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diff --git a/perl6.html.markdown b/perl6.html.markdown deleted file mode 100644 index 2821f0d4..00000000 --- a/perl6.html.markdown +++ /dev/null @@ -1,1799 +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 comment start with a pound - -#`( - Multiline comments use #` and a quoting construct. - (), [], {}, 「」, etc, will work. -) -``` - -## Variables - -```perl6 -## In Perl 6, you declare a lexical variable using `my` -my $variable; -## Perl 6 has 3 basic types of variables: scalars, arrays, and hashes. -``` - -### Scalars - -```perl6 -# Scalars represent a single value. They start with a `$` - -my $str = 'String'; -# double quotes allow for interpolation (which we'll see later): -my $str2 = "String"; - -## Variable names can contain but not end with simple quotes and dashes, -## and can contain (and end with) underscores : -my $weird'variable-name_ = 5; # works ! - -my $bool = True; # `True` and `False` are Perl 6's boolean values. -my $inverse = !$bool; # You can invert a bool with the prefix `!` operator -my $forced-bool = so $str; # And you can use the prefix `so` operator - # which turns its operand into a Bool -``` - -### Arrays and Lists - -```perl6 -## Arrays represent multiple values. Their name start with `@`. -## Lists are similar but are an immutable type. - -my @array = 'a', 'b', 'c'; -# equivalent to : -my @letters = <a b c>; # array of words, delimited by space. - # Similar to perl5's qw, or Ruby's %w. -my @array = 1, 2, 3; - -say @array[2]; # Array indices start at 0 -- This is the third element - -say "Interpolate all elements of an array using [] : @array[]"; -#=> Interpolate all elements of an array using [] : 1 2 3 - -@array[0] = -1; # Assign a new value to an array index -@array[0, 1] = 5, 6; # Assign multiple values - -my @keys = 0, 2; -@array[@keys] = @letters; # 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 = 1 => 2, - 3 => 4; -my %hash = foo => "bar", # keys get auto-quoted - "some other" => "value", # 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: -my %hash = <key1 value1 key2 value2>; - -my %hash = key1 => 'value1', key2 => 'value2'; # same result as above - -## You can also use the "colon pair" syntax: -## (especially handy for named parameters that you'll see later) -my %hash = :w(1), # equivalent to `w => 1` - # this is useful for the `True` shortcut: - :truey, # equivalent to `:truey(True)`, or `truey => True` - # and for the `False` one: - :!falsey, # equivalent to `:falsey(False)`, or `falsey => False` - ; - -say %hash{'key1'}; # You can use {} to get the value from a key -say %hash<key2>; # If it's a string, you can actually use <> - # (`{key1}` doesn't work, as Perl6 doesn't have barewords) -``` - -## Subs - -```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, $name !"; -} - -## A sub returns the last value of the block. -sub return-value { - 5; -} -say return-value; # prints 5 -sub return-empty { -} -say return-empty; # prints Nil - -## Some control flow structures produce a value, like if: -sub return-if { - if True { - "Truthy"; - } -} -say return-if; # prints Truthy - -## Some don't, like for: -sub return-for { - for 1, 2, 3 { } -} -say return-for; # prints Nil - -## A sub can have optional arguments: -sub with-optional($arg?) { # the "?" marks the argument optional - say "I might return `(Any)` (Perl's 'null'-like value) if I don't have - an argument passed, or I'll return my argument"; - $arg; -} -with-optional; # returns Any -with-optional(); # returns Any -with-optional(1); # returns 1 - -## You can also give them a default value when they're not passed: -sub hello-to($name = "World") { - say "Hello, $name !"; -} -hello-to; #=> Hello, World ! -hello-to(); #=> Hello, World ! -hello-to('You'); #=> Hello, You ! - -## You can also, by using a syntax akin to the one of hashes -## (yay unified syntax !), pass *named* arguments to a `sub`. -## They're optional, and will default to "Any". -sub with-named($normal-arg, :$named) { - say $normal-arg + $named; -} -with-named(1, named => 6); #=> 7 -## There's one gotcha to be aware of, here: -## If you quote your key, Perl 6 won't be able to see it at compile time, -## and you'll have a single Pair object as a positional parameter, -## which means this fails: -with-named(1, 'named' => 6); - -with-named(2, :named(5)); #=> 7 - -## To make a named argument mandatory, you can use `?`'s inverse, `!` -sub with-mandatory-named(:$str!) { - say "$str !"; -} -with-mandatory-named(str => "My String"); #=> My String ! -with-mandatory-named; # run time error: "Required named parameter not passed" -with-mandatory-named(3);# run time error:"Too many positional parameters passed" - -## If a sub takes a named boolean argument ... -sub takes-a-bool($name, :$bool) { - say "$name takes $bool"; -} -## ... you can use the same "short boolean" hash syntax: -takes-a-bool('config', :bool); # config takes True -takes-a-bool('config', :!bool); # config takes False - -## You can also provide your named arguments with defaults: -sub named-def(:$def = 5) { - say $def; -} -named-def; #=> 5 -named-def(def => 15); #=> 15 - -## Since you can omit parenthesis to call a function with no arguments, -## you need "&" in the name to store `say-hello` in a variable. -my &s = &say-hello; -my &other-s = sub { say "Anonymous function !" } - -## A sub can have a "slurpy" parameter, or "doesn't-matter-how-many" -sub as-many($head, *@rest) { #`*@` (slurpy) will "take everything else" -## Note: you can have parameters *before* a slurpy one (like here), -## but not *after*. - say @rest.join(' / ') ~ " !"; -} -say as-many('Happy', 'Happy', 'Birthday'); #=> Happy / Birthday ! - # Note that the splat (the *) did not - # consume the parameter before. - -## You can call a