Pharo

Pharo

Developer	Pharo community
First appeared	2008 (2008)
Stable release	6.1 / July 24, 2017 (2017-07-24)
Implementation language	Smalltalk
OS	Windows, Linux, macOS, others
License	MIT license, partly Apache License 2.0[1]
Website	pharo.org
Influenced by
Smalltalk (Squeak)

Pharo is an open source dynamic and reflective language inspired from the programming language and integrated development environment (IDE) Smalltalk. Pharo offers strong live programming features such as immediate object manipulation, live update and hot recompiling. The live programming environment is at the heart of the system.

Introduction

Pharo is a pure object-oriented dynamically typed and reflective language. It was influenced by Smalltalk. The goal of Pharo is to revisit Smalltalk design and enhance it. Pharo syntax fits on a single postcard. The object model is simple: only objects. Methods are virtual public (dynamically looked up). Fields are protected (only visible from class and subclasses). There is single inheritance between classes. A class can also be composed of traits, which are a group of methods. Fields are first class entities, named slots.

A full massive open online course (MOOC) is available to learn Pharo. Several books are available on-line.

An industrial consortium has been created to sustain the development of Pharo. An association gathers Pharo enthusiasts.

Pharos is a Greek word (Φάρος) which means lighthouse. The Pharo logo shows a drawing of a lighthouse inside the final letter O of the name.

Key features

Pharo benefits from an elegant design that enables relatively simple implementation of many advanced programming techniques.

• optional fusion of developed program and development environment
• advanced run-time reflectivity
• pure object-oriented approach
• simple language syntax
• immediate objects identity swapping
• fast resumable exceptions
• live customizable objects inspection
• run-time classes and objects migration
• dynamic inheritance
• advanced fast multiplatform virtual machine with JIT, combined generational garbage collector, ephemerons, forwarders
• virtual machine written mostly in the language itself
• easy call stack manipulation
• continuations
• fast objects enumeration
• objects as methods
• traits
• optional Green threads
• AST metalinks
• first-class customizable instance variables
• customizable metaclasses
• relatively low memory consumption
• platform independent user interface
• customizable compiler
• moldable development tools
• optional complete object memory persistence
• integrated Git support
• fast objects serialization
• easy use of proxy objects
• simple connection to native libraries

Relation to Smalltalk

Pharo is a standalone language. It is not supposed to be an implementation of Smalltalk-80 nor ANSI Smalltalk. Pharo is based on general concepts of Smalltalk but does not want to be limited by them. The basic syntax of the language shares most of the elements with Smalltalk, however, the Smalltalk syntax provides only a frame for construction of custom languages. So for example, the way how classes are defined in Pharo differs from other Smalltalk dialects although they use the same or very similar language grammar.

Language syntax

Pharo syntax postcard

The Pharo syntax is based on Smalltalk-80 language syntax with several extensions. Some of them are common for most of the modern Smalltalk dialects.

• literals for dynamic arrays. The expressions that specify the array content are evaluated in time of the program execution

{1. 2. 1+2}

• literals for byte arrays that can be composed only of integer numbers in the range from 0 to 255

#[1 2 3 4]

• literals for scaled decimals, a representation of fixed point decimal numbers able to accurately represent decimal fractions

3.14s2

• pragmas. In Smalltalk-80 the pragmas are used only for primitive methods. In Pharo they are fully capable method annotations

<gtInspectorPresentationOrder: 30>

• two double quotes inside a comment are interpreted as a single double quotes character that is part of the content of the comment

The Pharo language syntax is supposed to be very simple and minimalistic. The basic language elements are often presented on a single postcard. The grammar is classified as LL(1).

The language grammar does not specify directly how the code should be stored in files. Pharo uses Tonel as the preferred code serialization format.

History

Pharo emerged as a fork of Squeak, an open source Smalltalk environment created by the Smalltalk-80 team (Dan Ingalls and Alan Kay). Pharo was created by S. Ducasse and M. Denker in March 2008. It focuses on modern software engineering and development techniques. Pharo is supported by the Pharo consortium (for legal entities) and the Pharo association for physical persons .

Use of Pharo

Performance and virtual machine (VM)

Pharo relies on a virtual machine that is written almost entirely in Smalltalk itself. Beginning in 2008, a new virtual machine (Cog) for Squeak, Pharo and Newspeak has been developed that has a level of performance close to the fastest Smalltalk virtual machine.^[17] In 2014/2015 the VM community is working on Spur, a new Memory Manager for Cog that should again increase performance and provide better 64-bit VM support.^[18]

See also

• Amber Smalltalk
• GNU Smalltalk
• Squeak
• VisualWorks

References

External links

• Official website