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diff --git a/perl6.html.markdown b/perl6.html.markdown deleted file mode 100644 index c7fde218..00000000 --- a/perl6.html.markdown +++ /dev/null @@ -1,1976 +0,0 @@ ---- -category: language -language: perl6 -filename: learnperl6.p6 -contributors: - - ["vendethiel", "http://github.com/vendethiel"] - - ["Samantha McVey", "https://cry.nu"] ---- - -Perl 6 is a highly capable, feature-rich programming language made for at -least the next hundred years. - -The primary Perl 6 compiler is called [Rakudo](http://rakudo.org), which runs on -the JVM and [the MoarVM](http://moarvm.com). - -Meta-note: double pound signs (`##`) are used to indicate paragraphs, -while single pound signs (`#`) indicate notes. - -`#=>` represents the output of a command. - -```perl6 -# Single line comments start with a pound sign. - -#`( Multiline comments use #` and a quoting construct. - (), [], {}, 「」, etc, will work. -) - -# Use the same syntax for multiline comments to embed comments. -for #`(each element in) @array { - put #`(or print element) $_ #`(with newline); -} -``` - -## Variables - -```perl6 -## In Perl 6, you declare a lexical variable using the `my` keyword: -my $variable; -## Perl 6 has 3 basic types of variables: scalars, arrays, and hashes. -``` - -### Scalars - -```perl6 -# Scalars represent a single value. They start with the `$` sigil: -my $str = 'String'; - -# Double quotes allow for interpolation (which we'll see later): -my $str2 = "String"; - -## Variable names can contain but not end with simple quotes and dashes, -## and can contain (and end with) underscores: -my $person's-belongings = 'towel'; # this works! - -my $bool = True; # `True` and `False` are Perl 6's boolean values. -my $inverse = !$bool; # Invert a bool with the prefix `!` operator. -my $forced-bool = so $str; # And you can use the prefix `so` operator -$forced-bool = ?$str; # to turn its operand into a Bool. Or use `?`. -``` - -### Arrays and Lists - -```perl6 -## Arrays represent multiple values. An array variable starts with the `@` -## sigil. Unlike lists, from which arrays inherit, arrays are mutable. - -my @array = 'a', 'b', 'c'; -# equivalent to: -my @letters = <a b c>; # array of words, delimited by space. - # Similar to perl5's qw, or Ruby's %w. -@array = 1, 2, 3; - -say @array[2]; # Array indices start at 0. Here the third element - # is being accessed. - -say "Interpolate an array using []: @array[]"; -#=> Interpolate an array using []: 1 2 3 - -@array[0] = -1; # Assigning a new value to an array index -@array[0, 1] = 5, 6; # Assigning multiple values - -my @keys = 0, 2; -@array[@keys] = @letters; # Assignment using an array containing index values -say @array; #=> a 6 b -``` - -### Hashes, or key-value Pairs. - -```perl6 -## Hashes are pairs of keys and values. You can construct a `Pair` object -## using the syntax `Key => Value`. Hash tables are very fast for lookup, -## and are stored unordered. Keep in mind that keys get "flattened" in hash -## context, and any duplicated keys are deduplicated. -my %hash = 'a' => 1, 'b' => 2; - -%hash = a => 1, # keys get auto-quoted when => (fat comma) is used. - b => 2, # Trailing commas are okay. -; - -## Even though hashes are internally stored differently than arrays, -## Perl 6 allows you to easily create a hash from an even numbered array: -%hash = <key1 value1 key2 value2>; # Or: -%hash = "key1", "value1", "key2", "value2"; - -%hash = key1 => 'value1', key2 => 'value2'; # same result as above - -## You can also use the "colon pair" syntax. This syntax is especially -## handy for named parameters that you'll see later. -%hash = :w(1), # equivalent to `w => 1` - :truey, # equivalent to `:truey(True)` or `truey => True` - :!falsey, # equivalent to `:falsey(False)` or `falsey => False` -; -## The :truey and :!falsey constructs are known as the -## `True` and `False` shortcuts respectively. - -say %hash{'key1'}; # You can use {} to get the value from a key. -say %hash<key2>; # If it's a string without spaces, you can actually use - # <> (quote-words operator). `{key1}` doesn't work, - # as Perl6 doesn't have barewords. -``` - -## Subs - -```perl6 -## Subroutines, or functions as most other languages call them, are -## created with the `sub` keyword. -sub say-hello { say "Hello, world" } - -## You can provide (typed) arguments. If specified, the type will be checked -## at compile-time if possible, otherwise at runtime. -sub say-hello-to( Str $name ) { - say "Hello, $name !"; -} - -## A sub returns the last value of the block. Similarly, the semicolon in -## the last can be omitted. -sub return-value { 5 } -say return-value; # prints 5 - -sub return-empty { } -say return-empty; # prints Nil - -## Some control flow structures produce a value, like `if`: -sub return-if { - if True { "Truthy" } -} -say return-if; # prints Truthy - -## Some don't, like `for`: -sub return-for { - for 1, 2, 3 { 'Hi' } -} -say return-for; # prints Nil - -## Positional arguments are required by default. To make them optional, use -## the `?` after the parameters' names. -sub with-optional( $arg? ) { - # This sub returns `(Any)` (Perl's null-like value) if - # no argument is passed. Otherwise, it returns its argument. - $arg; -} -with-optional; # returns Any -with-optional(); # returns Any -with-optional(1); # returns 1 - -## You can also give them a default value when they're not passed. -## Required parameters must come before optional ones. -sub greeting( $name, $type = "Hello" ) { - say "$type, $name!"; -} - -greeting("Althea"); #=> Hello, Althea! -greeting("Arthur", "Good morning"); #=> Good morning, Arthur! - -## You can also, by using a syntax akin to the one of hashes -## (yay unified syntax !), pass *named* arguments to a `sub`. They're -## optional, and will default to "Any". -sub with-named( $normal-arg, :$named ) { - say $normal-arg + $named; -} -with-named(1, named => 6); #=> 7 - -## There's one gotcha to be aware of, here: If you quote your key, Perl 6 -## won't be able to see it at compile time, and you'll have a single `Pair` -## object as a positional parameter, which means -## `with-named(1, 'named' => 6);` fails. - -with-named(2, :named(5)); #=> 7 - -## To make a named argument mandatory, you can append `!` to the parameter, -## which is the inverse of `?`: -sub with-mandatory-named( :$str! ) { - say "$str!"; -} -with-mandatory-named(str => "My String"); #=> My String! -with-mandatory-named; # runtime error:"Required named parameter not passed" -with-mandatory-named(3);# runtime error:"Too many positional parameters passed" - -## If a sub takes a named boolean argument... -sub takes-a-bool( $name, :$bool ) { - say "$name takes $bool"; -} -## ... you can use the same "short boolean" hash syntax: -takes-a-bool('config', :bool); #=> config takes True -takes-a-bool('config', :!bool); #=> config takes False - -## You can also provide your named arguments with default values: -sub named-def( :$def = 5 ) { - say $def; -} -named-def; #=> 5 -named-def(def => 15); #=> 15 - -## Since you can omit parenthesis to call a function with no arguments, -## you need `&` in the name to store `say-hello` in a variable. This means -## `&say-hello` is a code object and not a subroutine call. -my &s = &say-hello; -my &other-s = sub { say "Anonymous function!" } - -## A sub can have a "slurpy" parameter, or "doesn't-matter-how-many". For -## this, you must use `*@` (slurpy) which will "take everything else". You can -## have as many parameters *before* a slurpy one, but not *after*. -sub as-many($head, *@rest) { - say @rest.join(' / ') ~ " !"; -} -say as-many('Happy', 'Happy', 'Birthday');#=> Happy / Birthday ! - # Note that the splat (the *) did not - # consume the parameter before it. - -## You can call a function with an array using the "argument list flattening" -## operator `|` (it's not actually the only role of this operator, -## but it's one of them). -sub concat3($a, $b, $c) { - say "$a, $b, $c"; -} -concat3(|@array); #=> a, b, c - # `@array` got "flattened" as a part of the argument list -``` - -## Containers - -```perl6 -## In Perl 6, values are actually stored in "containers". The assignment -## operator asks the container on the left to store the value on its right. -## When passed around, containers are marked as immutable which means that, -## in a function, you'll get an error if you try to mutate one of your -## arguments. If you really need to, you can ask for a mutable container by -## using the `is rw` trait: -sub mutate( $n is rw ) { - $n++; # postfix ++ operator increments its argument but returns its old value -} - -my $m = 42; -mutate $m; # the value is incremented but the old value is returned - #=> 42 -say $m; #=> 43 - -## This works because we are passing the container $m to the `mutate` sub. -## If we try to just pass a number instead of passing a variable it won't work -## because there is no container being passed and integers are