Sugar :More sweetness for

programming languages

Sébastien Pierre, Datalicious@FreeHackers's Union Mtl, Mar. 2009

www.datalicious.ca | github.com/sebastien/sugar

1: The Origin

3

Much in common

Many languages

… Java, C#, Python, Ruby, JavaScript, ActionScript ....

have a lot in common

Primitive types : numbers, strings, arrays, etc.

Control structures : if, for, while, etc.

Constructs : functions, objects, modules, etc.

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So what's the difference ?

Syntax, of course !

F (1) (Algol­style)

(f 1) (Lisp­style)

[f withN:1] (Smalltalk­style)

f 1← (Why not ?)

5

Syntax only ?

Well, we have traits*

Never change anything (Purely functional)

Everything is an object (Purely object­oriented)

Evaluate only when needed (Lazy evaluation)

Code as data (Homoiconic)

* we could actually call that “ language features”

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Syntax, Traits, and ... ?

… the base library !

Lisp : lambda, car, cdr

C : libc, POSIX

JavaScript : ECMA standard library

Java : everything but the kitchen sink

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The Idea

Considerations

Languages have a lot in common

But I keep rewriting the same code in different languages

I came to learn how I prefer to express myself

Ideally

I would like to write once, in my syntax of choice

And translate to the target language

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However...

Languages are still “ black boxes”

Cannot change syntax easily

Difficult to access program representation

We think that the program is the source code, but...

The source code is one expression of the program

The program is a compound construct interpreted by a runtime system

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So...

Let's do “ something*” that

Is a syntactic wrapper for other languages

Offers full program model representation

Translates to commonly used languages

Can be easily customized by mortals

* This would be a program that writes programs (meta­program)

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2: SugarA Meta­Programming

Language

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It's all about syntax

And we can have the luxury to design it !

readability : visual cues, typographic rhythm

expressiveness : constructs to describe common patterns

consistency : many developers, same code

accessibility : learn it in a few hours

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We can reuse a lot

We take advantage of

Language­specific primitive types (lists, maps)

Language­specific libraries (file, os, etc.)

And we provide

Abstraction over language­specific traits

Emulation of non­supported primitive types, constructs or operations

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Design Goals

“ A program is a design expressed in code”

Goals

Be learned in a couple of hours

Put focus on software architecture

Encourage clear, readable code

Favor thinking over typing

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Inspiration

Python : expressiveness and consistency

Eiffel : formalizing structure and dynamics

Smalltalk : objects and message­passing

JavaScript : functions and objects having fun together !

And indirectly, Lisp, Io, Erlang and Scala.

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The syntax : Primitive Types

Lists

[] [1,2,3] [“ a” , 2, [3, 4]]

Maps/objects­as­maps

{} {a:1, b:2} {name:” bob” , email:” bob@gmail.com” }

And of course... numbers

1 ­1.0 0xFFAAD0

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The syntax : Indexes and Slices

value [ start index : end index]

var list = [1,2,3,4,5,6,7,8,9]

list [0] 1 (first element)

list [­1] 9 (last element)

list [:] [1,2,3,4,5,6,7,8,9] (list copy)

list [1:] [2,3,4,5,6,7,8,9] (copy after index 1)

list [:­1] [1,2,3,4,5,6,7,8] (copy until last index)

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The syntax : Iterators

The traditional “ for each in”

for value, index in [1,2,3,4]

print (value, index)

end

With objects too, one one line

for value, index in {a:1,b:2,c:3} ­> print (value, index)

And the compact form (with a closure)

[1,2,3,4] :: {v,k | print (v,k) }

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The syntax : Closures

Closures as blocks

var hello = {message|

print (“ You said:” + message)

}

Compact syntax for callbacks (here using jQuery)

$ (“ .sayhello” ) click {alert (“ say hello” )}

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The syntax : Idioms (1)

Spaces instead of dots

var user = {name:” bob” , email:” bob gmail.com” }

print (user name)

Why ?Less dense code / more whitespace

space denotes “ message sending”

dot denotes “ structural resolution” (ask me for details ;)

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The syntax : Idioms (2)

Indentation instead of commas or semicolons

var user = {name:” bob” , email:” bob@gmail.com” }

var user = {name : “ bob” no trailing comma here←

email : “ bob@gmail.com”

}

Why ?Got too many errors for missing or extra trailing comma

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The syntax : Idioms (3)

Optional parens in single­argument invocationsprint “ Hello, world !”

user addPoints 10

$ “ .sayhello” click {alert “ Hello” }

article setAuthor 'user single quote to denote single­argument←

Why ?A lot of invocations are single argument

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The syntax: Constructs

Constructs start with @, body is indented@function name arg1, arg2,...rest

| Documentation string

...

@end

The flavors@module, @function

@class, @property, @shared, @constructor, @method, @operation

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Under The Hood

Full program model API (LambdaFactory)

Constructs Program, Module, Class, Function, ...

Control Iteration, Selection, ...

Operations Computation, Evaluation, Resolution

Meta­programming

Flexible plug­in “ program pass” system:

Modify, manipulate, analyze your program

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Plugin Languages

Multiple back­ends (provided by LambdaFactory)

JavaScript (production quality)

ActionScript (not so bad)

Python (mature, but missing some stuff)

Pnuts (for fast scripting on the JDK)

Multiple front­ends

Sugar is just one of them !

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3: What's In It for Me ?Sugar in practice

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Why would I use Sugar ?

To replace JavaScript for front (or back) end Web dev :

simplified syntax fewer errors

simplified semantics less surprised

higher level constructs more structured code

easy to learn no excuse !

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You will code like Douglas Crockford !

In JavaScriptrequestNumber = JSONRequest.post( "https://json.penzance.org/request", { user: "doctoravatar@yahoo.com", t: "vlIj", zip: 94089, forecast: 7 }, function (requestNumber, value, exception) { if (value) { processResponse(value); } else { processError(exception); } });

In Sugar (with mandatory indentation)var requestNumber = JSONRequest post ( "https://json.penzance.org/request" { user : "doctoravatar@yahoo.com" t : "vlIj" zip : 94089 forecast : 7 } {requestNumber, value, exception| if value processResponse(value) else processError(exception) end })

From Douglas Crockford : http://www.json.org/JSONRequest.html

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Get started !

You'll need

Python 2.4+

And install these

git clone git://github.com/sebastien/lambdafactory.git

git clone git://github.com/sebastien/sugar.git

The end

Thank you !www.datalicious.ca

www.github.com/sebastiensebastien@datalicious.ca