Scratch (programming language)
The Scratch Cat, mascot
|Paradigm||Event-driven, Block Based Programming Language|
|Developer||MIT Media Lab Lifelong Kindergarten Group|
|First appeared||2002(test) 2005 (official) 2013 (Scratch 2)|
|Implementation language||Squeak (Scratch 0.x, 1.x)
ActionScript (Scratch 2.0)
|OS||Windows, macOS, Linux|
|License||GPLv2 and Scratch Source Code License|
|Filename extensions||.scratch (Scratch 0.x)
.sb, .sprite (Scratch 1.x)
.sb2, .sprite2 (Scratch 2.0+)
|Logo, Smalltalk, HyperCard, StarLogo, AgentSheets, Etoys|
|Scratch Jr, Snap!|
Scratch is a free visual programming language developed by the MIT (Massachusetts Institute of Technology) Media Lab. Scratch is used by students, scholars, teachers, and parents to easily create animations, games, etc. It provides a stepping stone to the more advanced world of computer programming. It can also be used for a range of educational and entertainment constructionist 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 requires no online registration.
Scratch allows users to use event-driven programming with multiple active objects called sprites. Sprites can be drawn, as vector or bitmap graphics, from scratch in a simple editor that is part of Scratch, or can be imported from external sources, including webcams.
As of 2013, Scratch 2 is available online and as an application for Windows, macOS, Linux (Adobe Air Required), and unofficially for android as an apk file. The Scratch 2.0 Offline editor can be downloaded for windows, Mac and Linux directly from Scratch's website. However, the unofficial mobile version must be downloaded from the scratch forums.  The source code of Scratch 1.x is released under GPLv2 license and Scratch Source Code License. Scratch 3.0 is also being made as part of a collaboration with Google.
Origin of name
"Scratching" in the language of computer science means to reuse code that can be beneficial and effectively used for other purposes and easily combined, shared and adapted to new scenarios, which is a key feature in Scratch – "remix", in which users can download and build upon public projects uploaded and developed by other users. It also gives credit to the participant who built on the original work and to the participant who created the original program. The name was derived from turntablism's technique of scratching (i.e., mixing sounds), relating the ease of mixing sounds to the ease of mixing projects made with Scratch.
This research advanced understanding of the effective and innovative design of new technologies to enhance learning in after-school centers and other informal education settings, and broadened opportunities for youth from under-represented groups who became designers and inventors with new technologies. Scratch was iteratively developed based on ongoing interaction with youth and staff at Computer Clubhouses. The use of Scratch at Computer Clubhouses served as a model for other after-school centers demonstrating how informal learning settings can support the development of technological fluency, enabling young people to design and program projects that are meaningful to themselves and their communities.
The MIT Media Lab's Lifelong Kindergarten group, led by Mitchel Resnick, in partnership with the Montreal-based consulting firm, the Playful Invention Company, co-founded by Brian Silverman and Paula Bonta, together developed the first desktop-only version of Scratch in 2003. Its purpose was to aid young people, mainly for ages 8 and up, to learn programming.
Scratch was made popular in the UK through Code Clubs. Scratch is used as the introductory language because creation of interesting programs is relatively easy, and skills learnt can be applied to other basic programming languages such as Python and Java.
Scratch is not exclusively for creating games. With the provided visuals, programmers can create animated stories, informational texts, and more. There are already many programs which students can use to learn topics in math, history, and even photography. Scratch flexibility allows teachers to create conceptual and visual lessons and science lab assignments, as Scratch is a useful tool to create animations that help visualize difficult concepts such as plant cell mitosis, the water cycle, Galileo Thermometer or Hooke's Law Experiment. Within the social sciences, instructors can create quizzes, games, and tutorials that stimulate the mind and interact with the student. Using Scratch allows young people to understand the logic of programming and how to creatively build and collaborate. Scratch lets students create "meaningful personal as well as educational projects" which gives students a "practical tool" to express themselves after learning to use the language.
Harvard University lecturer Dr. David J. Malan prefers using Scratch over commonly used introductory programming languages, such as Java or C, in his introductory computer science course. However, there is a limited benefit in a college level education. Malan switches his course's language to C after the first week.
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. The stage uses x and y coordinates, with 0,0 being the stage center. The stage is 480 pixels wide, and 360 pixels tall, x:240 being the far right, x:-240 being the far left, y:180 being the top, and y:-180 being the bottom.
