- 1. Introduction
- 2. Operators
- 3. Variables
- 4. Functions and mutators
- 5. Loops and conditions
- 6. I/O
- 7. Subroutines
- 8. Functional Programming
- 9. Classes & Objects
- 10. Exception Handling
- 11. Regular Expressions
- 12. Raku Modules
- 13. Unicode
- 14. Parallelism, Concurrency and Asynchrony
- 15. Native Calling Interface
- 16. The Community
This document is intended to give you a quick overview of the Raku programming language.
For those new to Raku, it should get you up and running.
Some sections of this document refer to other (more complete and accurate) parts of the Raku documentation. You should read them if you need more information on a specific subject.
Throughout this document, you will find examples for most discussed topics. To better understand them, take the time to reproduce all examples.
This work is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License. To view a copy of this license, visit
If you would like to contribute to this document, head over to:
All feedback is welcomed: [email protected]
If you liked this work, Star the repository on Github.
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Bulgarian: https://raku.guide/bg
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Chinese: https://raku.guide/zh
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Dutch: https://raku.guide/nl
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French: https://raku.guide/fr
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German: https://raku.guide/de
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Indonesian: https://raku.guide/id
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Italian https://raku.guide/it
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Japanese: https://raku.guide/ja
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Portuguese: https://raku.guide/pt
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Spanish: https://raku.guide/es
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Turkish: https://raku.guide/tr
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Russian: https://raku.guide/ru
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Ukrainian: https://raku.guide/uk
Raku is a high-level, general-purpose, gradually typed language. Raku is multi-paradigmatic. It supports Procedural, Object Oriented, and Functional programming.
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TMTOWTDI (Pronounced Tim Toady): There is more than one way to do it.
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Raku: Is a language specification with a test suite. Implementations that pass the specification test suite are considered Raku.
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Rakudo: Is a compiler for Raku.
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Zef: Is a Raku module installer.
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Rakudo Star: Is a bundle that includes Rakudo, Zef, a collection of Raku modules, and documentation.
https://rakubrew.org is a platform independent environment manager (think pyenv for Raku)
To install Rakudo Star, run the following commands from your terminal:
mkdir ~/rakudo && cd $_
curl -LJO https://rakudo.org/latest/star/src
tar -xzf rakudo-star-*.tar.gz
mv rakudo-star-*/* .
rm -fr rakudo-star-*
./bin/rstar install
echo "export PATH=$(pwd)/bin/:$(pwd)/share/perl6/site/bin:$(pwd)/share/perl6/vendor/bin:$(pwd)/share/perl6/core/bin:\$PATH" >> ~/.bashrc
source ~/.bashrcFor other Unix options, go to https://rakudo.org/star/source
Four options are available:
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Follow the same steps listed for installing on Linux
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Install with homebrew:
brew install rakudo-star -
Install with MacPorts:
sudo port install rakudo -
Get the latest installer (file with .dmg extension) from https://rakudo.org/latest/star/macos
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For 64-bit architectures: Get the latest installer (file with .msi extension) from https://rakudo.org/latest/star/win
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After installation, make sure
C:\rakudo\binis in the PATH
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Get the official Docker image
docker pull rakudo-star -
Then run a container with the image
docker run -it rakudo-star
Running Raku code can be done using the REPL (Read-Eval-Print Loop).
To do this, open a terminal, type raku into the terminal window,
and hit [Enter]. This will cause a prompt of > to appear.
Next, type a line of code and hit [Enter]. The REPL will print out
the value of the line. You may then type another line, or type exit
and hit [Enter] to leave the REPL.
Alternatively, write your code in a file, save it and run it.
It is recommended that Raku scripts have a .raku file name extension.
Run the file by typing raku filename.raku into the terminal window
and hitting [Enter]. Unlike the REPL, this will not automatically print
the result of each line: the code must contain a statement like say
to print output.
The REPL is mostly used for trying a specific piece of code, typically a single line. For programs with more than a single line it is recommended to store them in a file and then run them.
Single lines may also be tried non-interactively on the command-line by
typing raku -e 'your code here' and hitting [Enter].
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Tip
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Rakudo Star bundles a line editor that helps you get the most out of the REPL. If you installed plain Rakudo instead of Rakudo Star then you probably don’t have line editing features enabled (using the up and down arrows for history, left and right to edit input, TAB completion). Consider running the following command and you shall be all set:
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Since most of the time we will be writing and storing our Raku programs in files, we should have a decent text editor that recognizes Raku syntax.
The community uses frequently the following editors:
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Visual Studio Code: syntax highlighting and error checking enabled using raku-navigator
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Nano: syntax highlighting enabled using raku.nanorc
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Notepad++: syntax highlighting available out of the box
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Kate: syntax highlighting available out of the box
We shall begin with The hello world ritual.
say 'hello world';that can also be written as:
'hello world'.say;Raku is free form: Most of the time you are free to use any amount of whitespace, although in certain cases whitespace carries meaning.
Statements are typically a single line of code separated with semicolons:
say "Hello" if True;
say "World" if False;Semicolons are not required after the last statement in a file or block of code, but it’s good practice to include them anyway.
Blocks can contain a collection of statements. Surround statements with curly braces to create a block:
{
say "First statement in the block.";
say "Second statement in the block.";
}Expressions are a special type of statement that returns a value:
1+2 will return 3
Expressions are made of Terms and Operators.
Terms are:
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Variables: A value that can be manipulated and changed.
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Literals: A constant value like a number or a string.
Operators are classified into types:
Type |
Explanation |
Example |
Prefix |
Before the term. |
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Infix |
Between terms |
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Postfix |
After the term |
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Circumfix |
Around the term |
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Postcircumfix |
After one term, around another |
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Identifiers are the names given to terms when you define them.
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They must start with an alphabetic character or an underscore.
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They can contain digits (except the first character).
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They can contain dashes or apostrophes (except the first and last character), provided there’s an alphabetic character to the right side of each dash or apostrophe.
Valid |
Invalid |
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Camel case:
variableNo1 -
Kebab case:
variable-no1 -
Snake case:
variable_no1
You are free to name your identifiers as you like, but it is good practice to adopt one naming convention consistently.
Using meaningful names will ease your (and other’s) programming life.
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var1 = var2 * var3is syntactically correct but its purpose is not evident. -
monthly-salary = daily-rate * working-dayswould be a better way to name your variables.
A comment is text ignored by the compiler and used as a note.
Comments are divided into 3 types:
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Single line:
# This is a single line comment -
Embedded:
say #`(This is an embedded comment) "Hello World."
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Multi line:
=begin comment This is a multi line comment. Comment 1 Comment 2 =end comment
Strings need to be delimited by either double quotes or single quotes.
Always use double quotes:
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if your string contains an apostrophe.
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if your string contains a variable that needs to be interpolated.
say 'Hello World'; # Hello World
say "Hello World"; # Hello World
say "Don't"; # Don't
my $name = 'John Doe';
say 'Hello $name'; # Hello $name
say "Hello $name"; # Hello John DoeThe below table lists the most commonly used operators.
| Operator | Type | Description | Example | Result |
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Addition |
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Subtraction |
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Multiplication |
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Power |
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Division |
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Integer Division (rounds down) |
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Modulo |
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Divisibility |
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Greatest common divisor |
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Least common multiple |
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Numeric equal |
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Numeric not equal |
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Numeric less than |
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Numeric greater than |
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Numeric less than or equal |
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Numeric greater than or equal |
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Numeric three-way comparator |
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String equal |
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String not equal |
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String less than |
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String greater than |
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String less than or equal |
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String greater than or equal |
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String three-way comparator |
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Smart three-way comparator |
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Assignment |
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String concatenation |
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String replication |
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Smart match |
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Increment |
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Increment |
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Decrement |
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Decrement |
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Coerce the operand to a numeric value |
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Coerce the operand to a numeric value and return the negation |
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Coerce the operand to a boolean value |
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Coerce the operand to a boolean value and return the negation |
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Range Constructor |
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Range Constructor |
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Range Constructor |
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Range Constructor |
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Range Constructor |
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Lazy List Constructor |
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Flattening |
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Adding R before any operator will have the effect of reversing its operands.
| Normal Operation | Result | Reversed Operator | Result |
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Reduction operators work on lists of values.
