A VISUAL INTERACTIVE PROGRAMMING ENVIRONMENT

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G. FRENCHJ. R . KENNAWAY

A. M. DAY

EUROPYTHON 2011

The Larch Environment

Image by alcomm, flickr.com

Motivation

We look at three problems

Textual output in a Python console can be difficult to understand

(DEMO)

Source code in a text editor is not interactive enough

Consoles are only good for a few lines at a time

Textual source code can be difficult to understand and comprehend

(think the vertices of a polygon in code form)

What is‘The Larch Environment’?

A visual interactive programming environment

The goal is:To make programming more visual

How do we do that?

• Visual object presentation• Programming environment– Visual console–Worksheets

• Visual programming via embedded objects

Visual object presentation

“Pictures are pretty”

DEMOVisual console

What design pattern do we commonly use for developing GUI

apps?

Model

View Controller

MVC Architecture

MVC requires:Model class, View class, Controller

class

Our approach:Type coercion

Type coercion: coerce an object to another type.

Type coercion used throughout Python

Examples:

repr(), str()

__index__()

etc

Its simple

The Larch Environment:Use type coercion for visual

presentation

Coerce objects to something visual(a Pres)

HOWTO:The simplified version

Define the following method:def __present__(self, fragment,

inherited_state)

For Java objects:Implement Presentable interface

Presentations constructed using a combinatorial API

Label( ‘Hello’ ) Hello

Button.buttonWithLabel( ‘Button’ )

Button

a = Label( ‘A’ )b = Label( ‘B’ )c = Label( ‘C’ )d = Label( ‘D’ )

Row( [ a, b, c, d ] ) ABCD

Column( [ a, b, c, d ] ) ABCD

Presentation combinators:Many more

Flow layouts, mathematical fractions, superscript

Rich text, other utilitiesWrite your own by combining existing ones!

P.S. Appearance controlled with style sheets

“Type coercion is easy”

DEMO:__present__()

Can also handle objects in the Java or Python standard libraries

Create an ‘object presenter’.Register it for the relevant class.

When asked to present an instance of the class, Larch finds the

appropriate presenter and uses it.(no monkeypatching required)

Thats how the images were shown;they are java.awt.BufferedImage

objects

Perspectives

Different perspectives present an object in different ways

Like different views in MVC

The one I have talked about (__present__, Presentable, etc) is the

‘Default perspective’

There are other perspectives

E.g. The inspector perspectives

“Visual Introspection”

DEMO: INSPECTOR PERSPECTIVE

Programming Environment-

Visual console

You’ve seen most of it

So lets look at some of the more ‘esoteric’ features

Model dragging

Everything in Larch is an object being presented (via type coercion)

The home page

Projects

The console itself!

What if we want to manipulate an object that we can see?

CTRL+ALT +drag it!

“I see something: how does it work?”

DEMO: inspect a project

An interesting side fact!

Our source code editor does not edit text

Its a structured editor

Code is represented as an abstract syntax tree (AST)

A perspective is used to present is as something that looks and behaves (mostly) like text

It means our code is in tree form

We can write our own refactorings!

“Change your code fast!”

DEMO:Refactoring

Programming Environment-

Worksheets

Interactive consoles are great.

Caveat: gets difficult when working with more than a few lines of code at a time

E.g. Whole modules

For complete programs we turn to a text editor

We lose the interactivity

What if we could blend the two?

“Python modules. With pictures.”

DEMO: WORKSHEET(with cellular automata)

Act as modulesCan import code from other

worksheets within the project

You can divide your module code into a number of blocks

Each block can show a result – a step along the path of a

computation

To refresh results: hit F5

Rapid Edit-Run-Debug cycle:

Alter codeF5

Repeat

“Code faster!”

DEMO: Edit-Run-Debug cycle(cellular automata)

Visual Programming

Quite a rich history in the research community

Circuit diagrams, data-flow diagrams, etc

Nice for small simple programs

Large programs look like rat’s nests

Not practical

Text remains the dominant medium for source code

Diagrams are still appropriate in certain circumstances

Lets use diagrams (or visual layout) where we need them!

“Play God.”

DEMO: OrrerySub-demos:

Table editorsEmbedded table

“Drawings. Inside code.”

DEMO: Polygon

Embedded objects can use a protocol to customise their

behaviour

__py_eval__ Act like an expression - return the result of evaluating

__py_evalmodel__ Act like an expression - return an AST

__py_exec__ Act like a statement – called at runtime

__py_execmodel__ Act like a statement – return an AST

AST Generation

What does this sound like?

AST Generation

~=

Visual LISP macros

Crosses compile-time / run-time barrier

Compile-time (edit-time) objects available at run time

Run-time objects / values can modify or be modified by compile-

time objects

“LISPy Smalltalky goodness”

DEMO: LZW compressor

Conclusions

Visual object presentation by type-coercion

Encourages a functional approach to UI composition

State changes:Just throw UI elements away

andre-create.

DON’T MUTATE

Visual representation of values is a BIG EPIC WIN

Even if you use only visual cues (e.g. borders around text)

Visual console and worksheets

Worksheets expand on the rapid edit-run cycle of the console

Allow for rapid development of visual interactive applications

Visual programming by embedded objects

Visual programming

where you need it

Allows you to visually extend the syntax of the language

No need to alter the compiler – its just embedded object references

References to objects you implement

yourself

Embedded object referencesCan cross compile-time / run-time

barrier

LISPy / Smalltalky stuff

IN PYTHON

PROJECT STATUS

Research Prototype

(not ready for real use )

TODOs:

DocumentationBug fixes

Too much more........

Acknowledgements

Academic supervisory team

Dr. Richard KennawayProf. Andy Day

University of East Anglia, Norwich, UK

The Jython team

Developing The Larch would have been very difficult

without Jython

IF TIME ALLOWS:DEMO: KD-Tree

IF TIME ALLOWS:DEMO: SIMPLE COMPILER

G. FRENCHJ. R . KENNAWAY

A. M. DAY

ht tp : / / s i t e s .goog le . com/s i t e / l a r chenv

THANK YOU!

Image by alcomm, flickr.com