an infinite loop,
+                            #  because Perl 6 can't figure out the end
+my @list = 1, 2, 3 ...^ 10; # as with ranges, you can exclude the last element
+                            # (the iteration when the predicate matches).
+my @list = 1, 3, 9 ... * > 30; # you can use a predicate
+                               # (with the Whatever Star, here).
+my @list = 1, 3, 9 ... { $_ > 30 }; # (equivalent to the above)
+
+my @fib = 1, 1, *+* ... *; # lazy infinite list of fibonacci series,
+                           #  computed using a closure!
+my @fib = 1, 1, -> $a, $b { $a + $b } ... *; # (equivalent to the above)
+my @fib = 1, 1, { $^a + $^b } ... *; #(... also equivalent to the above)
+# $a and $b will always take the previous values, meaning here
+#  they'll start with $a = 1 and $b = 1 (values we set by hand).
+#  then $a = 1 and $b = 2 (result from previous $a+$b), and so on.
+
+say @fib[^10]; #=> 1 1 2 3 5 8 13 21 34 55
+               # (using a range as the index)
+# Note : as for ranges, once reified, elements aren't re-calculated.
+# That's why `@primes[^100]` will take a long time the first time you print
+#  it, then be instant.
+
+### Regular Expressions
+# I'm sure a lot of you have been waiting for this one.
+# Well, now that you know a good deal of Perl 6 already, we can get started.
+# First off, you'll have to forget about "PCRE regexps" (perl-compatible regexps).
+#
+# IMPORTANT: Don't skip them because you know PCRE. They're different.
+# Some things are the same (like `?`, `+`, and `*`),
+#  but sometimes the semantics change (`|`).
+# Make sure you read carefully, because you might trip over a new behavior.
+#
+# Perl 6 has many features related to RegExps. After all, Rakudo parses itself.
+# We're first going to look at the syntax itself,
+#  then talk about grammars (PEG-like), differences between
+#  `token`, `regex` and `rule` declarators, and some more.
+# Side note: you still have access to PCRE regexps using the `:P5` modifier.
+#  (we won't be discussing this in this tutorial, however)
+#
+# In essence, Perl 6 natively implements PEG ("Parsing Expression Grammars").
+# The pecking order for ambiguous parses is determined by a multi-level
+#  tie-breaking test:
+#  - Longest token matching. `foo\s+` beats `foo` (by 2 or more positions)
+#  - Longest literal prefix. `food\w*` beats `foo\w*` (by 1)
+#  - Declaration from most-derived to less derived grammars
+#     (grammars are actually classes)
+#  - Earliest declaration wins
+say so 'a' ~~ /a/; #=> True
+say so 'a' ~~ / a /; # More readable with some spaces!
+
+# In all our examples, we're going to use the smart-matching operator against
+#  a regexp. We're converting the result using `so`, but in fact, it's
+#  returning a `Match` object. They know how to respond to list indexing,
+#  hash indexing, and return the matched string.
+# The results of the match are available as `$/` (implicitly lexically-scoped).
+# You can also use the capture variables (`$0`, `$1`, ... starting at 0, not 1 !).
+#
+# You can also note that `~~` does not perform start/end checking
+#  (meaning the regexp can be matched with just one char of the string),
+#  we're going to explain later how you can do it.
+
+# In Perl 6, you can have any alphanumeric as a literal,
+# everything else has to be escaped, using a backslash or quotes.
+say so 'a|b' ~~ / a '|' b /; # `True`. Wouln't mean the same if `|` wasn't escaped
+say so 'a|b' ~~ / a \| b /; # `True`. Another way to escape it.
+
+# The whitespace in a regexp is actually not significant,
+#  unless you use the `:s` (`:sigspace`, significant space) modifier.
+say so 'a b c' ~~ / a b c /; # `False`. Space is not significant here
+say so 'a b c' ~~ /:s a b c /; # `True`. We added the modifier `:s` here.
+
+# It is, however, important as for how modifiers (that you're gonna see just below)
+#  are applied ...
+
+## Quantifying - `?`, `+`, `*` and `**`.
+# - `?` - 0 or 1
+so 'ac' ~~ / a b c /; # `False`
+so 'ac' ~~ / a b? c /; # `True`, the "b" matched 0 times.
+so 'abc' ~~ / a b? c /; # `True`, the "b" matched 1 time.
