2014-06-28 20:59:14 +00:00
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---
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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 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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```perl6
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# Single line comment start with a pound
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### Variables
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# In Perl 6, you declare a lexical variable using `my`
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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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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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my $weird'variable-name_ = 5;
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## - Arrays. They represent multiple values. They 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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2014-07-13 18:42:29 +00:00
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my @array = <a b c>; # array of string, delimited by space. similar to perl5's qw, or Ruby's %w
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2014-06-28 20:59:14 +00:00
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say @array[2]; # Arrays are 0-indexed
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## - Hashes
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my %hash = 1 => 2,
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3 => 4;
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my %hash = autoquoted => "key",
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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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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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## - Subs (subroutines, or functions in most other languages). Stored in variable, they use `&`
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sub say-hello { say "Hello, world" }
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2014-07-13 18:42:29 +00:00
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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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2014-06-28 20:59:14 +00:00
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# since you can omit parenthesis to call a function with no arguments, you need to use `&` also 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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# `->`, lambda with arguments, and string interpolation
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my &lambda = -> $argument { "The argument passed to this lambda is $argument" }
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2014-07-13 20:28:41 +00:00
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# add 3 to each value of an array using map :
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map({ $_ + 3 }, @array); # $_ is the implicit argument (the same as for `given` and `for`)
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# a sub (`sub {}`) has different semantics than a block (`{}` or `-> {}`) :
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# a block doesn't have a function context (though it can have arguments), which means that if you
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# return from it, you're going to return from the parent function, compare:
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sub is-in(@array, $elem) {
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map({ return True if $_ == $elem }, @array); # this will `return` out of `is-in`
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}
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sub truthy-array(@array) {
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# this will produce an array of `True` and `False` :
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# (you can also say `anon sub` for "anonymous subroutine")
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map(sub { if $_ { return True } else { return False } }, @array);
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}
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# `-> {}` and `{}` are pretty much the same thing, except taht the former can take arguments,
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# and that the latter can be mistaken as a hash by the compiler
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2014-07-16 18:07:35 +00:00
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# You can also use the "whatever star" to create an anonymous function
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# (it'll stop at the furthest operator in the current expression)
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map(*+3, @array); # `*+3` is the same as `{ $_ + 3 }`
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map(*+*+3, @array); # also works. Same as `-> $a, $b { $a + $b + 3 }`
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say ((*+3)/5)(5); # immediatly execute the function Whatever created -- works even in parens !
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# but if you need to have more than one argument (`$_`) in a block (without wanting to resort to `-> {}`),
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# you can also use the implicit argument syntax, `$^` :
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map({ $^a + $^b + 3 }, @array); # same as the above
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# Note : those are sorted lexicographically. `{ $^b / $^a }` is like `-> $a, b { $ b / $a }`
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## Multiple Dispatch
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# Perl 6 can decide which variant of a `sub` to call based on the type of the arguments,
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# or on arbitrary preconditions, using `where` :
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# with types
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multi sub sayit(Int $n) { # note the `multi` keyword here
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say "Number: $n";
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}
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multi sayit(Str $s) } # the `sub` is implicit
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say "String: $s";
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}
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sayit("foo"); # prints "String: foo"
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sayit(True); # fails at *compile time* with "calling 'sayit' will never work with arguments of types ..."
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# with arbitrary precondition :
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multi is-big(Int $n where * > 10) { True }
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multi is-big(Int $) { False }
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2014-07-16 18:07:35 +00:00
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# you can also name these checks, by creating "subsets" :
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subset Even of Int where * %% 2;
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2014-07-13 18:42:29 +00:00
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### Containers
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# In Perl 6, values are actually stored in "containers".
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# the assignment operator asks the container on the left to store the value on its right
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# When passed around, containers are marked as immutable. Which means that, in a function,
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# you'll get an error if you try to mutate one of your argument.