function with an array using the -## "argument list flattening" operator `|` -## (it's not actually the only role of this operator, but it's one of them) -sub concat3($a, $b, $c) { - say "$a, $b, $c"; -} -concat3(|@array); #=> a, b, c - # `@array` got "flattened" as a part of the argument list -``` - -## Containers - -```perl6 -## In Perl 6, values are actually stored in "containers". -## The assignment operator asks the container on the left to store the value on -## its right. When passed around, containers are marked as immutable. -## Which means that, in a function, you'll get an error if you try to -## mutate one of your arguments. -## If you really need to, you can ask for a mutable container using `is rw`: -sub mutate($n is rw) { - $n++; - say "\$n is now $n !"; -} - -my $m = 42; -mutate $m; # $n is now 43 ! - -## This works because we are passing the container $m to mutate. If we try -## to just pass a number instead of passing a variable it won't work because -## there is no container being passed and integers are immutable by themselves: - -mutate 42; # Parameter '$n' expected a writable container, but got Int value - -## If what you want a copy instead, use `is copy`. - -## A sub itself returns a container, which means it can be marked as rw: -my $x = 42; -sub x-store() is rw { $x } -x-store() = 52; # in this case, the parentheses are mandatory - # (else Perl 6 thinks `x-store` is an identifier) -say $x; #=> 52 -``` - -## Control Flow Structures -### Conditionals - -```perl6 -## - `if` -## Before talking about `if`, we need to know which values are "Truthy" -## (represent True), and which are "Falsey" (or "Falsy") -- represent False. -## Only these values are Falsey: 0, (), {}, "", Nil, A type (like `Str` or -## `Int`) and of course False itself. -## Every other value is Truthy. -if True { - say "It's true !"; -} - -unless False { - say "It's not false !"; -} - -## As you can see, you don't need parentheses around conditions. -## However, you do need the brackets around the "body" block: -# if (true) say; # This doesn't work ! - -## You can also use their postfix versions, with the keyword after: -say "Quite truthy" if True; - -## - Ternary conditional, "?? !!" (like `x ? y : z` in some other languages) -## returns $value-if-true if the condition is true and $value-if-false -## if it is false. -## my $result = $value condition ?? $value-if-true !! $value-if-false; - -my $age = 30; -say $age > 18 ?? "You are an adult" !! "You are under 18"; -``` - -### given/when, or switch - -```perl6 -## - `given`-`when` looks like other languages' `switch`, but is much more -## powerful thanks to smart matching and Perl 6's "topic variable", $_. -## -## This variable contains the default argument of a block, -## a loop's current iteration (unless explicitly named), etc. -## -## `given` simply puts its argument into `$_` (like a block would do), -## and `when` compares it using the "smart matching" (`~~`) operator. -## -## Since other Perl 6 constructs use this variable (as said before, like `for`, -## blocks, etc), this means the powerful `when` is not only applicable along -## with a `given`, but instead anywhere a `$_` exists. - -given "foo bar" { - say $_; #=> foo bar - when /foo/ { # Don't worry about smart matching yet – just know `when` uses it - # This is equivalent to `if $_ ~~ /foo/`. - say "Yay !"; - } - when $_.chars > 50 { # smart matching anything with True is True, - # i.e. (`$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` - Passes through an array -for @array -> $variable { - say "I've got $variable !"; -} - -## As we saw with given, for's default "current iteration" variable is `$_`. -## That means you can use `when` in a `for` just like you were in a `given`. -for @array { - say "I've got $_"; - - .say; # This is also allowed. - # A dot call with no "topic" (receiver) is sent to `$_` by default - $_.say; # the above and this are equivalent. -} - -for @array { - # You can... - next if $_ == 3; # Skip to the next iteration (`continue` in C-like languages) - redo if $_ == 4; # Re-do the iteration, keeping the same topic variable (`$_`) - last if $_ == 5; # Or break out of a loop (like `break` in C-like languages) -} - -## The "pointy block" syntax isn't specific to for. -## It's just a way to express a block in Perl6. -if long-computation() -> $result { - say "The result is $result"; -} -``` - -## Operators - -```perl6 -## Since Perl languages are very much operator-based languages, -## Perl 6 operators are actually just funny-looking subroutines, in syntactic -## categories, like infix:<+> (addition) or prefix:<!> (bool not). - -## The categories are: -## - "prefix": before (like `!` in `!True`). -## - "postfix": after (like `++` in `$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'; -'a' ne 'b'; # not equal -'a' !eq 'b'; # same as above - -## - `eqv` is canonical equivalence (or "deep equality") -(1, 2) eqv (1, 3); - -## - 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 "has type" (can check superclasses and roles) - -1 ~~ Int; # True - -## Smart-matching against a boolean always returns that boolean (and will warn). - -1 ~~ True; # True -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 - -## You also, of course, have `<`, `<=`, `>`, `>=`. -## Their string equivalent are also available : `lt`, `le`, `gt`, `ge`. -3 > 4; - -## * Range constructors -3 .. 7; # 3 to 7, both included -## `^` on either side them exclusive on that side : -3 ^..^ 7; # 3 to 7, not included (basically `4 .. 6`) -## This also works as a shortcut for `0..^N`: -^10; # means 0..^10 - -## This also allows us to demonstrate that Perl 6 has lazy/infinite arrays, -## using the Whatever Star: -my @array = 1..