diff options
| author | Luis F. Uceta <uzluisf@users.noreply.github.com> | 2019-12-07 13:03:36 -0500 |
|---|---|---|
| committer | ven <vendethiel@hotmail.fr> | 2019-12-07 19:03:36 +0100 |
| commit | 6688d18f61fd0e54ef2513cc2c9f0c7b336cf799 (patch) | |
| tree | ba93861a5d79f6cedb812fbc675a970dce8c63f4 /raku.html.markdown | |
| parent | 7b8042992513386cc77008cb38bc5682243e4759 (diff) | |
Add changes regarding rename and more: (#3758)
- Replace mentions of Perl 6 with Raku
(See https://github.com/perl6/problem-solving/blob/master/solutions/language/Path-to-Raku.md)
- Document's sections is now part of the resulting raku file
- The resulting Raku file can now be executed without runtime/compile-time
errors
- Some examples had minor updates or fixes
- Update links, extensions and commands.
Diffstat (limited to 'raku.html.markdown')
| -rw-r--r-- | raku.html.markdown | 2412 |
1 files changed, 2412 insertions, 0 deletions
diff --git a/raku.html.markdown b/raku.html.markdown new file mode 100644 index 00000000..4f397589 --- /dev/null +++ b/raku.html.markdown @@ -0,0 +1,2412 @@ +--- +category: language +language: Raku +filename: learnraku.raku +contributors: + - ["vendethiel", "http://github.com/vendethiel"] + - ["Samantha McVey", "https://cry.nu"] +--- + +Raku (formerly Perl 6) is a highly capable, feature-rich programming language +made for at least the next hundred years. + +The primary Raku compiler is called [Rakudo](http://rakudo.org), which runs on +the JVM and the [MoarVM](http://moarvm.com). + +Meta-note: + +* Although the pound sign (`#`) is used for sentences and notes, Pod-styled + comments (more below about them) are used whenever it's convenient. +* `# OUTPUT:` is used to represent the output of a command to any standard + stream. If the output has a newline, it's represented by the `` symbol. + The output is always enclosed by angle brackets (`«` and `»`). +* `#=>` represents the value of an expression, return value of a sub, etc. + In some cases, the value is accompanied by a comment. +* Backticks are used to distinguish and highlight the language constructs + from the text. + +```perl6 +#################################################### +# 0. Comments +#################################################### + +# Single line comments start with a pound sign. + +#`( Multiline comments use #` and a quoting construct. + (), [], {}, 「」, etc, will work. +) + +=for comment +Use the same syntax for multiline comments to embed comments. +for #`(each element in) @array { + put #`(or print element) $_ #`(with newline); +} + +# You can also use Pod-styled comments. For example: + +=comment This is a comment that extends until an empty +newline is found. + +=comment +The comment doesn't need to start in the same line as the directive. + +=begin comment +This comment is multiline. + +Empty newlines can exist here too! +=end comment + +#################################################### +# 1. Variables +#################################################### + +# In Raku, you declare a lexical variable using the `my` keyword: +my $variable; + +# Raku has 3 basic types of variables: scalars, arrays, and hashes. + +# +# 1.1 Scalars +# + +# Scalars represent a single value. They start with the `$` sigil: +my $str = 'String'; + +# Double quotes allow for interpolation (which we'll see later): +my $str2 = "$str"; + +# 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 Raku'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 `?`. + +# +# 1.2 Arrays and Lists +# + +# 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>; +# In the previous statement, we use the quote-words (`<>`) term for array +# of words, delimited by space. Similar to perl5's qw, or Ruby's %w. + +@array = 1, 2, 4; + +# Array indices start at 0. Here the third element is being accessed. +say @array[2]; # OUTPUT: «4» + +say "Interpolate an array using []: @array[]"; +# OUTPUT: «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; # OUTPUT: «a 6 b» + +# +# 1.3 Hashes, or key-value Pairs. +# + +=begin comment +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. +=end comment +my %hash = 'a' => 1, 'b' => 2; + +# Keys get auto-quoted when the fat comman (`=>`) is used. Trailing commas are +# okay. +%hash = a => 1, b => 2, ; + +# Even though hashes are internally stored differently than arrays, +# Raku 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 = :n(2), # equivalent to `n => 2` + :is-even, # equivalent to `:is-even(True)` or `is-even => True` + :!is-odd, # equivalent to `:is-odd(False)` or `is-odd => False` +; +# The `:` (as in `:is-even`) and `:!` (as `:!is-odd`) constructs are known +# as the `True` and `False` shortcuts respectively. + +=begin comment +As demonstrated in the example below, you can use {} to get the value from a key. +If it's a string without spaces, you can actually use the quote-words operator +(`<>`). Since Raku doesn't have barewords, as Perl does, `{key1}` doesn't work +though. +=end comment +say %hash{'n'}; # OUTPUT: «2», gets value associated to key 'n' +say %hash<is-even>; # OUTPUT: «True», gets value associated to key 'is-even' + +#################################################### +# 2. Subroutines +#################################################### + +# 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 expression can be omitted. +sub return-value { 5 } +say return-value; # OUTPUT: «5» + +sub return-empty { } +say return-empty; # OUTPUT: «Nil» + +# Some control flow structures produce a value, for instance `if`: +sub return-if { + if True { "Truthy" } +} +say return-if; # OUTPUT: «Truthy» + +# Some don't, like `for`: +sub return-for { + for 1, 2, 3 { 'Hi' } +} +say return-for; # OUTPUT: «Nil» + +=begin comment +Positional arguments are required by default. To make them optional, use +the `?` after the parameters' names. + +In the following example, the sub `with-optional` returns `(Any)` (Perl's +null-like value) if no argument is passed. Otherwise, it returns its argument. +=end comment +sub with-optional( $arg? ) { + $arg; +} +with-optional; # returns Any +with-optional(); # returns Any +with-optional(1); # returns 1 + +=begin comment +You can also give provide a default value when they're not passed. Doing +this make said parameter optional. Required parameters must come before +optional ones. + +In the sub `greeting`, the parameter `$type` is optional. +=end comment +sub greeting( $name, $type = "Hello" ) { + say "$type, $name!"; +} + +greeting("Althea"); # OUTPUT: «Hello, Althea!» +greeting("Arthur", "Good morning"); # OUTPUT: «Good morning, Arthur!» + +=begin comment +You can also, by using a syntax akin to the one of hashes (yay unified syntax!), +declared named parameters and thus pass named arguments to a subroutine. +By default, named parameter are optional and will default to `Any`. +=end comment +sub with-named( $normal-arg, :$named ) { + say $normal-arg + $named; +} +with-named(1, named => 6); # OUTPUT: «7» + +=begin comment +There's one gotcha to be aware of, here: If you quote your key, Raku +won't be able to see it at compile time, and you'll have a single `Pair` +object as a positional parameter, which means the function subroutine +`with-named(1, 'named' => 6);` fails. +=end comment +with-named(2, :named(5)); # OUTPUT: «7» + +# Similar to positional parameters, you can provide your named arguments with +# default values. +sub named-def( :$def = 5 ) { + say $def; +} +named-def; # OUTPUT: «5» +named-def(def => 15); # OUTPUT: «15» + +=begin comment +In order to make a named parameter mandatory, you can append `!` to the +parameter. This is the inverse of `?