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# If you really need to, you can ask for a mutable container using `is rw` :
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sub mutate($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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say $x; #=> 52
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2014-06-28 20:59:14 +00:00
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### Control Flow Structures
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# You don't need to put parenthesis around the condition, but that also means you always have to use brackets (`{ }`) for their body :
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## Conditionals
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2014-07-13 20:28:41 +00:00
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# - `if`
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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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# if (true) say; # Won't work
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2014-07-13 20:28:41 +00:00
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# - Ternary conditional
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my $a = $condition ?? $value-if-true !! $value-if-false; # `??` and `!!` are like `?` and `:` in other languages'
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# - `given`-`when` looks like other languages `switch`, but it's much more powerful thanks to smart matching :
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given "foo bar" { # given just puts its argument into `$_`, and `when` uses it using the "smart matching" operator.
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when /foo/ { # you'll read about the smart-matching operator below
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say "Yay !";
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}
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when $_.chars > 50 { # smart matching anything with True gives True, so you can also put "normal" conditionals
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say "Quite a long string !";
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}
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}
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## Looping constructs
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2014-07-13 20:28:41 +00:00
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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 {
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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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say "This is a C-style for loop !";
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}
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2014-07-13 20:28:41 +00:00
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# - `for` - Foreaches 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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# default variable is $_
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for array {
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say "I've got $_";
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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 $result";
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}
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2014-06-29 19:41:57 +00:00
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2014-07-13 20:28:41 +00:00
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### Operators
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## Since Perl languages are very much operator-based languages
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## Perl 6 operators are actually just funny-looking subroutines, in syntactic categories,
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## like infix:<+> (addition) or prefix:<!> (bool not)
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## The categories are :
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# - "prefix" : before (like `!` in `!True`).
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# - "postfix" : after (like `++` in `$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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2014-06-29 19:41:57 +00:00
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2014-07-10 20:23:56 +00:00
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## The associativity and precedence list are explained below.
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2014-07-13 20:28:41 +00:00
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# Alright, you're set to go !
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## * Equality Checking
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2014-07-13 20:28:41 +00:00
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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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2014-07-13 20:28:41 +00:00
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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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2014-07-13 20:28:41 +00:00
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# - `eqv` is canonical equivalence
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(1, 2) eqv (1, 3);
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2014-07-13 20:28:41 +00:00
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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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'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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2014-07-13 20:28:41 +00:00
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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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2014-06-29 19:41:57 +00:00
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2014-07-13 20:28:41 +00:00
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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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2014-07-13 20:28:41 +00:00
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## * And, Or
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3 && 4; # True. Calls `.Bool` on `3`
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0 || False; # False. Calls `.Bool` on `0`
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2014-07-13 20:28:41 +00:00
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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 || $b;
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2014-07-10 20:23:56 +00:00
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2014-07-13 20:28:41 +00:00
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### Object Model
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## Perl 6 has a quite comprehensive object model
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## You declare a class with the keyword `class`, fields with `has`, methods with `method`
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## `$.` declares a public field, `$!` declares a private field
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## (a public field also has `$!`, which is its private interface)
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2014-07-13 20:28:41 +00:00
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# (Perl 6's object model ("P6Model") is very flexible, and allows you to dynamically add methods,
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# change semantics, etc -- This will not be covered here, and you should refer to the Synopsis)
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2014-07-13 18:42:29 +00:00
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class A {
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has $.field;
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has Int $!private-field = 10;
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method get-value {
