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1345 lines
51 KiB
Markdown
1345 lines
51 KiB
Markdown
---
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name: perl6
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category: language
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language: perl6
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filename: learnperl6.pl
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contributors:
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- ["Nami-Doc", "http://github.com/Nami-Doc"]
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---
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Perl 6 is a highly capable, feature-rich programming language made for the
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upcoming hundred years.
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Perl 6 runs on [the Parrot VM](http://parrot.org/), the JVM
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and [the MoarVM](http://moarvm.com).
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Meta-note : the triple pound signs are here to denote headlines,
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double paragraphs, and single notes.
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`#=>` represents the output of a command.
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```perl
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# Single line comment start with a pound
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#`(
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Multiline comments use #` and a quoting construct.
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(), [], {}, 「」, etc, will work.
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)
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### Variables
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# In Perl 6, you declare a lexical variable using `my`
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my $variable;
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# Perl 6 has 4 kinds of variables:
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## * Scalars. They represent a single value. They start with a `$`
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my $str = 'String';
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my $str2 = "String"; # double quotes allow for interpolation
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# variable names can contain but not end with simple quotes and dashes,
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# and can contain (and end with) underscores :
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# my $weird'variable-name_ = 5; # works !
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my $bool = True; # `True` and `False` are Perl 6's boolean
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my $inverse = !$bool; # You can invert a bool with the prefix `!` operator
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my $forced-bool = so $str; # And you can use the prefix `so` operator
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# which turns its operand into a Bool
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## * Arrays. They represent multiple values. Their name start with `@`.
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my @array = 1, 2, 3;
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my @array = 'a', 'b', 'c';
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# equivalent to :
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my @array = <a b c>; # array of words, delimited by space.
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# Similar to perl5's qw, or Ruby's %w.
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say @array[2]; # Array indices start at 0 -- This is the third element
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say "Interpolate an array using [] : @array[]";
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#=> Interpolate an array using [] : a b c
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## * Hashes. Key-Value Pairs.
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# Hashes are actually arrays of Pairs (`Key => Value`),
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# except they get "flattened", removing duplicated keys.
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my %hash = 1 => 2,
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3 => 4;
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my %hash = autoquoted => "key", # keys *can* get auto-quoted
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"some other" => "value", # trailing commas are okay
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;
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my %hash = <key1 value1 key2 value2>; # you can also create a hash
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# from an even-numbered array
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my %hash = key1 => 'value1', key2 => 'value2'; # same as this
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# You can also use the "colon pair" syntax:
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# (especially handy for named parameters that you'll see later)
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my %hash = :w(1), # equivalent to `w => 1`
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# this is useful for the `True` shortcut:
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:truey, # equivalent to `:truey(True)`, or `truey => True`
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# and for the `False` one:
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:!falsey, # equivalent to `:falsey(False)`, or `falsey => False`
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;
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say %hash{'key1'}; # You can use {} to get the value from a key
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say %hash<key2>; # If it's a string, you can actually use <>
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# (`{key1}` doesn't work, as Perl6 doesn't have barewords)
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## * Subs (subroutines, or functions in most other languages).
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# Stored in variable, they use `&`.
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sub say-hello { say "Hello, world" }
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sub say-hello-to(Str $name) { # You can provide the type of an argument
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# and it'll be checked at compile-time.
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say "Hello, $name !";
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}
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# Since you can omit parenthesis to call a function with no arguments,
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# you need "&" in the name to capture `say-hello`.
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my &s = &say-hello;
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my &other-s = sub { say "Anonymous function !" }
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# A sub can have a "slurpy" parameter, or "doesn't-matter-how-many"
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sub as-many($head, *@rest) { # `*@` (slurpy) will basically "take everything else".
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# Note: you can have parameters *before* (like here)
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# a slurpy one, but not *after*.
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say @rest.join(' / ') ~ " !";
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}
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say as-many('Happy', 'Happy', 'Birthday'); #=> Happy / Birthday !
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# Note that the splat did not consume
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# the parameter before.
