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Perl 6 is a planned major revision to the Perl programming language. Perl 6 introduces elements of many modern and historical languages. Perl 6 is not intended to be backwards-compatible with earlier versions of Perl, though a compatibility mode is part of the specification. Programming Republic of Perl logo This image is trademarked. ... A programming paradigm is a paradigmatic style of programming (compare with a methodology, which is a paradigmatic style of doing software engineering). ... A multiparadigm programming language is a programming language that supports more than one programming paradigm. ... Larry Wall Larry Wall (born September 27, 1954) is a programmer, linguist, and author, most widely known for his creation of the Perl programming language in 1987. ... A software release refers to the creation and availability of a new version of a computer software product. ... In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ... Wikibooks has a book on the topic of Perl Programming Perl is a dynamic programming language created by Larry Wall and first released in 1987. ... // Haskell may refer ro: Haskell (programming language), a standardized pure functional programming language with non-strict semantics Haskell Indian Nations University, a four year degree granting university in Lawrence, Kansas which offers free tuition to members of registered Native American tribes in the United States Haskell Free Library and Opera... An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. ... A cross-platform (or platform independent) programming language, software application or hardware device works on more than one system platform (e. ... A software license is a legal agreement which may take the form of a proprietary or gratuitous license as well as a memorandum of contract between a producer and a user of computer software. ... GPL redirects here. ... The Artistic License is a software license used for certain free software packages, most notably the standard Perl implementation, most of CPAN modules and Parrot, which are dual-licensed under the Artistic License and the GNU General Public License (GPL). ... A website (alternatively, Web site or web site) is a collection of Web pages, images, videos or other digital assets that is hosted on one or several Web server(s), usually accessible via the Internet, cell phone or a LAN. A Web page is a document, typically written in HTML... Image File history File links Gnome_globe_current_event. ... Software redirects here. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... Image File history File links Nuvola_apps_kpager. ... Wikibooks has a book on the topic of Perl Programming Perl is a dynamic programming language created by Larry Wall and first released in 1987. ... A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. ... This article or section does not cite its references or sources. ... A mode in which the computers operating system emulates an older processor and/or hardware platform to allow obsolete software to remain compatible with the computers newer hardware. ...

Perl 6 has been under development for over seven years, prompting some commentators^{[attribution needed]} to suggest that Perl 6 may be vaporware. The Perl 6 project has never had a clear timeline, although various contributors have given estimates over the years. In early 2007 Jesse Vincent, the Perl 6 Project Manager said, "The Perl 6 project has no schedule ... one doesn't want to rush a largely volunteer effort to design and implement a worthy successor to Perl 5."^[1] Vaporware is software or hardware product which is announced by a developer well in advance of release, but which then fails to emerge, either with or without a protracted development cycle. ...

There is currently a slow, but mostly complete, implementation written in the Haskell programming language called Pugs, and two alternative implementations exist, one based on Parrot and PGE and the other on Perl 5. Haskell is a standardized purely functional programming language with non-strict semantics, named after the logician Haskell Curry. ... Pugs is a compiler and interpreter for the Perl 6 programming language, started on February 1, 2005 by Audrey Tang. ... Parrot is a register-based virtual machine being developed using the C programming language and intended to run dynamic languages efficiently. ... The Parser Grammar Engine (originally Parrot Grammar Engine) or PGE is a compiler and runtime for a Perl 6 rules for the Parrot virtual machine. ... Wikibooks has a book on the topic of Perl Programming Perl is a dynamic programming language created by Larry Wall and first released in 1987. ...

History

The Perl 6 design process was first announced on July 19, 2000, on day 4 of that year's Perl Conference,^[2] by Larry Wall in his State of the Onion 2000 talk.^[3] At that time, the primary goals were to remove "historical warts" from the language; "easy things should stay easy, hard things should get easier, and impossible things should get hard;" a general cleanup of the internal design and APIs. The process began with a series of requests for comments or "RFCs". This process was open to all contributors, and left no aspect of the language closed to change.^[4] Year 2000 (MM) was a leap year starting on Saturday (link will display full 2000 Gregorian calendar). ... An OSCON (Open Source Convention) is an annual convention to talk about Open Source software, such as Linux, MySQL, Perl, and Python. ... Larry Wall Larry Wall (born September 27, 1954) is a programmer, linguist, and author, most widely known for his creation of the Perl programming language in 1987. ... In internetworking and computer network engineering, Request for Comments (RFC) documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies. ...