They are formed by surrounding the operator with brackets []
| Normal Operation | Result | Reduction Operator | Result |
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Note
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For the complete list of operators, including their precedence, go to https://docs.raku.org/language/operators |
Raku variables are classified into 3 categories: Scalars, Arrays and Hashes.
A sigil (Sign in Latin) is a character that is used as a prefix to categorize variables.
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$is used for scalars -
@is used for arrays -
%is used for hashes
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Note
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This guide offers a simplified model of variables suitable for learning the basics of Raku. For a deeper understanding of variables, see https://docs.raku.org/language/containers |
A scalar holds one value or reference.
# String
my $name = 'John Doe';
say $name;
# Integer
my $age = 99;
say $age;A specific set of operations can be performed on a scalar, depending on the value it holds.
my $name = 'John Doe';
say $name.uc;
say $name.chars;
say $name.flip;JOHN DOE
8
eoD nhoJ|
Note
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For the complete list of methods applicable to Strings, see https://docs.raku.org/type/Str |
my $age = 17;
say $age.is-prime;True|
Note
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For the complete list of methods applicable to Integers, see https://docs.raku.org/type/Int |
my $age = 2.3;
say $age.numerator;
say $age.denominator;
say $age.nude;23
10
(23 10)|
Note
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For the complete list of methods applicable to Rational Numbers, see https://docs.raku.org/type/Rat |
Arrays are lists containing multiple values.
my @animals = 'camel','llama','owl';
say @animals;Many operations can be performed on arrays as shown in the below example:
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Tip
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The tilde ~ is used for string concatenation.
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Scriptmy @animals = 'camel','vicuña','llama';
say "The zoo contains " ~ @animals.elems ~ " animals";
say "The animals are: " ~ @animals;
say "I will adopt an owl for the zoo";
@animals.push("owl");
say "Now my zoo has: " ~ @animals;
say "The first animal we adopted was the " ~ @animals[0];
@animals.pop;
say "Unfortunately the owl got away and we're left with: " ~ @animals;
say "We're closing the zoo and keeping one animal only";
say "We're going to let go: " ~ @animals.splice(1,2) ~ " and keep the " ~ @animals;OutputThe zoo contains 3 animals
The animals are: camel vicuña llama
I will adopt an owl for the zoo
Now my zoo has: camel vicuña llama owl
The first animal we adopted was the camel
Unfortunately the owl got away and we're left with: camel vicuña llama
We're closing the zoo and keeping one animal only
We're going to let go: vicuña llama and keep the camel.elems returns the number of elements in an array.
.push() adds one or more elements to the array.
We can access a specific element in the array by specifying its position @animals[0].
.pop removes the last element from the array and returns it.
.splice(a,b) will remove b elements starting at position a.
A basic array is declared as following:
my @array;The basic array can have indefinite length and thus is called auto-extending.
The array will accept any number of values with no restriction.
In contrast, we can also create fixed-size arrays.
These arrays cannot be accessed beyond their defined size.
To declare an array of fixed size, specify its maximum number of elements in square brackets immediately after its name:
my @array[3];This array will be able to hold a maximum of 3 values, indexed from 0 to 2.
my @array[3];
@array[0] = "first value";
@array[1] = "second value";
@array[2] = "third value";You will not be able to add a fourth value to this array:
my @array[3];
@array[0] = "first value";
@array[1] = "second value";
@array[2] = "third value";
@array[3] = "fourth value";Index 3 for dimension 1 out of range (must be 0..2)The arrays we saw until now are one-dimensional.
Fortunately, we can define multi-dimensional arrays in Raku.
my @tbl[3;2];This array is two-dimensional. The first dimension can have a maximum of 3 values and the second dimension a maximum of 2 values.
Think of it as a 3x2 grid.
my @tbl[3;2];
@tbl[0;0] = 1;
@tbl[0;1] = "x";
@tbl[1;0] = 2;
@tbl[1;1] = "y";
@tbl[2;0] = 3;
@tbl[2;1] = "z";
say @tbl[[1 x] [2 y] [3 z]][1 x]
[2 y]
[3 z]|
Note
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For the complete Array reference, see https://docs.raku.org/type/Array |
my %capitals = 'UK','London','Germany','Berlin';
say %capitals;my %capitals = UK => 'London', Germany => 'Berlin';
say %capitals;Some of the methods that can be called on hashes are:
Scriptmy %capitals = UK => 'London', Germany => 'Berlin';
%capitals.push: (France => 'Paris');
say %capitals.kv;
say %capitals.keys;
say %capitals.values;
say "The capital of France is: " ~ %capitals<France>;Output(France Paris Germany Berlin UK London)
(France Germany UK)
(Paris Berlin London)
The capital of France is: Paris.push: (key => 'Value') adds a new key/value pair.
.kv returns a list containing all keys and values.
.keys returns a list that contains all keys.
.values returns a list that contains all values.
We can access a specific value in the hash by specifying its key %hash<key>
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Note
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For the complete Hash reference, see https://docs.raku.org/type/Hash |
In the previous examples, we did not specify what type of values the variables should hold.
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Tip
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.WHAT will return the type of value held in a variable.
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my $var = 'Text';
say $var;
say $var.WHAT;
$var = 123;
say $var;
say $var.WHAT;As you can see in the above example, the type of value in $var was once (Str) and then (Int).
This style of programming is called dynamic typing. Dynamic in the sense that variables may contain values of Any type.
Now try running the below example:
Notice Int before the variable name.
my Int $var = 'Text';
say $var;
say $var.WHAT;It will fail and return this error message: Type check failed in assignment to $var; expected Int but got Str
What happened is that we specified beforehand that the variable should be of type (Int). When we tried to assign an (Str) to it, it failed.
This style of programming is called static typing. Static in the sense that variable types are defined before assignment and cannot change.
Raku is classified as gradually typed; it allows both static and dynamic typing.
my Int @array = 1,2,3;
say @array;
say @array.WHAT;
my Str @multilingual = "Hello","Salut","Hallo","您好","안녕하세요","こんにちは";
say @multilingual;
say @multilingual.WHAT;
my Str %capitals = UK => 'London', Germany => 'Berlin';
say %capitals;
say %capitals.WHAT;
my Int %country-codes = UK => 44, Germany => 49;
say %country-codes;
say %country-codes.WHAT;You will most probably never use the first two but they are listed for informational purpose.
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Introspection is the process of getting information about an object properties like its type.
In one of the previous example we used .WHAT to return the type of the variable.
my Int $var;
say $var.WHAT; # (Int)
my $var2;
say $var2.WHAT; # (Any)
$var2 = 1;
say $var2.WHAT; # (Int)
$var2 = "Hello";
say $var2.WHAT; # (Str)
$var2 = True;
say $var2.WHAT; # (Bool)
$var2 = Nil;
say $var2.WHAT; # (Any)The type of a variable holding a value is correlated to its value.
The type of a strongly declared empty variable is the type with which it was declared.
The type of an empty variable that wasn’t strongly declared is (Any)
To clear the value of a variable, assign Nil to it.
Before using a variable for the first time, it needs to be declared.
Several declarators are used in Raku. We’ve been using my, so far.
my $var=1;The my declarator give the variable lexical scope.
In other words, the variable will only be accessible in the same block it was declared.
A block in Raku is delimited by { }.
If no block is found, the variable will be available in the whole Raku script.
{
my Str $var = 'Text';
say $var; # is accessible
}
say $var; # is not accessible, returns an errorSince a variable is only accessible in the block where it is defined, the same variable name can be used in another block.
{
my Str $var = 'Text';
say $var;
}
my Int $var = 123;
say $var;We’ve seen in the previous examples, how to assign values to variables.
Assignment is done using the = operator.
my Int $var = 123;
say $var;We can change the value assigned to a variable:
my Int $var = 123;
say $var;
$var = 999;
say $var;Output123
999On the other hand, we cannot change the value bound to a variable.