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## You can call a function with an array using the
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# "argument list flattening" operator `|`
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# (it's not actually the only role of this operator, but it's one of them)
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sub concat3($a, $b, $c) {
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say "$a, $b, $c";
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}
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concat3(|@array); #=> a, b, c
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# `@array` got "flattened" as a part of the argument list
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## It can also have optional arguments:
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sub with-optional($arg?) { # the "?" marks the argument optional
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say "I might return `(Any)` if I don't have an argument passed,
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or I'll return my argument";
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$arg;
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}
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with-optional; # returns Any
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with-optional(); # returns Any
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with-optional(1); # returns 1
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## You can also give them a default value when they're not passed:
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sub hello-to($name = "World") {
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say "Hello, $name !";
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}
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hello-to; #=> Hello, World !
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hello-to(); #=> Hello, World !
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hello-to('You'); #=> Hello, You !
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## You can also, by using a syntax akin to the one of hashes (yay unification !),
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## pass *named* arguments to a `sub`.
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sub with-named($normal-arg, :$named) {
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say $normal-arg + $named;
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}
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with-named(1, named => 6); #=> 7
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# There's one gotcha to be aware of, here:
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# If you quote your key, Perl 6 won't be able to see it at compile time,
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# and you'll have a single Pair object as a positional paramater.
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with-named(2, :named(5)); #=> 7
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with-named(3, :4named); #=> 7
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# (special colon pair syntax for numbers,
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# to be used with s// and such, see later)
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with-named(3); # warns, because we tried to use the undefined $named in a `+`:
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# by default, named arguments are *optional*
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# To make a named argument mandatory, you can use `?`'s inverse, `!`
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sub with-mandatory-named(:$str!) {
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say "$str !";
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}
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with-mandatory-named(str => "My String"); #=> My String !
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with-mandatory-named; # run time error: "Required named parameter not passed"
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with-mandatory-named(3); # run time error: "Too many positional parameters passed"
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## If a sub takes a named boolean argument ...
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sub takes-a-bool($name, :$bool) {
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say "$name takes $bool";
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}
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# ... you can use the same "short boolean" hash syntax:
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takes-a-bool('config', :bool); # config takes True
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takes-a-bool('config', :!bool); # config takes False
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# or you can use the "adverb" form:
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takes-a-bool('config'):bool; #=> config takes True
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takes-a-bool('config'):!bool; #=> config takes False
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# You'll learn to love (or maybe hate, eh) that syntax later.
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## You can also provide your named arguments with defaults:
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sub named-def(:$def = 5) {
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say $def;
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}
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named-def; #=> 5
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named-def(:10def); #=> 10
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named-def(def => 15); #=> 15
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# -- Note: we're going to learn *more* on subs really soon,
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# but we need to grasp a few more things to understand their real power. Ready?
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### Containers
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# In Perl 6, values are actually stored in "containers".
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# The assignment operator asks the container on the left to store the value on
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# its right. When passed around, containers are marked as immutable.
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# Which means that, in a function, you'll get an error if you try to
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# mutate one of your arguments.
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# If you really need to, you can ask for a mutable container using `is rw`:
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sub mutate($n is rw) {
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$n++;
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say "\$n is now $n !";
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}
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# If what you want is a copy instead, use `is copy`.
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# A sub itself returns a container, which means it can be marked as rw:
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my $x = 42;
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sub mod() is rw { $x }
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mod() = 52; # in this case, the parentheses are mandatory
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# (else Perl 6 thinks `mod` is a "term")
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say $x; #=> 52
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### Control Flow Structures
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# You don't need to put parenthesis around the condition,
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# but that also means you always have to use brackets (`{ }`) for their body:
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## Conditionals
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# - `if`
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# Before talking about `if`, we need to know which values are "Truthy"
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# (represent True), and which are "Falsey" (or "Falsy") -- represent False.
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# Only these values are Falsey: (), 0, "0", Nil, A type (like `Str` or `Int`),
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# and of course False itself.
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# Every other value is Truthy.
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if True {
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say "It's true !";
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}
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unless False {
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say "It's not false !";
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}
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# You can also use their postfix versions, with the keyword after:
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say "Quite truthy" if True;
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# if (true) say; # This doesn't work !
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# - Ternary conditional, "?? !!" (like `x ? y : z` in some other languages)
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my $a = $condition ?? $value-if-true !! $value-if-false;
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# - `given`-`when` looks like other languages `switch`, but much more
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# powerful thanks to smart matching and thanks to Perl 6's "topic variable", $_.