Once the RFC process was complete, Wall reviewed and classified each request. He then began the process of writing the Apocalypses, the name of which refers to "a revealing" according to the first such document.^[5] While the original goal was to write one Apocalypse for each chapter of Programming Perl, it became obvious that, as each Apocalypse was written, previous Apocalypses were being invalidated by later changes. For this reason, a set of Synopses were published, each one relating the contents of an Apocalypse, but with any subsequent changes reflected in updates. Today, Perl 6 specification continues almost entirely within the Synopses.^[6]

There are also a series of Exegeses written by Damian Conway that explain the content of each Apocalypse in terms of practical usage. Each Exegesis consists of code examples along with discussion of the usage and implications of the examples.^[7] Damian Conway at the 2005 European Open Source Convention. ...

There are three primary methods of communication used in the development of Perl 6 today. The first is the #perl6 IRC channel on freenode. The second is a set of mailing lists on The Perl Foundation's servers at perl.org.^[8] The third is the Subversion source code repository used by the pugs team. Pugs is an early implementation of Perl 6; see the Implementations section for more detail. IRC redirects here. ... The title of this article should be freenode. ... A mailing list is a collection of names and addresses used by an individual or an organization to send material to multiple recipients. ... The Perl Foundation (TPF) is dedicated to the advancement of the Perl programming language through open discussion, collaboration, design, and code. ... In computing, Subversion (SVN) is a version control system (VCS) initiated in 2000 by CollabNet Inc. ... A source code repository is a place where large amounts of source code are kept, either publicly or privately. ... Pugs is a compiler and interpreter for the Perl 6 programming language, started on February 1, 2005 by Audrey Tang. ...

As of 2007, Perl 6 was still under development, with no planned completion date. 2007 is a common year starting on Monday of the Gregorian calendar. ...

Goals

The break in compatibility was mandated from the start of the project, and immediately allowed some of the changes that Larry Wall had suggested in his initial speech. "Historical warts" such as the confusion surrounding sigil usage for containers; the ambiguity between the select functions; the syntactic impact of bareword filehandles; and many other problems that Perl programmers had discussed fixing for years were some of the first issues addressed.

Over the years, Perl 6 has undergone several alterations in its direction. The introduction of concepts from Python and Ruby were early influences, but as the pugs interpreter was written in the Haskell programming language, many functional programming influences were absorbed by the Perl 6 design team. Python is a high-level programming language first released by Guido van Rossum in 1991. ... Ruby is a reflective, object-oriented programming language. ... Haskell is a standardized purely functional programming language with non-strict semantics, named after the logician Haskell Curry. ... Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. ...

Implementations

Pugs is an implementation of Perl 6 written in Haskell. It is currently the closest thing to a full implementation of Perl 6. It will be used for bootstrapping, providing a platform on which to write the Perl 6 compiler in Perl 6, and the test suite to validate it. This could, for example, involve translating the Pugs Haskell source code to Perl 6.^[9] After that, Perl 6 will be self-hosted—it will be used to compile itself. Much of the implementation of Perl will then be exposed to programmers using the language. For example, this would make it possible to extend the parser from within a program or library. Pugs can execute Perl 6 code directly, and has also compiled Perl 6 to JavaScript, Perl 5 and Parrot bytecode. Lacking funding, even the key developer Audrey Tang is only working part time, so progress has not been as rapid as many wish. Haskell is a standardized purely functional programming language with non-strict semantics, named after the logician Haskell Curry. ... Bootstrapping is a term used in computer science to describe the techniques involved in writing a compiler (or assembler) in the target programming language which it is intended to compile. ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ... Self-hosting refers to the use of a computer program as part of the toolchain or operating system that produces new versions of that same program—for example, a compiler that can compile its own source code. ... A diagram of the operation of a typical multi-language, multi-target compiler. ... JavaScript is a scripting language most often used for client-side web development. ... Wikibooks has a book on the topic of Perl Programming Perl is a dynamic programming language created by Larry Wall and first released in 1987. ... Parrot is a register-based virtual machine being developed using the C programming language and intended to run dynamic languages efficiently. ... Bytecode is a binary representation of an executable program designed to be executed by a virtual machine rather than by dedicated hardware. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ...

