Scratch (programming language)
|This article relies too much on references to primary sources. (March 2014)|
|Designed by||Mitchel Resnick|
|Developer||MIT Media Lab Lifelong Kindergarten Group|
|2.0 / May 9, 2013|
|Squeak, ActionScript (Scratch 2.0)|
|License||GPLv2 and Scratch Source Code License|
|.sb, .sprite (Scratch 1.4 and below) .sb2, .sprite2 (Scratch 2.0)|
Scratch is a free desktop and online multimedia authoring tool that can be used by students, scholars, teachers, and parents to easily create games and provide a stepping stone to the more advanced world of computer programming or even be used for a range of educational and entertainment constructivist purposes from math and science projects, including simulations and visualizations of experiments, recording lectures with animated presentations, to social sciences animated stories, and interactive art and music. Viewing the existing projects available on the Scratch website, or modifying and testing any modification without saving it requires no online registration.
Scratch allows users to use event driven programming with multiple active objects called "sprites". Sprites can be drawn — as either vector or bitmap graphics — from scratch in a simple editor that is part of the Scratch, or can be imported from external sources, including webcam.
Scratch 2 is currently available online and as an application for Windows, Mac OS X and Linux. The source code of Scratch 1.x is made available under GPLv2 license and Scratch Source Code License.
Origin of name
The MIT Media Lab's Lifelong Kindergarten group, led by Mitchel Resnick, and its Montreal-based consulting company Playful Invention Company, co-funded by the latter with Brian Silverman and Paula Bonta, together developed the first desktop-only version of Scratch in 2003. Since 2007, projects could be shared online with other users and the shared projects could be "remixed" (i.e. saved with changes) by other users.
Since the introduction of Scratch version 2.0, custom blocks can be defined by a user within a project.
Mitchel Resnick created Scratch for the purpose of aiding young people (mainly for ages 8 and up) to learn programming.
From left to right, in the upper left area of the screen there is a "stage area", featuring the results (i.e. animations, turtle graphics, etc., everything either in small or normal size, full-screen also available) and all sprites thumbnails listed in the bottom area.
With a sprite thumbnail selected in the bottom-left area of the screen, blocks of commands can be applied to it by dragging them from the Blocks Palette onto the right area of the screen, containing all the scripts associated with the selected sprite. Under the Scripts tab, all available blocks are listed and categorized as the Motion, Looks, Sound, Pen, Data, Events, Control, Sensing, Operators, and More blocks as shown in the table below. Each can also be individually tested under different conditions and parameters via double-click.
|Motion||Moves sprites and
|Events||Contains event handlers
placed on the top of each group of blocks
costumes, and output
|Control||If statements and
|Sound||Plays audio files and
programmable sequenced audio
|Sensing||All sprite hit detection
and user input
|More Blocks||Custom procedures (blocks) and external devices control.|
Besides the Script tab, there are two additional tabs, the Costumes tab and the Sounds tab. An expandable bar at the right is Help area.
In comparison to the previous versions of Scratch, the areas have been rearranged in version 2.0, as previously the blocks palette was in the left area, the selected sprite area and scripts area associated with a selected sprite were in the middle of the screen, and the stage area with sprites thumbnails listed below it were in the right area of the screen.
Community of users
Scratch is used in many different settings: schools, museums, community centers, and homes. For example, younger children can create projects using ScratchJr (Scratch Junior) or using Scratch with their parents or older siblings as it's quite simple, and college students use Scratch in some introductory computer science classes (including Harvard's introductory computer class). Via localization files downloaded with Scratch its interface language can be changed to a language of choice since Scratch is used in different parts of the world. The Johns Hopkins University Center for Talented Youth offers an online course on Scratch programming for students in grade 6 and up through the CTYOnline program.
Empirical studies were made of various features—those that interfered with intuitive learning were discarded, while those that encouraged beginners and made it easy for them to explore and learn were kept. Some of the results are surprising, making Scratch quite different from other teaching languages (such as BASIC, Logo, or Alice).
The Scratch online community's slogan "Imagine, Program, Share" indicates that sharing and the social aspects of creativity are important parts of the philosophy behind Scratch. A few influential members of the Scratch online community made great personal strides in innovative methods with scratch programming.
Scratch projects are not seen as "black boxes", but as objects for remixing to make new projects. Projects can be uploaded directly from the development environment to the Scratch website and any member of the community can download their full source code to study or to remix into new projects. Members can also create project studios, comment, tag, favorite and "love" others' projects, follow another member to see their projects and activity, and share ideas. Projects range from games to animations to chatbots. All projects on the website are shared under a Creative Commons attribution and share-alike license and can be played in a web browser (using the Flash Player, which is not available for iOS devices). The website receives close to 10 million page views per month and as of August 10, 2014 it had 3,726,565 registered members (however, only 402,697 users have shared projects), and over 6,100,000 projects (every minute more than one project gets uploaded). The website frequently establishes "Scratch Design Studio" challenges to encourage creation and sharing by providing users with a basic design concept. There are custom home pages for Mexico and Israel that display local content in some sections of the home page. Scratch has participated in Hour of Code several times. There are also local independent Scratch websites in countries such as Portugal and the United Arab Emirates. In 2008, the Scratch online community platform (named "ScratchR") received an honorary mention in the Ars Electronica Prix. There is also an online community for educators, called ScratchEd. Scratch is also a fun literary structure, with online roleplays that range in many different genres.
Features and derivatives
The current version of Scratch does not treat procedures as first class structures and has limited file I/O options with Scratch 2.0 Extension Protocol; an experimental extension feature that allows interaction between Scratch 2.0 and other programs.  The Extension protocol allows interfacing with hardware boards such as Lego Mindstorms or Arduino. In addition Scratch 2 only supports one-dimensional arrays, known as "lists". Floating point scalars and strings are supported as of version 1.4, but with limited string manipulation capability. There is a strong contrast between the powerful multimedia functions and multi-threaded programming style and the rather limited scope of the Scratch programming language. On May 6, 2013, Scratch closed for 3 days to update to Scratch 2.0. The update changed the look of the site and included an online project editor. A new beta version of the Scratch 2 Offline Editor is currently available. This version replaces the old Scratch 2.0. 
A number of Scratch derivatives called Scratch Modifications have been created using the source code of Scratch version 1.4. These programs are a variation of Scratch that normally include a few extra blocks or changes to the GUI.
Some of them additionally introduce shifts in underlying approach to computing, such as Snap! programming language, featuring first class procedures (their mathematical foundations are called also "Lambda calculus"), first class lists (including lists of lists), and first class truly object oriented sprites with prototyping inheritance, and nestable sprites, which are not part of Scratch. Snap! (its previous version was called BYOB) was developed by Jens Mönig with documentation provided by Brian Harvey from University of California, Berkeley and has been used to teach "The Beauty and Joy of Computing" introductory course in CS for non-CS-major students.
Catrobat is a visual programming language for smartphones and tablets inspired by Scratch. Pocket Code is an app with which you can create, download and upload programs created in Catrobat. Catrobat and Pocket Code are available under open source licenses.
The following youth computing projects also originated in the MIT Lifelong Kindergarten Group:
Other educational programming languages include:
- Blockly, the snap-together block language used at Code.org
- Microsoft Small Basic
- Microsoft's Kodu (proprietary)
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