+
+# ... As you read just before, whitespace is important because it determines
+#  which part of the regexp is the target of the modifier:
+so 'def' ~~ / a b c? /; # `False`. Only the `c` is optional
+so 'def' ~~ / ab?c /; # `False`. Whitespace is not significant
+so 'def' ~~ / 'abc'? /; # `True`. The whole "abc" group is optional.
+
+# Here (and below) the quantifier applies only to the `b`
+
+# - `+` - 1 or more
+so 'ac' ~~ / a b+ c /; # `False`; `+` wants at least one matching
+so 'abc' ~~ / a b+ c /; # `True`; one is enough
+so 'abbbbc' ~~ / a b+ c /; # `True`, matched 4 "b"s
+
+# - `*` - 0 or more
+so 'ac' ~~ / a b* c /; # `True`, they're all optional.
+so 'abc' ~~ / a b* c /; # `True`
+so 'abbbbc' ~~ / a b* c /; # `True`
+so 'aec' ~~ / a b* c /; # `False`. "b"(s) are optional, not replaceable.
+
+# - `**` - (Unbound) Quantifier
+# If you squint hard enough, you might understand
+#  why exponentation is used for quantity.
+so 'abc' ~~ / a b ** 1 c /; # `True` (exactly one time)
+so 'abc' ~~ / a b ** 1..3 c /; # `True` (one to three times)
+so 'abbbc' ~~ / a b ** 1..3 c /; # `True`
+so 'abbbbbbc' ~~ / a b ** 1..3 c /; # `False` (too much)
+so 'abbbbbbc' ~~ / a b ** 3..* c /; # `True` (infinite ranges are okay)
+
+# - `<[]>` - Character classes
+# Character classes are the equivalent of PCRE's `[]` classes, but
+#  they use a more perl6-ish syntax:
+say 'fooa' ~~ / f <[ o a ]>+ /; #=> 'fooa'
+# You can use ranges:
+say 'aeiou' ~~ / a <[ e..w ]> /; #=> 'aeiou'
+# Just like in normal regexes, if you want to use a special character, escape it
+#  (the last one is escaping a space)
+say 'he-he !' ~~ / 'he-' <[ a..z \! \  ]> + /; #=> 'he-he !'
+# You'll get a warning if you put duplicate names
+#  (which has the nice effect of catching the wrote quoting:)
+'he he' ~~ / <[ h e ' ' ]> /; # Warns "Repeated characters found in characters class"
+
+# You can also negate them ... (equivalent to `[^]` in PCRE)
+so 'foo' ~~ / <-[ f o ]> + /; # False
+
+# ... and compose them: :
+so 'foo' ~~ / <[ a..z ] - [ f o ]> + /; # False (any letter except f and o)
+so 'foo' ~~ / <-[ a..z ] + [ f o ]> + /; # True (no letter except f and o)
+so 'foo!' ~~ / <-[ a..z ] + [ f o ]> + /; # True (the + doesn't replace the left part)
+
+## Grouping and capturing
+# Group: you can group parts of your regexp with `[]`.
+# These groups are *not* captured (like PCRE's `(?:)`).
+so 'abc' ~~ / a [ b ] c /; # `True`. The grouping does pretty much nothing
+so 'fooABCABCbar' ~~ / foo [ A B C ] + bar /;
+# The previous line returns `True`.
+# We match the "abc" 1 or more time (the `+` was applied to the group).
+
+# But this does not go far enough, because we can't actually get back what
+#  we matched.
+# Capture: We can actually *capture* the results of the regexp, using parentheses.
+so 'fooABCABCbar' ~~ / foo ( A B C ) + bar /; # `True`. (using `so` here, `$/` below)
+
+# So, starting with the grouping explanations.
+# As we said before, our `Match` object is available as `$/`:
+say $/; # Will print some weird stuff (we'll explain) (or "Nil" if nothing matched).
+
+# As we also said before, it has array indexing:
+say $/[0]; #=> ｢ABC｣ ｢ABC｣
+           # These weird brackets are `Match` objects.
+           # Here, we have an array of these.
+say $0; # The same as above.
+
+# Our capture is `$0` because it's the first and only one capture in the regexp.
+# You might be wondering why it's an array, and the answer is simple:
+# Some capture (indexed using `$0`, `$/[0]` or a named one) will be an array
+#  IFF it can have more than one element
+#  (so, with `*`, `+` and `**` (whatever the operands), but not with `?`).
+# Let's use examples to see that:
+so 'fooABCbar' ~~ / foo ( A B C )? bar /; # `True`
+say $/[0]; #=> ｢ABC｣
+say $0.WHAT; #=> (Match)
+             # It can't be more than one, so it's only a single match object.