Parrot is a virtual machine designed for interpreted languages, primarily for Perl 6. The self-hosting Perl 6 compiler will (according to plan) target and also run on Parrot.^[10][11] Parrot is a register-based virtual machine being developed using the C programming language and intended to run dynamic languages efficiently. ... In computer science, a virtual machine is software that creates a virtualized environment between the computer platform and its operating system, so that the end user can operate software on an abstract machine. ...

v6.pm is a pure Perl 5 implementation of Perl 6, making liberal use of existing CPAN modules, such as Moose and Pugs::Compiler::Rule. It aims to make the existing perl runtime a first-class virtual machine for both Perl 5 and Perl 6.^[12] v6 is a Perl module which runs under Perl version 5, and transforms Perl 6 code into Perl 5 code on the fly. ... CPAN is an acronym standing for Comprehensive Perl Archive Network. ...

In 2007, v6-MiniPerl6 ("mp6") and its reimplementation, v6-KindaPerl6 ("kp6") were written as a means to bootstrap the Perl-6.0.0 STD, using Perl 5. The STD is a full grammar for Perl 6, and is written in Perl 6. In theory, anything capable of parsing the STD and generating executable code is a suitable bootstrapping system for Perl 6. kp6 is currently compiled by mp6 and can work with multiple backends.^[13][14] mp6 and kp6 are not full Perl 6 implementations, and are designed only to implement the minimum featureset required to bootstrap a full Perl 6 compiler. Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ...

Major changes from Perl 5

Perl 5 and Perl 6 differ fundamentally, though in general the intent has been to "keep Perl 6 Perl". Most of the changes are intended to normalize the language, to make it easier for learning and expert programmers alike to understand, and to make "easy things easier and hard things more possible".

A specification

A major, but non-technical difference between Perl 5 and Perl 6 is that Perl 6 began as a specification.^[10] This means that Perl 6 can be re-implemented if needed, and it also means that programmers don't have to read the source code for the ultimate authority on any given feature. Perl 5's documentation was regarded as excellent, even outside of the Perl community where even mixed reviews typically noted its maturity and breadth. However, if the documentation and the source code of the Perl 5 interpreter disagreed, the documentation was not considered authoritative, and would be changed.

A type system

In Perl 6, the dynamic type system of Perl 5 has been augmented by the addition of static types.^[15] For example: In computer science, a datatype or data type (often simply a type) is a name or label for a set of values and some operations which one can perform on that set of values. ...

 my Int $i = 0; my Num $n = 3.142; my Str $s = "Hello, world"; 

However, as with Perl 5, programmers can do most things without any explicit typing at all:

 my $i = "25" + 10; # $i is 35 

Proponents of static typing claim that it is beneficial to compiler optimization, reducing programming errors and increasing maintainability, especially in large software projects. In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ...

On the other hand, dynamic typing reduces input source code size, which is the bottleneck on smaller projects. It is helpful when writing quick scripts, one-liners or "one-off" code (i.e., code that is written to achieve some temporary purpose and will be run once). In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ... Scripting programming languages (commonly called scripting languages or script languages) are computer programming languages designed for scripting the operation of a computer. ... A one-liner is a computer program or expression that takes no more than a single line. ...

Perl 6 offers a hybrid typing system whereby the programmer may choose to use Static Typing, Dynamic Typing or mix the two.

Formal subroutine parameter lists

Perl 5 defined subroutines without formal parameter lists at all (though simple parameter counting and some very loose type checking can be done using Perl 5's "prototypes"). Subroutine arguments passed in were aliased into the elements of the array @_. If @_ were modified, the changes would be reflected in the original data. In computer programming, a parameter is a variable which takes on the meaning of a corresponding argument passed in a call to a subroutine. ...