immutable by -## themselves: - -mutate 42; # Parameter '$n' expected a writable container, but got Int value - -## Similar error would be obtained, if a bound variable is passed to -## to the subroutine: - -my $v := 50; # binding 50 to the variable $v -mutate $v; # Parameter '$n' expected a writable container, but got Int value - -## If what you want is a copy instead, use the `is copy` trait which will -## cause the argument to be copied and allow you to modify the argument -## inside the routine. - -## A sub itself returns a container, which means it can be marked as rw: -my $x = 42; -sub x-store() is rw { $x } -x-store() = 52; # in this case, the parentheses are mandatory - # (else Perl 6 thinks `x-store` is an identifier) -say $x; #=> 52 -``` - -## Control Flow Structures - -### Conditionals - -```perl6 -## - `if` -## Before talking about `if`, we need to know which values are "Truthy" -## (represent True), and which are "Falsey" (represent False). Only these -## values are Falsey: 0, (), {}, "", Nil, A type (like `Str` or `Int`) and -## of course False itself. Any other value is Truthy. -if True { - say "It's true!"; -} - -unless False { - say "It's not false!"; -} - -## As you can see, you don't need parentheses around conditions. However, you -## do need the curly braces around the "body" block. For example, -## `if (true) say;` doesn't work. - -## You can also use their statement modifier (postfix) versions: -say "Quite truthy" if True; #=> Quite truthy -say "Quite falsey" unless False; #=> Quite falsey - -## - Ternary operator, "x ?? y !! z" -## This returns $value-if-true if the condition is true and $value-if-false -## if it is false. -## my $result = condition ?? $value-if-true !! $value-if-false; - -my $age = 30; -say $age > 18 ?? "You are an adult" !! "You are under 18"; -#=> You are an adult -``` - -### given/when, or Perl 6's switch construct - -```perl6 -## `given...when` looks like other languages' `switch`, but is much more -## powerful thanks to smart matching and Perl 6's "topic variable", $_. -## -## The topic variable $_ contains the default argument of a block, a loop's -## current iteration (unless explicitly named), etc. -## -## `given` simply puts its argument into `$_` (like a block would do), -## and `when` compares it using the "smart matching" (`~~`) operator. -## -## Since other Perl 6 constructs use this variable (as said before, like `for`, -## blocks, etc), this means the powerful `when` is not only applicable along -## with a `given`, but instead anywhere a `$_` exists. - -given "foo bar" { - say $_; #=> foo bar - when /foo/ { # Don't worry about smart matching yet. Just know - say "Yay !"; # `when` uses it. This is equivalent to `if $_ ~~ /foo/`. - - } - when $_.chars > 50 { # smart matching anything with True is True, - # i.e. (`$a ~~ True`) - # so you can also put "normal" conditionals. - # This `when` is equivalent to this `if`: - # `if $_ ~~ ($_.chars > 50) {...}` - # which means: `if $_.chars > 50 {...}` - say "Quite a long string !"; - } - default { # same as `when *` (using the Whatever Star) - say "Something else" - } -} -``` - -### Looping constructs - -```perl6 -## - `loop` is an infinite loop if you don't pass it arguments, but can also -## be a C-style `for` loop: -loop { - say "This is an infinite loop !"; - last; # last breaks out of the loop, like - # the `break` keyword in other languages -} - -loop (my $i = 0; $i < 5; $i++) { - next if $i == 3; # `next` skips to the next iteration, like `continue` - # in other languages. Note that you can also use postfix - # conditionals, loops, etc. - say "This is a C-style for loop!"; -} - -## - `for` - Iterating through an array - -my @array = 1, 2, 6, 7, 3; - -## Accessing the array's elements with the topic variable $_. -for @array { - say "I've got $_ !"; -} - -## Accessing the array's elements with a "pointy block", `->`. -## Here each element is read-only. -for @array -> $variable { - say "I've got $variable !"; -} - -## Accessing the array's elements with a "doubly pointy block", `<->`. -## Here each element is read-write so mutating `$variable` mutates -## that element in the array. -for @array <-> $variable { - say "I've got $variable !"; -} - -## As we saw with given, a for loop's default "current iteration" variable -## is `$_`. That means you can use `when` in a `for`loop just like you were -## able to in a `given`. -for @array { - say "I've got $_"; - - .say; # This is also allowed. A dot call with no "topic" (receiver) - # is sent to `$_` by default - $_.say; # This is equivalent to the above statement. -} - -for @array { - # You can... - next if $_ == 3; # Skip to the next iteration (`continue` in C-like lang.) - redo if $_ == 4; # Re-do iteration, keeping the same topic variable (`$_`) - last if $_ == 5; # Or break out of loop (like `break` in C-like lang.) -} - -## The "pointy block" syntax isn't specific to the `for` loop. It's just a way -## to express a block in Perl 6. -sub long-computation { "Finding factors of large primes" } -if long-computation() -> $result { - say "The result is $result."; -} -``` - -## Operators - -```perl6 -## Since Perl languages are very much operator-based languages, Perl 6 -## operators are actually just funny-looking subroutines, in syntactic -## categories, like infix:<+> (addition) or prefix:<!> (bool not). - -## The categories are: -## - "prefix": before (like `!` in `!True`). -## - "postfix": after (like `++` in `$a++`). -## - "infix": in between (like `*` in `4 * 3`). -## - "circumfix": around (like `[`-`]` in `[1, 2]`). -## - "post-circumfix": around, after another term (like `{`-`}` in -## `%hash{'key'}`) - -## The associativity and precedence list are explained below. - -## Alright, you're set to go! - -## Equality Checking -##------------------ - -## - `==` is numeric comparison -3 == 4; #=> False -3 != 4; #=> True - -## - `eq` is string comparison -'a' eq 'b'; #=> False -'a' ne 'b'; #=> True, not equal -'a' !eq 'b'; #=> True, same as above - -## - `eqv` is canonical equivalence (or "deep equality") -(1, 2) eqv (1, 3); #=> False -(1, 2) eqv (1, 2); #=> True -Int === Int #=> True - -## - `~~` is the smart match operator -## Aliases the left hand side to $_ and then evaluates the right hand side. -## Here are some common comparison semantics: - -## String or numeric equality -'Foo' ~~ 'Foo'; # True if strings are equal. -12.5 ~~ 12.50; # True if numbers are equal. - -## Regex - For matching a regular expression against the left side. -## Returns a `Match` object, which evaluates as True if regexp matches. - -my $obj = 'abc' ~~ /a/; -say $obj; #=> ｢a｣ -say $obj.WHAT; #=> (Match) - -## Hashes -'key' ~~ %hash; # True if key exists in hash. - -## Type - Checks if left side "is of type" (can check superclasses and -## roles). -say 1 ~~ Int; #=> True - -## Smart-matching against a boolean always returns that boolean -## (and will warn). -say 1 ~~ True; #=> True -say False ~~ True; #=> True - -## General syntax is `$arg ~~ &bool-returning-function;`. For a complete list -## of combinations, use this table: -## http://perlcabal.org/syn/S03.html#Smart_matching - -## Of course, you also use `<`, `<=`, `>`, `>=` for numeric comparison. -## Their string equivalent are also available: `lt`, `le`, `gt`, `ge`. -3 > 4; # False -3 >= 4; # False -3 < 4; # True -3 <= 4; # True -'a' gt 'b'; # False -'a' ge 'b'; # False -'a' lt 'b'; # True -'a' le 'b'; # True - - -## Range constructor -##------------------ -3 .. 7; # 3 to 7, both included. -3 ..^ 7; # 3 to 7, exclude right endpoint. -3 ^.. 7; # 3 to 7, exclude left endpoint. -3 ^..^ 7; # 3 to 7, exclude both endpoints. - # 3 ^.. 7 almost like 4 .. 7 when we only consider integers. - # But when we consider decimals : -3.5 ~~ 4 .. 7; # False -3.5 ~~ 3 ^.. 7; # True, This Range also contains decimals greater than 3. - # We describe it like this in some math books: 3.5 ∈ (3,7] - # If you don’t want to understand the concept of interval - # for the time being. At least we should know： -3 ^.. 7 ~~ 4 .. 7; # False - - -## This also works as a shortcut for `0..^N`: -^10; # means 0..^10 - -## This also allows us to demonstrate that Perl 6 has lazy/infinite arrays, -## using the Whatever Star: -my @array = 1..*; # 1 to Infinite! Equivalent to `1..Inf`. -say @array[^10]; # You can pass ranges as subscripts and it'll return - # an array of results. This will print - # "1 2 3 4 5 6 7 8 9 10" (and not run out of memory!) - -## Note: when reading an infinite list, Perl 6 will "reify" the elements -## it needs, then keep them in memory. They won't be calculated more than once. -## It also will never calculate more elements that are needed. - -## An array subscript can also be a closure. It'll be called with the length -## as the argument: -say join(' ', @array[15..*]); #=> 15 16 17 18 19 -## which is equivalent to: -say join(' ', @array[-> $n { 15..