+so 'foobar' ~~ / foo ( A B C )? bar /; #=> True
+say $0.WHAT; #=> (Any)
+             # This capture did not match, so it's empty
+so 'foobar' ~~ / foo ( A B C ) ** 0..1 bar /; # `True`
+say $0.WHAT; #=> (Array)
+             # A specific quantifier will always capture an Array,
+             #  may it be a range or a specific value (even 1).
+
+# The captures are indexed per nesting. This means a group in a group will be nested
+#  under its parent group: `$/[0][0]`, for this code:
+'hello-~-world' ~~ / ( 'hello' ( <[ \- \~ ]> + ) ) 'world' /;
+say $/[0].Str; #=> hello~
+say $/[0][0].Str; #=> ~
+
+# This stems from a very simple fact: `$/` does not contain strings, integers or arrays,
+#  it only contains match objects. These contain the `.list`, `.hash` and `.Str` methods.
+#  (but you can also just use `match<key>` for hash access and `match[idx]` for array access)
+say $/[0].list.perl; #=> (Match.new(...),).list
+                     # We can see it's a list of Match objects. Those contain a bunch of infos:
+                     # where the match started/ended, the "ast" (see actions later), etc.
+                     # You'll see named capture below with grammars.
+
+## Alternatives - the `or` of regexps
+# WARNING: They are DIFFERENT from PCRE regexps.
+so 'abc' ~~ / a [ b | y ] c /; # `True`. Either "b" or "y".
+so 'ayc' ~~ / a [ b | y ] c /; # `True`. Obviously enough ...
+
+# The difference between this `|` and the one you're used to is LTM.
+# LTM means "Longest Token Matching". This means that the engine will always
+#  try to match as much as possible in the strng
+'foo' ~~ / fo | foo /; # `foo`, because it's longer.
+# To decide which part is the "longest", it first splits the regex in two parts:
+# The "declarative prefix" (the part that can be statically analyzed)
+#  and the procedural parts.
+# Declarative prefixes include alternations (`|`), conjuctions (`&`),
+#  sub-rule calls (not yet introduced), literals, characters classes and quantifiers.
+# The latter include everything else: back-references, code assertions,
+#  and other things that can't traditionnaly be represented by normal regexps.
+#
+# Then, all the alternatives are tried at once, and the longest wins.
+# Exemples:
+# DECLARATIVE | PROCEDURAL
+/ 'foo' \d+     [ <subrule1> || <subrule2> ] /;
+# DECLARATIVE (nested groups are not a problem)
+/ \s* [ \w & b ] [ c | d ] /;
+# However, closures and recursion (of named regexps) are procedural.
+# ... There are also more complicated rules, like specificity
+#  (literals win over character classes)
+
+# Note: the first-matching `or` still exists, but is now spelled `||`
+'foo' ~~ / fo || foo /; # `fo` now.
+
+
+
+
+### Extra: the MAIN subroutime
+# The `MAIN` subroutine is called when you run a Perl 6 file directly.
+# It's very powerful, because Perl 6 actually parses the argument
+#  and pass them as such to the sub. It also handles named argument (`--foo`)
+#  and will even go as far as to autogenerate a `--help`
+sub MAIN($name) { say "Hello, $name !" }
+# This produces:
+#    $ perl6 cli.pl
+#    Usage:
+#      t.pl <name>
+
+# And since it's a regular Perl 6 sub, you can haz multi-dispatch:
+# (using a "Bool" for the named argument so that we can do `--replace`
+#  instead of `--replace=1`)
+subset File of Str where *.IO.d; # convert to IO object to check the file exists
+
+multi MAIN('add', $key, $value, Bool :$replace) { ... }
+multi MAIN('remove', $key) { ... }
+multi MAIN('import', File, Str :$as) { ... } # omitting parameter name
+# This produces:
+#    $ perl 6 cli.pl
+#    Usage:
+#      t.pl [--replace] add <key> <value>
+#      t.pl remove <key>
+#      t.pl [--as=<Str>] import (File)
+# As you can see, this is *very* powerful.
+# It even went as far as to show inline the constants.
+# (the type is only displayed if the argument is `$`/is named)
+
+###
+### APPENDIX A:
+###
+### List of things
+###
+
+# It's considered by now you know the Perl6 basics.