Perl 6 introduces true formal parameters to the language.^[16] In Perl 6, a subroutine declaration looks like this:

 sub do_something(Str $thing, Int $other) { ... } 

As in Perl 5, the formal parameters (i.e., the variables in the parameter list) are aliases to the actual parameters (the values passed in), but by default, the aliases are constant so they cannot be modified. They may be declared explicitly as read-write aliases for the original value or as copies using the is rw or is copy directives should the programmer require them to be modified locally. In computer science and mathematics, a variable (pronounced ) (sometimes called an object or identifier in computer science) is a symbolic representation used to denote a quantity or expression. ...

Parameter passing modes

Perl 6 provides three basic modes of parameter passing:

• Positional
• Named
• Slurpy

Positional parameters are the typical ordered list of parameters that most programming languages use. All parameters may also be passed by using their name in an unordered way. A named-only parameter can only be passed by specifying its name (that is, it never captures a positional argument), and are indicated with a leading : character. Slurpy parameters (indicated by an * before the parameter name) are Perl 6's tool for creating variadic functions. A slurpy hash will capture remaining passed-by-name parameters, whereas a slurpy array will capture remaining passed-by-position parameters. In computer programming, a variadic function is a function of variable arity; that is, one which can take different numbers of arguments. ...

Here is an example of the use of all three parameter-passing modes:

 sub somefunction($a, $b, :$c, :$d, *@e) {...} somefunction(1, 2, :d<3>, 4, 5, 6); # $a=1, $b=2, $d=3, @e=(4,5,6) somefunction(:b<2>, :a<1>); # $a=1, $b=2 

Positional parameters, such as those used above are always required, unless followed by ? to indicate that they are optional. Named parameters are optional by default, but may be marked as required by adding ! after the variable name. Slurpy parameters are always optional.

Blocks and closures

Parameters can also be passed to arbitrary blocks, which act as closures. This is how, for example, for and while loop iterators are named. In the following example, a list is traversed, 3 elements at a time, and passed to the loop's block as the variables, $a, $b, $c. In computer science, a closure is a function that is evaluated in an environment containing one or more bound variables. ...

 for @list -> ($a, $b, $c) { ... } 

This is generally referred to as a "pointy sub" or "pointy block", and the arrow behaves almost exactly like the sub keyword, introducing an anonymous closure (or anonymous subroutine in Perl 5 terminology).^[16]

Sigil invariance

In Perl 5, sigils — the punctuation characters that precede a variable name — changed depending on how the variable was used: In computer programming, a sigil is a symbol attached to a variable name, showing the variables datatype. ...

 # Perl 5 code my @array = (1, 2, 3); my $element = $array[1]; # $element equals 2 

In Perl 6, sigils are invariant, which mean they do not change based on whether it is the array or the array element that is needed:^[15]

 # Perl 6 code my @array = (1, 2, 3); my $element = @array[1]; # $element equals 2 

The variance in Perl 5 was inspired by natural language:

 "The apple". # CORRECT "These apples. # CORRECT "The third one of the apples". # CORRECT "These third one of the apples". # WRONG 

The change in Perl 6 is meant to reduce the cognitive load of recognizing when to use the @ or the $. Cognitive Load is a term (used in psychology and other fields of study) that refers to the level of effort associated with problem solving, thinking and reasoning (including perception, memory, language, etc. ...

Object-oriented programming

Perl 5 supported object-oriented programming via a mechanism known as blessing. Any reference could be blessed into being an object of a particular class, a blessed object could have methods invoked on it using the "arrow syntax" which would cause Perl to locate or "dispatch" an appropriate subroutine by name, and call it with the blessed variable as its first argument. Object-oriented programming (OOP) is a programming paradigm that uses objects and their interactions to design applications and computer programs. ... This article is about a general notion of reference in computing. ... In object-oriented programming, the term method refers to a subroutine that is exclusively associated either with a class (called class methods, static methods, or factory methods) or with an object (called instance methods). ... In computer science, a subroutine (function, method, procedure, or subprogram) is a portion of code within a larger program, which performs a specific task and can be relatively independent of the remaining code. ...