*; # 1 to Infinite ! `1..Inf` is the same. -say @array[^10]; # you can pass arrays as subscripts and it'll return - # an array of results. This will print - # "1 2 3 4 5 6 7 8 9 10" (and not run out of memory !) -## Note : when reading an infinite list, Perl 6 will "reify" the elements -## it needs, then keep them in memory. They won't be calculated more than once. -## It also will never calculate more elements that are needed. -## Trying - -## 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 assigning to an array -my @numbers = ^20; - -## Here numbers increase by "6"; more on `...` 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 `4` and gets `True`. -0 || False; # False. Calls `.Bool` on `0` - -## * Short-circuit (and tight) versions of the above -# Returns 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 -@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 -## It's 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 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]) { $fst } -first-of-array(@small); #=> 1 -first-of-array(@tail); # Throws an error "Too many positional parameters passed" - # (which means the array is too big). - -## You can also use a slurp ... -sub slurp-in-array(@ [$fst, *@rest]) { # You could keep `*@rest` anonymous - say $fst + @rest.elems; # `.elems` returns a list's length. - # Here, `@rest` is `(3,)`, since `$fst` holds the `2`. -} -slurp-in-array(@tail); #=> 3 - -## You could even extract on a slurpy (but it's pretty useless ;-).) -sub fst(*@ [$fst]) { # or simply : `sub fst($fst) { ... }` - say $fst; -} -fst(1); #=> 1 -fst(1, 2); # errors with "Too many positional parameters passed" - -## You can also destructure hashes (and classes, which you'll learn about later) -## The syntax is basically `%hash-name (:key($variable-to-store-value-in))`. -## The hash can stay anonymous if you only need the values you extracted. -sub key-of(% (:value($val), :qua($qua))) { - say "Got val $val, $qua times."; -} - -## Then call it with a hash: (you need to keep the brackets for it to be a hash) -key-of({value => 'foo', qua => 1}); -#key-of(%hash); # the same (for an equivalent `%hash`) - -## The last expression of a sub is returned automatically -## (though you may use the `return` keyword, of course): -sub next-index($n) { - $n + 1; -} -my $new-n = next-index(3); # $new-n is now 4 - -## This is true for everything, except for the looping constructs -## (due to performance reasons): there's reason to build a list -## if we're just going to discard all the results. -## If you still want to build one, you can use the `do` statement prefix: -## (or the `gather` prefix, which we'll see later) -sub list-of($n) { - do for ^$n { # note the use of the range-to prefix operator `^` (`0..^N`) - $_ # current loop iteration - } -} -my @list3 = list-of(3); #=> (0, 1, 2) -``` - -### lambdas - -```perl6 -## You can create a lambda with `-> {}` ("pointy block") or `{}` ("block") -my &lambda = -> $argument { "The argument passed to this lambda is $argument" } -## `-> {}` and `{}` are pretty much the same thing, except that the former can -## take arguments, and that the latter can be mistaken as a hash by the parser. - -## We can, for example, add 3 to each value of an array using map: -my @arrayplus3 = map({ $_ + 3 }, @array); # $_ is the implicit argument - -## A sub (`sub {}`) has different semantics than a block (`{}` or `-> {}`): -## A block doesn't have a "function context" (though it can have arguments), -## which means that if you return from it, -## you're going to return from the parent function. Compare: -sub is-in(@array, $elem) { - # this will `return` out of the `is-in` sub - # once the condition evaluated to True, the loop won't be run anymore - map({ return True if $_ == $elem }, @array); -} -sub truthy-array(@array) { - # this will produce an array of `True` and `False`: - # (you can also say `anon sub` for "anonymous subroutine") - map(sub ($i) { if $i { return True } else { return False } }, @array); - # ^ the `return` only returns from the anonymous `sub` -} - -## You can also use the "whatever star" to create an anonymous function -## (it'll stop at the furthest operator in the current expression) -my @arrayplus3 = map(*+3, @array); # `*+3` is the same as `{ $_ + 3 }` -my @arrayplus3 = map(*+*+3, @array); # Same as `-> $a, $b { $a + $b + 3 }` - # also `sub ($a, $b) { $a + $b + 3 }` -say (*/2)(4); #=> 2 - # Immediately execute the function Whatever created. -say ((*+3)/5)(5); #=> 1.6 - # works even in parens ! - -## But if you need to have more than one argument (`$_`) -## in a block (without wanting to resort to `-> {}`), -## you can also use the implicit argument syntax, `$^` : -map({ $^a + $^b + 3 }, @array); # equivalent to following: -map(sub ($a, $b) { $a + $b + 3 }, @array); # (here with `sub`) - -## Note : those are sorted lexicographically. -# `{ $^b / $^a }` is like `-> $a, $b { $b / $a }` -``` - -### About types... - -```perl6 -## Perl6 is gradually typed. This means you can specify the type -## of your variables/arguments/return types, or you can omit them -## and they'll default to "Any". -## You obviously get access to a few base types, like Int and Str. -## The constructs for declaring types are "class", "role", -## which you'll see later. - -## For now, let us examine "subset": -## a "subset" is a "sub-type" with additional checks. -## For example: "a very big integer is an Int that's greater than 500" -## You can specify the type you're subtyping (by default, Any), -## and add additional checks with the "where" keyword: -subset VeryBigInteger of Int where * > 500; -``` - -### Multiple Dispatch - -```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 a `where`: - -## with types -multi sub sayit(Int $n) { # note the `multi` keyword here - say "Number: $n"; -} -multi sayit(Str $s) { # a multi