$n }]); - -## Note: if you try to do either of those with an infinite array, -## you'll trigger an infinite loop (your program won't finish). - -## You can use that in most places you'd expect, even when assigning to -## an array: -my @numbers = ^20; - -## Here the numbers increase by 6, like an arithmetic sequence; more on the -## sequence (`...`) operator later. -my @seq = 3, 9 ... * > 95; # 3 9 15 21 27 [...] 81 87 93 99; -@numbers[5..*] = 3, 9 ... *; # even though the sequence is infinite, - # only the 15 needed values will be calculated. -say @numbers; #=> 0 1 2 3 4 3 9 15 21 [...] 81 87 - # (only 20 values) - -## and (&&), or (||) -##------------------ -3 && 4; # 4, which is Truthy. Calls `.Bool` on both 3 and 4 and gets `True` - # so it returns 4 since both are `True`. -3 && 0; # 0 -0 && 4; # 0 - -0 || False; # False. Calls `.Bool` on `0` and `False` which are both `False` - # so it retusns `False` since both are `False`. - -## Short-circuit (and tight) versions of the above -## Return the first argument that evaluates to False, or the last argument. - -my ( $a, $b, $c ) = 1, 0, 2; -$a && $b && $c; # Returns 0, the first False value - -## || Returns the first argument that evaluates to True -$b || $a; # 1 - -## And because you're going to want them, you also have compound assignment -## operators: -$a *= 2; # multiply and assignment. Equivalent to $a = $a * 2; -$b %%= 5; # divisible by and assignment. Equivalent to $b = $b %% 2; -$c div= 3; # return divisor and assignment. Equivalent to $c = $c div 3; -$d mod= 4; # return remainder and assignment. Equivalent to $d = $d mod 4; -@array .= sort; # calls the `sort` method and assigns the result back -``` - -## More on subs! - -```perl6 -## As we said before, Perl 6 has *really* powerful subs. We're going -## to see a few more key concepts that make them better than in any -## other language :-). -``` - -### Unpacking! - -```perl6 -## Unpacking is the ability to "extract" arrays and keys -## (AKA "destructuring"). It'll work in `my`s and in parameter lists. -my ($f, $g) = 1, 2; -say $f; #=> 1 -my ($, $, $h) = 1, 2, 3; # keep the non-interesting values anonymous (`$`) -say $h; #=> 3 - -my ($head, *@tail) = 1, 2, 3; # Yes, it's the same as with "slurpy subs" -my (*@small) = 1; - -sub unpack_array( @array [$fst, $snd] ) { - say "My first is $fst, my second is $snd! All in all, I'm @array[]."; - # (^ remember the `[]` to interpolate the array) -} -unpack_array(@tail); #=> My first is 2, my second is 3! All in all, I'm 2 3. - - -## If you're not using the array itself, you can also keep it anonymous, -## much like a scalar: -sub first-of-array( @ [$fst] ) { $fst } -first-of-array(@small); #=> 1 -first-of-array(@tail); # Error: "Too many positional parameters passed" - # (which means the array is too big). - -## You can also use a slurp... -sub slurp-in-array(@ [$fst, *@rest]) { # You could keep `*@rest` anonymous - say $fst + @rest.elems; # `.elems` returns a list's length. - # Here, `@rest` is `(3,)`, since `$fst` - # holds the `2`. -} -slurp-in-array(@tail); #=> 3 - -## You could even extract on a slurpy (but it's pretty useless ;-).) -sub fst(*@ [$fst]) { # or simply: `sub fst($fst) { ... }` - say $fst; -} -fst(1); #=> 1 -fst(1, 2); # errors with "Too many positional parameters passed" - -## You can also destructure hashes (and classes, which you'll learn about -## later). The syntax is basically the same as -## `%hash-name (:key($variable-to-store-value-in))`. -## The hash can stay anonymous if you only need the values you extracted. -sub key-of( % (:value($val), :qua($qua)) ) { - say "Got val $val, $qua times."; -} - -## Then call it with a hash. You need to keep the curly braces for it to be a -## hash or use `%()` instead to indicate a hash is being passed. -key-of({value => 'foo', qua => 1}); #=> Got val foo, 1 times. -key-of(%(value => 'foo', qua => 1)); #=> Got val foo, 1 times. -#key-of(%hash); # the same (for an equivalent `%hash`) - -## The last expression of a sub is returned automatically (though you may -## indicate explicitly by using 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 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 range-to prefix operator `^` (`0..^N`) - $_ # current loop iteration known as the "topic" variable - } -} -my @list3 = list-of(3); #=> (0, 1, 2) -``` - -### lambdas (or anonymous subroutines) - -```perl6 -## You can create a lambda with `-> {}` ("pointy block") , -## `{}` ("block") or `sub {}`. - -my &lambda1 = -> $argument { - "The argument passed to this lambda is $argument" -} - -my &lambda2 = { - "The argument passed to this lambda is $_" -} - -my &lambda3 = sub ($argument) { - "The argument passed to this lambda is $argument" -} - -## `-> {}` and `{}` are pretty much the same thing, except that the former can -## take arguments, and that the latter can be mistaken as a hash by the parser. - -## We can, for example, add 3 to each value of an array using the -## `map` function with a lambda: -my @arrayplus3 = map({ $_ + 3 }, @array); # $_ is the implicit argument - -## A sub (`sub {}`) has different semantics than a block (`{}` or `-> {}`): -## A block doesn't have a "function context" (though it can have arguments), -## which means that if you return from it, you're going to return from the -## parent function. Compare: -sub is-in( @array, $elem ) { - # this will `return` out of the `is-in` sub once the condition evaluated - ## to True, the loop won't be run anymore. - map({ return True if $_ == $elem }, @array); -} -## with: -sub truthy-array( @array ) { - # this will produce an array of `True` and `False`: - # (you can also say `anon sub` for "anonymous subroutine") - map(sub ($i) { if $i { return True } else { return False } }, @array); - # ^ the `return` only returns from the anonymous `sub` -} - -## The `anon` declarator can be used to create an anonymous sub from a -## regular subroutine. The regular sub knows its name but its symbol is -## prevented from getting installed in the lexical scope, the method table -## and everywhere else. - -my $anon-sum = anon sub summation(*@a) { [+] *@a } -say $anon-sum.name; #=> summation -say $anon-sum(2, 3, 5); #=> 10 -#say summation; #=> Error: Undeclared routine: ... - -## You can also use the "whatever star" to create an anonymous subroutine. -## (it'll stop at the furthest operator in the current expression) -my @arrayplus3 = map(*+3, @array); # `*+3` is the same as `{ $_ + 3 }` -my @arrayplus3 = map(*+*+3, @array); # Same as `-> $a, $b { $a + $b + 3 }` - # also `sub ($a, $b) { $a + $b + 3 }` -say (*/2)(4); #=> 2 - # Immediately execute the function Whatever created. -say ((*+3)/5)(5); #=> 1.6 - # It works even in parens! - -## But if you need to have more than one argument (`$_`) in a block (without -## wanting to resort to `-> {}`), you can also use the implicit argument -## syntax, `$^`: -map({ $^a + $^b + 3 }, @array); -# which is equivalent to the following which uses a `sub`: -map(sub ($a, $b) { $a + $b + 3 }, @array); - -## The parameters `$^a`, `$^b`, etc. are known as placeholder parameters or -## self-declared positional parameters. They're sorted lexicographically so -## `{ $^b / $^a }` is equivalent `-> $a, $b { $b / $a }`. -``` - -### About types... - -```perl6 -## Perl 6 is gradually typed. This means you can specify the type of your -## variables/arguments/return types, or you can omit the type annotations in -## in which case they'll default to `Any`. Obviously you get access to a few -## base types, like `Int` and `Str`. The constructs for declaring types are -## "subset", "class", "role", etc. which you'll see later. - -## For now, let us examine "subset" which is a "sub-type" with additional -## checks. For example, "a very big integer is an Int that's greater than 500". -## You can specify the type you're subtyping (by default, `Any`), and add -## additional checks with the `where` clause: -subset VeryBigInteger of Int where * > 500; -## Or the set of the whole numbers: -subset WholeNumber of Int where * >= 0; -``` - -### Multiple Dispatch - -```perl6 -## 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 `where`: - -## with types: -multi sub sayit( Int $n ) { # note the `multi` keyword here - say "Number: $n"; -} -multi sayit( Str $s ) { # a multi is a `sub` by default - say "String: $s"; -} -sayit("foo"); #=> "String: foo" -sayit(25); #=> "Number: 25" -sayit(True); # fails at *compile time* with "calling 'sayit' will never - # work with arguments of types ..." - -## with arbitrary preconditions (remember subsets?): -multi is-big(Int $n where * > 50) { "Yes!" } # using a closure -multi is-big(Int $n where {$_ > 50}) { "Yes!" } # similar to above -multi is-big(Int $ where 10..50) { "Quite." } # Using smart-matching - # (could use a regexp, etc) -multi is-big(Int $) { "No" } - -subset Even of Int where * %% 2; -multi odd-or-even(Even) { "Even" } # The main case using the type. - # We don't name the argument. -multi odd-or-even($) { "Odd" } # "everthing else" hence the $ variable - -## You can even dispatch