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# This variable contains the default argument of a block,
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# a loop's current iteration (unless explicitly named), etc.
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# `given` simply puts its argument into `$_` (like a block would do),
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# and `when` compares it using the "smart matching" (`~~`) operator.
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# Since other Perl 6 constructs use this variable (as said before, like `for`,
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# blocks, etc), this means the powerful `when` is not only applicable along with
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# a `given`, but instead anywhere a `$_` exists.
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given "foo bar" {
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when /foo/ { # Don't worry about smart matching -- just know `when` uses it.
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# This is equivalent to `if $_ ~~ /foo/`.
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say "Yay !";
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}
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when $_.chars > 50 { # smart matching anything with True (`$a ~~ True`) is True,
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# so you can also put "normal" conditionals.
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say "Quite a long string !";
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}
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default { # same as `when *` (using the Whatever Star)
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say "Something else"
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}
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}
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## Looping constructs
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# - `loop` is an infinite loop if you don't pass it arguments,
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# but can also be a c-style `for`:
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loop {
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say "This is an infinite loop !";
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last; # last breaks out of the loop, like the `break` keyword in other languages
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}
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loop (my $i = 0; $i < 5; $i++) {
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next if $i == 3; # `next` skips to the next iteration, like `continue`
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# in other languages. Note that you can also use postfix
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# conditionals, loops, etc.
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say "This is a C-style for loop !";
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}
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# - `for` - Passes through an array
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for @array -> $variable {
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say "I've found $variable !";
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}
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# As we saw with given, for's default "current iteration" variable is `$_`.
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# That means you can use `when` in a `for` just like you were in a when.
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for @array {
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say "I've got $_";
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.say; # This is also allowed.
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# A dot call with no "topic" (receiver) is sent to `$_` by default
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$_.say; # the above and this are equivalent.
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}
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for @array {
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# You can...
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next if $_ == 3; # Skip to the next iteration (`continue` in C-like languages).
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redo if $_ == 4; # Re-do the iteration, keeping the same topic variable (`$_`).
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last if $_ == 5; # Or break out of a loop (like `break` in C-like languages).
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}
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# Note - the "lambda" `->` syntax isn't reserved to `for`:
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if long-computation() -> $result {
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say "The result is $result";
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}
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### Operators
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## Since Perl languages are very much operator-based languages
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## Perl 6 operators are actually just funny-looking subroutines, in syntactic
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## categories, like infix:<+> (addition) or prefix:<!> (bool not).
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## The categories are:
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# - "prefix": before (like `!` in `!True`).
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# - "postfix": after (like `++` in `$a++`).
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# - "infix": in between (like `*` in `4 * 3`).
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# - "circumfix": around (like `[`-`]` in `[1, 2]`).
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# - "post-circumfix": around, after another term (like `{`-`}` in `%hash{'key'}`)
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## The associativity and precedence list are explained below.
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# Alright, you're set to go !
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## * Equality Checking
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# - `==` is numeric comparison
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3 == 4; # False
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3 != 4; # True
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# - `eq` is string comparison
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'a' eq 'b';
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'a' ne 'b'; # not equal
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'a' !eq 'b'; # same as above
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# - `eqv` is canonical equivalence (or "deep equality")
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(1, 2) eqv (1, 3);
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# - `~~` is smart matching
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# For a complete list of combinations, use this table:
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# http://perlcabal.org/syn/S03.html#Smart_matching
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'a' ~~ /a/; # true if matches regexp
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'key' ~~ %hash; # true if key exists in hash
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$arg ~~ &bool-returning-function; # `True` if the function, passed `$arg`
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# as an argument, returns `True`.
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1 ~~ Int; # "has type" (check superclasses and roles)
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1 ~~ True; # smart-matching against a boolean always returns that boolean
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# (and will warn).
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# - `===` is value identity and uses `.WHICH` on the objects to compare them
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# - `=:=` is container identity and uses `VAR()` on the objects to compare them
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# You also, of course, have `<`, `<=`, `>`, `>=`.
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# Their string equivalent are also avaiable : `lt`, `le`, `gt`, `ge`.