is a `sub` by default - say "String: $s"; -} -sayit("foo"); # prints "String: foo" -sayit(True); # fails at *compile time* with - # "calling 'sayit' will never work with arguments of types ..." - -## with arbitrary precondition (remember subsets?): -multi is-big(Int $n where * > 50) { "Yes !" } # using a closure -multi is-big(Int $ where 10..50) { "Quite." } # Using smart-matching - # (could use a regexp, etc) -multi is-big(Int $) { "No" } - -subset Even of Int where * %% 2; - -multi odd-or-even(Even) { "Even" } # The main case using the type. - # We don't name the argument. -multi odd-or-even($) { "Odd" } # "else" - -## You can even dispatch based on a positional's argument presence ! -multi with-or-without-you(:$with!) { # You need make it mandatory to - # be able to dispatch against it. - say "I can live ! Actually, I can't."; -} -multi with-or-without-you { - say "Definitely can't live."; -} -## This is very, very useful for many purposes, like `MAIN` subs (covered -## later), and even the language itself is using it in several places. -## -## - `is`, for example, is actually a `multi sub` named `trait_mod:<is>`, -## and it works off that. -## - `is rw`, is simply a dispatch to a function with this signature: -## sub trait_mod:<is>(Routine $r, :$rw!) {} -## -## (commented because running this would be a terrible idea !) -``` - -## Scoping - -```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 `$outer_scoped` were captured. -## But if we were to try and use `$bar` outside of `foo`, -## the variable would be undefined (and you'd get a compile time error). -``` - -## Twigils - -```perl6 -## There are many special `twigils` (composed sigil's) 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 (class member) -## . 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: -## => $object.method -## Classes are declared with the `class` keyword. Attributes are declared -## with the `has` keyword, and methods declared with `method`. -## Every attribute that is private uses the ! twigil for example: `$!attr`. -## Immutable public attributes use the `.` twigil. -## (you can make them mutable with `is rw`) -## The easiest way to remember the `$.` twigil is 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 ... -## (these will not all be covered here, and you should refer to: -## https://docs.perl6.org/language/objects.html. - -class Attrib-Class { - has $.attrib; # `$.attrib` is immutable. - # From inside the class, use `$!attrib` to modify it. - has $.other-attrib is rw; # You can mark a public attribute `rw`. - has Int $!private-attrib = 10; - - method get-value { - $.attrib + $!private-attrib; - } - - method set-value($param) { # Methods can take parameters - $!attrib = $param; # This works, because `$!` is always mutable. - # $.attrib = $param; # Wrong: You can't use the `$.` immutable version. - - $.other-attrib = 5; # This works, because `$.other-attrib` is `rw`. - } - - method !private-method { - say "This method is private to the class !"; - } -}; - -## Create a new instance of Attrib-Class with $.attrib set to 5 : -## Note: you can't set private-attribute from here (more later on). -my $class-obj = Attrib-Class.new(attrib => 5); -say $class-obj.get-value; #=> 15 -# $class-obj.attrib = 5; # This fails, because the `has $.attrib` is immutable -$class-obj.other-attrib = 10; # This, however, works, because the public - # attribute is mutable (`rw`). -``` - -### Object Inheritance - -```perl6 -## Perl 6 also has inheritance (along with multiple inheritance) -## While `method`'s are inherited, `submethod`'s 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 Child. - 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, he knows how to say his name. - -my Child $Madison .= new(age => 1, name => 'Madison'); -$Madison.talk; # prints "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 properties too, so you can pass `val => 5`. -``` - -### Roles, or Mixins - -```perl6 -## Roles are supported too (also called Mixins in other languages) -role PrintableVal { - has $!counter = 0; - method print { - say $.val; - } -} - -## you "import" a mixin (a "role") with "does": -class Item does PrintableVal { - has $.val; - - ## When `does`-ed, a `role` literally "mixes in" the class: - ## the methods and 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: -die X::AdHoc.new(payload => '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 avoid it being automatically handled and printing lots of scary -## error messages to the screen. -## We can use the exception method on $_ to access the exception -open 'foo' orelse say "Something happened {.exception}"; - -## This also works: -open 'foo' orelse say "Something happened $_"; #> Something happened - #> Failed to open file foo: no such file or directory -## Both of those above work but in case we get an object from the left side that -## is not a failure we will probably get a warning. We see below how we can use -## `try` and `CATCH` to be more specific with the exceptions we catch. -``` - -### Using `try` and `CATCH` - -```perl6 -## By using `try` and `CATCH` you can contain and handle exceptions without -## disrupting the rest of the program. `try` will set the last exception to -## the special variable `$!