Learning from Smalltalk





Sasha Gerrand

@sgerrand
Programmer
Bigcommerce

Jim Weirich

1956 - 2014

ENV=reality rake vale:jim

What is Smalltalk anyway?

(isn't this a Ruby conference?)

Smalltalk


  • is an object-oriented, dynamically typed, interpreted, reflective
    programming language
  • was created as the language to underpin the "new world" of computing exemplified by "human–computer symbiosis",
    a popular theme in the 1960s


It was designed and created at the Learning Research Group (LRG) of Xerox PARC by Alan Kay, Dan Ingalls, Adele Goldberg,
Ted Kaehler, Scott Wallace, and others during the 1970s

Alan Kay


  • One of the fathers of object-oriented programming
  • Architect of the modern windowing graphic user interface

Dan Ingalls


  • Pioneer of object-orientated programming
  • Primary architect and implementer of 5 generations of Smalltalk

Adele Goldberg


  • Key role in the development of Smalltalk
  • Developed 'design templates', a forerunner of design patterns

Smalltalk

"Most ideas come from previous ideas."


It is "called "Smalltalk"--as in "programming should be a matter of ..." [Smalltalk] and "children should program in ..." [Smalltalk].

I figured that "Smalltalk" was so innocuous a label that if it ever did anything nice people would be pleasantly surprised."

-- Alan Kay, The Early History of Smalltalk

A Brief History


  • 1960s - Alan Kay develops early concepts, based on Lisp and Simula and exposure to educational languages like Logo
  • 1969 - Smalltalk first coined
  • 1971 - Initial working version, Smalltalk-72, created in just over a week at Xerox PARC
  • 1972 - Smalltalk-72 becomes the first released version
  • 1974 - Smalltalk-74 released
  • 1976 - Smalltalk-76 released
  • 1980 - Smalltalk-80 released - first version provided to external companies for 'peer review'
  • 1980s - Digitalk and ParcPlace systems release commercial versions of Smalltalk-80, developer base shrinks
  • 1990s - Java released for free, Smalltalk usage shrinks further

Patches welcome


Not all doom and gloom. 

Open Source versions of Smalltalk do exist:

  • Pharo
  • Squeak
  • GNU Smalltalk

Design concepts revisited


Purely object-orientated:

  • An object is always an instance of a class
  • Classes describe the behaviour and properties of instances
  • Polymorphism: classes extend a superclass 
    (except the special 'root' class) and can be subclassed
  • All values are objects

Design concepts


Smalltalk objects can do exactly 3 things:
  1. Hold state
  2. Receive messages
  3. Send messages
    (while receiving messages)

Syntax

Literals

"this is a comment" 
'this is a string' 
#'this is a symbol' 
#thisIsAlsoASymbol
Numbers
42
-42
123.45
1.2345e2
2r10010010
16rA000
Arrays
#(1 2 3 4)

Syntax

Variables

Declarations
|a|
|a b c|
Assignment
a := 3b := 'the quick fox'
Equality comparison
a = b
Identity comparison
a == b

Syntax

(I'll stop now)

Different to Ruby

Smalltalk is more than just a language

Different to Ruby

Image based

Smalltalk systems store the entire program state
(including both Class and non-Class objects)
in an image file, which can be loaded.

Smalltalk images are similar to (restartable) core dumps and can  provide similar functionality, such as delayed or remote debugging with full access to the program state.

Different to Ruby

Image based

Smalltalk = VM + Language
Smalltalk program = VM

Different to Ruby

Amazing tools

The VM was the first IDE as we know it

  • Code editor
  • Class browser
  • Standard graphics library and importer
  • Debugger
  • Profiler
  • Test runner
  • and more

Semantics

In which I highlight a grab bag of differences

Semantics


Ruby has mixins
Smalltalk does not

Semantics


Ruby permits adding methods to individual objects
All methods reside inside classes in Smalltalk

Semantics


In Ruby, creating methods dynamically is a popular pattern
Methods and classes are generally treated statically in Smalltalk

Semantics


Ruby offers powerful macros in class definitions
Smalltalk has no macros whatsoever

Semantics


If an Array in Ruby needs to be sorted, it must be done explicitly
Smalltalk has an OrderedCollection implementation to maintain sorting order through mutations

Key learnings

(AKA get to the point)

Key learnings


The class browser is a great tool for viewing senders and implementors in a live system.

Being able to inspect code on the fly is extremely helpful

Key learnings


Debugging and incremental tracing of code is also valuable. Having persisted state available makes tracking down errors much faster.

Key learnings


Smalltalk, in many ways, is Light Table
(just 30 years ahead of its time)

Questions?







Sasha Gerrand

@sgerrand
Programmer
Bigcommerce

Further reading

History, papers, etc

Smalltalk: http://smalltalk.org


Downloads

Pharo: http://www.pharo-project.org

Squeak: http://squeak.org


Sasha Gerrand

@sgerrand
Programmer
Bigcommerce
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