Binding is done using the := operator.
my Int $var := 123;
say $var;
$var = 999;
say $var;Output123
Cannot assign to an immutable valuemy $a;
my $b;
$b := $a;
$a = 7;
say $b;
$b = 8;
say $a;Output7
8Binding variables is bi-directional.
$a := $b and $b := $a have the same effect.
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Note
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For more info on variables, see https://docs.raku.org/language/variables |
It is important to differentiate between functions and mutators.
Functions do not change the state of the object they were called on.
Mutators modify the state of the object.
Scriptmy @numbers = [7,2,4,9,11,3];
@numbers.push(99);
say @numbers; #1
say @numbers.sort; #2
say @numbers; #3
@numbers.=sort;
say @numbers; #4Output[7 2 4 9 11 3 99] #1
(2 3 4 7 9 11 99) #2
[7 2 4 9 11 3 99] #3
[2 3 4 7 9 11 99] #4.push is a mutator; it changes the state of the array (#1)
.sort is a function; it returns a sorted array but doesn’t modify the state of the initial array:
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(#2) shows that it returned a sorted array.
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(#3) shows that the initial array is still unmodified.
In order to enforce a function to act as a mutator, we use .= instead of . (#4) (Line 9 of the script)
Raku has many conditional and looping constructs.
The code runs only if a condition has been met; i.e., an expression evaluates to True.
my $age = 19;
if $age > 18 {
say 'Welcome'
}In Raku, we can invert the code and the condition.
Even if the code and the condition have been inverted, the condition is always evaluated first.
my $age = 19;
say 'Welcome' if $age > 18;If the condition is not met, we can specify alternate blocks for execution by using:
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else -
elsif
# run the same code for different values of the variable
my $number-of-seats = 9;
if $number-of-seats <= 5 {
say 'I am a sedan'
} elsif $number-of-seats <= 7 {
say 'I am 7 seater'
} else {
say 'I am a van'
}The negated version of an if statement can be written using unless.
The following code:
my $clean-shoes = False;
if not $clean-shoes {
say 'Clean your shoes'
}can be written as:
my $clean-shoes = False;
unless $clean-shoes {
say 'Clean your shoes'
}Negation in Raku is done using either ! or not.
unless (condition) is used instead of if not (condition).
unless cannot have an else clause.
with behaves like the if statement, but checks if the variable is defined.
my Int $var=1;
with $var {
say 'Hello'
}If you run the code without assigning a value to the variable, nothing should happen.
my Int $var;
with $var {
say 'Hello'
}without is the negated version of with. You should be able to relate it to unless.
If the first with condition is not met, an alternate path can be specified using orwith.
with and orwith can be compared to if and elsif.
The for loop iterates over multiple values.
my @array = 1,2,3;
for @array -> $array-item {
say $array-item * 100
}Notice that we created an iteration variable $array-item and then performed the operation *100 on each array item.
given is the Raku equivalent of the switch statement in other languages,
but much more powerful.
my $var = 42;
given $var {
when 0..50 { say 'Less than or equal to 50'}
when Int { say "is an Int" }
when 42 { say 42 }
default { say "huh?" }
}After a successful match, the matching process will stop.
Alternatively proceed will instruct Raku to continue matching even after a successful match.
my $var = 42;
given $var {
when 0..50 { say 'Less than or equal to 50';proceed}
when Int { say "is an Int";proceed}
when 42 { say 42 }
default { say "huh?" }
}loop is another way of writing a for loop.
Actually, loop is how for loops are written in C-family programming languages.
Raku belongs to the C-family languages.
loop (my $i = 0; $i < 5; $i++) {
say "The current number is $i"
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Note
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For more info on loops and conditions, see https://docs.raku.org/language/control |
In Raku, two of the most common Input/Output interfaces are the Terminal and Files.
say writes to the standard output. It appends a newline at the end. In other words, the following code:
say 'Hello Mam.';
say 'Hello Sir.';will be written on 2 separate lines.
print on the other hand behaves like say but doesn’t add a new line.
Try replacing say with print and compare the results.
get is used to capture input from the terminal.
my $name;
say "Hi, what's your name?";
$name = get;
say "Dear $name welcome to Raku";When the above code runs, the terminal will be waiting for you to input your name. Enter it and then hit [Enter]. Subsequently, it will greet you.
Two subroutines can be used to run shell commands:
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runRuns an external command without involving a shell -
shellRuns a command through the system shell. It is platform and shell dependent. All shell meta characters are interpreted by the shell, including pipes, redirects, environment variable substitutions and so on.
my $name = 'Neo';
run 'echo', "hello $name";
shell "ls";shell "dir";echo and ls are common shell keywords on Linux:
echo prints text to the terminal (the equivalent of say in Raku)
ls lists all files and folders in the current directory
dir is the equivalent of ls on Windows.
slurp is used to read data from a file.
Create a text file with the following content:
John 9
Johnnie 7
Jane 8
Joanna 7my $data = slurp "datafile.txt";
say $data;Raku can list the contents of a directory without resorting to shell commands (by using ls, for example).
say dir; # List files and folders in the current directory
say dir "/Documents"; # List files and folders in the specified directoryIn addition, you can create and delete directories.
mkdir "newfolder";
rmdir "newfolder";mkdir creates a new directory.
rmdir deletes an empty directory and returns an error if not empty.
You can also check if a path exists; if it is a file; or a directory:
In the directory where you will be running the below script, create an empty folder folder123 and an empty raku file script123.raku
say "script123.raku".IO.e;
say "folder123".IO.e;
say "script123.raku".IO.d;
say "folder123".IO.d;
say "script123.raku".IO.f;
say "folder123".IO.f;IO.e checks if the directory/file exists.
IO.f checks if the path is a file.
IO.d checks if the path is a directory.
|
Warning
|
Windows users can use / or \\ to define directoriesC:\\rakudo\\binC:/rakudo/bin |
|
Note
|
For more info on I/O, see https://docs.raku.org/type/IO |
Subroutines (also called subs or functions) are a means of packaging and reusing functionality.
A subroutine definition begins with the keyword sub. After their definition, they can be called by their handle.
Check out the below example:
sub alien-greeting {
say "Hello earthlings";
}
alien-greeting;The previous example showcased a subroutine that doesn’t require any input.
Subroutines can require input. That input is provided by arguments. A subroutine may define zero or more parameters. The number and type of parameters that a subroutine defines is called its signature.
The below subroutine accepts a string argument.
sub say-hello (Str $name) {
say "Hello " ~ $name ~ "!!!!"
}
say-hello "Paul";
say-hello "Paula";It is possible to define multiple subroutines that have the same name but different signatures.
When the subroutine is called, the runtime environment will decide which version to use based on the number and type of supplied arguments. This type of subroutine is defined the same way as normal subs except that we use the multi keyword instead of sub.
multi greet($name) {
say "Good morning $name";
}
multi greet($name, $title) {
say "Good morning $title $name";
}
greet "Johnnie";
greet "Laura","Mrs.";If a subroutine is defined to accept an argument, and we call it without providing it with the required argument, it will fail.
Raku provides us the ability to define subroutines with:
-
Optional Parameters
-
Default Parameters
Optional parameters are defined by appending ? to the parameter name.
sub say-hello($name?) {
with $name { say "Hello " ~ $name }
else { say "Hello Human" }
}
say-hello;
say-hello("Laura");If the user doesn’t need to supply an argument, a default value can be defined.
This is done by assigning a value to the parameter within the subroutine definition.
sub say-hello($name="Matt") {
say "Hello " ~ $name;
}
say-hello;
say-hello("Laura");All the subroutines we’ve seen so far do something — they display some text on the terminal.
Sometimes, though, we execute a subroutine for its return value so we can use it later in the flow of our program.
If a function is allowed to run through it’s block to the end, the last statement or expression will determine the return value.
sub squared ($x) {
$x ** 2;
}
say "7 squared is equal to " ~ squared(7);For the sake of clarity, it might be a good idea to explicitly specify what we want returned.
This can be done using the return keyword.
sub squared ($x) {
return $x ** 2;
}
say "7 squared is equal to " ~ squared(7);In one of the previous examples, we saw how we can restrict the accepted argument to be of a certain type. The same can be done with return values.