` Note: This has no relation to $!variables. -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 $_ was set when we 'disarmed' the -## exception with orelse, we also use $_ in the CATCH block. -## Note: ($! is only set *after* the `try` block) -## By default, a `try` has a `CATCH` block 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: -try { - open 'foo'; - CATCH { # In the `CATCH` block, the exception is set to $_ - when X::AdHoc { say "Error: $_" } - #=>Error: Failed to open file /dir/foo: no such file or directory - - ## Any other exception will be re-raised, since we don't have a `default` - ## Basically, if a `when` matches (or there's a `default`) marks the - ## exception as - ## "handled" so that it doesn't get re-thrown from the `CATCH`. - ## You still can re-throw the exception (see below) by hand. - } -} - -## There are also some subtleties to exceptions. Some Perl 6 subs return a -## `Failure`, which is a kind of "unthrown exception". They're not thrown until -## you tried to look at their content, unless you call `.Bool`/`.defined` on -## them - then they're handled. -## (the `.handled` method is `rw`, so you can mark it as `False` back yourself) -## -## You can throw a `Failure` using `fail`. Note that if the pragma `use fatal` -## is on, `fail` will throw an exception (like `die`). -fail "foo"; # We're not trying to access the value, so no problem. -try { - fail "foo"; - CATCH { - default { say "It threw because we 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 `use` -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`. - -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 - -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` declarations happen at `INIT` time -- (see "Phasers" below) -## It's like `my`, but it also creates a package variable. -## (All packagish things (`class`, `role`, etc) are `our` by default) -module Var::Increment { - our $our-var = 1; # Note: you can't put a type constraint like Int on an - my $my-var = 22; # `our` variable. - our sub Inc { - - our sub available { # If you try to make inner `sub`s `our`... - # Better know what you're doing (Don't !). - say "Don't do that. Seriously. You'll get burned."; - } - - my sub unavailable { # `my sub` is the default - say "Can't access me from outside, I'm 'my'!"; - } - say ++$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` (happens at `BEGIN` time) -## You can use the `constant` keyword to declare a compile-time variable/symbol: -constant Pi = 3.14; -constant $var = 1; - -## And if you're wondering, yes, it can also contain infinite lists. -constant why-not = 5, 15 ... *; -say why-not[^5]; #=> 5 15 25 35 45 - -## * `state` (happens at run time, but only once) -## State variables are only initialized one time -## (they exist in other languages such as C as `static`) -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. -## (`CATCH` is actually a phaser!) -## Some of them can be used for their return values, some of them can't -## (those that can have a "[*]" in the beginning of their explanation text). -## Let's have a look ! - -## * Compile-time phasers -BEGIN { say "[*] Runs at compile time, as soon as possible, only once" } -CHECK { say "[*] Runs at compile time, 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 brackets `{` and `}`. - -## - `do` (that you already saw) - runs a block or a statement as a term -## You can't normally use a statement as a value (or "term"): -## -## my $value = if True { 1 } # `if` is a statement - parse error -## -## This works: -my $a = do if True { 5 } # with `do`, `if` is now a term. - -## - `once` - Makes sure a piece of code only runs once -for ^5 { once say 1 }; #=> 1 - # Only prints ... once. -## Like `state`, they're cloned per-scope -for ^5 { sub { once say 1 }() } #=> 1 1 1 1 1 - # Prints once per lexical scope - -## - `gather` - Co-routine thread -## Gather allows you to `take` several values in an array, -## much like `do`, but allows you to take any expression. -say gather for ^5 { - take $_ * 3 - 1; - take $_ * 3 + 1; -} #=> -1 1 2 4 5 7 8 10 11 13 -say join ',', gather if False { - take 1; - take 2; - take 3; -} # Doesn't print anything. - -## - `eager` - Evaluate statement eagerly (forces eager context) -## Don't try this at home: -## -## eager 1..*; # this will probably hang for a while (and might crash ...). -## -## But consider: -constant thrice = gather for ^3 { say take $_ }; # Doesn't print anything - -## versus: -constant thrice = eager gather for ^3 { say take $_ }; #=> 0 1 2 -``` - -## Iterables - -```perl6 -## Iterables are objects that can be iterated similar to the `for` construct -## `flat`, flattens iterables: -say (1, 10, (20, 10) ); #> (1 10 (20 10)) Notice how grouping is maintained -say (1, 10, (20, 10) ).flat; #> (1 10 20 10) Now the iterable is flat - -## - `lazy` - Defer actual evaluation until value is fetched -## (forces lazy context) -my @lazy-array = (1..100).lazy; -say @lazy-array.is-lazy; #> True # Check for laziness with the `is-lazy` method. -say @lazy-array; #> [...] List has not been iterated on! -my @lazy-array { .print }; # This works and will only do as much work as - # is needed. -[//]: # ( TODO explain that gather/take and map are all lazy) -## - `sink` - An `eager` that discards the results (forces sink context) -constant nilthingie = sink for ^3 { .say } #=> 0 1 2 -say nilthingie.perl; #=> Nil - -## - `quietly` blocks will suppress warnings: -quietly { warn 'This is a warning!' }; #=> No output - -## - `contend` - Attempts side effects under STM -## Not yet implemented ! -``` - -## More operators thingies ! - -```perl6 -## Everybody loves operators ! Let's get more of them - -## The precedence list can be found here: -## https://docs.perl6.org/language/operators#Operator_Precedence -## But first, we need a little explanation about associativity: - -## * Binary operators: -$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 I guess I should try -## to show you something exciting. -## I'll tell you a little secret (or not-so-secret): -## In Perl 6, all operators are actually just funny-looking subroutines. - -## You can declare an operator just like you declare a sub: -sub prefix:<win>($winner) { # refer to the operator categories - # (yes, it's the "words operator" `<>`) - say "$winner Won !"; -} -win "The King"; #=> The King Won ! - # (prefix is before) - -## you can still call the sub with its "full name": -say prefix:<!