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Update perl6 to fix some of its quirks
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@ -7,24 +7,29 @@ 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 upcoming hundred years.
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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 and [the MoarVM](http://moarvm.com).
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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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Meta-note : the triple pound signs are here to denote headlines, double paragraphs, 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. (), [], {}, 「」, etc, will work.
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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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a
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my $variable;
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# Perl 6 has 4 variable types :
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## * Scalars. They represent a single value. They start with a `$`
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@ -32,19 +37,22 @@ 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, and can contain (and end with) underscores :
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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 which turns its operand into a Bool
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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. similar to perl5's qw, or Ruby's %w
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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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@ -58,10 +66,12 @@ my %hash = 1 => 2,
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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 from an even-numbered array
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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: (especially handy for named parameters that you'll see later)
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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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@ -70,33 +80,37 @@ my %hash = :w(1), # equivalent to `w => 1`
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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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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). Stored in variable, they use `&`
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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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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, $name !";
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}
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# since you can omit parenthesis to call a function with no arguments,
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# you need "&" in the name to capture `say-hello`
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# Since you can omit parenthesis to call a function with no arguments,
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# you need "&" in the name to capture `say-hello`.
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my &s = &say-hello;
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my &other-s = sub { say "anonymous function !" }
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my &other-s = sub { say "Anonymous function !" }
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# A sub can have a "slurpy" parameter, or "doesn't-matter-how-many"
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sub as-many($head, *@rest) { # the `*@` slurpy will basically "take everything else".
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# Note: you can have parameters *before* (like here) a slurpy one,
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# but not *after*.
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sub as-many($head, *@rest) { # The `*@` slurpy will basically "take everything else".
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# Note: you can have parameters *before* (like here)
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# a slurpy one, but not *after*.
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say @rest.join(' / ') ~ " !";
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}
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say as-many('Happy', 'Happy', 'Birthday'); #=> Happy / Birthday !
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# Note that the splat did not consume the parameter before.
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# Note that the splat did not consume
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# the parameter before.
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## You can call a function with an array using the "argument list flattening" operator `|`
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# (it's not actually the only feature of the operator, but it's one of them)
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## You can call a function with an array using the
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# "argument list flattening" operator `|`
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# (it's not actually the only role of this operator, but it's one of them)
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sub concat3($a, $b, $c) {
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say "$a, $b, $c";
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}
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@ -105,7 +119,8 @@ concat3(|@array); #=> a, b, c
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## It can also have optional arguments:
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sub with-optional($arg?) { # the "?" marks the argument optional
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say "I might return `(Any)` if I don't have an argument passed, or I'll return my argument";
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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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@ -132,14 +147,15 @@ with-named(1, named => 6); #=> 7
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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, mainly useful for `:2nd` etc)
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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 "$named !";
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say "$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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@ -171,9 +187,10 @@ named-def(def => 15); #=> 15
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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 its right.
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# When passed around, containers are marked as immutable. Which means that, in a function,
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# you'll get an error if you try to mutate one of your arguments.
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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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@ -185,7 +202,8 @@ sub mutate($n is rw) {
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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 (else Perl 6 thinks it's a "term")
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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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@ -197,9 +215,10 @@ say $x; #=> 52
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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" (represent True),
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# and which are "Falsey" (or "Falsy") -- meaning they represent False.
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# Only these values are Falsey: (), 0, "0", Nil, A type, and of course False itself.
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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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@ -217,18 +236,18 @@ say "Quite truthy" if True;
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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 it's much more powerful thanks to smart matching,
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# and thanks to Perl 6's "topic variable", $_.
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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` uses it using the "smart matching" operator.
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# Since other Perl 6 constructs use this variable (as said before, like `for`, blocks, etc),
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# this means the powerful `when` is not only applicable along with a `given`,
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# but instead anywhere a `$_` exists.