`, which makes a required parameter +optional. +=end comment + +sub with-mandatory-named( :$str! ) { + say "$str!"; +} +with-mandatory-named(str => "My String"); # OUTPUT: «My String!» +# with-mandatory-named; # runtime error: "Required named parameter not passed" +# with-mandatory-named(3);# runtime error: "Too many positional parameters passed" + +=begin comment +If a sub takes a named boolean argument, you can use the same "short boolean" +hash syntax we discussed earlier. +=end comment +sub takes-a-bool( $name, :$bool ) { + say "$name takes $bool"; +} +takes-a-bool('config', :bool); # OUTPUT: «config takes True» +takes-a-bool('config', :!bool); # OUTPUT: «config takes False» + +=begin comment +Since paranthesis can be omitted when calling a subroutine, you need to use +`&` in order to distinguish between a call to a sub with no arguments and +the code object. + +For instance, in this example we must use `&` to store the sub `say-hello` +(i.e., the sub's code object) in a variable, not a subroutine call. +=end comment +my &s = &say-hello; +my &other-s = sub { say "Anonymous function!" } + +=begin comment +A sub can have a "slurpy" parameter, or what one'd call a +"doesn't-matter-how-many" parameter. This is Raku's way of supporting variadic +functions. For this, you must use `*@` (slurpy) which will "take everything +else". You can have as many parameters *before* a slurpy one, but not *after*. +=end comment +sub as-many($head, *@rest) { + @rest.join(' / ') ~ " !"; +} +say as-many('Happy', 'Happy', 'Birthday'); # OUTPUT: «Happy / Birthday !» +say 'Happy', ['Happy', 'Birthday'], 'Day'; # OUTPUT: «Happy / Birthday / Day !» + +# Note that the splat (the *) did not consume the parameter before it. + +=begin comment +There are other two variations of slurpy parameters in Raku. The previous one +(namely, `*@`), known as flattened slurpy, flattens passed arguments. The other +two are `**@` and `+@` known as unflattened slurpy and "single argument rule" +slurpy respectively. The unflattened slurpy doesn't flatten its listy +arguments (or Iterable ones). +=end comment +sub b(**@arr) { @arr.perl.say }; +b(['a', 'b', 'c']); # OUTPUT: «[["a", "b", "c"],]» +b(1, $('d', 'e', 'f'), [2, 3]); # OUTPUT: «[1, ("d", "e", "f"), [2, 3]]» +b(1, [1, 2], ([3, 4], 5)); # OUTPUT: «[1, [1, 2], ([3, 4], 5)]» + +=begin comment +On the other hand, the "single argument rule" slurpy follows the "single argument +rule" which dictates how to handle the slurpy argument based upon context and +roughly states that if only a single argument is passed and that argument is +Iterable, that argument is used to fill the slurpy parameter array. In any +other case, `+@` works like `**@`. +=end comment +sub c(+@arr) { @arr.perl.say }; +c(['a', 'b', 'c']); # OUTPUT: «["a", "b", "c"]» +c(1, $('d', 'e', 'f'), [2, 3]); # OUTPUT: «[1, ("d", "e", "f"), [2, 3]]» +c(1, [1, 2], ([3, 4], 5)); # OUTPUT: «[1, [1, 2], ([3, 4], 5)]» + +=begin comment +You can call a function with an array using the "argument list flattening" +operator `|` (it's not actually the only role of this operator, +but it's one of them). +=end comment +sub concat3($a, $b, $c) { + say "$a, $b, $c"; +} +concat3(|@array); # OUTPUT: «a, b, c» + # `@array` got "flattened" as a part of the argument list + +#################################################### +# 3. Containers +#################################################### + +=begin comment +In Raku, 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. +=end comment +sub mutate( $n is rw ) { + $n++; # postfix ++ operator increments its argument but returns its old value +} +my $m = 42; +mutate $m; #=> 42, the value is incremented but the old value is returned +say $m; # OUTPUT: «43» + +=begin comment +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 +=end comment + +=begin comment +Similar error would be obtained, if a bound variable is passed to +to the subroutine. In Raku, you bind a value to a variable using the binding +operator `:=`. +=end comment +my $v := 50; # binding 50 to the variable $v +# mutate $v; # Parameter '$n' expected a writable container, but got Int value + +=begin comment +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 without modifying the passed argument. + +A sub itself returns a container, which means it can be marked as `rw`. +Alternatively, you can explicitly mark the returned container as mutable +by using `return-rw` instead of `return`. +=end comment +my $x = 42; +my $y = 45; +sub x-store is rw { $x } +sub y-store { return-rw $y } + +# In this case, the parentheses are mandatory or else Raku thinks that +# `x-store` and `y-store` are identifiers. +x-store() = 52; +y-store() *= 2; + +say $x; # OUTPUT: «52» +say $y; # OUTPUT: «90» + +#################################################### +# 4.Control Flow Structures +#################################################### + +# +# 4.1 if/if-else/if-elsif-else/unless +# + +=begin comment +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`, `Int`, etc.) and +of course, `False` itself. Any other value is truthy. +=end comment +my $number = 5; +if $number < 5 { + say "Number is less than 5" +} +elsif $number == 5 { + say "Number is equal to 5" +} +else { + say "Number is greater than 5" +} + +unless False { + say "It's not false!"; +} + +# `unless` is the equivalent of `if not (X)` which inverts the sense of a +# conditional statement. However, you cannot use `else` or `elsif` with it. + +# 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 'It's true';` doesn't work. + +# You can also use their statement modifier (postfix) versions: +say "Quite truthy" if True; # OUTPUT: «Quite truthy» +say "Quite falsey" unless False; # OUTPUT: «Quite falsey» + +=begin comment +The ternary operator (`??..!!`) is structured as follows `condition ?? +expression1 !! expression2` and it returns expression1 if the condition is +true. Otherwise, it returns expression2. +=end comment +my $age = 30; +say $age > 18 ?? "You are an adult" !! "You are under 18"; +# OUTPUT: «You are an adult» + +# +# 4.2 with/with-else/with-orwith-else/without +# + +=begin comment +The `with` statement is like `if`, but it tests for definedness rather than +truth, and it topicalizes on the condition, much like `given` which will +be discussed later. +=end comment +my $s = "raku"; +with $s.index("r") { say "Found a at $_" } +orwith $s.index("k") { say "Found c at $_" } +else { say "Didn't find r or k" } + +# Similar to `unless` that checks un-truthiness, you can use `without` to +# check for undefined-ness. +my $input01; +without $input01 { + say "No input given." +} +# OUTPUT: «No input given.» + +# There are also statement modifier versions for both `with` and `without`. +my $input02 = 'Hello'; +say $input02 with $input02; # OUTPUT: «Hello» +say "No input given." without $input02; + +# +# 4.3 given/when, or Raku's switch construct +# + +=begin comment +`given...when` looks like other languages' `switch`, but is much more +powerful thanks to smart matching and Raku's "topic variable", `$_`. + +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 Raku constructs use this variable (as said before, like `for`, +blocks, `with` statement etc), this means the powerful `when` is not only +applicable along with a `given`, but instead anywhere a `$_` exists. +=end comment + +given "foo bar" { + say $_; # OUTPUT: «foo bar» + + # Don't worry about smart matching yet. Just know `when` uses it. This is + # equivalent to `if $_ ~~ /foo/`. + when /foo/ { + say "Yay !"; + } + + # smart matching anything with `True` is `True`, i.e. (`$a ~~ True`) + # so you can also put "normal" conditionals. For example, this `when` is + # equivalent to this `if`: `if $_ ~~ ($_.chars > 50) {...}` + # which means: `if $_.chars > 50 {...