To restrict the return value to a certain type, we use the arrow notation --> in the signature.
sub squared ($x --> Int) {
return $x ** 2;
}
say "1.2 squared is equal to " ~ squared(1.2);If we fail to provide a return value that matches the type constraint, an error will be thrown.
Type check failed for return value; expected Int but got Rat (1.44)|
Tip
|
Not only can type constraints control the type of the return value; they can also control its definedness. In the previous examples, we specified that the return value should be an We could also have specified that the returned That being said, it is good practice to use those type constraints. sub squared ($x --> Int:D) {
return $x ** 2;
}
say "1.2 squared is equal to " ~ squared(1.2); |
|
Note
|
For more info on subroutines and functions, see https://docs.raku.org/language/functions |
In this chapter we will take a look at some of the features that facilitate Functional Programming.
Functions/subroutines are first-class citizens:
-
They can be passed as arguments
-
They can be returned from other functions
-
They can be assigned to variables
A great example is the map function.
map is a higher order function, it can accept another function as an argument.
my @array = <1 2 3 4 5>;
sub squared($x) {
$x ** 2
}
say map(&squared,@array);(1 4 9 16 25)We defined a subroutine called squared that takes an argument and multiplies that argument by itself.
Next, we used map, a higher order function, and gave it two arguments, the squared subroutine and an array.
The result is a list of the squared elements of the array.
Notice that when passing a subroutine as an argument, we need to prepend & to its name.
An anonymous function is also called a lambda.
An anonymous function is not bound to an identifier (it has no name).
Let’s rewrite the map example and have it use an anonymous function
my @array = <1 2 3 4 5>;
say map(-> $x {$x ** 2},@array);Notice that instead of declaring the squared subroutine and passing it as an argument to map, we defined
it within the anonymous subroutine as -> $x {$x ** 2}.
In Raku parlance, we call this notation a pointy block
my $squared = -> $x {
$x ** 2
}
say $squared(9);In Raku, methods can be chained, so you’re not required to pass the result of one method to another as an argument.
To illustrate: Given an array, you may need to return the unique values of the array, sorted from biggest to smallest.
Here’s a non-chained solution:
my @array = <7 8 9 0 1 2 4 3 5 6 7 8 9>;
my @final-array = reverse(sort(unique(@array)));
say @final-array;Here, we call unique on @array, pass the result as an argument to sort, and then pass that result to reverse.
In contrast, with chained methods, the above example can be rewritten as:
my @array = <7 8 9 0 1 2 4 3 5 6 7 8 9>;
my @final-array = @array.unique.sort.reverse;
say @final-array;You can already see that chaining methods is easier on the eye.
The feed operator, called pipe in some functional programming languages, further illustrates method chaining.
my @array = <7 8 9 0 1 2 4 3 5 6 7 8 9>;
@array ==> unique()
==> sort()
==> reverse()
==> my @final-array;
say @final-array;Start with `@array` then return a list of unique elements
then sort it
then reverse it
then store the result in @final-arrayNote that the flow of the method calls is top-down — from first to final step.
my @array = <7 8 9 0 1 2 4 3 5 6 7 8 9>;
my @final-array-v2 <== reverse()
<== sort()
<== unique()
<== @array;
say @final-array-v2;The backward feed is like the forward feed, but in reverse.
The flow of the method calls is bottom-up — from final to first step.
The hyper operator >>. will call a method on all elements of a list and return a list of the results.
my @array = <0 1 2 3 4 5 6 7 8 9 10>;
sub is-even($var) { $var %% 2 };
say @array>>.is-prime;
say @array>>.&is-even;Using the hyper operator we can call methods already defined in Raku, e.g. is-prime that tells us if a number is prime or not.
In addition we can define new subroutines and call them using the hyper operator. In this case we have to prepend & to the name of the method; e.g., &is-even.
This is very practical as it relieves us from writing a for loop to iterate over each value.
|
Warning
|
Raku guarantees that the order of the results is the same as that of the original list.
However, there is no guarantee that Raku will actually call the methods in list order or in the same thread. So, be careful with methods that have side-effects, such as say or print.
|
A junction is a logical superposition of values.
In the below example 1|2|3 is a junction.
my $var = 2;
if $var == 1|2|3 {
say "The variable is 1 or 2 or 3"
}The use of junctions usually triggers autothreading; the operation is carried out for each junction element, and all the results are combined into a new junction and returned.
A lazy list is a list that is lazily evaluated.
Lazy evaluation delays the evaluation of an expression until required, and avoids repeating evaluations by storing results in a lookup table.
The benefits include:
-
Performance increase by avoiding needless calculations
-
The ability to construct potentially infinite data structures
-
The ability to define control flow
To build a lazy list we use the infix operator …
A lazy list has initial element(s), a generator and an endpoint.
my $lazylist = (1 ... 10);
say $lazylist;The initial element is 1 and the endpoint is 10. No generator was defined so the default generator is the successor (+1)
In other words this lazy list may return (if requested) the following elements (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
my $lazylist = (1 ... Inf);
say $lazylist;This list may return (if requested) any integer between 1 and infinity, in other words any integer number.
my $lazylist = (0,2 ... 10);
say $lazylist;The initial elements are 0 and 2 and the endpoint is 10.
No generator was defined, but using the initial elements, Raku will deduce that the generator is (+2)
This lazy list may return (if requested) the following elements (0, 2, 4, 6, 8, 10)
my $lazylist = (0, { $_ + 3 } ... 12);
say $lazylist;In this example, we defined explicitly a generator enclosed in { }
This lazy list may return (if requested) the following elements (0, 3, 6, 9, 12)
|
Warning
|
When using an explicit generator, the endpoint must be one of the values that the generator can return. Alternatively you can replace This will not stop the generator
my $lazylist = (0, { $_ + 3 } ... 10);
say $lazylist;This will stop the generator
my $lazylist = (0, { $_ + 3 } ...^ * > 10);
say $lazylist; |
All code objects in Raku are closures, which means they can reference lexical variables from an outer scope.
sub generate-greeting {
my $name = "John Doe";
sub greeting {
say "Good Morning $name";
};
return &greeting;
}
my $generated = generate-greeting;
$generated();If you run the above code, it will display Good Morning John Doe on the terminal.
While the result is fairly simple, what is interesting about this example, is that the greeting inner subroutine was returned from the outer subroutine before being executed.
$generated has become a closure.
A closure is a special kind of object that combines two things:
-
A Subroutine
-
The Environment in which that subroutine was created.
The environment consists of any local variable that was in-scope at the time that the closure was created.
In this case, $generated is a closure that incorporates both the greeting subroutine and the John Doe string that existed when the closure was created.
Let’s take a look at a more interesting example.
sub greeting-generator($period) {
return sub ($name) {
return "Good $period $name"
}
}
my $morning = greeting-generator("Morning");
my $evening = greeting-generator("Evening");
say $morning("John");
say $evening("Jane");In this example, we have defined a subroutine greeting-generator($period) that accepts a single argument $period
and returns a new subroutine. The subroutine it returns accepts a single argument $name and returns the constructed greeting.
Basically, greeting-generator is a subroutine factory. In this example, we used greeting-generator to create two new subroutines,
one that says Good Morning and one that says Good Evening.
$morning and $evening are both closures. They share the same subroutine body definition, but store different environments.
In $morning 's environment $period is Morning. In $evening 's environment $period is Evening.
In the previous chapter, we learned how Raku facilitates Functional Programming.
In this chapter we will take a look at Object Oriented programming in Raku.
Object Oriented programming is one of the widely used paradigms nowadays.
An object is a set of variables and subroutines bundled together.
The variables are called attributes and the subroutines are called methods.
Attributes define the state and methods define the behavior of an object.
A class is a template for creating objects.
In order to understand the relationship consider the below example:
There are 4 people present in a room |
objects ⇒ 4 people |
These 4 people are humans |
class ⇒ Human |
They have different names, age, sex and nationality |
attributes ⇒ name, age, sex, nationality |
In object oriented parlance, we say that objects are instances of a class.
Consider the below script:
class Human {
has $.name;
has $.age;
has $.sex;
has $.nationality;
}
my $john = Human.new(name => 'John', age => 23, sex => 'M', nationality => 'American');
say $john;The class keyword is used to define a class.