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# `given` simply puts its argument into `$_` (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/ { # you'll read about the smart-matching operator below -- just know `when` uses it
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# this is equivalent to `if $_ ~~ /foo/`
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when /foo/ { # You'll read about the smart-matching operator below -- 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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@ -242,15 +261,17 @@ given "foo bar" {
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## Looping constructs
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# - `loop` is an infinite loop if you don't pass it arguments, but can also be a c-style `for` :
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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` in other languages.
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# Notice that you can also use postfix conditionals, loops, etc.
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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 conditionals,
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# loops, etc.
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say "This is a C-style for loop !";
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}
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@ -270,9 +291,10 @@ for @array {
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}
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for @array {
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next if $_ == 3; # you can skip to the next iteration (like `continue` in C-like languages)
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redo if $_ == 4; # you can re-do the iteration, keeping the same topic variable (`$_`)
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last if $_ == 5; # you can also break out of a loop (like `break` in C-like languages)
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# You can...
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next if $_ == 3; # Skip to the next iteration (like `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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@ -283,8 +305,8 @@ if long-computation() -> $result {
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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 categories,
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## like infix:<+> (addition) or prefix:<!> (bool not)
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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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@ -312,12 +334,14 @@ if long-computation() -> $result {
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(1, 2) eqv (1, 3);
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# - `~~` is smart matching
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# for a complete combinations list, use this table : http://perlcabal.org/syn/S03.html#Smart_matching
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# For a complete list of combinations, use this table : http://perlcabal.org/syn/S03.html#Smart_matching
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'a' ~~ /a/; # true if matches regexp
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'key' ~~ %hash; # true if key exists in hash
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$arg ~~ &bool-returning-function; # true if the function, passed `$arg` as an argument, returns True
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1 ~~ Int; # "is of type"
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1 ~~ True; # smart-matching against a boolean always returns that boolean (and will warn).
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$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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@ -330,17 +354,19 @@ $arg ~~ &bool-returning-function; # true if the function, passed `$arg` as an ar
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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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# 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, using the Whatever Star :
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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 an array of results
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# this will print "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 it needs, then keep them in memory
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# They won't be calculated more than once.
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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 juste put `1..*`,
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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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@ -349,19 +375,23 @@ say @array[^10]; # you can pass arrays as subscripts and it'll return an array o
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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 && $c; # returns the first argument that evaluates to False, or the last argument
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$a && $b && $c; # Returns the first argument that evaluates to False,
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# or the last argument.
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$a || $b;
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# And because you're going to want them, you also have composed assignment operators:
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# And because you're going to want them,
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# you also have composed assignment operators:
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$a *= 2; # multiply and assignment
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$b %%= 5; # divisible by and assignment
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$c .= say; # method call 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.
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# We're going to see a few more key concepts that make them better than in any other language :-).
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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 ! It's the ability to "extract" arrays and keys. It'll work in `my`s and parameters.
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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 $a; #=> 1
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my ($, $, $c) = 1, 2, 3; # keep the non-interesting anonymous
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@ -377,14 +407,17 @@ sub foo(@array [$fst, $snd]) {
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foo(@tail); #=> My first is 2, my second is 3 ! All in all, I'm 2 3
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# If you're not using the array itself, you can also keep it anonymous, much like a scalar:
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# If you're not using the array itself, you can also keep it anonymous,
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# much like a scalar:
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sub first-of-array(@ [$fst]) { $fst }
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first-of-array(@small); #=> 1
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first-of-array(@tail); # errors with "Too many positional parameters passed" (the array is too big)
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first-of-array(@tail); # Throws an error "Too many positional parameters passed"
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# (which means the array is too big).
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# You can also use a slurp ...