}` + when $_.chars > 50 { + say "Quite a long string !"; + } + + # same as `when *` (using the Whatever Star) + default { + say "Something else" + } +} + +# +# 4.4 Looping constructs +# + +# The `loop` construct 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; +} +# In the previous example, `last` breaks out of the loop very much +# like the `break` keyword in other languages. + +# The `next` keyword skips to the next iteration, like `continue` in other +# languages. Note that you can also use postfix conditionals, loops, etc. +loop (my $i = 0; $i < 5; $i++) { + next if $i == 3; + say "This is a C-style for loop!"; +} + +# The `for` constructs iterates over a list of elements. +my @odd-array = 1, 3, 5, 7, 9; + +# Accessing the array's elements with the topic variable $_. +for @odd-array { + say "I've got $_ !"; +} + +# Accessing the array's elements with a "pointy block", `->`. +# Here each element is read-only. +for @odd-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 @odd-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 @odd-array { + say "I've got $_"; + + # This is also allowed. A dot call with no "topic" (receiver) is sent to + # `$_` (topic variable) by default. + .say; + + # This is equivalent to the above statement. + $_.say; +} + +for @odd-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 Raku. +sub long-computation { "Finding factors of large primes" } +if long-computation() -> $result { + say "The result is $result."; +} + +#################################################### +# 5. Operators +#################################################### + +=begin comment +Since Perl languages are very much operator-based languages, Raku +operators are actually just funny-looking subroutines, in syntactic +categories, like infix:<+> (addition) or prefix:<!> (bool not). + +The categories are: + - "prefix": before (like `!` in `!True`). + - "postfix": after (like `++` in `$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! +=end comment + +# +# 5.1 Equality Checking +# + +# `==` is numeric comparison +say 3 == 4; # OUTPUT: «False» +say 3 != 4; # OUTPUT: «True» + +# `eq` is string comparison +say 'a' eq 'b'; # OUTPUT: «False» +say 'a' ne 'b'; # OUTPUT: «True», not equal +say 'a' !eq 'b'; # OUTPUT: «True», same as above + +# `eqv` is canonical equivalence (or "deep equality") +say (1, 2) eqv (1, 3); # OUTPUT: «False» +say (1, 2) eqv (1, 2); # OUTPUT: «True» +say Int === Int; # OUTPUT: «True» + +# `~~` is the smart match operator which aliases the left hand side to $_ and +# then evaluates the right hand side. +# Here are some common comparison semantics: + +# String or numeric equality +say 'Foo' ~~ 'Foo'; # OUTPU: «True», if strings are equal. +say 12.5 ~~ 12.50; # OUTPU: «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; # OUTPUT: «｢a｣» +say $obj.WHAT; # OUTPUT: «(Match)» + +# Hashes +say 'key' ~~ %hash; # OUTPUT:«True», if key exists in hash. + +# Type - Checks if left side "is of type" (can check superclasses and roles). +say 1 ~~ Int; # OUTPUT: «True» + +# Smart-matching against a boolean always returns that boolean (and will warn). +say 1 ~~ True; # OUTPUT: «True», smartmatch against True always matches +say False.so ~~ True; # OUTPUT: «True», use .so for truthiness + +# General syntax is `$arg ~~ &bool-returning-function;`. For a complete list +# of combinations, refer to the table at: +# https://docs.raku.org/language/operators#index-entry-smartmatch_operator + +# Of course, you also use `<`, `<=`, `>`, `>=` for numeric comparison. +# Their string equivalent are also available: `lt`, `le`, `gt`, `ge`. +say 3 > 4; # OUTPUT: «False» +say 3 >= 4; # OUTPUT: «False» +say 3 < 4; # OUTPUT: «True» +say 3 <= 4; # OUTPUT: «True» +say 'a' gt 'b'; # OUTPUT: «False» +say 'a' ge 'b'; # OUTPUT: «False» +say 'a' lt 'b'; # OUTPUT: «True» +say 'a' le 'b'; # OUTPUT: «True» + +# +# 5.2 Range constructor +# + +say 3 .. 7; # OUTPUT: «3..7», both included. +say 3 ..^ 7; # OUTPUT: «3..^7», exclude right endpoint. +say 3 ^.. 7; # OUTPUT: «3^..7», exclude left endpoint. +say 3 ^..^ 7; # OUTPUT: «3^..^7», exclude both endpoints. + +# The range 3 ^.. 7 is similar like 4 .. 7 when we only consider integers. +# But when we consider decimals: + +say 3.5 ~~ 4 .. 7; # OUTPUT: «False» +say 3.5 ~~ 3 ^.. 7; # OUTPUT: «True», + +# This is because the range `3 ^.. 7` only excludes anything strictly +# equal to 3. Hence, it contains decimals greater than 3. This could +# mathematically be described as 3.5 ∈ (3,7] or in set notation, +# 3.5 ∈ { x | 3 < x ≤ 7 }. + +say 3 ^.. 7 ~~ 4 .. 7; # OUTPUT: «False» + +# This also works as a shortcut for `0..^N`: +say ^10; # OUTPUT: «^10», which means 0..^10 + +# This also allows us to demonstrate that Raku has lazy/infinite arrays, +# using the Whatever Star: +my @natural = 1..*; # 1 to Infinite! Equivalent to `1..Inf`. + +# You can pass ranges as subscripts and it'll return an array of results. +say @natural[^10]; # OUTPUT: «1 2 3 4 5 6 7 8 9 10», doesn't run out of memory! + +=begin comment +NOTE: when reading an infinite list, Raku 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. +=end comment + +# An array subscript can also be a closure. It'll be called with the array's +# length as the argument. The following two examples are equivalent: +say join(' ', @array[15..*]); # OUTPUT: «15 16 17 18 19» +say join(' ', @array[-> $n { 15..$n }]); # OUTPUT: «15 16 17 18 19» + +# 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; + +# In this example, even though the sequence is infinite, only the 15 +# needed values will be calculated. +@numbers[5..*] = 3, 9 ... *; +say @numbers; # OUTPUT: «0 1 2 3 4 3 9 15 21 [...] 81 87», only 20 values + +# +# 5.3 and (&&), or (||) +# + +# Here `and` calls `.Bool` on both 3 and 4 and gets `True` so it returns +# 4 since both are `True`. +say (3 and 4); # OUTPUT: «4», which is truthy. +say (3 and 0); # OUTPUT: «0» +say (0 and 4); # OUTPUT: «0» + +# Here `or` calls `.Bool` on `0` and `False` which are both `False` +# so it returns `False` since both are `False`. +say (0 or False); # OUTPUT: «False». + +# Both `and` and `or` have tighter versions which also shortcut circuits. +# They're `&&` and `||` respectively. + +# `&&` returns the first operand that evaluates to `False`. Otherwise, +# it returns the last operand. +my ($a, $b, $c, $d, $e) = 1, 0, False, True, 'pi'; +say $a && $b && $c; # OUTPUT: «0», the first falsey value +say $a && $b && $c; # OUTPUT: «False», the first falsey value +say $a && $d && $e; # OUTPUT: «pi», last operand since everthing before is truthy + +# `||` returns the first argument that evaluates to `True`. +say $b || $a || $d; # OUTPUT: «1» +say $e || $d || $a; # OUTPUT: «pi» + +# And because you're going to want them, you also have compound assignment +# operators: +$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 = $d mod 4; +@array .= sort; # calls the `sort` method and assigns the result back + +#################################################### +# 6. More on subs! +#################################################### + +# As we said before, Raku has *really* powerful subs. We're going +# to see a few more key concepts that make them better than in any +# other language :-). + +# +# 6.1 Unpacking! +# + +# Unpacking is the ability to "extract" arrays and keys +# (AKA "destructuring"). It'll work in `my`s and in parameter lists. +my ($f, $g) = 1, 2; +say $f; # OUTPUT: «1» +my ($, $, $h) = 1, 2, 3; # keep the non-interesting values anonymous (`$`) +say $h; # OUTPUT: «3» + +my ($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 $snd! All in all, I'm @array[]."; + # (^ remember the `[]` to interpolate the array) +} +unpack_array(@tail); +# OUTPUT: «My first is 3, my second is 3! All in all, I'm 2 3.» + +# If you're not using the array itself, you can also keep it anonymous, +# much like a scalar: +sub first-of-array( @ [$fst] ) { $fst } +first-of-array(@small); #=> 1 + +# However calling `first-of-array(@tail);` will throw an error ("Too many +# positional parameters passed"), which means the `@tail` has too many +# elements. + +# You can also use a slurpy parameter. You could keep `*@rest` anonymous +# Here, `@rest` is `(3,)`, since `$fst` holds the `2`. This results +# since the length (.elems) of `@rest` is 1. +sub slurp-in-array(@ [$fst, *@rest]) { + say $fst + @rest.elems; +} +slurp-in-array(@tail); # OUTPUT: «3» + +# You could even extract on a slurpy (but it's pretty useless ;-).) +sub fst(*@ [$fst]) { # or simply: `sub fst($fst) { ... }` + say $fst; +} +fst(1); # OUTPUT: «1» + +# Calling `fst(1, 2);` will throw an error ("Too many positional parameters +# passed") though. After all, the `fst` sub declares only a single positional +# parameter. + +=begin comment +You can also destructure hashes (and classes, which you'll learn about later). +The syntax is basically the same as +`%hash-name (:key($variable-to-store-value-in))`. +The hash can stay anonymous if you only need the values you extracted. + +In order to call the function, you must supply a hash wither created with +curly braces or with `%()` (recommended). Alternatively, you can pass +a variable that contains a hash. +=end comment + +sub key-of( % (:value($val), :qua($qua)) ) { + say "Got value $val, $qua time" ~~ + $qua == 1 ?? '' !! 