based on the presence of positional and -## named arguments: -multi with-or-without-you($with) { - say "I wish I could but I can't"; -} -multi with-or-without-you(:$with) { - say "I can live! Actually, I can't."; -} -multi with-or-without-you { - say "Definitely can't live."; -} - -## This is very, very useful for many purposes, like `MAIN` subs (covered -## later), and even the language itself uses it in several places. -## -## - `is`, for example, is actually a `multi sub` named `trait_mod:<is>`, -## and it works off that. -## - `is rw`, is simply a dispatch to a function with this signature: -## sub trait_mod:<is>(Routine $r, :$rw!) {} -## -## (commented out because running this would be a terrible idea!) -``` - -## Scoping - -```perl6 -## In Perl 6, unlike many scripting languages, (such as Python, Ruby, PHP), -## you must declare your variables before using them. The `my` declarator -## you have learned uses "lexical scoping". There are a few 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 $file_scoped = 'Foo'; -sub outer { - my $outer_scoped = 'Bar'; - sub inner { - say "$file_scoped $outer_scoped"; - } - &inner; # return the function -} -outer()(); #=> 'Foo Bar' - -## As you can see, `$file_scoped` and `$outer_scoped` were captured. -## But if we were to try and use `$outer_scoped` outside the `outer` sub, -## the variable would be undefined (and you'd get a compile time error). -``` - -## Twigils - -```perl6 -## There are many special `twigils` (composed sigils) in Perl 6. Twigils -## define the variables' scope. -## The * and ? twigils work on standard variables: -## * Dynamic variable -## ? Compile-time variable -## The ! and the . twigils are used with Perl 6's objects: -## ! Attribute (instance attribute) -## . Method (not really a variable) - -## `*` twigil: Dynamic Scope -## These variables use the `*` twigil to mark dynamically-scoped variables. -## Dynamically-scoped variables are looked up through the caller, not through -## the outer scope. - -my $*dyn_scoped_1 = 1; -my $*dyn_scoped_2 = 10; - -sub say_dyn { - say "$*dyn_scoped_1 $*dyn_scoped_2"; -} - -sub call_say_dyn { - my $*dyn_scoped_1 = 25; # Defines $*dyn_scoped_1 only for this sub. - $*dyn_scoped_2 = 100; # Will change the value of the file scoped variable. - say_dyn(); #=> 25 100, $*dyn_scoped 1 and 2 will be looked - # for in the call. - # It uses the value of $*dyn_scoped_1 from inside - # this sub's lexical scope even though the blocks - # aren't nested (they're call-nested). -} -say_dyn(); #=> 1 10 -call_say_dyn(); #=> 25 100 - # Uses $*dyn_scoped_1 as defined in call_say_dyn even though - # we are calling it from outside. -say_dyn(); #=> 1 100 We changed the value of $*dyn_scoped_2 in - # call_say_dyn so now its value has changed. -``` - -## Object Model - -```perl6 -## To call a method on an object, add a dot followed by the method name: -## `$object.method` - -## Classes are declared with the `class` keyword. Attributes are declared -## with the `has` keyword, and methods declared with the `method` keyword. - -## Every attribute that is private uses the ! twigil. For example: `$!attr`. -## Immutable public attributes use the `.` twigil which creates a read-only -## method named after the attribute. In fact, declaring an attribute with `.` -## is equivalent to declaring the same attribute with `!` and then creating -## a read-only method with the attribute's name. However, this is done for us -## by Perl 6 automatically. The easiest way to remember the `$.` twigil is -## by comparing it to how methods are called. - -## Perl 6's object model ("SixModel") is very flexible, and allows you to -## dynamically add methods, change semantics, etc... Unfortunately, these will -## not all be covered here, and you should refer to: -## https://docs.perl6.org/language/objects.html. - -class Human { - has Str $.name; # `$.name` is immutable but with an accessor method. - has Str $.bcountry; # Use `$!bcountry` to modify it inside the class. - has Str $.ccountry is rw; # This attribute can be modified from outside. - has Int $!age = 0; # A private attribute with default value. - - method birthday { - $!age += 1; # Add a year to human's age - } - - method get-age { - return $!age; - } - - # This method is private to the class. Note the `!` before the - # method's name. - method !do-decoration { - return "$!name was born in $!bcountry and now lives in $!ccountry." - } - - # This method is public, just like `birthday` and `get-age`. - method get-info { - self.do-decoration; # Invoking a method on `self` inside the class. - # Use `self!priv-method` for private method. - # Use `self.publ-method` for public method. - } -}; - -## Create a new instance of Human class. -## Note: you can't set private-attribute from here (more later on). -my $person1 = Human.new( - name => "Jord", - bcountry = "Togo", - ccountry => "Togo" -); - -say $person1.name; #=> Jord -say $person1.bcountry; #=> Togo -say $person1.ccountry; #=> Togo - - -# $person1.bcountry = "Mali"; # This fails, because the `has $.bcountry` - # is immutable. Jord can't change his birthplace. -$person1.ccountry = "France"; # This works because the `$.ccountry` is mutable - # (`is rw`). Now Jord's current country is France. - -# Calling methods on the instance objects. -$person1.birthday; #=> 1 -$person1.get-info; #=> Jord was born in Togo and now lives in France. -$person1.do-decoration; # This fails since the method `do-decoration` is - # private. -``` - -### Object Inheritance - -```perl6 -## Perl 6 also has inheritance (along with multiple inheritance). While -## methods are inherited, submethods are not. Submethods are useful for -## object construction and destruction tasks, such as BUILD, or methods that -## must be overridden by subtypes. We will learn about BUILD later on. - -class Parent { - has $.age; - has $.name; - - # This submethod won't be inherited by the Child class. - submethod favorite-color { - say "My favorite color is Blue"; - } - - # This method is inherited - method talk { say "Hi, my name is $!name" } -} - -# Inheritance uses the `is` keyword -class Child is Parent { - method talk { say "Goo goo ga ga" } - # This shadows Parent's `talk` method. - # This child hasn't learned to speak yet! -} - -my Parent $Richard .= new(age => 40, name => 'Richard'); -$Richard.favorite-color; #=> "My favorite color is Blue" -$Richard.talk; #=> "Hi, my name is Richard" -## $Richard is able to access the submethod and he knows how to say his name. - -my Child $Madison .= new(age => 1, name => 'Madison'); -$Madison.talk; #=> "Goo goo ga ga", due to the overridden method. -# $Madison.favorite-color # does not work since it is not inherited. - -## When you use `my T $var`, `$var` starts off with `T` itself in it, -## so you can call `new` on it. -## (`.=` is just the dot-call and the assignment operator: -## `$a .= b` is the same as `$a = $a.b`) -## Also note that `BUILD` (the method called inside `new`) -## will set parent's properties too, so you can pass `val => 5`. -``` - -### Roles, or Mixins - -```perl6 -## Roles are supported too (which are called Mixins in other languages) -role PrintableVal { - has $!counter = 0; - method print { - say $.val; - } -} - -## you "apply" a role (or mixin) with `does` keyword: -class Item does PrintableVal { - has $.val; - - ## When `does`-ed, a `role` literally "mixes in" the class: - ## the methods and attributes are put together, which means a class - ## can access the private attributes/methods of its roles (but - ## not the inverse!): - method access { - say $!counter++; - } - - ## However, this: - ## method print {} - ## is ONLY valid when `print` isn't a `multi` with the same dispatch. - ## (this means a parent class can shadow a child class's `multi print() {}`, - ## but it's an error if a role does) - - ## NOTE: You can use a role as a class (with `is ROLE`). In this case, - ## methods will be shadowed, since the compiler will consider `ROLE` - ## to be a class. -} -``` - -## Exceptions - -```perl6 -## Exceptions are built on top of classes, in the package `X` (like `X::IO`). -## In Perl6 exceptions are automatically 'thrown': -open 'foo'; #=> Failed to open file foo: no such file or directory -## It will also print out what line the error was thrown at -## and other error info. - -## You can throw an exception using `die`: -die 'Error!'; #=> Error! - -## Or more explicitly: -X::AdHoc.new(payload => 'Error!').throw; #=> Error! - -## In Perl 6, `orelse` is similar to the `or` operator, except it only matches -## undefined variables instead of anything evaluating as `False`. -## Undefined values include: `Nil`, `Mu` and `Failure` as well as `Int`, `Str` -## and other types that have not been initialized to any value yet. -## You can check if something is defined or not using the defined method: -my $uninitialized; -say $uninitiazilzed.defined; #=> False - -## When using `orelse` it will disarm the exception and alias $_ to that -## failure. This will prevent it to being automatically handled and printing -## lots of scary error messages to the screen. We can use the `exception` -## method on the `$_` variable to access the exception -open 'foo' orelse say "Something happened {.exception}"; - -## This also works: -open 'foo' orelse say "Something happened $_"; #=> Something happened - #=> Failed to open file foo: no such file or directory -## Both of those above work but in case we get an object from the left side -## that is not a failure we will probably get a warning. We see below how we -## can use try` and `CATCH` to be more specific with the exceptions we catch. -``` - -### Using `try` and `CATCH` - -```perl6 -## By using `try` and `CATCH` you can contain and handle exceptions without -## disrupting the rest of the program. The `try` block will set the last -## exception to the special variable `$!