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sub slurp-in-array(@ [$fst, *@rest]) { # you could decide to keep `*@rest` anonymous
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say $fst + @rest.elems;
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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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@ -403,18 +436,21 @@ sub key-of(% (:value($val), :qua($qua))) {
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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 => 1});
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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 (though you may use the `return` keyword, of course):
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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):
|
||||
sub next-index($n) {
|
||||
$n + 1;
|
||||
}
|
||||
my $new-n = next-index(3); # $new-n is now 4
|
||||
|
||||
# This is true for everything, except for the looping constructs (due to performance reasons):
|
||||
# there's no purpose in building a list if we're just going to discard all the results.
|
||||
# If you still want to build one, you can use the `do` prefix: (or the `gather` prefix, which we'll see later)
|
||||
# This is true for everything, except for the looping constructs
|
||||
# (due to performance reasons): there's reason to build a list
|
||||
# if we're just going to discard all the results.
|
||||
# If you still want to build one, you can use the `do` statement prefix:
|
||||
# (or the `gather` prefix, which we'll see later)
|
||||
sub list-of($n) {
|
||||
do for ^$n { # note the use of the range-to prefix operator `^` (`0..^N`)
|
||||
$_ # current loop iteration
|
||||
@ -424,15 +460,16 @@ 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.
|
||||
# `-> {}` 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:
|
||||
# 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
|
||||
@ -441,7 +478,7 @@ sub is-in(@array, $elem) {
|
||||
sub truthy-array(@array) {
|
||||
# this will produce an array of `True` and `False`:
|
||||
# (you can also say `anon sub` for "anonymous subroutine")
|
||||
map(sub { if $_ { return True } else { return False } }, @array);
|
||||
map(sub ($i) { if $i { return True } else { return False } }, @array);
|
||||
# ^ the `return` only returns from the anonymous `sub`
|
||||
}
|
||||
|
||||
@ -454,15 +491,17 @@ say (*/2)(4); #=> 2
|
||||
say ((*+3)/5)(5); #=> 1.6
|
||||
# works even in parens !
|
||||
|
||||
# but if you need to have more than one argument (`$_`) in a block (without wanting to resort to `-> {}`),
|
||||
# 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); # same as the above
|
||||
|
||||
# Note : those are sorted lexicographically. `{ $^b / $^a }` is like `-> $a, $b { $b / $a }`
|
||||
# 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`:
|
||||
# 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
|
||||
@ -472,21 +511,25 @@ 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 ..."
|
||||
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." } # this uses smart-matching (could use a regexp, etc)
|
||||
multi is-big(Int $ where 10..50) { "Quite." } # Using smart-matching
|
||||
# (could use a regexp, etc)
|
||||
multi is-big(Int $) { "No" }
|
||||
|
||||
# you can also name these checks, by creating "subsets":
|
||||
# You can also name these checks, by creating "subsets":
|
||||
subset Even of Int where * %% 2;
|
||||
|
||||
multi odd-or-even(Even) { "Even" } # the main case using the type. We don't name the argument
|
||||
multi odd-or-even(Even) { "Even" } # The main case using the type.
|
||||
# We don't name the argument.
|
||||
multi odd-or-even($) { "Odd" } # "else"
|
||||
|
||||
# You can even dispatch based on a positional's argument presence !
|
||||
multi with-or-without-you(:$with!) { # make it mandatory to be able to dispatch against it
|
||||
multi with-or-without-you(:$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 {
|
||||
@ -494,17 +537,21 @@ multi with-or-without-you {
|
||||
}
|
||||
# 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`, for example, is a dispatch to a function with this signature:
|
||||
#
|
||||
# - `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 probably lead to some very surprising side-effects !)
|
||||
#
|
||||
# (commented because running this would be a terrible idea !)
|
||||
|
||||
|
||||
### Scoping
|
||||
# In Perl 6, contrarily to many scripting languages (Python, Ruby, PHP, for example),
|
||||
# you are to declare your variables before using them. You already saw it, with `my`.
|
||||
# (there are other declarator keywords, like `our`, `has` and `state`, but we'll talk about them later)
|
||||
# This is called "lexical scoping", where in inner blocks, you can access variables from outer blocks.
|
||||
# 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 $bar = 'Bar';
|
||||
@ -516,13 +563,14 @@ sub foo {
|
||||
foo()(); #=> 'Foo Bar'