's'; +} + +my %foo-once = %(value => 'foo', qua => 1); +key-of({value => 'foo', qua => 2}); # OUTPUT: «Got val foo, 2 times.» +key-of(%(value => 'foo', qua => 0)); # OUTPUT: «Got val foo, 0 times.» +key-of(%foo-once); # OUTPUT: «Got val foo, 1 time.» + +# 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 + +=begin comment +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: +=end comment + +sub list-of( $n ) { + do for ^$n { $_ } +} +my @list3 = list-of(3); #=> (0, 1, 2) + +# +# 6.2 Lambdas (or anonymous subroutines) +# + +# You can create a lambda by using a pointy block (`-> {}`), a +# block (`{}`) or creating a `sub` without a name. + +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 $argument" +} + +=begin comment +Both pointy blocks and blocks are pretty much the same thing, except that +the former can take arguments, and that the latter can be mistaken as +a hash by the parser. That being said, blocks can declare what's known +as placeholders parameters through the twigils `$^` (for positional +parameters) and `$:` (for named parameters). More on them latern on. +=end comment + +my &mult = { $^numbers * $:times } +say mult 4, :times(6); #=> «24» + +# Both pointy blocks and blocks are quite versatile when working with functions +# that accepts other functions such as `map`, `grep`, etc. For example, +# we add 3 to each value of an array using the `map` function with a lambda: +my @nums = 1..4; +my @res1 = map -> $v { $v + 3 }, @nums; # pointy block, explicit parameter +my @res2 = map { $_ + 3 }, @nums; # block using an implicit parameter +my @res3 = map { $^val + 3 }, @nums; # block with placeholder parameter + +=begin comment +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. +=end comment + +# Compare: +sub is-in( @array, $elem ) { + say map({ return True if $_ == $elem }, @array); + say 'Hi'; +} + +# with: +sub truthy-array( @array ) { + say map sub ($i) { $i ?? return True !! return False }, @array; + say 'Hi'; +} + +=begin comment +In the `is-in` sub, the block will `return` out of the `is-in` sub once the +condition evaluates to `True`, the loop won't be run anymore and the +following statement won't be executed. The last statement is only executed +if the block never returns. + +On the contrary, the `truthy-array` sub will produce an array of `True` and +`False`, which will printed, and always execute the last execute statement. +Thus, the `return` only returns from the anonymous `sub` +=end comment + +=begin comment +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. +=end comment +my $anon-sum = anon sub summation(*@a) { [+] @a } +say $anon-sum.name; # OUTPUT: «summation» +say $anon-sum(2, 3, 5); # OUTPUT: «10» +#say summation; # Error: Undeclared routine: ... + +# You can also use the Whatever Star to create an anonymous subroutine. +# (it'll stop at the furthest operator in the current expression). +# The following is the same as `{$_ + 3 }`, `-> { $a + 3 }`, +# `sub ($a) { $a + 3 }`, or even `{$^a + 3}` (more on this later). +my @arrayplus3v0 = map * + 3, @nums; + +# The following is the same as `-> $a, $b { $a + $b + 3 }`, +# `sub ($a, $b) { $a + $b + 3 }`, or `{ $^a + $^b + 3 }` (more on this later). +my @arrayplus3v1 = map * + * + 3, @nums; + +say (*/2)(4); # OUTPUT: «2», immediately execute the Whatever function created. +say ((*+3)/5)(5); # OUTPUT: «1.6», it works even in parens! + +# But if you need to have more than one argument (`$_`) in a block (without +# wanting to resort to `-> {}`), you can also either `$^` and `$:` which +# declared placeholder parameters or self-declared positional/named parameters. +say map { $^a + $^b + 3 }, @nums; + +# which is equivalent to the following which uses a `sub`: +map sub ($a, $b) { $a + $b + 3 }, @nums; + +# Placeholder parameters are sorted lexicographically so the following two +# statements are equivalent: +say sort { $^b <=> $^a }, @nums; +say sort -> $a, $b { $b <=> $a }, @nums; + +# +# 6.3 Multiple Dispatch +# + +# Raku 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"; # OUTPUT: «String: foo» +sayit 25; # OUTPUT: «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 +multi is-big(Int $) { "No" } + +subset Even of Int where * %% 2; +multi odd-or-even(Even) { "Even" } # Using the type. We don't name the argument. +multi odd-or-even($) { "Odd" } # "everything 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."; +} + +=begin comment +This is very, very useful for many purposes, like `MAIN` subs (covered +later), and even the language itself uses it in several places. + +For example, the `is` trait is actually a `multi sub` named `trait_mod:<is>`, +and it works off that. Thus, `is rw`, is simply a dispatch to a function with +this signature `sub trait_mod:<is>(Routine $r, :$rw!) {}` +=end comment + +#################################################### +# 7. About types... +#################################################### + +=begin comment +Raku 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. +=end comment +subset VeryBigInteger of Int where * > 500; + +# Or the set of the whole numbers: +subset WholeNumber of Int where * >= 0; +my WholeNumber $whole-six = 6; # OK +#my WholeNumber $nonwhole-one = -1; # Error: type check failed... + +# Or the set of Positive Even Numbers whose Mod 5 is 1. Notice we're +# using the previously defined WholeNumber subset. +subset PENFO of WholeNumber where { $_ %% 2 and $_ mod 5 == 1 }; +my PENFO $yes-penfo = 36; # OK +#my PENFO $no-penfo = 2; # Error: type check failed... + +#################################################### +# 8. Scoping +#################################################### + +=begin comment +In Raku, unlike many scripting languages, (such as Python, Ruby, PHP), +you must declare your variables before using them. The `my` declarator +we've used so far 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. +=end comment + +my $file_scoped = 'Foo'; +sub outer { + my $outer_scoped = 'Bar'; + sub inner { + say "$file_scoped $outer_scoped"; + } + &inner; # return the function +} +outer()(); # OUTPUT: «Foo Bar» + +# As you can see, `$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). + +#################################################### +# 9. Twigils +#################################################### + +=begin comment +There are many special `twigils` (composed sigils) in Raku. Twigils +define a variable's scope. +The `*` and `?` twigils work on standard variables: + * for dynamic variables + ? for compile-time variables + +The `!` and the `.` twigils are used with Raku's objects: + ! for attributes (instance attribute) + . for methods (not really a variable) +=end comment + +# +# `*` 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 { + # Defines $*dyn_scoped_1 only for this sub. + my $*dyn_scoped_1 = 25; + + # Will change the value of the file scoped variable. + $*dyn_scoped_2 = 100; + + # $*dyn_scoped 1 and 2 will be looked for in the call. + say_dyn(); # OUTPUT: «25 100» + + # The call to `say_dyn` 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(); # OUTPUT: «1 10» + +# Uses $*dyn_scoped_1 as defined in `call_say_dyn` even though we are calling it +# from outside. +call_say_dyn(); # OUTPUT: «25 100» + +# We changed the value of $*dyn_scoped_2 in `call_say_dyn` so now its +# value has changed. +say_dyn(); # OUTPUT: «1 100» + +# TODO: Add information about remaining twigils + +#################################################### +# 10. Object Model +#################################################### + +=begin comment +To call a method on an object, add a dot followed by the method name: +`$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: `$!attr`. +Immutable public attributes use the `.