>(True); #=> False - -sub postfix:<!>(Int $n) { - [*] 2..$n; # using the reduce meta-operator ... See below ;-) ! -} -say 5!; #=> 120 - # Postfix operators (after) have to come *directly* after the term. - # No whitespace. You can use parentheses to disambiguate, i.e. `(5!)!` - - -sub infix:<times>(Int $n, Block $r) { # infix in the middle - for ^$n { - $r(); # You need the explicit parentheses to call the function in `$r`, - # else you'd be referring at the variable itself, like with `&r`. - } -} -3 times -> { say "hello" }; #=> hello - #=> hello - #=> hello - # You're very recommended to put spaces - # around your infix operator calls. - -## For circumfix and post-circumfix ones -sub circumfix:<[ ]>(Int $n) { - $n ** $n -} -say [5]; #=> 3125 - # circumfix is around. Again, 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, $key, :delete); # (you can call operators like that) - -## It's *all* using the same building blocks! -## Syntactic categories (prefix infix ...), named arguments (adverbs), ..., -## - used to build the language - are available to you. -## (you are, obviously, recommended against making an operator out of -## *everything* -- with great power comes great responsibility) -``` - -### Meta operators ! - -```perl6 -## Oh boy, get ready. Get ready, because we're delving deep -## into the rabbit's hole, and you probably won't want to go -## back to other languages after reading that. -## (I'm guessing you don't want to already at that point). -## Meta-operators, as their name suggests, are *composed* operators. -## Basically, they're operators that apply another operator. - -## * Reduce meta-operator -## It's a prefix meta-operator that takes a binary function and -## one or many lists. If it doesn't get passed any argument, -## it either returns a "default value" for this operator -## (a meaningless value) or `Any` if there's none (examples below). -## -## Otherwise, it pops an element from the list(s) one at a time, and applies -## the binary function to the last result (or the list's first element) -## and the popped element. -## -## To sum a list, you could use the reduce meta-operator with `+`, i.e.: -say [+] 1, 2, 3; #=> 6 -## equivalent to `(1+2)+3` - -say [*] 1..5; #=> 120 -## equivalent to `((((1*2)*3)*4)*5)`. - -## You can reduce with any operator, not just with mathematical ones. -## For example, you could reduce with `//` to get -## the first defined element of a list: -say [//] Nil, Any, False, 1, 5; #=> False - # (Falsey, but still defined) - -## Default value examples: -say [*] (); #=> 1 -say [+] (); #=> 0 - # meaningless values, since N*1=N and N+0=N. -say [//]; #=> (Any) - # There's no "default value" for `//`. - -## You can also call it with a function you made up, using double brackets: -sub add($a, $b) { $a + $b } -say [[&add]] 1, 2, 3; #=> 6 - -## * Zip meta-operator -## This one is an infix meta-operator than also can be used as a "normal" -## operator. It takes an optional binary function (by default, it just creates -## a pair), and will pop one value off of each array and call its binary -## function on these until it runs out of elements. It returns an array with -## all of these new elements. -(1, 2) Z (3, 4); # ((1, 3), (2, 4)), since by default, the function - # makes an array. -1..3 Z+ 4..6; # (5, 7, 9), using the custom infix:<+> function - -## Since `Z` is list-associative (see the list above), -## you can use it on more than one list -(True, False) Z|| (False, False) Z|| (False, False); # (True, False) - -## And, as it turns out, you can also use the reduce meta-operator with it: -[Z||] (True, False), (False, False), (False, False); # (True, False) - - -## And to end the operator list: - -## * Sequence operator -## The sequence operator is one of Perl 6's most powerful features: -## it's composed of first, on the left, the list you want Perl 6 to deduce from -## (and might include a closure), and on the right, a value or the predicate -## that says when to stop (or Whatever for a lazy infinite list). -my @list = 1, 2, 3 ... 10; # basic deducing -#my @list = 1, 3, 6 ... 10; # this 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 when the predicate matches). -my @list = 1, 3, 9 ... * > 30; # you can use a predicate - # (with the Whatever Star, here). -my @list = 1, 3, 9 ... { $_ > 30 }; # (equivalent to the above) - -my @fib = 1, 1, *+* ... *; # lazy infinite list of fibonacci series, - # computed using a closure! -my @fib = 1, 1, -> $a, $b { $a + $b } ... *; # (equivalent to the above) -my @fib = 1, 1, { $^a + $^b } ... *; #(... also equivalent to the above) -## $a and $b will always take the previous values, meaning here -## they'll start with $a = 1 and $b = 1 (values we set by hand). -## then $a = 1 and $b = 2 (result from previous $a+$b), and so on. - -say @fib[^10]; #=> 1 1 2 3 5 8 13 21 34 55 - # (using a range as the index) -## Note : as for ranges, once reified, elements aren't re-calculated. -## That's why `@primes[^100]` will take a long time the first time you print -## it, then be instant. -``` - -## Regular Expressions - -```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. -## (we won't be discussing this in this tutorial, however) -## -## In essence, Perl 6 natively implements PEG ("Parsing Expression Grammars"). -## The pecking order for ambiguous parses is determined by a multi-level -## tie-breaking test: -## - Longest token matching. `foo\s+` beats `foo` (by 2 or more positions) -## - Longest literal prefix. `food\w*` beats `foo\w*` (by 1) -## - Declaration from most-derived to less derived grammars -## (grammars are actually classes) -## - Earliest declaration wins -say so 