` (known as the error variable). -## Note: This has no relation to $!variables seen inside class definitions. - -try open 'foo'; -say "Well, I tried! $!" if defined $!; -#=> Well, I tried! Failed to open file foo: no such file or directory - -## Now, what if we want more control over handling the exception? -## Unlike many other languages, in Perl 6, you put the `CATCH` block *within* -## the block to `try`. Similar to how the `$_` variable was set when we -## 'disarmed' the exception with `orelse`, we also use `$_` in the CATCH block. -## Note: The `$!` variable is only set *after* the `try` block has caught an -## exception. By default, a `try` block has a `CATCH` block of its own that -## catches any exception (`CATCH { default {} }`). - -try { - my $a = (0 %% 0); - CATCH { - say "Something happened: $_" - } -} -#=> Something happened: Attempt to divide by zero using infix:<%%> - -## You can redefine it using `when`s (and `default`) to handle the exceptions -## you want to catch explicitly: - -try { - open 'foo'; - CATCH { - # In the `CATCH` block, the exception is set to the $_ variable. - when X::AdHoc { - say "Error: $_" - } - when X::Numeric::DivideByZero { - say "Error: $_"; - } - ## Any other exceptions will be re-raised, since we don't have a `default`. - ## Basically, if a `when` matches (or there's a `default`), the - ## exception is marked as "handled" so as to prevent its re-throw - ## from the `CATCH` block. You still can re-throw the exception (see below) - ## by hand. - } -} -#=>Error: Failed to open file /dir/foo: no such file or directory - -## There are also some subtleties to exceptions. Some Perl 6 subs return a -## `Failure`, which is a wrapper around an `Exception` object which is -## "unthrown". They're not thrown until you try to use the variables containing -## them unless you call `.Bool`/`.defined` on them - then they're handled. -## (the `.handled` method is `rw`, so you can mark it as `False` back yourself) -## You can throw a `Failure` using `fail`. Note that if the pragma `use fatal` -## is on, `fail` will throw an exception (like `die`). - -fail "foo"; # We're not trying to access the value, so no problem. -try { - fail "foo"; - CATCH { - default { - say "It threw because we tried to get the fail's value!" - } - } -} - -## There is also another kind of exception: Control exceptions. -## Those are "good" exceptions, which happen when you change your program's -## flow, using operators like `return`, `next` or `last`. -## You can "catch" those with `CONTROL` (not 100% working in Rakudo yet). -``` - -## Packages - -```perl6 -## 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 denominator) -## Packages are important - especially as Perl is well-known for CPAN, -## the Comprehensive Perl Archive Network. - -## You can use a module (bring its declarations into scope) with -## the `use` keyword: -use JSON::Tiny; # if you installed Rakudo* or Panda, you'll have this module -say from-json('[1]').perl; #=> [1] - -## You should not declare packages using the `package` keyword (unlike Perl 5). -## Instead, use `class Package::Name::Here;` to declare a class, or if you only -## want to export variables/subs, you can use `module` instead. - -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 ... -} - -unit module Parse::Text; # file-scoped form which extends until - # the end of the file - -grammar Parse::Text::Grammar { - # A grammar is a package, which you could `use`. - # You will learn more about grammars in the regex section -} - -## As said before, any part of the six model is also a package. -## Since `JSON::Tiny` uses its own `JSON::Tiny::Actions` class, you can use it: -my $actions = JSON::Tiny::Actions.new; - -## We'll see how to export variables and subs in the next part. -``` - -## Declarators - -```perl6 -## In Perl 6, you get different behaviors based on how you declare a variable. -## You've already seen `my` and `has`, we'll now explore the others. - -## `our` - these declarations happen at `INIT` time -- (see "Phasers" below). -## It's like `my`, but it also creates a package variable. All packagish -## things such as `class`, `role`, etc. are `our` by default. - -module Var::Increment { - our $our-var = 1; # Note: `our`-declared variables cannot be typed. - my $my-var = 22; - - our sub Inc { - our sub available { # If you try to make inner `sub`s `our`... - # ... Better know what you're doing (Don't !). - say "Don't do that. Seriously. You'll get burned."; - } - - my sub unavailable { # `sub`s are `my`-declared by default - say "Can't access me from outside, I'm 'my'!"; - } - say ++$our-var; # Increment the package variable and output its value - } - -} - -say $Var::Increment::our-var; #=> 1, this works! -say $Var::Increment::my-var; #=> (Any), this will not work! - -Var::Increment::Inc; #=> 2 -Var::Increment::Inc; #=> 3 , notice how the value of $our-var was - # retained. -Var::Increment::unavailable; #=> Could not find symbol '&unavailable' - -## `constant` - these declarations happen at `BEGIN` time. You can use -## the `constant` keyword to declare a compile-time variable/symbol: -constant Pi = 3.14; -constant $var = 1; - -## And if you're wondering, yes, it can also contain infinite lists. -constant why-not = 5, 15 ... *; -say why-not[^5]; #=> 5 15 25 35 45 - -## `state` - these declarations happen at run time, but only once. State -## variables are only initialized one time. In other languages such as C -## they exist as `static` variables. -sub fixed-rand { - state $val = rand; - say $val; -} -fixed-rand for ^10; # will print the same number 10 times - -## Note, however, that they exist separately in different enclosing contexts. -## If you declare a function with a `state` within a loop, it'll re-create the -## variable for each iteration of the loop. See: -for ^5 -> $a { - sub foo { - state $val = rand; # This will be a different value for - # every value of `$a` - } - for ^5 -> $b { - say foo; # This will print the same value 5 times, - # but only 5. Next iteration will re-run `rand`. - } -} -``` - -## Phasers - -```perl6 -## Phasers in Perl 6 are blocks that happen at determined points of time in -## your program. They are called phasers because they mark a change in the -## phase of a program. For example, when the program is compiled, a for loop -## runs, you leave a block, or an exception gets thrown (The `CATCH` block is -## actually a phaser!). Some of them can be used for their return values, -## some of them can't (those that can have a "[*]" in the beginning of their -## explanation text). Let's have a look! - -## Compile-time phasers -BEGIN { say "[*] Runs at compile time, as soon as possible, only once" } -CHECK { say "[*] Runs at compile time, as late as possible, only once" } - -## Run-time phasers -INIT { say "[*] Runs at run time, as soon as possible, only once" } -END { say "Runs at run time, as late as possible, only once" } - -## Block phasers -ENTER { say "[*] Runs everytime you enter a block, repeats on loop blocks" } -LEAVE { - say "Runs everytime you leave a block, even when an exception - happened. Repeats on loop blocks." -} - -PRE { - say "Asserts a precondition at every block entry, - before ENTER (especially useful for loops)"; - say "If this block doesn't return a truthy value, - an exception of type X::Phaser::PrePost is thrown."; -} - -## Example: -for 0..2 { - PRE { $_ > 1 } # This is going to blow up with "Precondition failed" -} - -POST { - say "Asserts a postcondition at every block exit, - after LEAVE (especially useful for loops)"; - say "If this block doesn't return a truthy value, - an exception of type X::Phaser::PrePost is thrown, like PRE."; -} - -for 0..2 { - POST { $_ < 2 } # This is going to blow up with "Postcondition failed" -} - -## Block/exceptions phasers -sub { - KEEP { say "Runs when you exit a block successfully - (without throwing an exception)" } - UNDO { say "Runs when you exit a block unsuccessfully - (by throwing an exception)" } -} - -## Loop phasers -for ^5 { - FIRST { say "[*] The first time the loop is run, before ENTER" } - NEXT { say "At loop continuation time, before LEAVE" } - LAST { say "At loop termination time, after LEAVE" } -} - -## Role/class phasers -COMPOSE { "When a role is composed into a class. /!