` twigil which creates a read-only +method named after the attribute. In fact, declaring an attribute with `.` +is equivalent to declaring the same attribute with `!` and then creating +a read-only method with the attribute's name. However, this is done for us +by Raku automatically. The easiest way to remember the `$.` twigil is +by comparing it to how methods are called. + +Raku'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.raku.org/language/objects.html. +=end comment + +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 born in $!bcountry and now lives in $!ccountry." + } + + # This method is public, just like `birthday` and `get-age`. + method get-info { + # Invoking a method on `self` inside the class. + # Use `self!priv-method` for private method. + say self!do-decoration; + + # Use `self.public-method` for public method. + say "Age: ", self.get-age; + } +}; + +# Create a new instance of Human class. +# NOTE: Only attributes declared with the `.` twigil can be set via the +# default constructor (more later on). This constructor only accepts named +# arguments. +my $person1 = Human.new( + name => "Jord", + bcountry => "Togo", + ccountry => "Togo" +); + +# Make human 10 years old. +$person1.birthday for 1..10; + +say $person1.name; # OUTPUT: «Jord» +say $person1.bcountry; # OUTPUT: «Togo» +say $person1.ccountry; # OUTPUT: «Togo» +say $person1.get-age; # OUTPUT: «10» + +# This fails, because the `has $.bcountry`is immutable. Jord can't change +# his birthplace. +# $person1.bcountry = "Mali"; + +# This works because the `$.ccountry` is mutable (`is rw`). Now Jord's +# current country is France. +$person1.ccountry = "France"; + +# Calling methods on the instance objects. +$person1.birthday; #=> 1 +$person1.get-info; #=> Jord born in Togo and now lives in France. Age: 10 +# $person1.do-decoration; # This fails since the method `do-decoration` is private. + +# +# 10.1 Object Inheritance +# + +=begin comment +Raku 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. +=end comment + +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; # OUTPUT: «My favorite color is Blue» +$Richard.talk; # OUTPUT: «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; # OUTPUT: «Goo goo ga ga», due to the overridden method. +# $Madison.favorite-color # does not work since it is not inherited. + +=begin comment +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). +Thus, `$a .= b` is the same as `$a = $a.b`. Also note that `BUILD` (the method +called inside `new`) will set parent's properties too, so you can pass `val => +5`. +=end comment + +# +# 10.2 Roles, or Mixins +# + +# 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 the `does` keyword: +class Item does PrintableVal { + has $.val; + + =begin comment + 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!): + =end comment + method access { + say $!counter++; + } + + =begin comment + 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. + =end comment +} + +#################################################### +# 11. Exceptions +#################################################### + +=begin comment +Exceptions are built on top of classes, in the package `X` (like `X::IO`). +In Raku, exceptions are automatically 'thrown': + +open 'foo'; # OUTPUT: «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. +=end comment + +# You can throw an exception using `die`. Here it's been commented out to +# avoid stopping the program's execution: +# die 'Error!'; # OUTPUT: «Error!» + +# Or more explicitly (commented out too): +# X::AdHoc.new(payload => 'Error!').throw; # OUTPUT: «Error!» + +=begin comment +In Raku, `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: +=end comment +my $uninitialized; +say $uninitialized.defined; # OUTPUT: «False» + +=begin comment +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 +=end comment +open 'foo' orelse say "Something happened {.exception}"; + +# This also works: +open 'foo' orelse say "Something happened $_"; +# OUTPUT: «Something happened Failed to open file foo: no such file or directory» + +=begin comment +Both of those above work but in case we get an object from the left side +that is not a failure we will probably get a warning. We see below how we +can use try` and `CATCH` to be more specific with the exceptions we catch. +=end comment + +# +# 11.1 Using `try` and `CATCH` +# + +=begin comment +By using `try` and `CATCH` you can contain and handle exceptions without +disrupting the rest of the program. The `try` block will set the last +exception to the special variable `$!` (known as the error variable). +NOTE: This has no relation to $!variables seen inside class definitions. +=end comment + +try open 'foo'; +say "Well, I tried! $!" if defined $!; +# OUTPUT: «Well, I tried! Failed to open file foo: no such file or directory» + +=begin comment +Now, what if we want more control over handling the exception? +Unlike many other languages, in Raku, you put the `CATCH` block *within* +the block to `try`. Similar to how the `$_` 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 {} }`). +=end comment + +try { + my $a = (0 %% 0); + CATCH { + default { say "Something happened: $_" } + } +} +# OUTPUT: «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: $_"; + } + + =begin comment + 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. + =end comment + default { + say "Any other error: $_" + } + } +} +# OUTPUT: «Failed to open file /dir/foo: no such file or directory» + +=begin comment +There are also some subtleties to exceptions. Some Raku 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`). +=end comment + +my $value = 0/0; # We're not trying to access the value, so no problem. +try { + say 'Value: ', $value; # Trying to use the value + CATCH { + default { + say "It threw because we tried to get the fail's value!" + } + } +} + +=begin comment +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). +=end comment + +#################################################### +# 12. Packages +#################################################### + +=begin comment +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. +=end comment + +# 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; # OUTPUT: «[1]» + +=begin comment +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. +=end comment + +# If `Hello` doesn't exist yet, it'll just be a "stub", that can be redeclared +# as something else later. +module Hello::World { # bracketed form + # declarations here +} + +# The file-scoped form which extends until the end of the file. For +# instance, `unit module Parse::Text;` will extend until of the file. + +# A grammar is a package, which you could `use`. You will learn more about +# grammars in the regex section. +grammar Parse::Text::Grammar { +} + +# 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. + +#################################################### +# 13. Declarators +#################################################### + +=begin comment +In Raku, 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. +=end comment + +module Var::Increment { + # NOTE: `our`-declared variables cannot be typed. + our $our-var = 1; + 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; # OUTPUT: «1», this works! +say $Var::Increment::my-var; # OUTPUT: «(Any)», this will not work! + +say Var::Increment::Inc; # OUTPUT: «2» +say Var::Increment::Inc; # OUTPUT: «3», notice how the value of $our-var was retained. + +# Var::Increment::unavailable; # OUTPUT: «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]; # OUTPUT: «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 -> $a { + sub foo { + # This will be a different value for every value of `$a` + state $val = rand; + } + for ^5 -> $b { + # This will print the same value 5 times, but only 5. Next iteration + # will re-run `rand`. + say foo; + } +} + +#################################################### +# 14. Phasers +#################################################### + +=begin comment +Phasers in Raku 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! +=end comment + +# +# 14.1 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" } + +# +# 14.2 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" } + +# +# 14.3 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 (commented out): +for 0..2 { + # PRE { $_ > 1 } # OUTPUT: «Precondition '{ $_ > 1 }' 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."; +} + +# Example (commented out): +for 0..2 { + # POST { $_ < 1 } # OUTPUT: «Postcondition '{ $_ < 1 }' failed +} + +# +# 14.4 Block/exceptions phasers +# +{ + 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)" } +} + +# +# 14.5 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" } +} + +# +# 14.6 Role/class phasers +# +COMPOSE { + say "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: +class DB { + method start-transaction { say "Starting transation!" } + method commit { say "Commiting transaction..." } + method rollback { say "Something went wrong. Rollingback!" } +} + +sub do-db-stuff { + my DB $db .= new; + $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 +} + +do-db-stuff(); + +#################################################### +# 15. Statement prefixes +#################################################### + +=begin comment +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 `}`. + +=end comment + +# +# 15.1 `do` - It 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. With `do`, an `if`, for example, becomes a term returning a value. +=for comment :reason<this fails since `if` is a statement> +my $value = if True { 1 } + +# this works! +my $get-five = do if True { 5 } + +# +# 15.1 `once` - makes sure a piece of code only runs once. +# +for ^5 { + once say 1 +}; +# OUTPUT: «1», only prints ... once + +# Similar to `state`, they're cloned per-scope. +for ^5 { + sub { once say 1 }() +}; +# OUTPUT: «1 1 1 1 1», prints once per lexical scope. + +# +# 15.2 `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; +} +# OUTPUT: «-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. + +# +# 15.3 `eager` - evaluates a statement eagerly (forces eager context). + +# Don't try this at home. This will probably hang for a while (and might crash) +# so commented out. +# eager 1..*; + +# But consider, this version which doesn't print anything +constant thricev0 = gather for ^3 { say take $_ }; +# to: +constant thricev1 = eager gather for ^3 { say take $_ }; # OUTPUT: «0 1 2» + +#################################################### +# 16. Iterables +#################################################### + +# Iterables are objects that can be iterated over for things such as +# the `for` construct. + +# +# 16.1 `flat` - flattens iterables. +# +say (1, 10, (20, 10) ); # OUTPUT: «(1 10 (20 10))», notice how nested + # lists are preserved +say (1, 10, (20, 10) ).flat; # OUTPUT: «(1 10 20 10)», now the iterable is flat + +# +# 16.2 `lazy` - defers actual evaluation until value is fetched by forcing lazy context. +# +my @lazy-array = (1..100).lazy; +say @lazy-array.is-lazy; # OUTPUT: «True», check for laziness with the `is-lazy` method. + +say @lazy-array; # OUTPUT: «[...]», List has not been iterated on! + +# This works and will only do as much work as is needed. +for @lazy-array { .print }; + +# (**TODO** explain that gather/take and map are all lazy) + +# +# 16.3 `sink` - an `eager` that discards the results by forcing sink context. +# +constant nilthingie = sink for ^3 { .say } #=> 0 1 2 +say nilthingie.perl; # OUTPUT: «Nil» + +# +# 16.4 `quietly` - suppresses warnings in blocks. +# +quietly { warn 'This is a warning!' }; # No output + +#################################################### +# 17. More operators thingies! +#################################################### + +# Everybody loves operators! Let's get more of them. + +# The precedence list can be found here: +# https://docs.raku.org/language/operators#Operator_Precedence +# But first, we need a little explanation about associativity: + +# +# 17.1 Binary operators +# + +my ($p, $q, $r) = (1, 2, 3); + +=begin comment +Given some binary operator § (not a Raku-supported operator), then: + +$p § $q § $r; # with a left-associative §, this is ($p § $q) § $r +$p § $q § $r; # with a right-associative §, this is $p § ($q § $r) +$p § $q § $r; # with a non-associative §, this is illegal +$p § $q § $r; # with a chain-associative §, this is ($p § $q) and ($q § $r)§ +$p § $q § $r; # with a list-associative §, this is `infix:<>` +=end comment + +# +# 17.2 Unary operators +# + +=begin comment +Given some unary operator § (not a Raku-supported operator), then: +§$p§ # with left-associative §, this is (§$p)§ +§$p§ # with right-associative §, this is §($p§) +§$p§ # with non-associative §, this is illegal +=end comment + +# +# 17.3 Create your own operators! +# + +=begin comment +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 Raku, all operators are actually just funny-looking subroutines. + +You can declare an operator just like you declare a sub. In the following +example, `prefix` refers to the operator categories (prefix, infix, postfix, +circumfix, and post-circumfix). +=end comment +sub prefix:<win>( $winner ) { + say "$winner Won!"; +} +win "The King"; # OUTPUT: «The King Won!» + +# you can still call the sub with its "full name": +say prefix:<!>(True); # OUTPUT: «False» +prefix:<win>("The Queen"); # OUTPUT: «The Queen Won!» + +sub postfix:<!>( Int $n ) { + [*] 2..$n; # using the reduce meta-operator... See below ;-)! +} +say 5!; # OUTPUT: «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 { + # You need the explicit parentheses to call the function in `$r`, + # else you'd be referring at the code object itself, like with `&r`. + $r(); + } +} +3 times -> { say "hello" }; # OUTPUT: «hellohellohello» + +# It's recommended to put spaces around your infix operator calls. + +# For circumfix and post-circumfix ones +multi circumfix:<[ ]>( Int $n ) { + $n ** $n +} +say [5]; # OUTPUT: «3125» + +# Circumfix means 'around'. Again, no whitespace. + +multi postcircumfix:<{ }>( Str $s, Int $idx ) { + $s.substr($idx, 1); +} +say "abc"{1}; # OUTPUT: «b», after the term `"abc"`, and around the index (1) + +# Post-circumfix is 'after a term, around something' + +=begin comment +This really means a lot -- because everything in Raku uses this. +For example, to delete a key from a hash, you use the `:delete` adverb +(a simple named argument underneath). For instance, the following statements +are equivalent. +=end comment +my %person-stans = + 'Giorno Giovanna' => 'Gold Experience', + 'Bruno Bucciarati' => 'Sticky Fingers'; +my $key = 'Bruno Bucciarati'; +%person-stans{$key}:delete; +postcircumfix:<{ }>( %person-stans, 'Giorno Giovanna', :delete ); +# (you can call operators like this) + +=begin comment +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. +=end comment + +# +# 17.4 Meta operators! +# + +=begin comment +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 first element of a list) and the popped element. +=end comment + +# To sum a list, you could use the reduce meta-operator with `+`, i.e.: +say [+] 1, 2, 3; # OUTPUT: «6», equivalent to (1+2)+3. + +# To multiply a list +say [*] 1..5; # OUTPUT: «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; # OUTPUT: «False» + # (Falsey, but still defined) +# Or with relational operators, i.e., `>` to check elements of a list +# are ordered accordingly: +say [>] 234, 156, 6, 3, -20; # OUTPUT: «True» + +# Default value examples: +say [*] (); # OUTPUT: «1», empty product +say [+] (); # OUTPUT: «0», empty sum +say [//]; # OUTPUT: «(Any)» + # There's no "default value" for `//`. + +# You can also use it with a function you made up, +# You can also surround using double brackets: +sub add($a, $b) { $a + $b } +say [[&add]] 1, 2, 3; # OUTPUT: «6» + +=begin comment +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. +=end comment +say (1, 2) Z (3, 4); # OUTPUT: «((1, 3), (2, 4))» +say 1..3 Z+ 4..6; # OUTPUT: «(5, 7, 9)» + +# 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: + +=begin comment +The sequence operator (`...