blockly-block-lexical-variables

This plugin adds a set of Blockly blocks that support lexical (aka local) variables, as well as a dynamic UI for obtaining variable and parameter getters and setters and for renaming variables. It also updates the UI for existing blocks that are implicitly lexically scoped, i.e.:

• Function/Procedure definitions
• For loops

For variable getter and setter blocks this plugin also provides dropdowns which allow the user to change the variable name to any variable allowed by scope. The plugin will also mark any variable blocks that are moved out of their allowable scope.

The plugin also adds a dropdown for procedure call blocks, allowing the user to change the call to be any other procedure of the same basic shape (i.e. statement shape or expression shape).

This plugin is based on code originally written for MIT App Inventor.

You can see a demo version of a Blockly app that has integrated this plugin here. The code for that demo is here.

Blocks

Lexical/local variable declarations

Block type: 'local-declaration-statement' - The variable name will be scoped to be valid within the body of the block.

While hovering over the variable name:

Global variable declaration

Block type: 'global-declaration-statement' - An block which declares a global variable. The variable name is scoped to the entire program.

and while hovering over the variable name:

Variable/Parameter setters and getters

Setter

Block type: 'lexical_variable_set' - Note that despite the block type name, the same block is used for global variables, local variables, loop variables and function/procedure parameters. The names that appear in the dropdown will change according to the placement of the block. I.e., it will show the variables that are in scope for that getter according to which blocks it is within.

###Getter Block type: 'lexical_variable_get' - Exactly analogous to the setter block.

Loops

For

Block type: 'controls_for' - A block which enables a for loop

Block type: 'controls_forEach' - A block which enables a loop over the items in a list

Functions/procedures

Function/procedure definition with no return value.

Block type: 'procedures_defnoreturn'

Function/procedure definition with a return value.

Block type: 'procedures_defreturn'

Function/procedure call with no value

Block type: 'procedures_callnoreturn' - Note that, though I don't show it here, the procedure name field is a dropdown which allows the user to select any procedure and the block will change to match that procedures name and parameters.

or

Function/procedure call with value

Block type: 'procedures_callreturn' - This has the same dropdown behavior as the previous procedure call block.

or

Notes

Right now the new fields and the new (or redefined) blocks are somewhat co-dependent. At some point they will be disentangled. At that point this plugin might split into two; one for the fields and one for the blocks, with the latter plugin dependent on the first. At that point you will also be able to build you own blocks using the fields.

Installation

Yarn

yarn add @mit-app-inventor/blockly-block-lexical-variables

npm

npm install @mit-app-inventor/blockly-block-lexical-variables --save

Usage

Please make sure that your app which includes this plugin uses a relatively recent version of Blockly. As of this writing that would be version 10.0.0.

You'll want to include something like the following in your app:

import * as Blockly from 'blockly';
import {LexicalVariablesPlugin} from '@mit-app-inventor/blockly-block-lexical-variables';
...
const workspace = Blockly.inject(...);
...
// Load lexical variable plugin
LexicalVariablesPlugin.init(workspace);

Note that unlike with standard Blockly, you should not use a custom toolbox category for your variables, as this would interfere with the way that variables are declared and used with this plugin. Just create an ordinary Variables category, if you want, and place the lexical-variable-get and lexical-variable-set blocks in there.

In theory, you can also use the lexical variable fields to build your own blocks, but the process is not documented yet. If you're really curious, take a look at the block definitions. Basically, in addition to using the fields there are a bunch of properties and methods that you need to define on your blocks to make it all work.

Credits

As mentioned earlier, this plugin is based on code written for MIT App Inventor. The lexical variable implementation (and supporting blocks and UI) in App Inventor was developed primarily by Lyn Turbak but has had many contributors over the years including (in roughly chronological order):

• Sharon Perl
• Andrew McKinney
• Hal Abelson
• PMW
• Ralph Morelli
• Jeffry Schiller
• Jose Flores
• Joanie Weaver
• Shirley Lu
• mphox
• Leo Burd
• Dave Wolber
• Harry Davis
• WeiHua Li
• jbensal
• Shruti Rijhwani
• Liz Looney
• Evan Patton
• Susan Lane
• Colin Yang
• Beka Westberg
• Siddharth
• Mark Friedman

If you contributed to this code at some point and I somehow neglected to mention you, I apologise. Let me know, file a bug or just submit a pull request on this file.

License

Apache 2.0