There are many ways to create personal sprites and backgrounds. First, users can draw their own sprite manually with "Paint Editor" provided by Scratch. Second, users can choose a Sprite from the Scratch library that contains default sprite, user's past creations, a picture using a camera, or clip art.
With a sprite 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 changes angles and change X and Y values||Events||Contains event handlers placed on the top of each group of blocks|
|Looks||Controls the visuals of the sprite; attach speech or thought bubble, change of background, enlarge or shrink, transparency, shade||Control||Conditional if-else statement, "forever", "repeat", and "stop"|
|Sound||Plays audio files and programmable sequences||Sensing||Sprites can interact with the surroundings the user has created|
|Pen||Draw on the portrait by controlling pen width, color, and shade. Allows for turtle graphics.||Operators||Mathematical operators, random number generator, and-or statement that compares sprite positions|
|Data||Variable and List usage and assignment||More Blocks||Custom procedures (blocks) and external devices control and can import from PicoBoard or Lego WeDo 1.0/2.0|
Besides the Scripts tab, there are two additional tabs, the Costumes tab and the Sounds tab. An expandable bar at the right is Help area.
Next to the Scripts tab, there is the Costumes tab, where users can change the look of the sprite in order to create various effects, including animation. And the last tab is the Sounds tab, where users insert sounds and music to a sprite.
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, libraries, community centers, and homes. Its users are mostly kids aged 8–16. Scratch is also used in some introductory computer science classes (including Harvard's introductory computer class).
There is an annual "Scratch Day" declared in May each year. Community members are encouraged to host an event on or around this day, large or small, that celebrates Scratch. These events are held worldwide, and a listing can be found on the Scratch Day website.
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.
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 other members to see their projects and activity, and share ideas. Projects range from games to animations to practical tools. Chat rooms are not allowed. 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.
The website receives over 125 million page views per month and as of July 12, 2016, it had 12,561,189 registered members (however, only 180,000 users created a project within the last month), and over 15,700,000 projects and growing rapidly. A longitudinal dataset of the five years of public activity in the community were made available in 2017 
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. This community exchanges resources, coordinates group meetups, and allows educators to connect with each other.
The Scratch Wiki is a collaboratively-written wiki available for free at https://wiki.scratch.mit.edu that provides information about the Scratch programming language, its website, history and phenomena surrounding it. The wiki is supported by the Scratch Team, but is primarily written by Scratchers. The Scratch Wiki is a popular source of information for scripts and tutorials and it continues to grow as Scratchers use it as their primary source of information. This could also include advanced articles for Scratchers around the world to build, share and see.
On December 6th, 2008, the Scratch Programming Wiki was created by a single user, without the involvement of the Scratch Team. The user later passed on bureaucracy to two other users, and they advertised the wiki in the Miscellaneous section of the Scratch Forums. Although the original articles were about projects and users, more and more people saw it and the wiki steadily grew.
Eventually, the Scratch Team saw the wiki, liked the idea, and wanted to advertise it on the Scratch Website, but they had two main concerns: the wiki had advertisements, and there was no way to ascertain that users on the Scratch Wiki were who they were on the website. These were solved when the Scratch Team, along with three other users, moved the entire wiki from its previous domain to a new one, the one it is at now.
On the Scratch Wiki, only logged in users may edit, and accounts must be requested. This is to make sure users on the Scratch Wiki are who they are on the website, and to minimize possible vandalism (although it does still occur; this is unavoidable).
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 ability. 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 variant of Scratch that normally include a few extra blocks or changes to the GUI.
In July 2014, a program called ScratchJr was released for iPad. Although it was heavily inspired by Scratch and co-led by Mitch Resnik, the original creator of Scratch, it is nonetheless a complete rewrite designed for younger children.
Some Modifications additionally introduce shifts in underlying approach to computing, such as the language Snap!, 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 which you can create, download and upload programs created in Catrobat. Catrobat and Pocket Code are released under open source licenses.
The following youth computing projects also originated in the MIT Lifelong Kindergarten Group:
Other educational programming languages include:
- Alice (software)
- Blockly, the snap-together block language used at Code.org
- Microsoft Small Basic
- Microsoft Kodu Game Lab
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