While extremely powerful—virtually any other computer language's object model could be simulated using this simple facility—it made the most common case of object orientation, a struct-like object with some associated code, unnecessarily difficult. In addition, because Perl could make no assumptions about the object model in use, method invocation could not be optimized very well. In the computing discipline object model has two related but distinct meanings: 1. ... A struct is the C programming languages notion of a record, a datatype that aggregates a fixed set of labelled objects, possibly of different types, into a single object. ...

In the spirit of making the "easy things easy but hard things possible", Perl 6 retains the blessing model but supplies a more robust object model for the common cases.^[17] For example, a class to encapsulate a Cartesian point could be defined and used this way: Fig. ... A spatial point is an entity with a location in space but no extent (volume, area or length). ...

 class Point is rw { has $.x; has $.y; } my Point $point .= new( :x<1.2>, :y<-3.7> ); # Now change x (note method "x" used as lvalue): $point.x = 2; say "Point is at X location: ", $point.x; 

The dot replaces the arrow in a nod to the many other languages (e.g. Java, Python, etc.) that have coalesced around dot as the syntax for method invocation. Java language redirects here. ... Python is a high-level programming language first released by Guido van Rossum in 1991. ...

In the terminology of Perl 6, $.x is called an "attribute". Some languages call these fields or members. The method used to access an attribute is called an "accessor". Auto-accessors are methods that are created automatically, as the method x is in the example above. These accessor functions return the value of the attribute. When a class or individual attribute is declared with the is rw modifier (short for "read/write"), the auto-accessor can be passed a new value to set the attribute to, or it can be directly assigned to as an lvalue (as in the example). Auto-accessors can be replaced by user-defined methods, should the programmer desire a richer interface to an attribute. Attributes can only be accessed directly from within a class definition. All other access must go through the accessor methods. In computer science, a value may be a number, literal string, array and anything that can be treated as if it were a number. ...

Roles

Roles in Perl 6 take on the function of both interfaces in Java and traits^[18] in the Smalltalk variant Squeak. These are much like classes, but are entirely abstract. These are used to perform composition when used with classes rather than adding to their inheritance chain. Roles define nominal types; they provide semantic names for collections of behavior and state. The fundamental difference between a role and a class is that classes are instantiable; roles are not.^[19] Traits is an abstract type, used as a simple conceptual model for structuring object oriented programs. ... For other uses, see Small talk. ... Screenshot of the Squeak VM running under X11 on Kubuntu Linux. ... In computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time. ... This article or section does not cite any references or sources. ...

Essentially, a role is a bundle of (possibly abstract) methods and attributes that can be added to a class without using inheritance. A role can even be added to an individual object; in this case, Perl 6 will create an anonymous subclass, add the role to the subclass, and change the object's class to the anonymous subclass.

For example, a Dog is a Mammal. Dogs inherit certain characteristics from Mammals, such as mammary glands and (through Mammal's parent, Vertebrate) a backbone. Dogs may have one of several distinct types of behavior; for example, a Dog may be a Pet, a Stray, or a Guide for the blind. However, these are simply sets of additional behaviors that can be added to a Dog; a Cat can equally be a Pet or Stray, for example. Hence, Dog and Mammal are classes, while Pet, Stray, and Guide are roles. Trinomial name Canis lupus familiaris The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex... Mammary glands are the organs that, in the female mammal, produce milk for the sustenance of the young. ... This article does not cite any references or sources. ... Look up Backbone in Wiktionary, the free dictionary. ... This article is about animals kept for companionship. ... A feral horse (an American mustang) in Wyoming A feral animal or plant is one that has escaped from domestication and returned, partly or wholly, to its wild state. ... A blind man is led by his guide dog in Brasília, Brazil. ... Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ...

 class Mammal is Vertebrate {...} class Dog is Mammal {...} role Pet {...} role Stray {...} role Guide {...} 