`) is one of Raku's most powerful features: +It's composed by the list (which might include a closure) you want Raku to +deduce from on the left and a value (or either a predicate or a Whatever Star +for a lazy infinite list) on the right that states when to stop. +=end comment + +# Basic arithmetic sequence +my @listv0 = 1, 2, 3...10; + +# This dies because Raku can't figure out the end +# my @list = 1, 3, 6...10; + +# As with ranges, you can exclude the last element (the iteration ends when +# the predicate matches). +my @listv1 = 1, 2, 3...^10; + +# You can use a predicate (with the Whatever Star). +my @listv2 = 1, 3, 9...* > 30; + +# Equivalent to the example above but using a block here. +my @listv3 = 1, 3, 9 ... { $_ > 30 }; + +# Lazy infinite list of fibonacci sequence, computed using a closure! +my @fibv0 = 1, 1, *+* ... *; + +# Equivalent to the above example but using a pointy block. +my @fibv1 = 1, 1, -> $a, $b { $a + $b } ... *; + +# Equivalent to the above example but using a block with placeholder parameters. +my @fibv2 = 1, 1, { $^a + $^b } ... *; + +=begin comment +In the examples with explicit parameters (i.e., $a and $b), $a and $b +will always take the previous values, meaning that for the Fibonacci sequence, +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. +=end comment + +=begin comment +# In the example we use a range as an index to access the sequence. However, +# it's worth noting that for ranges, once reified, elements aren't re-calculated. +# That's why, for instance, `@primes[^100]` will take a long time the first +# time you print it but then it will be instateneous. +=end comment +say @fibv0[^10]; # OUTPUT: «1 1 2 3 5 8 13 21 34 55» + +#################################################### +# 18. Regular Expressions +#################################################### + +=begin comment +I'm sure a lot of you have been waiting for this one. Well, now that you know +a good deal of Raku 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. + +Raku 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, Raku 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 +=end comment +say so 'a' ~~ /a/; # OUTPUT: «True» +say so 'a' ~~ / a /; # OUTPUT: «True», more readable with some spaces! + +=begin comment +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 Raku, you can have any alphanumeric as a literal, everything else has +to be escaped by using a backslash or quotes. +=end comment +say so 'a|b' ~~ / a '|' b /; # OUTPUT: «True», it wouldn't mean the same + # thing if `|` wasn't escaped. +say so 'a|b' ~~ / a \| b /; # OUTPUT: «True», another way to escape it. + +# The whitespace in a regex 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, Raku will warn us +# about space being not signicant in the regex: +say so 'a b c' ~~ / a b c /; # OUTPUT: «False» +say so 'a b c' ~~ / a b c /; # OUTPUT: «False» + +=begin comment +NOTE: 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. +=end comment + +# 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/; # OUTPUT: «True» + +# By using `m` to specify 'match', we can also use other delimiters: +say so 'abc' ~~ m{a b c}; # OUTPUT: «True» +say so 'abc' ~~ m[a b c]; # OUTPUT: «True» + +# `m/.../` is equivalent to `/.../`: +say 'raku' ~~ m/raku/; # OUTPUT: «True» +say 'raku' ~~ /raku/; # OUTPUT: «True» + +# Use the `:i` adverb to specify case insensitivity: +say so 'ABC' ~~ m:i{a b c}; # OUTPUT: «True» + +# However, whitespace is important as for how modifiers are applied +# (which you'll see just below) ... + +# +# 18.1 Quantifiers - `?`, `+`, `*` and `**`. +# + +# `?` - zero or one match +say so 'ac' ~~ / a b c /; # OUTPUT: «False» +say so 'ac' ~~ / a b? c /; # OUTPUT: «True», the "b" matched 0 times. +say so 'abc' ~~ / a b? c /; # OUTPUT: «True», the "b" matched 1 time. + +# ... As you read before, whitespace is important because it determines which +# part of the regex is the target of the modifier: +say so 'def' ~~ / a b c? /; # OUTPUT: «False», only the "c" is optional +say so 'def' ~~ / a b? c /; # OUTPUT: «False», whitespace is not significant +say so 'def' ~~ / 'abc'? /; # OUTPUT: «True», the whole "abc" group is optional + +# Here (and below) the quantifier applies only to the "b" + +# `+` - one or more matches +say so 'ac' ~~ / a b+ c /; # OUTPUT: «False», `+` wants at least one 'b' +say so 'abc' ~~ / a b+ c /; # OUTPUT: «True», one is enough +say so 'abbbbc' ~~ / a b+ c /; # OUTPUT: «True», matched 4 "b"s + +# `*` - zero or more matches +say so 'ac' ~~ / a b* c /; # OUTPU: «True», they're all optional +say so 'abc' ~~ / a b* c /; # OUTPU: «True» +say so 'abbbbc' ~~ / a b* c /; # OUTPU: «True» +say so 'aec' ~~ / a b* c /; # OUTPU: «False», "b"(s) are optional, not replaceable. + +# `**` - (Unbound) Quantifier +# If you squint hard enough, you might understand why exponentation is used +# for quantity. +say so 'abc' ~~ / a b**1 c /; # OUTPU: «True», exactly one time +say so 'abc' ~~ / a b**1..3 c /; # OUTPU: «True», one to three times +say so 'abbbc' ~~ / a b**1..3 c /; # OUTPU: «True» +say so 'abbbbbbc' ~~ / a b**1..3 c /; # OUTPU: «Fals», too much +say so 'abbbbbbc' ~~ / a b**3..* c /; # OUTPU: «True», infinite ranges are ok + +# +# 18.2 `<[]>` - Character classes +# + +# Character classes are the equivalent of PCRE's `[]` classes, but they use a +# more raku-ish syntax: +say 'fooa' ~~ / f <[ o a ]>+ /; # OUTPUT: «fooa» + +# You can use ranges (`..`): +say 'aeiou' ~~ / a <[ e..w ]> /; # OUTPUT: «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 \! \ ]> + /; # OUTPUT: «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) +say so 'foo' ~~ / <-[ f o ]> + /; # OUTPUT: «False» + +# ... and compose them: +# any letter except "f" and "o" +say so 'foo' ~~ / <[ a..z ] - [ f o ]> + /; # OUTPUT: «False» + +# no letter except "f" and "o" +say so 'foo' ~~ / <-[ a..z ] + [ f o ]> + /; # OUTPUT: «True» + +# the + doesn't replace the left part +say so 'foo!' ~~ / <-[ a..z ] + [ f o ]> + /; # OUTPUT: «True» + +# +# 18.3 Grouping and capturing +# + +# Group: you can group parts of your regexp with `[]`. Unlike PCRE's `(?:)`, +# these groups are *not* captured. +say so 'abc' ~~ / a [ b ] c /; # OUTPUT: «True», the grouping does nothing +say so 'foo012012bar' ~~ / foo [ '01' <[0..9]> ] + bar /; # OUTPUT: «True» + +# The previous line returns `True`. The regex matches "012" one 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. +say so 'fooABCABCbar' ~~ / foo ( 'A' <[A..Z]> 'C' ) + bar /; # OUTPUT: «True» +# (using `so` here, see `$/` below) + +# So, starting with the grouping explanations. As we said before, our `Match` +# object is stored inside the `$/` variable: +say $/; # Will either print the matched object or `Nil` if nothing matched. + +# As we also said before, it has array indexing: +say $/[0]; # OUTPUT: «｢ABC｣ ｢ABC｣», + +# The corner brackets (｢..