You have probably noticed the excitement regarding functional programming and the new lambda expression in Java 8. But did you know that this also brings Java back to its object-oriented roots? The Smalltalk programming language shows how virtually any task can be achieved through good old object orientation. Everything is built with the basic ingredients of objects, messages and blocks (lambda). Smalltalk uses lambda expressions for conditional processing, iteration and exception handling. We will look at some fascinating examples, and discuss if and how to apply them in Java. We Java programmers now find ourselves with a brand new lambda tool in our toolbox. Lets take the time to learn from the past about the power of object orientation and lambdas.

1. Martin Skarsaune
Developer and Co-Owner
高
馬
丁
Small Lambda Talk

2. Small lambda talk
• Java 8 introduced lambda expressions
• focus on functional programming
• Also roots in object oriented programming: Smalltalk

3. Smalltalk – everything is simple
• Illustration, reserved words:
• self (=this), super, nil (=null), true, false
Java reserved words ….
abstract default goto package synchronized
assert do if private this
boolean double implements protected throw
break else import public throws
byte enum instanceof return transient
case extends int short true
catch false interface static try
char final long strictfp void
class finally native super volatile
const float new switch while
continue for null

4. Ingredient 1: Everything is an object!
• No primitive types
• nil is an object
• No void methods

5. Ingredient 2: Messages do everything!
• Three types of messages
• Unary
• Binary
• Keyword

6. Messages - unary
• No arguments
• Invocation example:
• Implementation in class Number:
2 negated
negated
^0 - self
public Number negated() {
return 0 - this;
}
2.negated()
Equivalent “Java” Syntax

7. Messages - binary
• Exactly one argument
• Message selector (method name) made from special
characters: = , + , - , > etc.
• Invocation
• Implementation in class Object:
a = b
= anObject
^self == anObject
public boolean equals(Object obj){
return this == obj;
}
a.equals(b)
Equivalent “Java” Syntax

8. Messages - keyword
• One or more arguments
• Each argument is separated by a keyword
• Invocation:
• Implementation:
a at: 1 put: ‘one’
at: key put: value
self cache
at: key put: value
public Object put(Integer key, String value){
this.cache()
.put(key,value);
return this;
}
a.put(1, “one”);
Equivalent “Java” Syntax

9. OO Conditional Processing
Boolean
True
true
False
false
true false

10. OO Conditional Processing Example
• Task:
• Use recursion to return root of
tree
• Each node may access its
parent by sending the parent
message

11. OO branching- blocks
root
^self parent = nil
ifTrue: [self]
ifFalse: [self parent root]
ifTrue: trueBlock ifFalse:
falseBlock
^trueBlock value
ifTrue: trueBlock
ifFalse: falseBlock
^falseBlock value
Implementation in True: Implementation in False:

12. OO branching- characteristics
• Voilla! We have made if else with only objects and
messages
• Boolean instance is an object
• Code blocks are objects
• Implemented as one message, one expression, one return
value.
root
^self parent = nil
ifTrue: [self]
ifFalse: [self parent root]

13. More OO conditional logic
and: block
^block value
True implementation:
boolExpr1 and: [boolExpr2].
boolExpr1 or: [boolExpr2].
boolExpr not
and: block
^self
False implementation:
or: block
^self
or: block
^block value
not
^false
not
^true
boolExpr1 && boolExpr2;
boolExpr1 || boolExpr2;
!boolExpr;

14. Learning points
• Anything may be expressed using objects, messages
and lambdas:
• Branches, loops, exception handling ….
• Common language features may be implemented with
lambdas
• Source code acts as documentation
• Possible to debug
• Many ways to arrange program flow
• Polymorphy
• Behavioural design patterns
Workshop 13:3
0 Room #2

15. Thank you for your time!
response
^self satisfied
ifTrue: [self clap]
ifFalse: [self boo]