\ NOT YET IMPLEMENTED" } - -## They allow for cute tricks or clever code...: -say "This code took " ~ (time - CHECK time) ~ "s to compile"; - -## ... or clever organization: -sub do-db-stuff { - $db.start-transaction; # start a new transaction - KEEP $db.commit; # commit the transaction if all went well - UNDO $db.rollback; # or rollback if all hell broke loose -} -``` - -## Statement prefixes - -```perl6 -## 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 -## elsewhere) Note: all of these (except start) don't need explicit curly -## braces `{` and `}`. - -## `do` - (which you already saw) runs a block or a statement as a term. -## Normally you cannot use a statement as a value (or "term"). `do` helps us -## do it. - -# my $value = if True { 1 } # this fails since `if` is a statement -my $a = do if True { 5 } # with `do`, `if` is now a term returning a value - -## `once` - makes sure a piece of code only runs once. -for ^5 { - once say 1 -}; #=> 1, only prints ... once - -## Similar to `state`, they're cloned per-scope. -for ^5 { - sub { once say 1 }() -}; #=> 1 1 1 1 1, prints once per lexical scope. - -## `gather` - co-routine thread. The `gather` constructs allows us to `take` -## several values from an array/list, much like `do`. -say gather for ^5 { - take $_ * 3 - 1; - take $_ * 3 + 1; -} -#=> -1 1 2 4 5 7 8 10 11 13 - -say join ',', gather if False { - take 1; - take 2; - take 3; -} -# Doesn't print anything. - -## `eager` - evaluates a statement eagerly (forces eager context) -## Don't try this at home: -# eager 1..*; # this will probably hang for a while (and might crash ...). -## But consider: -constant thrice = gather for ^3 { say take $_ }; # Doesn't print anything -## versus: -constant thrice = eager gather for ^3 { say take $_ }; #=> 0 1 2 -``` - -## Iterables - -```perl6 -## Iterables are objects that can be iterated over which are -## are similar to the `for` construct. - -## `flat` - flattens iterables. -say (1, 10, (20, 10) ); #=> (1 10 (20 10)), notice how neste lists are - # preserved -say (1, 10, (20, 10) ).flat; #=> (1 10 20 10), now the iterable is flat - -## - `lazy` - defers actual evaluation until value is fetched by forcing -## lazy context. -my @lazy-array = (1..100).lazy; -say @lazy-array.is-lazy; #=> True, check for laziness with the `is-lazy` method. -say @lazy-array; #=> [...] List has not been iterated on! -my @lazy-array { .print }; # This works and will only do as much work as - # is needed. - -# ( **TODO** explain that gather/take and map are all lazy) - -## `sink` - an `eager` that discards the results by forcing sink context. -constant nilthingie = sink for ^3 { .say } #=> 0 1 2 -say nilthingie.perl; #=> Nil - -## `quietly` - suppresses warnings in blocks. -quietly { warn 'This is a warning!' }; #=> No output - -## `contend` - attempts side effects under STM -## Not yet implemented! -``` - -## More operators thingies! - -```perl6 -## Everybody loves operators! Let's get more of them. - -## The precedence list can be found here: -## https://docs.perl6.org/language/operators#Operator_Precedence -## But first, we need a little explanation about associativity: - -## Binary operators: -$a ! $b ! $c; # with a left-associative `!`, this is `($a ! $b) ! $c` -$a ! $b ! $c; # with a right-associative `!`, this is `$a ! ($b ! $c)` -$a ! $b ! $c; # with a non-associative `!`, this is illegal -$a ! $b ! $c; # with a chain-associative `!`, this is `($a ! $b) and ($b ! $c)` -$a ! $b ! $c; # with a list-associative `!`, this is `infix:<>` - -## Unary operators: -!$a! # with left-associative `!`, this is `(!$a)!` -!$a! # with right-associative `!`, this is `!($a!)` -!$a! # with non-associative `!`, this is illegal -``` - -### Create your own operators! - -```perl6 -## Okay, you've been reading all of that, so you might want to try something -## more 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: -# prefix refers to the operator categories (prefix, infix, postfix, etc). -sub prefix:<win>( $winner ) { - say "$winner Won!"; -} -win "The King"; #=> The King Won! - # (prefix means 'before') - -## you can still call the sub with its "full name": -say prefix:<!>(True); #=> False -prefix:<win>("The Queen"); #=> The Queen Won! - -sub postfix:<!>( Int $n ) { - [*] 2..$n; # using the reduce meta-operator... See below ;-)! -} -say 5!; #=> 120 - # Postfix operators ('after') have to come *directly* after the term. - # No whitespace. You can use parentheses to disambiguate, i.e. `(5!)!` - -sub infix:<times>( Int $n, Block $r ) { # infix ('between') - for ^$n { - $r(); # You need the explicit parentheses to call the function in `$r`, - # else you'd be referring at the variable itself, like with `&r`. - } -} -3 times -> { say "hello" }; #=> hello - #=> hello - #=> hello -## It's recommended to put spaces around your -## infix operator calls. - -## For circumfix and post-circumfix ones -sub circumfix:<[ ]>( Int $n ) { - $n ** $n -} -say [5]; #=> 3125 - # circumfix means 'around'. Again, no whitespace. - -sub postcircumfix:<{ }>( Str $s, Int $idx ) { - ## post-circumfix is 'after a term, around something' - $s.substr($idx, 1); -} -say "abc"{1}; #=> b - # after the term `"abc"`, and around the index (1) - -## This really means a lot -- because everything in Perl 6 uses this. -## For example, to delete a key from a hash, you use the `:delete` adverb -## (a simple named argument underneath): -%h{$key}:delete; -## equivalent to: -postcircumfix:<{ }>( %h, $key, :delete ); # (you can call operators like this) - -## It's *all* using the same building blocks! Syntactic categories -## (prefix infix ...), named arguments (adverbs), ..., etc. used to build -## the language - are available to you. Obviously, you're advised against -## making an operator out of *everything* -- with great power comes great -## responsibility. -``` - -### Meta operators! - -```perl6 -## Oh boy, get ready!. Get ready, because we're delving deep into the rabbit's -## hole, and you probably won't want to go back to other languages after -## reading this. (I'm guessing you don't want to go back at this point but -## let's continue, for the journey is long and enjoyable!). - -## Meta-operators, as their name suggests, are *composed* operators. -## Basically, they're operators that act on another operators. - -## The reduce meta-operator is a prefix meta-operator that takes a binary -## function and one or many lists. If it doesn't get passed any argument, -## it either returns a "default value" for this operator (a meaningless value) -## or `Any` if there's none (examples below). Otherwise, it pops an element -## from the list(s) one at a time, and applies the binary function to the last -## result (or the list's first element) and the popped element. - -## To sum a list, you could use the reduce meta-operator with `+`, i.e.: -say [+] 1, 2, 3; #=> 6, equivalent to (1+2)+3. - -## To multiply a list -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 first defined element -## of a list: -say [//] Nil, Any, False, 1, 5; #=> False - # (Falsey, but still defined) -## Or with relational operators, i.e., `>` to check elements of a list -## are ordered accordingly: -say say [>] 234, 156, 6, 3, -20; #=> True - -## Default value examples: -say [*] (); #=> 1 -say [+] (); #=> 0 - # meaningless values, since N*1=N and N+0=N. -say [//]; #=> (Any) - # There's no "default value" for `//`. - -## You can also call it with a function you made up, using double brackets: -sub add($a, $b) { $a + $b } -say [[&add]] 1, 2, 3; #=> 6 - -## The zip meta-operator is an infix meta-operator that also can be used as a -## "normal" operator. It takes an optional binary function (by default, it -## just creates a pair), and will pop one value off of each array and call -## its binary function on these until it runs out of elements. It returns an -## array with all of these new elements. -say (1, 2) Z (3, 4); #=> ((1, 3), (2, 4)), since by default the function - # makes an array. -say 1..3 Z+ 4..6; #=> (5, 7, 9), using the custom infix:<+> function - -## Since `Z` is list-associative (see the list above), -## you can use it on more than one list -(True, False) Z|| (False, False) Z|| (False, False); # (True, False) - -## And, as it turns out, you can also use the reduce meta-operator with it: -[Z||] (True, False), (False, False), (False, False); # (True, False) - - -## And to end the operator list: - -## The sequence operator is one of Perl 6's most powerful features: -## it's composed of first, on the left, the list you want Perl 6 to deduce from -## (and might include a closure), and on the right, a value or the predicate -## that says when to stop (or a Whatever Star for a lazy infinite list). - -my @list = 1, 2, 3...10; # basic arithmetic sequence -# my @list = 1, 3, 6...10; # this dies 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 ends when the predicate matches). -my @list = 1, 3, 9...