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3 > 4;
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## * Range constructors
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3 .. 7; # 3 to 7, both included
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# `^` on either side them exclusive on that side :
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3 ^..^ 7; # 3 to 7, not included (basically `4 .. 6`)
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# This also works as a shortcut for `0..^N`:
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^10; # means 0..^10
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# This also allows us to demonstrate that Perl 6 has lazy arrays,
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# using the Whatever Star:
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my @array = 1..*; # 1 to Infinite !
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say @array[^10]; # you can pass arrays as subscripts and it'll return
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# an array of results. This will print
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# "1 2 3 4 5 6 7 8 9 10" (and not run out of memory !)
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# Note : when reading an infinite list, Perl 6 will "reify" the elements
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# it needs, then keep them in memory. They won't be calculated more than once.
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# Warning, though: if you try this example in the REPL and just put `1..*`,
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# Perl 6 will be forced to try and evaluate the whole array (to print it),
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# so you'll end with an infinite loop.
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## * And, Or
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3 && 4; # 4, which is Truthy. Calls `.Bool` on `4` and gets `True`.
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0 || False; # False. Calls `.Bool` on `0`
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## * Short-circuit (and tight) versions of the above
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$a && $b && $c; # Returns the first argument that evaluates to False,
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# or the last argument.
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$a || $b;
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# And because you're going to want them,
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# you also have composed assignment operators:
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$a *= 2; # multiply and assignment
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$b %%= 5; # divisible by and assignment
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@array .= sort; # calls the `sort` method and assigns the result back
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### More on subs !
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# As we said before, Perl 6 has *really* powerful subs. We're going to see
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# a few more key concepts that make them better than in any other language :-).
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## Unpacking !
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# It's the ability to "extract" arrays and keys.
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# It'll work in `my`s and in parameter lists.
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my ($a, $b) = 1, 2;
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say $a; #=> 1
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my ($, $, $c) = 1, 2, 3; # keep the non-interesting anonymous
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say $c; #=> 3
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my ($head, *@tail) = 1, 2, 3; # Yes, it's the same as with "slurpy subs"
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my (*@small) = 1;
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sub foo(@array [$fst, $snd]) {
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say "My first is $fst, my second is $snd ! All in all, I'm @array[].";
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# (^ remember the `[]` to interpolate the array)
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}
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foo(@tail); #=> My first is 2, my second is 3 ! All in all, I'm 2 3
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# If you're not using the array itself, you can also keep it anonymous,
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# much like a scalar:
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sub first-of-array(@ [$fst]) { $fst }
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first-of-array(@small); #=> 1
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first-of-array(@tail); # Throws an error "Too many positional parameters passed"
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# (which means the array is too big).
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# You can also use a slurp ...
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sub slurp-in-array(@ [$fst, *@rest]) { # You could keep `*@rest` anonymous
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say $fst + @rest.elems; # `.elems` returns a list's length.
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# Here, `@rest` is `(3,)`, since `$fst` holds the `2`.
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}
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slurp-in-array(@tail); #=> 3
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# You could even extract on a slurpy (but it's pretty useless ;-).)
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sub fst(*@ [$fst]) { # or simply : `sub fst($fst) { ... }`
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say $fst;
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}
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fst(1); #=> 1
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fst(1, 2); # errors with "Too many positional parameters passed"
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# You can also destructure hashes (and classes, which you'll learn about later !)
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# The syntax is basically `%hash-name (:key($variable-to-store-value-in))`.
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# The hash can stay anonymous if you only need the values you extracted.
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sub key-of(% (:value($val), :qua($qua))) {
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say "Got val $val, $qua times.";
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}
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# Then call it with a hash: (you need to keep the brackets for it to be a hash)
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key-of({value => 'foo', qua => 1});
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#key-of(%hash); # the same (for an equivalent `%hash`)
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## The last expression of a sub is returned automatically
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# (though you may use the `return` keyword, of course):
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sub next-index($n) {
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$n + 1;
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}
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my $new-n = next-index(3); # $new-n is now 4
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# This is true for everything, except for the looping constructs
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# (due to performance reasons): there's reason to build a list
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# if we're just going to discard all the results.