The has keyword is used to define attributes of a class.
The .new() method is called a constructor. It creates the object as an instance of the class it has been called on.
In the above script, a new variable $john holds a reference to a new instance of "Human" defined by Human.new().
The arguments passed to the .new() method are used to set the attributes of the underlying object.
A class can be given lexical scope using my:
my class Human {
}Encapsulation is an object oriented concept that bundles a set of data and methods together.
The data (attributes) within an object should be private, in other words, accessible only from within the object.
In order to access the attributes from outside the object, we use methods called accessors.
The below two scripts have the same result.
my $var = 7;
say $var;my $var = 7;
sub sayvar {
$var;
}
say sayvar;The method sayvar is an accessor. It lets us access the value of the variable without getting direct access to it.
Encapsulation is facilitated in Raku with the use of twigils.
Twigils are secondary sigils. They come between the sigil and the attribute name.
Two twigils are used in classes:
-
!is used to explicitly declare that the attribute is private. -
.is used to automatically generate an accessor for the attribute.
By default, all attributes are private but it is a good habit to always use the ! twigil.
Therefore, we should rewrite the above class as:
class Human {
has $!name;
has $!age;
has $!sex;
has $!nationality;
}
my $john = Human.new(name => 'John', age => 23, sex => 'M', nationality => 'American');
say $john;Append to the script the following statement: say $john.age;
It will return this error: Method 'age' not found for invocant of class 'Human'
because $!age is private and can only be used within the object.
Trying to access it outside the object will return an error.
Now replace has $!age with has $.age and observe the result of say $john.age;
In Raku, all classes inherit a default .new() constructor.
It can be used to create objects by providing it with arguments.
The default constructor can only be provided with named arguments.
In our example above, notice that the arguments supplied to .new() are defined by name:
-
name => 'John'
-
age => 23
What if I do not want to supply the name of each attribute each time I want to create an object?
Then I need to create another constructor that accepts positional arguments.
class Human {
has $.name;
has $.age;
has $.sex;
has $.nationality;
# new constructor that overrides the default one.
method new ($name,$age,$sex,$nationality) {
self.bless(:$name,:$age,:$sex,:$nationality);
}
}
my $john = Human.new('John',23,'M','American');
say $john;Methods are the subroutines of an object.
Like subroutines, they are a means of packaging a set of functionality, they accept arguments, have a signature and can be defined as multi.
Methods are defined using the method keyword.
In normal circumstances, methods are required to perform some sort of action on the objects' attributes.
This enforces the concept of encapsulation. Object attributes can only be manipulated from within the object using methods.
The outside world can only interact with the object methods, and has no direct access to its attributes.
class Human {
has $.name;
has $.age;
has $.sex;
has $.nationality;
has $.eligible;
method assess-eligibility {
if self.age < 21 {
$!eligible = 'No'
} else {
$!eligible = 'Yes'
}
}
}
my $john = Human.new(name => 'John', age => 23, sex => 'M', nationality => 'American');
$john.assess-eligibility;
say $john.eligible;Once methods are defined within a class, they can be called on an object using the dot notation:
object . method or as in the above example: $john.assess-eligibility
Within the definition of a method, if we need to reference the object itself to call another method we use the self keyword.
Within the definition of a method, if we need to reference an attribute we use ! even if it was defined with .
The rationale being that what the . twigil does is declare an attribute with ! and automate the creation of an accessor.
In the above example, if self.age < 21 and if $!age < 21 would have the same effect, although they are technically different:
-
self.agecalls the.agemethod (accessor)
Can be written alternatively as$.age -
$!ageis a direct call to the variable
Normal methods can be called on objects from outside the class.
Private methods are methods that can only be called from within the class.
A possible use case would be a method that calls another one for specific action.
The method that interfaces with the outside world is public while the one referenced should stay private.
We do not want users to call it directly, so we declare it as private.
The declaration of a private method requires the use of the ! twigil before its name.
Private methods are called with ! instead of .
method !iamprivate {
# code goes in here
}
method iampublic {
self!iamprivate;
# do additional things
}Class attributes are attributes that belong to the class itself and not to its objects.
They can be initialized during definition.
Class attributes are declared using my instead of has.
They are called on the class itself instead of its objects.
class Human {
has $.name;
my $.counter = 0;
method new($name) {
Human.counter++;
self.bless(:$name);
}
}
my $a = Human.new('a');
my $b = Human.new('b');
say Human.counter;Until now, all the examples that we’ve seen have used accessors to get information from the objects' attributes.
What if we need to modify the value of an attribute?
We need to label it as read/write using the keywords is rw
class Human {
has $.name;
has $.age is rw;
}
my $john = Human.new(name => 'John', age => 21);
say $john.age;
$john.age = 23;
say $john.age;By default, all attributes are declared as read only but you can explicitly do it using is readonly
Inheritance is another concept of object oriented programming.
When defining classes, soon enough we will realize that some attributes/methods are common to many classes.
Should we duplicate code?
NO! We should use inheritance
Let’s consider we want to define two classes, a class for Human beings and a class for Employees.
Human beings have 2 attributes: name and age.
Employees have 4 attributes: name, age, company and salary
One would be tempted to define the classes as:
class Human {
has $.name;
has $.age;
}
class Employee {
has $.name;
has $.age;
has $.company;
has $.salary;
}While technically correct, the above piece of code is considered conceptually poor.
A better way to write this would be:
class Human {
has $.name;
has $.age;
}
class Employee is Human {
has $.company;
has $.salary;
}The is keyword defines inheritance.
In object oriented parlance, we say Employee is a child of Human and that Human is a parent of Employee.
All child classes inherit the attributes and methods of the parent class, so there is no need to redefine them.
Classes inherit all attributes and methods from their parent classes.
There are cases where we need the method in the child class to behave differently than the one inherited.
To achieve this, we redefine the method in the child class.
This concept is called overriding.
In the below example, the method introduce-yourself is inherited by the Employee class.
class Human {
has $.name;
has $.age;
method introduce-yourself {
say 'Hi I am a human being, my name is ' ~ self.name;
}
}
class Employee is Human {
has $.company;
has $.salary;
}
my $john = Human.new(name =>'John', age => 23,);
my $jane = Employee.new(name =>'Jane', age => 25, company => 'Acme', salary => 4000);
$john.introduce-yourself;
$jane.introduce-yourself;Overriding works like this:
class Human {
has $.name;
has $.age;
method introduce-yourself {
say 'Hi I am a human being, my name is ' ~ self.name;
}
}
class Employee is Human {
has $.company;
has $.salary;
method introduce-yourself {
say 'Hi I am a employee, my name is ' ~ self.name ~ ' and I work at: ' ~ self.company;
}
}
my $john = Human.new(name =>'John',age => 23,);
my $jane = Employee.new(name =>'Jane',age => 25,company => 'Acme',salary => 4000);
$john.introduce-yourself;
$jane.introduce-yourself;Depending of which class the object is, the right method will be called.
Multiple inheritance is allowed in Raku. A class can inherit from multiple other classes.
class bar-chart {
has Int @.bar-values;
method plot {
say @.bar-values;
}
}
class line-chart {
has Int @.line-values;
method plot {
say @.line-values;
}
}
class combo-chart is bar-chart is line-chart {
}
my $actual-sales = bar-chart.new(bar-values => [10,9,11,8,7,10]);
my $forecast-sales = line-chart.new(line-values => [9,8,10,7,6,9]);
my $actual-vs-forecast = combo-chart.new(bar-values => [10,9,11,8,7,10],
line-values => [9,8,10,7,6,9]);
say "Actual sales:";
$actual-sales.plot;
say "Forecast sales:";
$forecast-sales.plot;
say "Actual vs Forecast:";
$actual-vs-forecast.plot;OutputActual sales:
[10 9 11 8 7 10]
Forecast sales:
[9 8 10 7 6 9]
Actual vs Forecast:
[10 9 11 8 7 10]The combo-chart class should be able to hold two series, one for the actual values plotted on bars,
and another for forecast values plotted on a line.