|
||||
|
||||
# As you can see, `$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)
|
||||
# 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 stack.
|
||||
# Dyamically-scoped variables depend on the current call stack,
|
||||
# instead of the current block depth.
|
||||
sub foo {
|
||||
my $*foo = 1;
|
||||
bar(); # call `bar` in-place
|
||||
@ -536,16 +584,18 @@ sub bar {
|
||||
### Object Model
|
||||
|
||||
## Perl 6 has a quite comprehensive object model
|
||||
## You declare a class with the keyword `class`, fields with `has`, methods with `method`.
|
||||
## In Perl 6, every field is private, and named `$!attr`, but if you declare it with `$.`,
|
||||
## you get a public (immutable) accessor along with it.
|
||||
# You declare a class with the keyword `class`, fields with `has`,
|
||||
# methods with `method`. Every field to private, and is named `$!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. Use `$!field` from inside the class to modify it.
|
||||
has $.other-field is rw; # You can, however, mark a public field as being read/write.
|
||||
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 {
|
||||
@ -556,7 +606,7 @@ class A {
|
||||
# $.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` was declared `rw` (mutable).
|
||||
$.other-field = 5; # This works, because `$.other-field` is `rw`.
|
||||
}
|
||||
|
||||
method !private-method {
|
||||
@ -565,13 +615,15 @@ class A {
|
||||
};
|
||||
|
||||
# Create a new instance of A with $.field set to 5 :
|
||||
# note : you can't set private-field from here (more later on)
|
||||
# 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`).
|
||||
$a.other-field = 10; # This, however, works, because the public field
|
||||
# is mutable (`rw`).
|
||||
|
||||
## Perl 6 also has inheritance (along with multiple inheritance ... Considered a misfeature by many)
|
||||
## Perl 6 also has inheritance (along with multiple inheritance)
|
||||
# (though considered a misfeature by many)
|
||||
|
||||
class A {
|
||||
has $.val;
|
||||
@ -591,12 +643,14 @@ class B is A { # inheritance uses `is`
|
||||
method bar { $.val * 10 } # this shadows A's `bar`
|
||||
}
|
||||
|
||||
my B $b .= new(val => 5); # When you use `my T $var`, `$var` starts off with `T` itself in it,
|
||||
# When you use `my T $var`, `$var` starts off with `T` itself in it,
|
||||
# so you can call `new` on it.
|
||||
# (`.=` is just the compound operator composed of the dot-call and of the assignment operator
|
||||
# (`.=` 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`
|
||||
# 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`
|
||||
@ -622,18 +676,21 @@ class Item does PrintableVal {
|
||||
|
||||
# However, this:
|
||||
# method print {}
|
||||
# is an error, since the compiler wouldn't know which `print` to use :
|
||||
# contrarily to inheritance, methods mixed in can't be shadowed - they're put at the same "level"
|
||||
# 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
|
||||
# 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, usually 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:
|
||||
# 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 {
|
||||
@ -649,17 +706,17 @@ die X::AdHoc.new(payload => 'Error !');
|
||||
# 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.
|
||||
# (you can say that packages are the lowest common denomitor between them)
|
||||
# Packages play a big part in a language, as Perl is well-known for CPAN,
|
||||
# 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 play a big part in a language, 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 created as an "empty package stub"
|
||||
# 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
|
||||
# ... declarations here ...
|
||||
}
|
||||
module Parse::Text; # file-scoped form
|
||||
grammar Parse::Text::Grammar { # A grammar is a fine package, which you could `use`
|
||||
@ -692,7 +749,8 @@ my $actions = JSON::Tiny::Actions.new;
|
||||
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 scoped `sub`s `our` ... Better know what you're doing (Don't !).
|
||||
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
|
||||
@ -725,23 +783,24 @@ sub fixed-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 loop. See:
|
||||
# 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`
|
||||
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 !)