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# If you still want to build one, you can use the `do` statement prefix:
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# (or the `gather` prefix, which we'll see later)
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sub list-of($n) {
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do for ^$n { # note the use of the range-to prefix operator `^` (`0..^N`)
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$_ # current loop iteration
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}
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}
|
|
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 }`
|
|
|
|
## 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) } # the `sub` is the 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:
|
|
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 $) { "No" }
|
|
|
|
# You can also name these checks, by creating "subsets":
|
|
subset Even of Int where * %% 2;
|
|
|
|
multi odd-or-even(Even) { "Even" } # The main case using the type.
|
|
# We don't name the argument.
|
|
multi odd-or-even($) { "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 + $n;
|
|
}
|
|
|
|
method set-value($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);
|
|
$a.get-value; #=> 18
|
|
#$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 "use" a mixin 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`
|
|
}
|
|
}
|
|
|
|
# You can throw an exception using `die`:
|
|
die X::AdHoc.new(payload => 'Error !');
|
|
# TODO warn
|
|
# TODO fail
|
|
# TODO CONTROL
|
|
|
|
### 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 3 4
|
|
|
|
# - `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 dwelving 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 value that wouldn't change the result if passed as one
|
|
# of the element of the list to be passed to the operator),
|
|
# 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
|
|
# In both cases, they're results that, were they in the lists,
|
|
# wouldn't have any impact on the final value
|
|
# (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 prime numbers,
|
|
# 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.
|
|
|
|
|
|
## * 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 $obj2; # sort comparison using eqv semantics
|
|
|
|
## * Generic ordering
|
|
3 before 4; # True
|
|
'b' after 'a'; # True
|
|
|
|
## * Short-circuit default operator
|
|
# Like `or` and `||`, but instead returns the first *defined* value :
|
|
say Any // Nil // 0 // 5; #=> 5
|
|
|
|
## * Short-circuit exclusive or (XOR)
|
|
# Returns `True` if one (and only one) of its arguments is true
|
|
say True ^^ False; #=> True
|
|
|
|
## * Flip Flop
|
|
# The flip flop operators (`ff` and `fff`, equivalent to P5's `..`/`...`).
|
|
# are operators that take two predicates to test:
|
|
# They are `False` until their left side returns `True`, then are `True` until
|
|
# their right side returns `True`.
|
|
# Like for ranges, you can exclude the iteration when it became `True`/`False`
|
|
# by using `^` on either side.
|
|
# Let's start with an example :
|
|
for <well met young hero we shall meet later> {
|
|
# by default, `ff`/`fff` smart-match (`~~`) against `$_`:
|
|
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
|
|
}
|
|
|
|
|
|
### 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.
|
|
|
|
# - `**` - "Quantify It Yourself".
|
|
# 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)
|
|
|
|
## 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 any `**`, 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 $0.WHAT; #=> (Array)
|
|
# A specific quantifier will always capture an Array,
|
|
# may it be a range or a specific value (even 1).
|
|
|
|
# If you're wondering how the captures are numbered, here's an explanation:
|
|
TODO use graphs from s05
|
|
|
|
|
|
## Alternatives - the `or` of regexps
|
|
# WARNING: They are DIFFERENT from PCRE regexps.
|
|
so 'abc' ~~ / a [ b | y ] c /; # `True`. Either "b" or "y".
|
|
so 'ayc' ~~ / a [ b | y ] c /; # `True`. Obviously enough ...
|
|
|
|
### Extra: the MAIN subroutime
|
|
# The `MAIN` subroutine is called when you run a Perl 6 file directly.
|
|
# It's very powerful, because Perl 6 actually parses the argument
|
|
# and pass them as such to the sub. It also handles named argument (`--foo`)
|
|
# and will even go as far as to autogenerate a `--help`
|
|
sub MAIN($name) { say "Hello, you !" }
|
|
# 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 get `--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:
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# $ perl 6 cli.pl
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# Usage:
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# t.pl [--replace] add <key> <value>
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# t.pl remove <key>
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# t.pl [--as=<Str>] import (File)
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# As you can see, this is *very* powerful.
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|
# It even went as far as to show inline the constants.
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# (the type is only displayed if the argument is `$`/is named)
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```
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If you want to go further, you can:
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|
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- Read the [Perl 6 Advent Calendar](http://perl6advent.wordpress.com/). This is probably the greatest source of Perl 6 information, snippets and such.
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- Come along on `#perl6` at `irc.freenode.net`. The folks here are always helpful.
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- 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).
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- Read the [Synopses](perlcabal.org/syn). They explain it from an implementor point-of-view, but it's still very interesting.
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|