22 - Smalltalk

22 - Smalltalk#

Basics#

Object-Oriented#

Everything is an object.

../../_images/smalltalk-objects.png

GNU Smalltalk#

ssh [email protected]

Interactive mode

gst
    st> 4+5
    9
    st> 4+5*6
    54
    st> ObjectMemory quit

You can also type CTRL-D to quit.

Literals#

  • Numbers: 12, 23.4

  • Characters: $a, $A

  • Strings: 'This is a string.'

  • Symbols (strings used for names): #foo

  • Arrays: #('three' 'four' 5 6 $Z)

  • Blocks: [:x | x + 2]

Naming#

Names in Smalltalk are a sequence of letters and digits beginning with a letter.

Global variables, class variables, pool dictionaries, and class names should start with an uppercase letter. Instance variables, methods, block arguments, and temporary variables start with a lowercase letter.

Only 6 “keywords” are reserved: true, false, nil, self, super, thisContext.

Variables#

  • Temporary variables

  • Instance variables

  • Class variables

  • Pool variables: A pool variable is a variable whose scope is a defined subset of classes.

  • Global variables (Smalltalk dictionary)

Expression#

  • A variable name

  • A literal

  • A message expression

  • A block expression

Messages#

  • Unary, keyword, and binary messages

  • Message chaining, evaluated from left to right

  • Unary messages take precedence over binary messages

  • Binary messages take precedence over keyword messages

  • All binary messages have the same precedence

  • Parantheses change the precedence

Assignment Statement#

variable := expression
quantity := 19
index :=  initialIndex
index := index + 1
y := quantity sqrt
z := 1 + 2 * 3
f := [:x|x+1]

Collections#

  • Arrays

  • Sets

  • Dictionaries

../../_images/collection-hierarchy.png

Array#

x := Array new: 20
x at: 1
x at: 1 put: 99

Note that the first index is 1.

Set#

x := Set new
x add: 5. x add: 7. x add: 'foo'
x add: 5; add: 7; add: 'foo'    "Message Cascading"
x remove: 5
x includes: 7

Dictionary#

y := Dictionary new
y at: 'name' put: 'John Smith'
y at: 'age' put: 25
y at: 'name'
y at: 'age'

Control Structures#

Selection#

aBoolean ifTrue: aBlock "evaluates aBlock if aBoolean is true"
aBoolean ifFalse: aBlock "evaluates aBlock if aBoolean is false"
aBoolean ifTrue: trueBlock ifFalse: falseBlock "evaluates trueBlock if aBoolean is true, falseBlock if false"
aBoolean ifFalse: falseBlock ifTrue: trueBlock "evaluates trueBlock if aBoolean is true, falseBlock if false"

index <= limit
    ifTrue: [total := total + (list at: index)]

index <= limit
    ifTrue: [total := total + (list at: index)]
    ifFalse: []

Iteration#

aBooleanBlock whileTrue: loopBlock  "as long as aBooleanBlock evaluates to true, loopBlock is evaluated"
aBooleanBlock whileFalse: loopBlock  "as long as aBooleanBlock evaluates to false, loopBlock is evaluated"
aBooleanBlock whileTrue "repeats evaluating aBooleanBlock until it returns false"
aBooleanBlock whileFalse "repeats evaluating aBooleanBlock until it returns true"

index := 1.
[index <= list size]
whileTrue: [list at: index put: 0.
            index := index + 1]

Multiple Iterations#

n timesRepeat: [
    ...
    repeated statements
    ...
]

5 timesRepeat: [100 printNl]

Interval and Iteration#

| anArray |
anArray := #('one' 'deux' 'drei' 'quatro' 5 6.0).

1 to: 6 do: [:idx | (anArray at: idx) printNl].

Collection and Iteration#

This uses the following form: aCollection do: aOneArgBlock.

| anArray |
anArray := #('one' 'deux' 'drei' 'quatro' 5 6.0).

anArray do:[:eachElement | eachElement printNl].

Collection Methods#

Detect:

#(4 7 10 3 17) detect: [ :each | each > 7 ]

Select, reject:

'now is the time' select: [ :each | each isVowel ]

Collect

#(1 2 3 4 5) collect: [ :i | i * i ]

Non-Interactive Mode#

"first.st"
"A program to print 'Hello World!' to the terminal."

'Hello World!' printNl

This can be run with:

gst first.st
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