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$.field + $!private-field + $n;
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}
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method set-value($n) {
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# $.field = $n; # This fails, because a public field is actually an immutable container
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# (even from inside the class)
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# You either need to use `is rw` on the `has`
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# (which will make it mutable, even from outside the class)
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# or you need to use the `$!` version :
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$!field = $n; # This works, because `$!` is always mutable
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}
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method !private-method {
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say "This method is private to the class !";
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}
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};
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# Create a new instance of A with $.field set to 5 :
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# note : you can't set private-field from here (more later on)
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my $a = A.new(field => 5);
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$a.get-value; #=> 18
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#$a.field = 5; # This fails, because the `has $.field` is lacking the `is rw`
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2014-07-13 20:28:41 +00:00
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## Perl 6 also has inheritance (along with multiple inheritance ... Considered a misfeature by many)
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class A {
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has $.val;
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submethod not-inherited {
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say "This method won't be available on B.";
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say "This is most useful for BUILD, which we'll see later";
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}
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method bar { $.val * 5 }
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}
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class B is A { # inheritance uses `is`
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method foo {
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say $.val;
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}
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method bar { $.val * 10 } # this shadows A's `bar`
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}
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my B $b .= new(val => 5); # When you use `my T $var`, `$var` starts off with `T` itself in it, so you can call `new` on it
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# (`.=` is just the compound operator composed of the dot-call and of the assignment operator)
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#
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# Also note that `BUILD` (the method called inside `new`) will set parent properties too,
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# so you can pass `val => 5`
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# $b.not-inherited; # This won't work, for reasons explained above
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$b.foo; # prints 5
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$b.bar; #=> 50, since it calls B's `bar`
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## Roles are supported too (also called Mixins in other languages)
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role PrintableVal {
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has $!counter = 0;
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method print {
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say $.val;
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}
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}
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# you "use" a mixin with "does" :
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class Item does PrintableVal {
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has $.val;
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# When `does`-ed, a `role` literally "mixes in" the class :
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# the methods and fields are put together, which means a class can access
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# the private fields/methods of its roles (but not the inverse !) :
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method access {
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say $!counter++;
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}
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# However, this :
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|
|
# method print {}
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|
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# is an error, since the compiler wouldn't know which `print` to use :
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# contrarily to inheritance, methods mixed in can't be shadowed - they're put at the same "level"
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# NOTE : You can use a role as a class (with `is ROLE`). In this case, methods will be shadowed,
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# since the compiler will consider `ROLE` to be a class
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}
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|
2014-07-13 18:42:29 +00:00
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|
2014-07-13 20:28:41 +00:00
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|
### More operators thingies !
|
2014-07-10 20:23:56 +00:00
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|
|
## Everybody loves operators ! Let's get more of them
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|
|
## The precedence list can be found here : http://perlcabal.org/syn/S03.html#Operator_precedence
|
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|
|
## But first, we need a little explanation about associativity :
|
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|
|
2014-07-13 20:28:41 +00:00
|
|
|
# - Binary operators:
|
2014-07-10 20:23:56 +00:00
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|
|
$a ! $b ! $c; # with a left-associative `!`, this is `($a ! $b) ! $c`
|
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|
|
$a ! $b ! $c; # with a right-associative `!`, this is `$a ! ($b ! $c)`
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|
|
$a ! $b ! $c; # with a non-associative `!`, this is illegal
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|
|
$a ! $b ! $c; # with a chain-associative `!`, this is `($a ! $b) and ($b ! $c)`
|
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|
|
$a ! $b ! $c; # with a list-associative `!`, this is `infix:<>`
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|
2014-07-13 20:28:41 +00:00
|
|
|
# - Unary operators:
|
2014-07-10 20:23:56 +00:00
|
|
|
!$a! # with left-associative `!`, this is `(!$a)!`
|
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|
|
!$a! # with right-associative `!`, this is `!($a!)`
|
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|
|
!$a! # with non-associative `!`, this is illegal
|
|
|
|
|
|
|
|
## And to end the list of operators ...
|
|
|
|
|
|
|
|
## * Sort comparison
|
2014-07-13 20:28:41 +00:00
|
|
|
# They return one value of the `Order` enum : `Less`, `Same` and `More` (which numerify to -1, 0 or +1).
|
2014-07-10 20:23:56 +00:00
|
|
|
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
|
|
|
|
|
2014-06-28 20:59:14 +00:00
|
|
|
```
|