+# This section is just here to list some common operations,
+#  but which are not in the "main part" of the tutorial to bloat it up
+
+## Operators
+
+
+## * Sort comparison
+# They return one value of the `Order` enum : `Less`, `Same` and `More`
+#  (which numerify to -1, 0 or +1).
+1 <=> 4; # sort comparison for numerics
+'a' leg 'b'; # sort comparison for string
+$obj eqv $obj2; # sort comparison using eqv semantics
+
+## * Generic ordering
+3 before 4; # True
+'b' after 'a'; # True
+
+## * Short-circuit default operator
+# Like `or` and `||`, but instead returns the first *defined* value :
+say Any // Nil // 0 // 5; #=> 0
+
+## * Short-circuit exclusive or (XOR)
+# Returns `True` if one (and only one) of its arguments is true
+say True ^^ False; #=> True
+## * Flip Flop
+# The flip flop operators (`ff` and `fff`, equivalent to P5's `..`/`...`).
+#  are operators that take two predicates to test:
+# They are `False` until their left side returns `True`, then are `True` until
+#  their right side returns `True`.
+# Like for ranges, you can exclude the iteration when it became `True`/`False`
+#  by using `^` on either side.
+# Let's start with an example :
+for <well met young hero we shall meet later> {
+  # by default, `ff`/`fff` smart-match (`~~`) against `$_`:
+  if 'met' ^ff 'meet' { # Won't enter the if for "met"
+                        #  (explained in details below).
+    .say
+  }
+
+  if rand == 0 ff rand == 1 { # compare variables other than `$_`
+    say "This ... probably will never run ...";
+  }
+}
+# This will print "young hero we shall meet" (excluding "met"):
+#  the flip-flop will start returning `True` when it first encounters "met"
+#  (but will still return `False` for "met" itself, due to the leading `^`
+#   on `ff`), until it sees "meet", which is when it'll start returning `False`.
+
+# The difference between `ff` (awk-style) and `fff` (sed-style) is that
+#  `ff` will test its right side right when its left side changes to `True`,
+#  and can get back to `False` right away
+#  (*except* it'll be `True` for the iteration that matched) -
+# While `fff` will wait for the next iteration to
+#  try its right side, once its left side changed:
+.say if 'B' ff 'B' for <A B C B A>; #=> B B
+                                    # because the right-hand-side was tested
+                                    # directly (and returned `True`).
+                                    # "B"s are printed since it matched that time
+                                    #  (it just went back to `False` right away).
+.say if 'B' fff 'B' for <A B C B A>; #=> B C B
+                                    # The right-hand-side wasn't tested until
+                                    #  `$_` became "C"
+                                    # (and thus did not match instantly).
+
+# A flip-flop can change state as many times as needed:
+for <test start print it stop not printing start print again stop not anymore> {
+  .say if $_ eq 'start' ^ff^ $_ eq 'stop'; # exclude both "start" and "stop",
+                                           #=> "print this printing again"
+}
+
+# you might also use a Whatever Star,
+# which is equivalent to `True` for the left side or `False` for the right:
+for (1, 3, 60, 3, 40, 60) { # Note: the parenthesis are superfluous here
+                            # (sometimes called "superstitious parentheses")
+ .say if $_ > 50 ff *; # Once the flip-flop reaches a number greater than 50,
+                       #  it'll never go back to `False`
+                       #=> 60 3 40 60
+}
+
+# You can also use this property to create an `If`
+#  that'll not go through the first time :
+for <a b c> {
+  .say if * ^ff *; # the flip-flop is `True` and never goes back to `False`,
+                   #  but the `^` makes it *not run* on the first iteration
+                   #=> b c
+}
+
+
+# - `===` is value identity and uses `.WHICH` on the objects to compare them
+# - `=:=` is container identity and uses `VAR()` on the objects to compare them
+
+```
+
+If you want to go further, you can:
+
+ - Read the [Perl 6 Advent Calendar](http://perl6advent.wordpress.com/). This is probably the greatest source of Perl 6 information, snippets and such.
+ - Come along on `#perl6` at `irc.freenode.net`. The folks here are always helpful.
+ - Check the [source of Perl 6's functions and classes](https://github.com/rakudo/rakudo/tree/nom/src/core). Rakudo is mainly written in Perl 6 (with a lot of NQP, "Not Quite Perl", a Perl 6 subset easier to implement and optimize).
+ - Read [the language design documents](http://design.perl6.org). They explain P6 from an implementor point-of-view, but it's still very interesting.
+