* > 30; # you can use a predicate (with the Whatever Star). -my @list = 1, 3, 9 ... { $_ > 30 }; # (equivalent to the above - # using a block here). - -my @fib = 1, 1, *+* ... *; # lazy infinite list of fibonacci sequence, - # computed using a closure! -my @fib = 1, 1, -> $a, $b { $a + $b } ... *; # (equivalent to the above) -my @fib = 1, 1, { $^a + $^b } ... *; # (also equivalent to the above) -## $a and $b will always take the previous values, meaning here -## they'll start with $a = 1 and $b = 1 (values we set by hand), -## then $a = 1 and $b = 2 (result from previous $a+$b), and so on. - -say @fib[^10]; #=> 1 1 2 3 5 8 13 21 34 55 - # (using a range as the index) -## Note: as for ranges, once reified, elements aren't re-calculated. -## That's why `@primes[^100]` will take a long time the first time you print -## it, then will be instateneous. -``` - -## Regular Expressions - -```perl6 -## I'm sure a lot of you have been waiting for this one. Well, now that you know -## a good deal of Perl 6 already, we can get started. First off, you'll have to -## forget about "PCRE regexps" (perl-compatible regexps). -## -## IMPORTANT: Don't skip them because you know PCRE. They're different. Some -## things are the same (like `?`, `+`, and `*`), but sometimes the semantics -## change (`|`). Make sure you read carefully, because you might trip over a -## new behavior. -## -## Perl 6 has many features related to RegExps. After all, Rakudo parses itself. -## We're first going to look at the syntax itself, then talk about grammars -## (PEG-like), differences between `token`, `regex` and `rule` declarators, -## and some more. Side note: you still have access to PCRE regexps using the -## `:P5` modifier which we won't be discussing this in this tutorial, though. -## -## In essence, Perl 6 natively implements PEG ("Parsing Expression Grammars"). -## The pecking order for ambiguous parses is determined by a multi-level -## tie-breaking test: -## - Longest token matching: `foo\s+` beats `foo` (by 2 or more positions) -## - Longest literal prefix: `food\w*` beats `foo\w*` (by 1) -## - Declaration from most-derived to less derived grammars -## (grammars are actually classes) -## - Earliest declaration wins -say so 'a' ~~ /a/; #=> True -say so 'a' ~~ / a /; #=> True, 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` to a Boolean value because, -## in fact, it's returning a `Match` object. They know how to respond to list -## indexing, hash indexing, and return the matched string. The results of the -## match are available in the `$/` variable (implicitly lexically-scoped). You -## can also use the capture variables which start at 0: `$0`, `$1', `$2`... -## -## You can also note that `~~` does not perform start/end checking, meaning -## the regexp can be matched with just one character of the string. We'll -## explain later how you can do it. - -## In Perl 6, you can have any alphanumeric as a literal, everything else has -## to be escaped by using a backslash or quotes. -say so 'a|b' ~~ / a '|' b /; #=> `True`, it wouldn't mean the same thing if - # `|` wasn't escaped. -say so 'a|b' ~~ / a \| b /; #=> `True`, another way to escape it. - -## The whitespace in a regexp is actually not significant, unless you use the -## `:s` (`:sigspace`, significant space) adverb. -say so 'a b c' ~~ / a b c /; #=> `False`, space is not significant here! -say so 'a b c' ~~ /:s a b c /; #=> `True`, we added the modifier `:s` here. - -## If we use only one space between strings in a regex, Perl 6 will warn us: -say so 'a b c' ~~ / a b c /; #=> `False`, with warning about space -say so 'a b c' ~~ / a b c /; #=> `False` - -## Please use quotes or :s (:sigspace) modifier (or, to suppress this warning, -## omit the space, or otherwise change the spacing). To fix this and make the -## spaces less ambiguous, either use at least two spaces between strings -## or use the `:s` adverb. - -## As we saw before, we can embed the `:s` inside the slash delimiters, but we -## can also put it outside of them if we specify `m` for 'match': -say so 'a b c' ~~ m:s/a b c/; #=> `True` - -## By using `m` to specify 'match', we can also use delimiters other than -## slashes: -say so 'abc' ~~ m{a b c}; #=> `True` -say so 'abc' ~~ m[a b c]; #=> `True` -# m/.../ is equivalent to /.../ - -## Use the :i adverb to specify case insensitivity: -say so 'ABC' ~~ m:i{a b c}; #=> `True` - -## However, whitespace is important as for how modifiers are applied ( -## (which you'll see just below) ... - -## Quantifying - `?`, `+`, `*` and `**`. -## `?` - zero or one match -so 'ac' ~~ / a b c /; #=> `False` -so 'ac' ~~ / a b? c /; #=> `True`, the "b" matched 0 times. -so 'abc' ~~ / a b? c /; #=> `True`, the "b" matched 1 time. - -## ...As you read before, whitespace is important because it determines which -## part of the regexp is the target of the modifier: -so 'def' ~~ / a b c? /; #=> `False`, only the `c` is optional -so 'def' ~~ / a b? c /; #=> `False`, whitespace is not significant -so 'def' ~~ / 'abc'? /; #=> `True`, the whole "abc" group is optional - -## Here (and below) the quantifier applies only to the `b` - -## `+` - one or more matches -so 'ac' ~~ / a b+ c /; #=> `False`, `+` wants at least one matching -so 'abc' ~~ / a b+ c /; #=> `True`, one is enough -so 'abbbbc' ~~ / a b+ c /; #=> `True`, matched 4 "b"s - -## `*` - zero or more matches -so 'ac' ~~ / a b* c /; #=> `True`, they're all optional. -so 'abc' ~~ / a b* c /; #=> `True` -so 'abbbbc' ~~ / a b* c /; #=> `True` -so 'aec' ~~ / a b* c /; #=> `False`. "b"(s) are optional, not replaceable. - -## `**` - (Unbound) Quantifier -## If you squint hard enough, you might understand why exponentation is used -## for quantity. -so 'abc' ~~ / a b**1 c /; #=> `True`, (exactly one time) -so 'abc' ~~ / a b**1..3 c /; #=> `True`, (one to three times) -so 'abbbc' ~~ / a b**1..3 c /; #=> `True` -so 'abbbbbbc' ~~ / a b**1..3 c /; #=> `False, (too much) -so 'abbbbbbc' ~~ / a b**3..* c /; #=> `True`, (infinite ranges are okay) - -## `<[]>` - Character classes -## Character classes are the equivalent of PCRE's `[]` classes, but they use a -## more perl6-ish syntax: -say 'fooa' ~~ / f <[ o a ]>+ /; #=> 'fooa' - -## You can use ranges: -say 'aeiou' ~~ / a <[ e..w ]> /; #=> 'ae' - -## Just like in normal regexes, if you want to use a special character, escape -## it (the last one is escaping a space which would be equivalent to using -## ' '): -say 'he-he !' ~~ / 'he-' <[ a..z \! \ ]> + /; #=> 'he-he !' - -## You'll get a warning if you put duplicate names (which has the nice effect -## of catching the raw quoting): -'he he' ~~ / <[ h e ' ' ]> /; -# Warns "Repeated character (') unexpectedly found in character class" - -## You can also negate character classes... (`<-[]>` equivalent to `[^]` in PCRE) -so 'foo' ~~ / <-[ f o ]> + /; #=> False - -## ... and compose them: -so 'foo' ~~ / <[ a..z ] - [ f o ]> + /; #=> `False`, (any letter except f and o) -so 'foo' ~~ / <-[ a..z ] + [ f o ]> + /; #=> `True`, (no letter except f and o) -so 'foo!' ~~ / <-[ a..z ] + [ f o ]> + /; #=> `True`, (the + doesn't replace the - # left part) -``` - -### Grouping and capturing - -```perl6 -## Group: you can group parts of your regexp with `[]`. Unlike PCRE's `(?:)`, -## these groups are *not* captured. -so 'abc' ~~ / a [ b ] c /; # `True`. The grouping does pretty much nothing -so 'foo012012bar' ~~ / foo [ '01' <[0..9]> ] + bar /; - -## The previous line returns `True`. The regex matches "012" 1 or more time -## (achieved by the the `+` applied to the group). - -## But this does not go far enough, because we can't actually get back what -## we matched. - -## Capture: The results of a regexp can be *captured* by using parentheses. -so 'fooABCABCbar' ~~ / foo ( 'A' <[A..Z]> 'C' ) + bar /; # `True`. (using `so` - # here, `$/` below) - -## So, starting with the grouping explanations. -## As we said before, our `Match` object is stored inside the `$/` variable: -say $/; # Will either print some weird stuff or `Nil` if nothing matched. - -## As we also said before, it has array indexing: -say $/[0]; #=> ｢ABC｣ ｢ABC｣ - # These corner 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 captures (indexed using `$0`, `$/[0]` or a named one) will be an array -## if and only if they can have more than one element. Thus any capture with -## `*`, `+` and `**` (whatever the operands), but not with `?