This is why we defined it as a child of line-chart and bar-chart.
You should have noticed that calling the method plot on the combo-chart didn’t yield the required result.
Only one series was plotted.
Why did this happen?
combo-chart inherits from line-chart and bar-chart, and both of them have a method called plot.
When we call that method on combo-chart Raku internals will try to resolve the conflict by calling one of the inherited methods.
In order to behave correctly, we should have overridden the method plot in the combo-chart.
class bar-chart {
has Int @.bar-values;
method plot {
say @.bar-values;
}
}
class line-chart {
has Int @.line-values;
method plot {
say @.line-values;
}
}
class combo-chart is bar-chart is line-chart {
method plot {
say @.bar-values;
say @.line-values;
}
}
my $actual-sales = bar-chart.new(bar-values => [10,9,11,8,7,10]);
my $forecast-sales = line-chart.new(line-values => [9,8,10,7,6,9]);
my $actual-vs-forecast = combo-chart.new(bar-values => [10,9,11,8,7,10],
line-values => [9,8,10,7,6,9]);
say "Actual sales:";
$actual-sales.plot;
say "Forecast sales:";
$forecast-sales.plot;
say "Actual vs Forecast:";
$actual-vs-forecast.plot;OutputActual sales:
[10 9 11 8 7 10]
Forecast sales:
[9 8 10 7 6 9]
Actual vs Forecast:
[10 9 11 8 7 10]
[9 8 10 7 6 9]Roles are similar to classes in that they are a collection of attributes and methods.
Roles are declared with the keyword role. Classes that wish to implement a role, do so using the does keyword.
role bar-chart {
has Int @.bar-values;
method plot {
say @.bar-values;
}
}
role line-chart {
has Int @.line-values;
method plot {
say @.line-values;
}
}
class combo-chart does bar-chart does line-chart {
method plot {
say @.bar-values;
say @.line-values;
}
}
my $actual-sales = bar-chart.new(bar-values => [10,9,11,8,7,10]);
my $forecast-sales = line-chart.new(line-values => [9,8,10,7,6,9]);
my $actual-vs-forecast = combo-chart.new(bar-values => [10,9,11,8,7,10],
line-values => [9,8,10,7,6,9]);
say "Actual sales:";
$actual-sales.plot;
say "Forecast sales:";
$forecast-sales.plot;
say "Actual vs Forecast:";
$actual-vs-forecast.plot;Run the above script and you will see that results are the same.
By now you’re asking yourself: If roles behave like classes, what’s their use?
To answer your question, modify the first script used to showcase multiple inheritance,
the one where we forgot to override the plot method.
role bar-chart {
has Int @.bar-values;
method plot {
say @.bar-values;
}
}
role line-chart {
has Int @.line-values;
method plot {
say @.line-values;
}
}
class combo-chart does bar-chart does line-chart {
}
my $actual-sales = bar-chart.new(bar-values => [10,9,11,8,7,10]);
my $forecast-sales = line-chart.new(line-values => [9,8,10,7,6,9]);
my $actual-vs-forecast = combo-chart.new(bar-values => [10,9,11,8,7,10],
line-values => [9,8,10,7,6,9]);
say "Actual sales:";
$actual-sales.plot;
say "Forecast sales:";
$forecast-sales.plot;
say "Actual vs Forecast:";
$actual-vs-forecast.plot;Output===SORRY!===
Method 'plot' must be resolved by class combo-chart because it exists in multiple roles (line-chart, bar-chart)If multiple roles are applied to the same class and a conflict exists, a compile-time error will be thrown.
This is a much safer approach than multiple inheritance, where conflicts are not considered errors and are simply resolved at runtime.
Roles will warn you that there’s a conflict.
Introspection is the process of getting information about an object, like its type, attributes or methods.
class Human {
has Str $.name;
has Int $.age;
method introduce-yourself {
say 'Hi I am a human being, my name is ' ~ self.name;
}
}
class Employee is Human {
has Str $.company;
has Int $.salary;
method introduce-yourself {
say 'Hi I am a employee, my name is ' ~ self.name ~ ' and I work at: ' ~ self.company;
}
}
my $john = Human.new(name =>'John',age => 23,);
my $jane = Employee.new(name =>'Jane',age => 25,company => 'Acme',salary => 4000);
say $john.WHAT;
say $jane.WHAT;
say $john.^attributes;
say $jane.^attributes;
say $john.^methods;
say $jane.^methods;
say $jane.^parents;
if $jane ~~ Human {say 'Jane is a Human'};Introspection is facilitated by:
-
.WHAT— returns the class from which the object was created -
.^attributes— returns all the attributes of the object -
.^methods— returns all the methods that can be called on the object -
.^parents— returns the parent classes of the object -
~~is called the smart-match operator. It evaluates to True if the object is created from the class it is being compared against or any of its inheritances.
|
Note
|
For more info on Object Oriented Programming in Raku, see: |
Exceptions are a special behavior that happens at runtime when something goes wrong.
We say that exceptions are thrown.
Consider the below script that runs correctly:
my Str $name;
$name = "Joanna";
say "Hello " ~ $name;
say "How are you doing today?"OutputHello Joanna
How are you doing today?Now consider this script that throws an exception:
my Str $name;
$name = 123;
say "Hello " ~ $name;
say "How are you doing today?"OutputType check failed in assignment to $name; expected Str but got Int
in block <unit> at exceptions.raku:2Notice that whenever an error occurs (in this case, assigning a number to a string variable) the program will stop and other lines of code will not be evaluated.
Exception handling is the process of catching an exception that has been thrown in order for the script to continue working.
my Str $name;
try {
$name = 123;
say "Hello " ~ $name;
CATCH {
default {
say "Can you tell us your name again, we couldn't find it in the register.";
}
}
}
say "How are you doing today?";OutputCan you tell us your name again, we couldn't find it in the register.
How are you doing today?Exception handling is done by using a try-catch block.
try {
# code goes in here
# if anything goes wrong, the script will enter the below CATCH block
# if nothing goes wrong, the CATCH block will be ignored
CATCH {
default {
# the code in here will be evaluated only if an exception has been thrown
}
}
}The CATCH block can be defined the same way a given block is defined.
This means we can catch and handle differently many types of exceptions.
try {
# code goes in here
# if anything goes wrong, the script will enter the below CATCH block
# if nothing goes wrong, the CATCH block will be ignored
CATCH {
when X::AdHoc { # do something if exception of type X::AdHoc is thrown }
when X::IO { # do something if exception of type X::IO is thrown }
when X::OS { # do something if exception of type X::OS is thrown }
default { # do something if exception is thrown and doesn't belong to the above types }
}
}Raku also allows you to explicitly throw exceptions.
Two types of exceptions can be thrown:
-
ad-hoc exceptions
-
typed exceptions
my Int $age = 21;
die "Error !";my Int $age = 21;
X::AdHoc.new(payload => 'Error !').throw;Ad-hoc exceptions are thrown using the die subroutine, followed by the exception message.
Typed exceptions are objects, hence the use of the .new() constructor in the above example.
All typed exceptions descend from class X , below are a few examples:
X::AdHoc is the simplest exception type
X::IO is related to IO errors
X::OS is related to OS errors
X::Str::Numeric related to trying to coerce a string to a number
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Note
|
For a complete list of exception types and their associated methods, go to https://docs.raku.org/type-exceptions.html |
A regular expression, or regex, is a sequence of characters that is used for pattern matching.
Think of it as a pattern.
if 'enlightenment' ~~ m/ light / {
say "enlightenment contains the word light";
}In this example, the smart match operator ~~ is used to check if a string (enlightenment) contains the word (light).
"Enlightenment" is matched against the regex m/ light /
A regular expression can be defined like this:
-
/light/ -
m/light/ -
rx/light/
Unless specified explicitly, white space is ignored; m/light/ and m/ light / are the same.
Alphanumeric characters and the underscore _ are written as is.
All other characters have to be escaped using a backslash or surrounded by quotes.
if 'Temperature: 13' ~~ m/ \: / {
say "The string provided contains a colon :";
}if 'Age = 13' ~~ m/ '=' / {
say "The string provided contains an equal character = ";
}if '[email protected]' ~~ m/ "@" / {
say "This is a valid email address because it contains an @ character";
}Characters can be classified into categories and we can match against them.