Roles are added to a class or object with the does keyword, as opposed to inheritance's is. The keywords reflect the differing meanings of the two features: role composition gives a class the behavior of the role, but doesn't indicate that it is truly the same thing as the role.

 class GuideDog is Dog does Guide {...} # Subclass composes role my $dog = new Dog; $dog does Guide; # Individual object composes role 

Although roles are distinct from classes, both are types, so a role can appear in a variable declaration where one would normally put a class. For example, a Blind role for a Human could include an attribute of type Guide; this attribute could contain a Guide Dog, a Guide Horse, a Guide Human, or even a Guide Machine. A guide horse is an alternative to a guide dog. ...

 class Human { has Dog $dog; # Can contain any kind of Dog, whether it does the ... # Guide role or not } role Blind { has Guide $guide; # Can contain any object that does the Guide role, ... # whether it is a Dog or something else } 

Regular expressions

Main article: Perl 6 rules

Perl's regular expression and string-processing support has always been one of its defining features.^[20] Since Perl's pattern-matching constructs have exceeded the capabilities of regular language expressions for some time,^{[citation needed]} Perl 6 documentation will exclusively refer to them as regexes, distancing the term from the formal definition. Perl 6 rules are Perl 6s regular expression, pattern matching and general-purpose parsing facility, and are a core part of the language. ... In computing, a regular expression is a string that is used to describe or match a set of strings, according to certain syntax rules. ... In theoretical computer science, a regular language is a formal language (i. ...

Perl 6 provides a superset of Perl 5 features with respect to regexes, folding them into a larger framework called "rules" which provide the capabilities of context-sensitive parsing formalisms (such as the syntactic predicates of parsing expression grammars and ANTLR), as well as acting as a closure with respect to their lexical scope.^[21] Rules are introduced with the rule keyword which has a usage quite similar to subroutine definition. Anonymous rules can also be introduced with the regex (or rx) keyword, or they can simply be used inline as regexps were in Perl 5 via the m (matching) or s (search and replace) operators. A context-sensitive grammar is a formal grammar G = (N, Σ, P, S) such that all rules in P are of the form αAβ → αγβ with A in N (i. ... An example of parsing a mathematical expression. ... A syntactic predicate specifies the syntactic validity of applying a production in a formal grammar and is analogous to a semantic predicate that specifies the semantic validity of applying a production. ... A parsing expression grammar, or PEG, is a type of analytic formal grammar that describes a formal language in terms of a set of rules for recognizing strings in the language. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... In computer science, a closure is a function that is evaluated in an environment containing one or more bound variables. ... In computer programming, scope is an enclosing context where values and expressions are associated. ...

In Apocalypse 5, Larry Wall enumerated 20 problems with "current regex culture". Among these were that Perl's regexes were "too compact and 'cute'", had "too much reliance on too few metacharacters", "little support for named captures", "little support for grammars", and "poor integration with [the] 'real' language".^[22]

Syntactic simplification

Some Perl 5 constructs have been changed in Perl 6, optimized for different syntactic cues for the most common cases. For example, the parentheses (round brackets) required in control flow constructs in Perl 5 are now optional:^[23] For technical reasons, :) and some similar combinations starting with : redirect here. ... In computer science control flow (or alternatively, flow of control) refers to the order in which the individual statements, instructions or function calls of an imperative or functional program are executed or evaluated. ...

 if is_true() { for @array { ... } } 

Also, the , (comma) operator is now a list constructor, so enclosing parentheses are no longer required around lists. The code

 @array = 1, 2, 3, 4; 

now makes @array an array with exactly the elements '1', '2', '3', and '4'.

Chained comparisons

Perl 6 allows comparisons to "chain". That is, a sequence of comparisons such as the following are allowed:

 if C(20) <= $temperature <= C(25) { say "Room temperature!" } 

This is treated as if each left-to-right comparison were performed on its own, and the result is logically combined via the and operation.

