Smalltalk - Revision history

Mguesdon at 14:29, 29 August 2005

2005-08-29T14:29:12Z

Stefan Urbanek: /* Array iteration */

2005-02-18T11:59:26Z

Array iteration

Stefan Urbanek: /* Cycles */

2005-02-18T11:59:13Z

Cycles

Stefan Urbanek: /* Blocks */

2005-02-18T11:59:01Z

Blocks

Stefan Urbanek at 09:47, 18 February 2005

2005-02-18T09:47:55Z

New page

Smalltalk is pure object oriented language with environment. In the context of the GNUstep, the Smalltalk is a ''[[Scripting language bundle]]'' for the [[StepTalk]] scripting framework.

Note that the language bundle offers Smalltalk language only, that sits on top of the Objective C object environment. Therefore, some classes and mechanisms known from Smalltalk are not (yet) available.

== The Language ==

The language has very straightforward and easy to learn syntax. It is said, that the syntax was inspired somehow by the english grammar.

=== Basics ===

The language is based on sending messages to objects, like:

anObject message

Here are few examples that you should try, for example by using the [[StepTalk shell]].
For example to see current date, just send message ''date'' to the object ''NSDate'':

NSDate date

To assign a result to a variable:

date := NSDate date

or

a := 10.
b := 20.
result := a + b.

=== Literals and basic operations ===

In a script you should have literal objects: strings, arrays, numbers and selectors.

{| border=1
|+
| Strings || 'This is a string' 'This is another \'String\' with apostrophes'
|+
| Array || #(1 2 3) #('one' 'two' 'three')
|+
| Numbers || 1 2 0.1 -1.1e10
|}

To join two strings use , (comma), like:

'This is ', 'a string'

To get an object from an array (indexed from 0):

#('one' 'two' 'three') @ 1

To do computations with numbers:

1 + 1

Important note: Smalltalk does not take into account operator priority, so you have to enclose an expression into parentheses. Try:

1 + 2 * 3
1 + (2 * 3)

You should use operators: + - * /

=== Blocks ===

Instead of explaining what blocks enclosed by [ ... ] are, try following examples, line by line, and you will get the idea:

( 1 = 1 ) ifTrue: [ Transcript showLine: 'Yes']
( 2 < 1 ) ifFalse: [ Transcript showLine: 'No']
( 1 >= 4 ) ifTrue: [ Transcript showLine: 'Yes'] ifFalse: [[ Transcript showLine: 'No']

=== Cycles ===

Cycles are created using blocks:

1 to: 10 do: [[ :i | Transcript showLine: (i description) ]
0 to: 100 step: 10 do: [[ :i | Transcript showLine: (i description) ]

Other possibilities are:

conditionBlock whileTrue: toDoBlock.
conditionBlock whileFalse: toDoBlock.

like:

a := 0 . [[ a < 10 ] whileTrue: [[ a := a + 1 . Transcript showLine: (a description) ]

=== Array iteration ===

array := #('one' 'two' 'three').
array do: [[ :item | Transcript showLine: item ]
array select: [[ :item | item hasPrefix:'t' ]

{| border=1
|+
| do: || Evaluate block for each object in array and return last evaluated expression
|+
| select: || Create new array which will contain those objects from receiver, for which value of block was true
|+
| reject: || Create new array which will contain those objects from receiver, for which value of block was false
|+
| collect:|| Create new array from block return values.
|+
| detect: || Return first object for which block evaluation result is true. Othervise return nil.
|}

== More information and examples ==

More examples are included in the StepTalk source distribution in Examples directory, please refer to that place.

For more information, please refer to the Documentation directory. For language reference see Smalltalk.txt file.

[[Category:Scripting]]

@@ Line 1: / Line 1: @@
 Smalltalk is pure object oriented language with environment. In the context of the GNUstep, the Smalltalk is a ''[[Scripting language bundle]]'' for the [[StepTalk]] scripting framework.
-Note that the language bundle offers Smalltalk language only, that sits on top of the Objective C object environment. Therefore, some classes and mechanisms known from Smalltalk are not (yet) available.
+Note that the language bundle offers Smalltalk language only, that sits on top of the [[Objective-C]] object environment. Therefore, some classes and mechanisms known from Smalltalk are not (yet) available.
 == The Language ==

@@ Line 87: / Line 87: @@
   array := #('one' 'two' 'three').
-  array do: [[ :item | Transcript showLine: item ]
+  array do: [ :item | Transcript showLine: item ]
-  array select: [[ :item | item hasPrefix:'t' ]
+  array select: [ :item | item hasPrefix:'t' ]
 {| border=1

@@ Line 72: / Line 72: @@
 Cycles are created using blocks:
-to: 10 do: [[ :i | Transcript showLine: (i description) ]
+to: 10 do: [ :i | Transcript showLine: (i description) ]
-to: 100 step: 10 do: [[ :i | Transcript showLine: (i description) ]
+to: 100 step: 10 do: [ :i | Transcript showLine: (i description) ]
 Other possibilities are:
@@ Line 82: / Line 82: @@
 like:
-  a := 0 . [[ a < 10 ] whileTrue: [[ a := a + 1 . Transcript showLine: (a description) ]
+  a := 0 . [ a < 10 ] whileTrue: [ a := a + 1 . Transcript showLine: (a description) ]
 === Array iteration ===

@@ Line 66: / Line 66: @@
   ( 1 = 1 ) ifTrue: [ Transcript showLine: 'Yes']
   ( 2 < 1 ) ifFalse: [ Transcript showLine: 'No']
-  ( 1 >= 4 ) ifTrue: [ Transcript showLine: 'Yes'] ifFalse: [[ Transcript showLine: 'No']
+  ( 1 >= 4 ) ifTrue: [ Transcript showLine: 'Yes'] ifFalse: [ Transcript showLine: 'No']
 === Cycles ===