`. -## Let's use examples to see that: - -## Note: We quoted A B C to demonstrate that the whitespace between them isn't -## significant. If we want the whitespace to *be* significant there, we -## can use the :sigspace modifier. -say so 'fooABCbar' ~~ / foo ( "A" "B" "C" )? bar /; #=> `True` -say $/[0]; #=> ｢ABC｣ -say $0.WHAT; #=> (Match) - # There can't be more than one, so it's only a single match object. -say so 'foobar' ~~ / foo ( "A" "B" "C" )? bar /; #=> True -say $0.WHAT; #=> (Any) - # This capture did not match, so it's empty -so 'foobar' ~~ / foo ( "A" "B" "C" ) ** 0..1 bar /; #=> `True` -say $0.WHAT; #=> (Array) - # A specific quantifier will always capture an Array, - # be a range or a specific value (even 1). - -## The captures are indexed per nesting. This means a group in a group will be -## nested under its parent group: `$/[0][0]`, for this code: -'hello-~-world' ~~ / ( 'hello' ( <[ \- \~ ]> + ) ) 'world' /; -say $/[0].Str; #=> hello~ -say $/[0][0].Str; #=> ~ - -## This stems from a very simple fact: `$/` does not contain strings, integers -## or arrays, it only contains Match objects. These contain the `.list`, `.hash` -## and `.Str` methods but you can also just use `match<key>` for hash access -## and `match[idx]` for array access. -say $/[0].list.perl; #=> (Match.new(...),).list - # We can see it's a list of Match objects. These contain - # a bunch of info: where the match started/ended, - # the "ast" (see actions later), etc. - # You'll see named capture below with grammars. - -## Alternation - the `or` of regexps -## WARNING: They are DIFFERENT from PCRE regexps. -say so 'abc' ~~ / a [ b | y ] c /; #=> `True`. Either "b" or "y". -say so 'ayc' ~~ / a [ b | y ] c /; #=> `True`. Obviously enough... - -## The difference between this `|` and the one you're used to is -## LTM ("Longest Token Matching"). This means that the engine will always -## try to match as much as possible in the string. -say 'foo' ~~ / fo | foo /; #=> `foo`, instead of `fo`, because it's longer. - -## To decide which part is the "longest", it first splits the regex in -## two parts: -## The "declarative prefix" (the part that can be statically analyzed) -## and the procedural parts: -## - The declarative prefixes include alternations (`|`), conjunctions (`&`), -## sub-rule calls (not yet introduced), literals, characters classes and -## quantifiers. -## - The procedural part include everything else: back-references, -## code assertions, and other things that can't traditionnaly be represented -## by normal regexps. -## -## Then, all the alternatives are tried at once, and the longest wins. -## Examples: -## DECLARATIVE | PROCEDURAL -/ 'foo' \d+ [ <subrule1> || <subrule2> ] /; -## DECLARATIVE (nested groups are not a problem) -/ \s* [ \w & b ] [ c | d ] /; -## However, closures and recursion (of named regexps) are procedural. -## There are also more complicated rules, like specificity (literals win over -## character classes). - -## Note: the first-matching `or` still exists, but is now spelled `||` -say 'foo' ~~ / fo || foo /; #=> `fo` now. -``` - -## Extra: the MAIN subroutine - -```perl6 -## The `MAIN` subroutine is called when you run a Perl 6 file directly. It's -## very powerful, because Perl 6 actually parses the arguments and pass them -## as such to the sub. It also handles named argument (`--foo`) and will even -## go as far as to autogenerate a `--help` flag. -sub MAIN($name) { - say "Hello, $name!"; -} -## This produces: -## $ perl6 cli.pl -## Usage: -## t.pl <name> - -## And since it's a regular Perl 6 sub, you can have multi-dispatch: -## (using a "Bool" for the named argument so that we can do `--replace` -## instead of `--replace=1`. The presence of `--replace` indicates truthness -## while its absence falseness). - -subset File of Str where *.IO.d; # convert to IO object to check the file exists - -multi MAIN('add', $key, $value, Bool :$replace) { ... } -multi MAIN('remove', $key) { ... } -multi MAIN('import', File, Str :$as) { ... } # omitting parameter name - -## This produces: -## $ perl6 cli.pl -## Usage: -## cli.p6 [--replace] add <key> <value> -## cli.p6 remove <key> -## cli.p6 [--as=<Str>] import <File> - -## As you can see, this is *very* powerful. It even went as far as to show inline -## the constants (the type is only displayed if the argument is `$`/is named). -``` - -## APPENDIX A: -### List of things - -```perl6 -## It's assumed by now you know the Perl6 basics. This section is just here to -## list some common operations, but which are not in the "main part" of the -## tutorial to avoid bloating it up. - -## Operators - -## Sort comparison - they return one value of the `Order` enum: `Less`, `Same` -## and `More` (which numerify to -1, 0 or +1 respectively). -1 <=> 4; # sort comparison for numerics -'a' leg 'b'; # sort comparison for string -$obj eqv $obj2; # sort comparison using eqv semantics - -## Generic ordering -3 before 4; # True -'b' after 'a'; # True - -## Short-circuit default operator - similar to `or` and `||`, but instead -## returns the first *defined* value: -say Any // Nil // 0 // 5; #=> 0 - -## Short-circuit exclusive or (XOR) - returns `True` if one (and only one) of -## its arguments is true -say True ^^ False; #=> True - -## Flip flops - these operators (`ff` and `fff`, equivalent to P5's `..` -## and `...`) are operators that take two predicates to test: They are `False` -## until their left side returns `True`, then are `True` until their right -## side returns `True`. Similar to ranges, you can exclude the iteration when -## it become `True`/`False` by using `^` on either side. Let's start with an -## example : -for <well met young hero we shall meet later> { - # by default, `ff`/`fff` smart-match (`~~`) against `$_`: - if 'met' ^ff 'meet' { # Won't enter the if for "met" - .say # (explained in details below). - } - - if rand == 0 ff rand == 1 { # compare variables other than `$_` - say "This ... probably will never run ..."; - } -} - -## This will print "young hero we shall meet" (excluding "met"): the flip-flop -## will start returning `True` when it first encounters "met" (but will still -## return `False` for "met" itself, due to the leading `^` on `ff`), until it -## sees "meet", which is when it'll start returning `False`. - -## The difference between `ff` (awk-style) and `fff` (sed-style) is that `ff` -## will test its right side right when its left side changes to `True`, and can -## get back to `False` right away (*except* it'll be `True` for the iteration -## that matched) while `fff` will wait for the next iteration to try its right -## side, once its left side changed: -.say if 'B' ff 'B' for <A B C B A>; #=> B B - # because the right-hand-side was tested - # directly (and returned `True`). - # "B"s are printed since it matched that - # time (it just went back to `False` - # right away). -.say if 'B' fff 'B' for <A B C B A>; #=> B C B - # The right-hand-side wasn't tested until - # `$_` became "C" - # (and thus did not match instantly). - -## A flip-flop can change state as many times as needed: -for <test start print it stop not printing start print again stop not anymore> { - .say if $_ eq 'start' ^ff^ $_ eq 'stop'; # exclude both "start" and "stop", - #=> "print it print again" -} - -## You might also use a Whatever Star, which is equivalent to `True` for the -## left side or `False` for the right: -for (1, 3, 60, 3, 40, 60) { # Note: the parenthesis are superfluous here - # (sometimes called "superstitious parentheses") - .say if $_ > 50 ff *; # Once the flip-flop reaches a number greater - # than 50, it'll never go back to `False` - #=> 60 3 40 60 -} - -## You can also use this property to create an `if` that'll not go through the -## first time: -for <a b c> { - .say if * ^ff *; # the flip-flop is `True` and never goes back to `False`, - # but the `^` makes it *not run* on the first iteration - #=> b c -} - -## The `===` operator is the value identity operator and uses `.WHICH` on the -## objects to compare them while `=:=` is the container identity operator -## and uses `VAR()` on the objects to compare them. -``` - -If you want to go further, you can: - - - Read the [Perl 6 Docs](https://docs.perl6.org/). This is a great - resource on Perl6. If you are looking for something, use the search bar. - This will give you a dropdown menu of all the pages referencing your search - term (Much better than using Google to find Perl 6 documents!). - - Read the [Perl 6 Advent Calendar](http://perl6advent.wordpress.com/). This - is a great source of Perl 6 snippets and explanations. If the docs don't - describe something well enough, you may find more detailed information here. - This information may be a bit older but there are many great examples and - explanations. Posts stopped at the end of 2015 when the language was declared - stable and Perl 6.c was released. - - Come along on `#perl6` at `irc.freenode.net`. The folks here are - always helpful. - - Check the [source of Perl 6's functions and - classes](https://github.com/rakudo/rakudo/tree/nom/src/core). Rakudo is - mainly written in Perl 6 (with a lot of NQP, "Not Quite Perl", a Perl 6 subset - easier to implement and optimize). - - Read [the language design documents](http://design.perl6.org). They explain - P6 from an implementor point-of-view, but it's still very interesting. |