Lazy evaluation

Perl 6 uses the technique of lazy evaluation of lists that has been a feature of some functional programming languages such as Haskell:^[24] In computer programming, lazy evaluation is a technique that attempts to delay computation of expressions until the results of the computation are known to be needed. ... Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. ... Haskell is a standardized purely functional programming language with non-strict semantics, named after the logician Haskell Curry. ...

 @integers = 0..Inf; # integers from 0 to infinity 

The code above will not crash by attempting to assign a list of infinite size to the array @integers, nor will it hang indefinitely in attempting to expand the list if a limited number of slots are searched.

This simplifies many common tasks in Perl 6 including input/output operations, list transformations and parameter passing.

Junctions

Perl 6 introduces the concept of junctions: values that are composites of other values.^[24] In the earliest days of Perl 6's design, these were called "superpositions", by analogy to the concept in quantum physics of quantum superpositions — waveforms that can simultaneously occupy several states until observation "collapses" them. A Perl 5 module released in 2000 by Damian Conway called Quantum::Superpositions^[25] provided an initial proof of concept. While at first, such superpositional values seemed like merely a programmatic curiosity, over time their utility and intuitiveness became widely recognized, and junctions now occupy a central place in Perl 6's design. Fig. ... Quantum superposition is the application of the superposition principle to quantum mechanics. ... Year 2000 (MM) was a leap year starting on Saturday (link will display full 2000 Gregorian calendar). ... Damian Conway at the 2005 European Open Source Convention. ... A proof of concept is a short and/or incomplete realization of a certain method or idea(s) to demonstrate its feasibility. ...

In their simplest form, junctions are created by combining a set of values with junctive operators: Programming languages generally have a set of operators that are similar to operators in mathematics: they are somehow special functions. ...

 my $any_even_digit = 0|2|4|6|8; # any(0, 2, 4, 6, 8) my $all_odd_digits = 1&3&5&7&9; # all(1, 3, 5, 7, 9) 

| indicates a value which is equal to either its left or right-hand arguments. & indicates a value which is equal to both its left and right-hand arguments. These values can be used in any code that would use a normal value. Operations performed on a junction act on all members of the junction equally, and combine according to the junctive operator. So, ("apple"|"banana") ~ "s" would yield "apples"|"bananas". In comparisons, junctions return a single true or false result for the comparison. | or any junctions return true if the comparison is true for any one of the elements of the junction. & or all junctions return true if the comparison is true for all of the elements of the junction.

Junctions can also be used to more richly augment the type system by introducing a style of generic programming that is constrained to junctions of types: Generic programming is a style of computer programming where algorithms are written in an extended grammar and are made adaptable by specifying variable parts that are then somehow instantiated later by the compiler with respect to the base grammar. ...

 sub get_tint ( RGB_Color|CMYK_Color $color, num $opacity) { ... } sub store_record (Record&Storable $rec) { ... } 

Autothreading

Junctions are unordered; 1|2|3 and 3|2|1 represent the same value. This lack of ordering means that the Perl 6 compiler can choose to evaluate junctive expressions in parallel. For instance, the code:

 for all(@array) { ... } 

would indicate to the compiler that the for loop should be run in parallel, possibly in separate threads. This feature is dubbed "autothreading"; its usage and implementation is not finalized and is a matter of debate in the development community.^[26] For the form of code consisting entirely of subroutine calls, see Threaded code. ...

Macros

In low-level languages, the concept of macros has become synonymous with textual substitution of source-code due to the widespread use of the C preprocessor. However, high-level languages such as Lisp pre-dated C in their use of macros that were far more powerful.^[27] It is this Lisp-like macro concept that Perl 6 will take advantage of.^[16] The power of this sort of macro stems from the fact that it operates on the program as a high-level data structure, rather than as simple text, and has the full capabilities of the programming language at its disposal. For other uses, see Macro (disambiguation) A macro in computer science is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure. ... The C preprocessor (cpp) is the preprocessor for the C programming language. ... Lisp is a family of computer programming languages with a long history and a distinctive fully-parenthesized syntax. ... A binary tree, a simple type of branching linked data structure. ...