|
||||
# 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 !
|
||||
@ -791,7 +850,7 @@ sub do-db-stuff {
|
||||
# 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 `}`) for their block.
|
||||
# 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"):
|
||||
@ -848,8 +907,9 @@ say nilthingie.perl; #=> Nil
|
||||
|
||||
## 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 :
|
||||
# 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`
|
||||
@ -864,8 +924,9 @@ $a ! $b ! $c; # with a list-associative `!`, this is `infix:<>`
|
||||
!$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 (actually not):
|
||||
# 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:
|
||||
@ -906,36 +967,46 @@ sub circumfix:<[ ]>(Int $n) {
|
||||
say [5]; #=> 3125
|
||||
# circumfix is around. Again, not whitespace.
|
||||
|
||||
sub postcircumfix:<{ }>(Str $s, Int $idx) { # post-circumfix is "after a term, around something"
|
||||
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 (named argument)
|
||||
# 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);
|
||||
# It's *all* using the same building blocks! Syntactic categories (prefix infix ...),
|
||||
# named arguments (adverbs), ..., used to build the language are available to you.
|
||||
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)
|
||||
# (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.
|
||||
# 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'd be non-meaningful if contained in a list) or `Any` if there's none.
|
||||
# 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`
|
||||
@ -943,7 +1014,8 @@ 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:
|
||||
# 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)
|
||||
|
||||
@ -951,10 +1023,11 @@ say [//] Nil, Any, False, 1, 5; #=> False
|
||||
# Default value examples:
|
||||
say [*] (); #=> 1
|
||||
say [+] (); #=> 0
|
||||
# In both cases, they're results that, if they were contained in the lists,
|
||||
# wouldn't have any impact on the final value (since N*1=N and N+0=N).
|
||||
# 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 `//`
|
||||
# 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 }
|
||||
@ -980,23 +1053,31 @@ say [[&add]] 1, 2, 3; #=> 6
|
||||
|
||||
## * 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 for when to stop, or even Whatever for a lazy infinite list.
|
||||
# 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 (when the predicate matches)
|
||||
my @list = 1, 3, 9 ... * > 30; # you can use a predicate (with the Whatever Star, here)
|
||||
#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, *+* ... *; # lazy infinite list of prime numbers,
|
||||
# computed using a closure!
|
||||
my @fib = 1, 1, -> $a, $b { $a + $b } ... *; # (equivalent to the above)
|
||||
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
|
||||
# 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).
|
||||
# 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 $obj2; # sort comparison using eqv semantics
|
||||
@ -1014,14 +1095,17 @@ say Any // Nil // 0 // 5; #=> 5
|
||||
say True ^^ False; #=> True
|
||||
|
||||
## * Flip Flop
|
||||
# The flip flop operators (`ff` and `fff`, equivalent to Perl 5/Ruby's `..` and `...`).
|
||||
# The flip flop operators (`ff` and `fff`, equivalent to P5's `..`/`...`).
|
||||
# are operators that take two predicates to test:
|
||||
# They are `False` until their left side returns `True`, then are `True` until their right side returns `True`.
|
||||
# Like for ranges, you can exclude the iteration when it became `True`/`False` by using `^` on either side.
|
||||
# They are `False` until their left side returns `True`, then are `True` until
|
||||
# their right side returns `True`.
|
||||
# Like for ranges, you can exclude the iteration when it became `True`/`False`
|
||||
# by using `^` on either side.
|
||||
# Let's start with an example :
|
||||
for <well met young hero we shall meet later> {
|
||||
# by default, `ff`/`fff` smart-match (`~~`) against `$_`:
|
||||
if 'met' ^ff 'meet' { # won't enter the if for "met" (explained in details below).
|
||||
if 'met' ^ff 'meet' { # Won't enter the if for "met"