'a' ~~ /a/; #=> True -say so 'a' ~~ / a /; #=> 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`, but in fact, it's -## returning a `Match` object. They know how to respond to list indexing, -## hash indexing, and return the matched string. -## The results of the match are available as `$/` (implicitly lexically-scoped). -## You can also use the capture variables 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 char of the string), -## we're going to explain later how you can do it. - -## In Perl 6, you can have any alphanumeric as a literal, -## everything else has to be escaped, using a backslash or quotes. -say so 'a|b' ~~ / a '|' b /; # `True`. Wouldn't mean the same if `|` wasn't - # escaped -say so 'a|b' ~~ / a \| b /; # `True`. Another way to escape it. - -## The whitespace in a regexp is actually not significant, -## unless you use the `:s` (`:sigspace`, significant space) 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' #> Space is not significant here; -## 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` - -## Use the :i adverb to specify case insensitivity: -say so 'ABC' ~~ m:i{a b c}; #> `True` - -## It is, however, important as for how modifiers (that you're gonna see just -## below) are applied ... - -## Quantifying - `?`, `+`, `*` and `**`. -## - `?` - 0 or 1 -so 'ac' ~~ / a b c /; # `False` -so 'ac' ~~ / a b? c /; # `True`, the "b" matched 0 times. -so 'abc' ~~ / a b? c /; # `True`, the "b" matched 1 time. - -## ... As you read just before, whitespace is important because it determines -## which part of the regexp is the target of the modifier: -so 'def' ~~ / a b c? /; # `False`. Only the `c` is optional -so 'def' ~~ / 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` - -## - `+` - 1 or more -so 'ac' ~~ / a b+ c /; # `False`; `+` wants at least one matching -so 'abc' ~~ / a b+ c /; # `True`; one is enough -so 'abbbbc' ~~ / a b+ c /; # `True`, matched 4 "b"s - -## - `*` - 0 or more -so 'ac' ~~ / a b* c /; # `True`, they're all optional. -so 'abc' ~~ / a b* c /; # `True` -so 'abbbbc' ~~ / a b* c /; # `True` -so 'aec' ~~ / a b* c /; # `False`. "b"(s) are optional, not replaceable. - -## - `**` - (Unbound) Quantifier -## If you squint hard enough, you might understand -## why exponentation is used for quantity. -so 'abc' ~~ / a b**1 c /; # `True` (exactly one time) -so 'abc' ~~ / a b**1..3 c /; # `True` (one to three times) -so 'abbbc' ~~ / a b**1..3 c /; # `True` -so 'abbbbbbc' ~~ / a b**1..3 c /; # `False` (too much) -so 'abbbbbbc' ~~ / a b**3..* c /; # `True` (infinite ranges are okay) - -## - `<[]>` - Character classes -## Character classes are the equivalent of PCRE's `[]` classes, but -## they use a more perl6-ish syntax: -say 'fooa' ~~ / f <[ o a ]>+ /; #=> 'fooa' - -## You can use ranges: -say 'aeiou' ~~ / a <[ e..w ]> /; #=> 'ae' - -## Just like in normal regexes, if you want to use a special character, -## escape it (the last one is escaping a space) -say 'he-he !' ~~ / 'he-' <[ a..z \! \ ]> + /; #=> 'he-he !' - -## You'll get a warning if you put duplicate names -## (which has the nice effect of catching the wrote quoting:) -'he he' ~~ / <[ h e ' ' ]> /; # Warns "Repeated characters found in characters - # class" - -## You can also negate them ... (equivalent to `[^]` in PCRE) -so 'foo' ~~ / <-[ f o ]> + /; # False - -## ... and compose them: : -so 'foo' ~~ / <[ a..z ] - [ f o ]> + /; # False (any letter except f and o) -so 'foo' ~~ / <-[ a..z ] + [ f o ]> + /; # True (no letter except f and o) -so 'foo!' ~~ / <-[ a..z ] + [ f o ]> + /; # True (the + doesn't replace the - # left part) -``` - -### Grouping and capturing - -```perl6 -## Group: you can group parts of your regexp with `[]`. -## These groups are *not* captured (like PCRE's `(?:)`). -so 'abc' ~~ / a [ b ] c /; # `True`. The grouping does pretty much nothing -so 'foo012012bar' ~~ / foo [ '01' <[0..9]> ] + bar /; -## The previous line returns `True`. -## We match the "012" 1 or more time (the `+` was applied to the group). - -## But this does not go far enough, because we can't actually get back what -## we matched. -## Capture: We can actually *capture* the results of the regexp, -## using parentheses. -so 'fooABCABCbar' ~~ / foo ( 'A' <[A..Z]> 'C' ) + bar /; # `True`. (using `so` - # here, `$/` below) - -## So, starting with the grouping explanations. -## As we said before, our `Match` object is available as `$/`: -say $/; # Will print some weird stuff (we'll explain) (or "Nil" if - # nothing matched). - -## As we also said before, it has array indexing: -say $/[0]; #=> ｢ABC｣ ｢ABC｣ - # These weird brackets are `Match` objects. - # Here, we have an array of these. -say $0; # The same as above. - -## Our capture is `$0` because it's the first and only one capture in the -## regexp. You might be wondering why it's an array, and the answer is simple: -## Some capture (indexed using `$0`, `$/[0]` or a named one) will be an array -## IFF it can have more than one element -## (so, with `*`, `+` and `**` (whatever the operands), but not with `?