A Perl 6 macro definition will look like a subroutine or method definition, and can operate on unparsed strings, an AST representing pre-parsed code, or a combination of the two. A macro definition would look like this: In computer science, an abstract syntax tree (AST) is a finite, labeled, directed tree, where the internal nodes are labeled by operators, and the leaf nodes represent the operands of the node operators. ...

 macro hello($what) { q:code { say "Hello { {{{$what}}} }" }; } 

In this particular example, the macro is no more complex than a C-style textual substitution, but because parsing of the macro parameter occurs before the macro operates on the calling code, diagnostic messages would be far more informative. However, because the body of a macro is executed at compile time each time it is used, many techniques of optimization can be employed. It is even possible to entirely eliminate complex computations from resulting programs by performing the work at compile-time. In computer science, compile time, as opposed to runtime, is the time when a compiler compiles code written in a programming language into an executable form. ... In computing, optimization is the process of modifying a system to make some aspect of it work more efficiently or use fewer resources. ...

Hello world

The hello world program is often used in demonstrating a programming language's most routine usage. In Perl 6, hello world can be written: A hello world program is a computer program that prints out Hello, World! on a display device. ...

 say "Hello, world" 

-- though there is more than one way to do it.The say function, which is new in Perl 6, prints its parameters (like the print function), but with a trailing newline. There is more than one way to do it (TIMTOWTDI, usually pronounced Tim Toady) is a Perl motto. ... In computing, a newline is a special character or sequence of characters signifying the end of a line of text. ...

References

Year 2000 (MM) was a leap year starting on Saturday (link will display full 2000 Gregorian calendar). ... is the 233rd day of the year (234th in leap years) in the Gregorian calendar. ... Larry Wall Larry Wall (born September 27, 1954) is a programmer, linguist, and author, most widely known for his creation of the Perl programming language in 1987. ... Year 2001 (MMI) was a common year starting on Monday (link displays the 2001 Gregorian calendar). ... is the 92nd day of the year (93rd in leap years) in the Gregorian calendar. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 222nd day of the year (223rd in leap years) in the Gregorian calendar. ... Autrijus Tang Born in 1981, Autrijus Tang (唐宗漢) is a Taiwanese Free software programmer, best known as the leader of the Pugs project, a joint effort from Haskell and Perl communities to implement the Perl 6 language. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 222nd day of the year (223rd in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 80th day of the year (81st in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... In music, chromatic indicates the inclusion of notes not in the prevailing scale and is also used for those notes themselves (Shir-Cliff et al 1965, p. ... Also see: 2002 (number). ... is the 175th day of the year (176th in leap years) in the Gregorian calendar. ... Also see: 2002 (number). ... is the 155th day of the year (156th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 231st day of the year (232nd in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 256th day of the year (257th in leap years) in the Gregorian calendar. ... Damian Conway at the 2005 European Open Source Convention. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 46th day of the year in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 342nd day of the year (343rd in leap years) in the Gregorian calendar. ...

External links

Specification

• Official Perl 6 Documentation. The Synopses (The official language specification). While the Apocalypses and Exegeses are linked here for reference, note that the Synopses are kept very much more up-to-date and are the primary recommended reference.
• The original community RFCs - For historical interest only.

Implementations

• The main site for Perl 6 development
• Pugs - A current implementation of Perl 6, written in Haskell.
• v6.pm - A pure-perl implementation, based on a Perl 6's CPAN stack.
• parrotcode - The main site for Parrot development.

Haskell is a standardized purely functional programming language with non-strict semantics, named after the logician Haskell Curry. ... Parrot is a register-based virtual machine being developed using the C programming language and intended to run dynamic languages efficiently. ...

Other

• Planet Perl 6 - Perl 6's blogs aggregrator.
• Present Continuous, Future Perfect - Larry Wall's talk about Perl 5 and Perl 6 at Open Source Developer Conference 2006 in Netanya, Israel (HTML, with links to slides and audio recording)
• Perl 6 FAQ - Answers a wide range of questions about Perl 6.
• Perl 6 Quick-Start - A step-by-step guide to writing and running your first Perl 6 program.
• Perl6::Perl5::Differences