|
||||
# (explained in details below).
|
||||
.say
|
||||
}
|
||||
|
||||
@ -1031,20 +1115,24 @@ for <well met young hero we shall meet later> {
|
||||
}
|
||||
# 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`.
|
||||
# (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 just as 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:
|
||||
# `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`).
|
||||
# because the right-hand-side was tested
|
||||
# directly (and returned `True`).
|
||||
# "B"s are still printed since it matched that time
|
||||
# (it just went back to `False` right away)
|
||||
# (it just went back to `False` right away).
|
||||
.say if 'B' fff 'B' for <A B C B A>; #=> B C B
|
||||
# because the right-hand-side wasn't tested until `$_` became "C"
|
||||
# (and thus did not match directly).
|
||||
# because the right-hand-side wasn't tested until
|
||||
# `$_` became "C"
|
||||
# (and thus did not match instantly).
|
||||
|
||||
# A flip-flop can change state as many times as needed:
|
||||
for <test start print this stop you stopped printing start printing again stop not anymore> {
|
||||
@ -1054,12 +1142,15 @@ for <test start print this stop you stopped printing start printing again stop n
|
||||
|
||||
# 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"
|
||||
.say if $_ > 50 ff *; # Once the flip-flop reaches a number greater than 50, it'll never go back to `False`
|
||||
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 execute the first time :
|
||||
# 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
|
||||
@ -1072,28 +1163,33 @@ for <a b c> {
|
||||
# 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: You may feel like you already know these because you know PCRE. You'd be wrong.
|
||||
# Some things are the same (like `?`, `+`, and `*`), but sometimes the semantics change (`|`).
|
||||
# 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 a looot of 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 the `token`, `regex` and `rule` keywords, and some more.
|
||||
# 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:
|
||||
# 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)
|
||||
# - 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).
|
||||
# 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 also available as `$/` (implicitly lexically-scoped).
|
||||
# You can also use the capture variables (`$0`, `$1`, ... - starting at 0, not 1 !).
|
||||
#
|
||||
@ -1101,8 +1197,8 @@ say so 'a' ~~ / a /; # More readable with some spaces!
|
||||
# (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.
|
||||
# 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.
|
||||
|
||||
@ -1140,7 +1236,8 @@ so 'abbbbc' ~~ / a b* c /; # `True`
|
||||
so 'aec' ~~ / a b* c /; # `False`. "b"(s) are optional, but can't be something else.
|
||||
|
||||
# - `**` - "Quantify It Yourself".
|
||||
# If you squint hard enough, you might understand the why exponentation means quantity.
|
||||
# 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`
|
||||
@ -1151,11 +1248,12 @@ so 'abbbbbbc' ~~ / a b ** 3..* c /; # `True` (infinite ranges are okay)
|
||||
# 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 /; # `True`.
|
||||
# We match the "abc" 1 or more time.
|
||||
# (the `+` was applied to the group)
|
||||
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.
|
||||
# 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`. (we keep `so` here and use `$/` below)
|
||||
|
||||
@ -1165,13 +1263,15 @@ say $/; # Will print some weird stuff (we'll explain) (or "Nil" if nothing match
|
||||
|
||||
# As we also said before, it has array indexing:
|
||||
say $/[0]; #=> ｢ABC｣ ｢ABC｣
|
||||
# These weird brackets are `Match` objects. So here, we have an array of that.
|
||||
say $0; # the same as above.
|
||||
# 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
|
||||
# IF it can have more than one element (so, with `*`, `+` and any `**`, but not with `?`).
|
||||
# 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 $/[0]; #=> ｢ABC｣
|
||||
@ -1206,7 +1306,8 @@ sub MAIN($name) { say "Hello, you !" }
|
||||
# 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=`)
|
||||
# (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, then check the file exists
|
||||
|
||||
multi MAIN('add', $key, $value, Bool :$replace) { ... }
|
||||
@ -1218,8 +1319,9 @@ multi MAIN('import', File, Str :$as) { ... } # omitting parameter name
|
||||
# t.pl [--replace] add <key> <value>
|
||||
# t.pl remove <key>
|
||||
# t.pl [--as=<Str>] import (File)
|
||||
# As you can see, this is *very* powerful. It even went as far as to show inline the constants.
|
||||
# (the type is only displayed if 1. there's no argument name 2. it's a named argument)
|
||||
# As you can see, this is *very* powerful.
|
||||
# It even went as far as to show inline the constants.
|
||||
# (the type is only displayed if the argument is `$`/is named)
|
||||
```
|
||||
|
||||
If you want to go further, you can:
|
||||
|
||||
Loading…
Reference in New Issue
Block a user