`). -## Let's use examples to see that: - -## 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. -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. -so 'foobar' ~~ / foo ( "A" "B" "C" )? bar /; #=> True -say $0.WHAT; #=> (Any) - # This capture did not match, so it's empty -so 'foobar' ~~ / foo ( "A" "B" "C" ) ** 0..1 bar /; # `True` -say $0.WHAT; #=> (Array) - # A specific quantifier will always capture an Array, - # may it be a range or a specific value (even 1). - -## The captures are indexed per nesting. This means a group in a group will be -## nested under its parent group: `$/[0][0]`, for this code: -'hello-~-world' ~~ / ( 'hello' ( <[ \- \~ ]> + ) ) 'world' /; -say $/[0].Str; #=> hello~ -say $/[0][0].Str; #=> ~ - -## This stems from a very simple fact: `$/` does not contain strings, integers -## or arrays, it only contains match objects. These contain the `.list`, `.hash` -## and `.Str` methods. (but you can also just use `match<key>` for hash access -## and `match[idx]` for array access) -say $/[0].list.perl; #=> (Match.new(...),).list - # We can see it's a list of Match objects. Those contain - # a bunch of infos: where the match started/ended, - # the "ast" (see actions later), etc. - # You'll see named capture below with grammars. - -## Alternatives - the `or` of regexps -## WARNING: They are DIFFERENT from PCRE regexps. -so 'abc' ~~ / a [ b | y ] c /; # `True`. Either "b" or "y". -so 'ayc' ~~ / a [ b | y ] c /; # `True`. Obviously enough ... - -## The difference between this `|` and the one you're used to is LTM. -## LTM means "Longest Token Matching". This means that the engine will always -## try to match as much as possible in the strng -'foo' ~~ / fo | foo /; # `foo`, because it's longer. -## To decide which part is the "longest", it first splits the regex in -## two parts: -## The "declarative prefix" (the part that can be statically analyzed) -## and the procedural parts. -## Declarative prefixes include alternations (`|`), conjunctions (`&`), -## sub-rule calls (not yet introduced), literals, characters classes and -## quantifiers. -## The latter include everything else: back-references, code assertions, -## and other things that can't traditionnaly be represented by normal regexps. -## -## Then, all the alternatives are tried at once, and the longest wins. -## 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 `||` -'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` -sub MAIN($name) { say "Hello, $name !" } -## This produces: -## $ perl6 cli.pl -## Usage: -## t.pl <name> - -## And since it's a regular Perl 6 sub, you can haz multi-dispatch: -## (using a "Bool" for the named argument so that we can do `--replace` -## instead of `--replace=1`) -subset File of Str where *.IO.d; # convert to IO object to check the file exists - -multi MAIN('add', $key, $value, Bool :$replace) { ... } -multi MAIN('remove', $key) { ... } -multi MAIN('import', File, Str :$as) { ... } # omitting parameter name -## This produces: -## $ perl6 cli.pl -## Usage: -## t.pl [--replace] add <key> <value> -## t.pl remove <key> -## t.pl [--as=<Str>] import (File) -## As you can see, this is *very* powerful. -## It even went as far as to show inline the constants. -## (the type is only displayed if the argument is `$`/is named) -``` - -## APPENDIX A: -### List of things - -```perl6 -## It's considered by now you know the Perl6 basics. -## This section is just here to list some common operations, -## but which are not in the "main part" of the tutorial to bloat it up - -## Operators - - -## * Sort comparison -## They return one value of the `Order` enum : `Less`, `Same` and `More` -## (which numerify to -1, 0 or +1). -1 <=> 4; # sort comparison for numerics -'a' leg 'b'; # sort comparison for string -$obj eqv $obj2; # sort comparison using eqv semantics - -## * Generic ordering -3 before 4; # True -'b' after 'a'; # True - -## * Short-circuit default operator -## Like `or` and `||`, but instead returns the first *defined* value : -say Any // Nil // 0 // 5; #=> 0 - -## * Short-circuit exclusive or (XOR) -## Returns `True` if one (and only one) of its arguments is true -say True ^^ False; #=> True -## * Flip Flop -## The flip flop operators (`ff` and `fff`, equivalent to P5's `..`/`...`). -## are operators that take two predicates to test: -## They are `False` until their left side returns `True`, then are `True` until -## their right side returns `True`. -## Like for ranges, you can exclude the iteration when it became `True`/`False` -## by using `^` on either side. -## Let's start with an example : -for <well met young hero we shall meet later> { - # by default, `ff`/`fff` smart-match (`~~`) against `$_`: - if 'met' ^ff 'meet' { # Won't enter the if for "met" - # (explained in details below). - .say - } - - if rand == 0 ff rand == 1 { # compare variables other than `$_` - say "This ... probably will never run ..."; - } -} -## This will print "young hero we shall meet" (excluding "met"): -## the flip-flop will start returning `True` when it first encounters "met" -## (but will still return `False` for "met" itself, due to the leading `^` -## on `ff`), until it sees "meet", which is when it'll start returning `False`. - -## The difference between `ff` (awk-style) and `fff` (sed-style) is that -## `ff` will test its right side right when its left side changes to `True`, -## and can get back to `False` right away -## (*except* it'll be `True` for the iteration that matched) - -## While `fff` will wait for the next iteration to -## try its right side, once its left side changed: -.say if 'B' ff 'B' for <A B C B A>; #=> B B - # because the right-hand-side was tested - # directly (and returned `True`). - # "B"s are printed since it matched that - # time (it just went back to `False` - # right away). -.say if 'B' fff 'B' for <A B C B A>; #=> B C B - # The right-hand-side wasn't tested until - # `$_` became "C" - # (and thus did not match instantly). - -## A flip-flop can change state as many times as needed: -for <test start print it stop not printing start print again stop not anymore> { - .say if $_ eq 'start' ^ff^ $_ eq 'stop'; # exclude both "start" and "stop", - #=> "print 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 -} - - -## - `===` is value identity and uses `.WHICH` on the objects to compare them -## - `=:=` is container identity and uses `VAR()` on the objects to compare them - -``` - -If you want to go further, you can: - - - Read the [Perl 6 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. |