We can also match against the inverse of that category (everything except it):
Category |
Regex |
Inverse |
Regex |
Word character (letter, digit or underscore) |
\w |
Any character except a word character |
\W |
Digit |
\d |
Any character except a digit |
\D |
Whitespace |
\s |
Any character except a whitespace |
\S |
Horizontal whitespace |
\h |
Any character except a horizontal whitespace |
\H |
Vertical whitespace |
\v |
Any character except a vertical whitespace |
\V |
Tab |
\t |
Any character except a Tab |
\T |
New line |
\n |
Any character except a new line |
\N |
if "John123" ~~ / \d / {
say "This is not a valid name, numbers are not allowed";
} else {
say "This is a valid name"
}
if "John-Doe" ~~ / \s / {
say "This string contains whitespace";
} else {
say "This string doesn't contain whitespace"
}Matching against categories of characters, as seen in the preceding section, is convenient.
That being said, a more systematic approach would be to use Unicode properties.
This allows you to match against categories of characters inside and outside of
the ASCII standard.
Unicode properties are enclosed in <: >
if "Devanagari Numbers १२३" ~~ / <:N> / {
say "Contains a number";
} else {
say "Doesn't contain a number"
}
if "Привет, Иван." ~~ / <:Lu> / {
say "Contains an uppercase letter";
} else {
say "Doesn't contain an upper case letter"
}
if "John-Doe" ~~ / <:Pd> / {
say "Contains a dash";
} else {
say "Doesn't contain a dash"
}Wildcards can also be used in a regex.
The dot . means any single character.
if 'abc' ~~ m/ a.c / {
say "Match";
}
if 'a2c' ~~ m/ a.c / {
say "Match";
}
if 'ac' ~~ m/ a.c / {
say "Match";
} else {
say "No Match";
}Quantifiers come after a character and are used to specify how many times we are expecting it.
The question mark ? means zero or one time.
if 'ac' ~~ m/ a?c / {
say "Match";
} else {
say "No Match";
}
if 'c' ~~ m/ a?c / {
say "Match";
} else {
say "No Match";
}The star * means zero or multiple times.
if 'az' ~~ m/ a*z / {
say "Match";
} else {
say "No Match";
}
if 'aaz' ~~ m/ a*z / {
say "Match";
} else {
say "No Match";
}
if 'aaaaaaaaaaz' ~~ m/ a*z / {
say "Match";
} else {
say "No Match";
}
if 'z' ~~ m/ a*z / {
say "Match";
} else {
say "No Match";
}The + means at least one time.
if 'az' ~~ m/ a+z / {
say "Match";
} else {
say "No Match";
}
if 'aaz' ~~ m/ a+z / {
say "Match";
} else {
say "No Match";
}
if 'aaaaaaaaaaz' ~~ m/ a+z / {
say "Match";
} else {
say "No Match";
}
if 'z' ~~ m/ a+z / {
say "Match";
} else {
say "No Match";
}Whenever the process of matching a string against a regex is successful,
the match result is stored in a special variable $/
if 'Rakudo is a Perl 6 compiler' ~~ m/:s Perl 6/ {
say "The match is: " ~ $/;
say "The string before the match is: " ~ $/.prematch;
say "The string after the match is: " ~ $/.postmatch;
say "The matching string starts at position: " ~ $/.from;
say "The matching string ends at position: " ~ $/.to;
}The match is: Perl 6
The string before the match is: Rakudo is a
The string after the match is: compiler
The matching string starts at position: 12
The matching string ends at position: 18$/ returns a Match Object (the string that matches the regex)
The following methods can be called on the Match Object:
.prematch returns the string preceding the match.
.postmatch returns the string following the match.
.from returns the starting position of the match.
.to returns the ending position of the match.
|
Tip
|
By default, whitespace in a regex definition is ignored. If we want to match against a regex containing whitespace, we have to do so explicitly. The :s in the regex m/:s Perl 6/ forces whitespace to be considered.Alternatively, we could have written the regex as m/ Perl\s6 / and used \s which represents a whitespace.If a regex contains more than a single whitespace, using :s is a better option than using \s for each and every whitespace.
|
Let’s check if an email is valid or not.
For the sake of this example we will assume that a valid email address has this format:
first name [dot] last name [at] company [dot] (com/org/net)
|
Warning
|
The regex used in this example for email validation is not very accurate. Its sole purpose is to demonstrate regex functionality in Raku. Do not use it as-is in production. |
my $email = '[email protected]';
my $regex = / <:L>+\.<:L>+\@<:L+:N>+\.<:L>+ /;
if $email ~~ $regex {
say $/ ~ " is a valid email";
} else {
say "This is not a valid email";
}[email protected] is a valid email
<:L> matches a single letter
<:L>` matches one or more letters +
`\.` matches a single [dot] character +
`\@` matches a single [at] character +
`<:L:N> matches a letter or a single number
<:L+:N>+ matches one or more letters or numbers
The regex can be decomposed as following:
-
first name
<:L>+ -
[dot]
\. -
last name
<:L>+ -
[at]
\@ -
company name
<:L+:N>+ -
[dot]
\. -
com/org/net
<:L>+
my $email = '[email protected]';
my regex many-letters { <:L>+ };
my regex dot { \. };
my regex at { \@ };
my regex many-letters-numbers { <:L+:N>+ };
if $email ~~ / <many-letters> <dot> <many-letters> <at> <many-letters-numbers> <dot> <many-letters> / {
say $/ ~ " is a valid email";
} else {
say "This is not a valid email";
}A named regex is defined using the following syntax: my regex regex-name { regex definition }
A named regex can be called using the following syntax: <regex-name>
|
Note
|
For more info on regexes, see https://docs.raku.org/language/regexes |
Raku is a general purpose programming language. It can be used to tackle a multitude of tasks including: text manipulation, graphics, web, databases, network protocols etc.
Reusability is a very important concept whereby programmers don’t have to reinvent the wheel each time they want to do a new task.
Raku allows the creation and redistribution of modules. Each module is a packaged set of functionality that can be reused once installed.
Zef is a module management tool that comes with Rakudo Star.
To install a specific module, type the below command in your terminal:
zef install "module name"
|
Note
|
The Raku modules directory can be found on: https://raku.land/ |
MD5 is a cryptographic hash function that produces a 128-bit hash value.
MD5 has a variety of applications, including the encryption of stored passwords in a database.
When a new user registers, their credentials are not stored as plain text but rather hashed.
The rationale behind this is that if the DB gets compromised, the attacker will not be able to know what the passwords are.
Luckily, you don’t need to implement the MD5 algorithm yourself; there’s a Raku module already implemented.
Let’s install it:
zef install Digest::MD5
Now, run the below script:
use Digest::MD5;
my $password = "password123";
my $hashed-password = md5( $password );
say $hashed-password;In order to run the md5() function that creates hashes, we need to load the required module.
The use keyword loads the module for use in the script which provides an md5 subroutine.
|
Warning
|
In practice MD5 hashing alone is not sufficient, because it is prone to dictionary attacks. It should be combined with a salt https://en.wikipedia.org/wiki/Salt_(cryptography). |
Unicode is a standard for encoding and representing text for most writing systems in the world.
UTF-8 is a character encoding capable of encoding all possible characters, or code points, in Unicode.
Characters are defined by a:
Grapheme: Visual representation.
Code point: A number assigned to the character.
Code point name: A name assigned to the character.
say "a";
say "\x0061";
say "\c[LATIN SMALL LETTER A]";The above 3 lines showcase different ways of building a character:
-
Writing the character directly (grapheme)
-
Using
\xand the code point -
Using
\cand the code point name
say "☺";
say "\x263a";
say "\c[WHITE SMILING FACE]";say "á";
say "\x00e1";
say "\x0061\x0301";
say "\c[LATIN SMALL LETTER A WITH ACUTE]";The letter á can be written:
-
using its unique code point
\x00e1 -
or as a combination of the code points of
aand acute\x0061\x0301
say "á".NFC;
say "á".NFD;
say "á".uniname;OutputNFC:0x<00e1>
NFD:0x<0061 0301>
LATIN SMALL LETTER A WITH ACUTENFC returns the unique code point.