｣) represent (and are) `Match` objects. In the +# previous example, we have an array of them. + +say $0; # The same as above. + +=begin comment +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. +=end comment +say so 'fooABCbar' ~~ / foo ( "A" "B" "C" )? bar /; # OUTPUT: «True» +say $/[0]; # OUTPUT: «｢ABC｣» +say $0.WHAT; # OUTPUT: «(Match)» + # There can't be more than one, so it's only a single match object. + +say so 'foobar' ~~ / foo ( "A" "B" "C" )? bar /; # OUTPUT: «True» +say $0.WHAT; # OUTPUT: «(Any)», this capture did not match, so it's empty. + +say so 'foobar' ~~ / foo ( "A" "B" "C" ) ** 0..1 bar /; #=> OUTPUT: «True» +say $0.WHAT; # OUTPUT: «(Array)», A specific quantifier will always capture + # an Array, be a range or a specific value (even 1). + +# The captures are indexed per nesting. This means a group in a group will be +# nested under its parent group: `$/[0][0]`, for this code: +'hello-~-world' ~~ / ( 'hello' ( <[ \- \~ ]> + ) ) 'world' /; +say $/[0].Str; # OUTPUT: «hello~» +say $/[0][0].Str; # OUTPUT: «~» + +=begin comment +This stems from a very simple fact: `$/` 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. + +In the following example, we can see `$_` is a list of `Match` objects. +Each of them contain a wealth of information: where the match started/ended, +the "ast" (see actions later), etc. You'll see named capture below with +grammars. +=end comment +say $/[0].list.perl; # OUTPUT: «(Match.new(...),).list» + +# Alternation - the `or` of regexes +# WARNING: They are DIFFERENT from PCRE regexps. +say so 'abc' ~~ / a [ b | y ] c /; # OUTPU: «True», Either "b" or "y". +say so 'ayc' ~~ / a [ b | y ] c /; # OUTPU: «True», Obviously enough... + +# The difference between this `|` and the one you're used to is +# LTM ("Longest Token Matching") strategy. This means that the engine will +# always try to match as much as possible in the string. +say 'foo' ~~ / fo | foo /; # OUTPUT: «foo», instead of `fo`, because it's longer. + +=begin comment +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) + which includes alternations (`|`), conjunctions (`&`), sub-rule calls (not + yet introduced), literals, characters classes and quantifiers. + + * The "procedural part" includes 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. +=end comment + +# 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 regexes) are procedural. +# There are also more complicated rules, like specificity (literals win +# over character classes). + +# NOTE: The alternation in which all the branches are tried in order +# until the first one matches still exists, but is now spelled `||`. +say 'foo' ~~ / fo || foo /; # OUTPUT: «fo», in this case. + +#################################################### +# 19. Extra: the MAIN subroutine +#################################################### + +=begin comment +The `MAIN` subroutine is called when you run a Raku file directly. It's +very powerful, because Raku 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. +=end comment + +sub MAIN($name) { + say "Hello, $name!"; +} +=begin comment +Supposing the code above is in file named cli.raku, then running in the command +line (e.g., $ raku cli.raku) produces: +Usage: + cli.raku <name> +=end comment + +=begin comment +And since MAIN is a regular Raku 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). For example: + + # convert to IO object to check the file exists + subset File of Str where *.IO.d; + + multi MAIN('add', $key, $value, Bool :$replace) { ... } + multi MAIN('remove', $key) { ... } + multi MAIN('import', File, Str :$as) { ... } # omitting parameter name + +Thus $ raku cli.raku produces: +Usage: + cli.raku [--replace] add <key> <value> + cli.raku remove <key> + cli.raku [--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 `$`/is named). +=end comment + +#################################################### +# 20. APPENDIX A: +#################################################### + +=begin comment +It's assumed by now you know the Raku basics. This section is just here to +list some common operations, but which are not in the "main part" of the +tutorial to avoid bloating it up. +=end comment + +# +# 20.1 Operators +# + +# Sort comparison - they return one value of the `Order` enum: `Less`, `Same` +# and `More` (which numerify to -1, 0 or +1 respectively). +say 1 <=> 4; # OUTPUT: «More», sort comparison for numerics +say 'a' leg 'b'; # OUTPUT: «Lessre», sort comparison for string +say 1 eqv 1; # OUTPUT: «Truere», sort comparison using eqv semantics +say 1 eqv 1.0; # OUTPUT: «False» + +# Generic ordering +say 3 before 4; # OUTPUT: «True» +say 'b' after 'a'; # OUTPUT: «True» + +# Short-circuit default operator - similar to `or` and `||`, but instead +# returns the first *defined* value: +say Any // Nil // 0 // 5; # OUTPUT: «0» + +# Short-circuit exclusive or (XOR) - returns `True` if one (and only one) of +# its arguments is true +say True ^^ False; # OUTPUT: «True» + +=begin comment +Flip flops. These operators (`ff` and `fff`, equivalent to P5's `..` +and `...`) are operators that take two predicates to test: They are `False` +until their left side returns `True`, then are `True` until their right +side returns `True`. Similar to ranges, you can exclude the iteration when +it become `True`/`False` by using `^` on either side. Let's start with an +example : +=end comment + +for <well met young hero we shall meet later> { + # by default, `ff`/`fff` smart-match (`~~`) against `$_`: + 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 `$_` + say "This ... probably will never run ..."; + } +} + +=begin comment +This will print "young hero we shall meet" (excluding "met"): the flip-flop +will start returning `True` when it first encounters "met" (but will still +return `False` for "met" itself, due to the leading `^` on `ff`), until it +sees "meet", which is when it'll start returning `False`. +=end comment + +=begin comment +The difference between `ff` (awk-style) and `fff` (sed-style) is that `ff` +will test its right side right when its left side changes to `True`, and can +get back to `False` right away (*except* it'll be `True` for the iteration +that matched) while `fff` will wait for the next iteration to try its right +side, once its left side changed: +=end comment + +# The output is due to the right-hand-side being tested directly (and returning +# `True`). "B"s are printed since it matched that time (it just went back to +# `False` right away). +.say if 'B' ff 'B' for <A B C B A>; # OUTPUT: «B B», + +# In this case the right-hand-side wasn't tested until `$_` became "C" +# (and thus did not match instantly). +.say if 'B' fff 'B' for <A B C B A>; #=> «B C B», + +# 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> { + # exclude both "start" and "stop", + .say if $_ eq 'start' ^ff^ $_ eq 'stop'; # OUTPUT: «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, as shown in this example. +# NOTE: the parenthesis are superfluous here (sometimes called "superstitious +# parentheses"). Once the flip-flop reaches a number greater than 50, it'll +# never go back to `False`. +for (1, 3, 60, 3, 40, 60) { + .say if $_ > 50 ff *; # OUTPUT: «6034060» +} + +# You can also use this property to create an `if` that'll not go through the +# first time. In this case, the flip-flop is `True` and never goes back to +# `False`, but the `^` makes it *not run* on the first iteration +for <a b c> { .say if * ^ff *; } # OUTPUT: «bc» + +# The `===` operator, which uses `.WHICH` on the objects to be compared, is +# the value identity operator whereas the `=:=` operator, which uses `VAR()` on +# the objects to compare them, is the container identity operator. +``` + +If you want to go further and learn more about Raku, you can: + +- Read the [Raku Docs](https://docs.raku.org/). This is a great +resource on Raku. 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 Raku documents!). + +- Read the [Raku Advent Calendar](http://perl6advent.wordpress.com/). This +is a great source of Raku 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 Raku 6.c was released. + +- Come along on `#raku` at `irc.freenode.net`. The folks here are +always helpful. + +- Check the [source of Raku's functions and +classes](https://github.com/rakudo/rakudo/tree/nom/src/core). Rakudo is +mainly written in Raku (with a lot of NQP, "Not Quite Perl", a Raku subset +easier to implement and optimize). + +- Read [the language design documents](https://design.raku.org/). They explain +Raku from an implementor point-of-view, but it's still very interesting. + |