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diff --git a/perl6.html.markdown b/perl6.html.markdown new file mode 100644 index 00000000..63c0830a --- /dev/null +++ b/perl6.html.markdown @@ -0,0 +1,1464 @@ +--- +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. + |