NFD decomposes the character and return the code point of each part.
uniname returns the code point name.
my $Δ = 1;
$Δ++;
say $Δ;my $var = 2 + ⅒;
say $var;Arabic numerals are the ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. This numeral set is the most used worldwide.
Nonetheless different sets of numerals are used to a lesser extent in different parts of the world.
No special care needs to be taken when using a numeral set different than the Arabic numerals. All methods/operators work as expected.
say (٤,٥,٦,1,2,3).sort; # (1 2 3 4 5 6)
say 1 + ٩; # 10If we were to use generic string operations, we might not always get the result that we were looking for, especially when comparing or sorting.
say 'a' cmp 'B'; # MoreThe above example shows that a is bigger than B. The reason being that the
code point of lowercase a is bigger than the code point of capital B.
While technically correct, this is probably not what we were looking for.
Luckily Raku has methods/operators that implement the Unicode Collation Algorithm.
One of them is unicmp that behaves like the above showcased cmp but is unicode-aware.
say 'a' unicmp 'B'; # LessAs you can see, using the unicmp operator now yields the expected result that a is smaller than B.
As an alternative to the sort method that sorts using code points, Raku provides a collate
method that implements the Unicode Collation Algorithm.
say ('a','b','c','D','E','F').sort; # (D E F a b c)
say ('a','b','c','D','E','F').collate; # (a b c D E F)Under normal circumstances, all tasks in a program run sequentially.
This might not be a problem, unless what you’re trying to do takes a lot of time.
Thankfully, Raku has features that will enable you to run things in parallel.
At this stage, it is important to note that parallelism can mean one of two things:
-
Task Parallelism: Two (or more) independent expressions running in parallel.
-
Data Parallelism: A single expression iterating over a list of elements in parallel.
Let’s begin with the latter.
my @array = 0..50000; # Array population
my @result = @array.map({ is-prime $_ }); # call is-prime for each array element
say now - INIT now; # Output the time it took for the script to completeWe are only doing one operation @array.map({ is-prime $_ })
The is-prime subroutine is being called for each array element sequentially:
is-prime @array[0] then is-prime @array[1] then is-prime @array[2] etc.
is-prime on multiple array elements at the same time:my @array = 0..50000; # Array population
my @result = @array.race.map({ is-prime $_ }); # call is-prime for each array element
say now - INIT now; # Output the time it took to completeNotice the use of race in the expression.
This method will enable parallel iteration of the array elements.
After running both examples (with and without race), compare the time it took for both scripts to complete.
|
Tip
|
race
my @array = 1..1000;
my @result = @array.race.map( {$_ + 1} );
.say for @result;hyper
my @array = 1..1000;
my @result = @array.hyper.map( {$_ + 1} );
.say for @result;If you run both examples, you should notice that one is sorted and the other is not. |
my @array1 = 0..49999;
my @array2 = 2..50001;
my @result1 = @array1.map( {is-prime($_ + 1)} );
my @result2 = @array2.map( {is-prime($_ - 1)} );
say @result1 eqv @result2;
say now - INIT now;-
We defined 2 arrays
-
applied a different operation for each array and stored the results
-
and checked if both results are the same
The script waits for @array1.map( {is-prime($_ + 1)} ) to finish
and then evaluates @array2.map( {is-prime($_ - 1)} )
Both operations applied to each array do not depend on each other.
my @array1 = 0..49999;
my @array2 = 2..50001;
my $promise1 = start @array1.map( {is-prime($_ + 1)} ).eager;
my $promise2 = start @array2.map( {is-prime($_ - 1)} ).eager;
my @result1 = await $promise1;
my @result2 = await $promise2;
say @result1 eqv @result2;
say now - INIT now;The start subroutine evaluates the code and returns an object of type promise or shortly a promise.
If the code is evaluated correctly, the promise will be kept.
If the code throws an exception, the promise will be broken.
The await subroutine waits for a promise.
If it’s kept it will get the returned values.
If it’s broken it will get the exception thrown.
Check the time it took each script to complete.
|
Warning
|
Parallelism always adds a threading overhead. If that overhead is not offset by gains in computational speed, the script will seem slower. This is why, using race, hyper, start and await for fairly simple scripts can actually slow them down.
|
|
Note
|
For more info on Concurrency and Asynchronous Programming, see https://docs.raku.org/language/concurrency |
Raku gives us the ability to use C libraries, using the Native Calling Interface.
NativeCall is a standard module that ships with Raku and offers a set of functionality to ease the job
of interfacing Raku and C.
Consider the below C code that defines a function called hellofromc.
This function prints on the terminal Hello from C. It doesn’t accept any argument nor return any value.
#include <stdio.h>
void hellofromc () {
printf("Hello from C\n");
}Depending on your OS run the following commands to compile the above C code into a library.
gcc -c -fpic ncitest.c
gcc -shared -o libncitest.so ncitest.ogcc -c ncitest.c
gcc -shared -o ncitest.dll ncitest.ogcc -dynamiclib -o libncitest.dylib ncitest.cWithin the same directory where you compiled your C library, create a new Raku file that contains the below code and run it.
use NativeCall;
constant LIBPATH = "$*CWD/ncitest";
sub hellofromc() is native(LIBPATH) { * }
hellofromc();First of all we declared that we will be using the NativeCall module.
Then we created a constant LIBPATH that holds the path to the C library.
Notice that $*CWD returns the current working directory.
Then we created a new Raku subroutine called hellofromc() that should act as a
wrapper to its counterpart C function having the same name and residing in the C
library found in LIBPATH.
All of this was done by using the is native trait.
Finally we called our Raku subroutine.
In essence, it all boils down to declaring a subroutine with the trait is native and the name of the C library.
In the above part, we saw how we can call a very simple C function by wrapping
it with a Raku subroutine having the same name, using the is native trait.
In some cases, we would want to change the name of the Raku subroutine.
To do so, we use the is symbol trait.
Lets modify the above Raku script and rename the Raku subroutine hello
instead of hellofromc
use NativeCall;
constant LIBPATH = "$*CWD/ncitest";
sub hello() is native(LIBPATH) is symbol('hellofromc') { * }
hello();In case the Raku subroutine has a different name than its C counterpart, we
should use the is symbol trait with the name of the original C function.
Compile the following modified C library and run the Raku script found below again.
Notice how we modified both C and Raku code to accept a string (char* in C and Str in Raku)
#include <stdio.h>
void hellofromc (char* name) {
printf("Hello, %s! This is C!\n", name);
}use NativeCall;
constant LIBPATH = "$*CWD/ncitest";
sub hello(Str) is native(LIBPATH) is symbol('hellofromc') { * }
hello('Jane');Lets repeat the process one more time and create a simple calculator that takes
2 integers and add them.
Compile the C library and run the Raku script.
int add (int a, int b) {
return (a + b);
}use NativeCall;
constant LIBPATH = "$*CWD/ncitest";
sub add(int32,int32 --> int32) is native(LIBPATH) { * }
say add(2,3);Notice how both C and Raku functions accept two integers and return one
(int in C and int32 in Raku)
You might have asked yourself why did we use int32 instead of Int in the latest Raku script.
Some Raku types like Int, Rat etc. can’t be used as is to pass and receive values from a C function.
One must use in Raku the same types as the ones in C.
Luckily Raku provides many types that map to their respective C counterpart.
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Arrays: For example |
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Note
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For more info on the Native Calling Interface, see https://docs.raku.org/language/nativecall |
-
#raku IRC channel. Much discussion happens on IRC.
This should be your go to place for any enquiry for which you want an immediate answer: https://raku.org/community/irc -
StackOverflow Raku questions is a place where questions about Raku can be answered more in-depth.
-
Rakudo Weekly a weekly overview of changes in and around Rakudo.
-
Planet Raku blog aggregator. Stay tuned by reading blog posts that focus on Raku.
-
/r/rakulang subscribe to the Raku subreddit.
-
@raku_news follow the community on X.
-
@rakulang follow the community on Mastodon.