Introducing GP: A General Purpose Block Language

GP is a new blocks-based programming language being developed by John Maloney (most well-known for developing Scratch), Jens Mönig (developer of Snap!), and Yoshiki Ohshima (one of the developers of Squeak EToys) in Alan Kay’s group. They are all part of the new partnership between Alan Kay and Y-Combinator Research: HARC (Human Advancement Research Community). GP started in the SAP-funded CDG (Communications Design Group).

GP is not yet released, and there’s not much publicly available on it yet. The GP Team published a paper and poster in the Blocks and Beyond Workshop at last year’s VL/HCC on GP. The best introductory article on GP so-far is on the Scratch Wiki at MIT based on John’s presentation at the Scratch conference last year.

What makes GP remarkable is that it aims to be a general purpose language. John’s vision for GP is to be the language that students might move to after Scratch, with the highest possible ceilings. Think about GP as Python or Smalltalk in blocks — and even more the latter than the former. From the virtual machine (VM) on which it runs to the class browser, GP feels like a blocks-based form of Smalltalk. Because GP is VM-based, it’s portable — there are versions for Mac, Windows, iOS, and even a JavaScript implementation of the VM so that GP runs in the browser.

GP is an exploration of the question, “How far can we go with a blocks-based programming language? Do we have to move students to a textual programming language to let them develop everything from data analyses to real applications?”

GP users can do a lot with GP’s built-in blocks. However, as they grow in mastery, some users may wish to add new blocks to GP (e.g. to manipulate images), or even to extend the GP programming environment itself (e.g. by adding an image editor). GP is designed to be extended in itself using the same blocks language that users already know. However, unlike Smalltalk or Snap!, the GP language itself cannot be extended (e.g. to add a new control structure) without modifying the virtual machine. Keeping the GP language simple and fixed is intended to ease the learning path for beginners.

A brief tour of Smalltalk-like features of GP

When you first start up GP, it looks like Scratch. The blocks palette is different, because it’s covering a larger space of blocks. GP includes blocks for dealing with data (e.g., JSON, comma-separated values), media generation and manipulation, connections to the network and external devices, and the ability to create and coordinate multiple objects.

There are even blocks in there for manipulating pixels in an image and samples in a sound. GP is the first blocks-based language in which I’ve been able to do both sound and pixel Media Computation examples. I built the first version of MediaComp blocks for GP, then John figured out which ones were actually useful and then re-implemented them in GP much more efficiently than what I did.

I’m introducing GP here with the GP Team’s permission in order to show you a prototype ebook I’ve been building the last few months. You can play with GP at http://home.cc.gatech.edu/GPBlocks. This is the browser-based version which is offered with no guarantees — the browser version will likely change dramatically as GP is still being developed, and even the examples in the ebook may break over time. (Note: These browser-based examples are best viewed in Firefox on a desktop or laptop computer; they do not yet work on iOS or Android tablets.)

Here’s a brief series of snapshots to give you a sense of what makes GP so interesting and powerful compared to most other blocks-based languages. In the stage area (upper right-hand corner) right-click (control-click on a Mac) to bring up the stage menu.

The menu options for a workspace and to browse will elicit warm feelings of recognition for Smalltalk and Self programmers. Go ahead and click on the browse menu item.

Scanning the classes along the left hand side you realize that this is a full Smalltalk-like language. All the pieces are there and inspectable. The middle panes show the instance variables in the class (top) and the methods for the class (bottom). The rightmost pane shows the code for the method — in blocks!

One of the big goals of GP is that all of GP is written in GP. Even the lowest levels of GP (e.g., how bitmaps and blocks are constructed) can be manipulated in GP, all in blocks. Those methods are real code and “live.” Change them and you change how GP is working immediately. Right now, that’s super dangerous — there is no “editing” mode. Move a block out of place, and the method is changed at that moment. Beware of re-defining how Integers work! The GP team is currently working to complete this part of GP, allowing the GP programming system to be used to modify itself, like Smalltalk.

The GP team is also exploring the stages between blocks and text. At the top right hand corner of GP is a slider between blocks and text. Switch it to text, and all of GP is presented and usable in a textual form. (There’s even an interesting middle stage between blocks and text.)

I’ve been using GP for about nine months. During the Spring semester, I’ve been using GP with an undergraduate research assistant, David Tran, to build a prototype of a new kind of ebook structure. Play around (muck/MOHQ around) in the GPBlocks MOHQ, and in the next blog post, I’ll explain what it is and what we’re exploring in it.

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My thanks to the GP team for review and comments on drafts of this post.