learnxinyminutes-docs/smalltalk.html.markdown

---
language: Smalltalk
filename: smalltalk.st
contributors:
    - ["Jigyasa Grover", "https://jigyasa-grover.github.io"]
    - ["tim Rowledge", "tim@rowledge.org"]
---

- Smalltalk is a fully object-oriented, dynamically typed, reflective programming language with no 'non-object' types.
- Smalltalk was created as the language to underpin the "new world" of computing exemplified by "human–computer symbiosis."
- It was designed and created in part for educational use, more so for constructionist learning, 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.

## The Basics

### Everything is an object
Yes, everything. Integers are instances of one of the numeric classes. Classes are instances of the class Metaclass and are just as manipulable as any other object. All classes are part of a single class tree; no disjoint class trees. Stack frames are objects and can be manipulated, which is how the debugger works. There are no pointers into memory locations that you can dereference and mess with.

### Functions are not called; messages are sent to objects
- Work is done by sending messages to objects, which decide how to respond to that message and run a method as a result, which eventually returns some object to the original message sending code.
- The system knows the class of the object receiving a message and looks up the message in that class's list of methods. If it is not found, the lookup continues in the super class until either it is found or the root of the classes is reached and there is still no relevant method. 
- If a suitable method is found the code is run, and the same process keeps on going with all the methods sent by that method and so on forever.
- If no suitable method is found an exception is raised, which typically results in a user interface notifier to tell the user that the message was not understood. It is entirely possible to catch the exception and do something to fix the problem, which might range from 'ignore it' to 'load some new packages for this class and try again'.
- A method (more strictly an instance of the class CompiledMethod) is a chunk of Smalltalk code that has been compiled into bytecodes. Executing methods start at the beginning and return to the sender when a return is encountered (we use ^ to signify 'return the following object') or the end of the code is reached, in which case the current object running the code is returned.

### Simple syntax
Smalltalk has a simple syntax with very few rules. 
The most basic operation is to send a message to an object
`anObject aMessage`

There are three sorts of messages

- unary - a single symbol that may be several words conjoined in what we call camelcase form, with no arguments. For example 'size', 'reverseBytes', 'convertToLargerFormatPixels'
- binary - a small set of symbols of the sort often used for arithmetic operations in most languages, requiring a single argument. For example '+', '//', '@'. We do not use traditional arithmetic precedence, something to keep an eye on.
- keyword - the general form where multiple arguments can be passed. As with the unary form we use camelcase to join words together but arguments are inserted in the midst of the message with colons used to separate them lexically. For example 'setTemperature:', 'at:put:', 'drawFrom:to:lineWidth:fillColor:'

#### An example
`result := myObject doSomethingWith: thatObject`
We are sending the message 'doSomethingWith:' to myObject. This happens to be a message that has a single argument but that's not important yet.
'myObject' is a 'MyExampleClass' instance so the system looks at the list of messages understood by MyExampleClass

- beClever
- doWeirdThing:
- doSomethingWith

In searching we see what initially looks like a match - but no, it lacks the final colon. So we find the super class of MyExampleClass - BigExampleClass. Which has a list of known messages of its own

- beClever
- doSomethingWith:
- buildCastleInAir
- annoyUserByDoing:

We find a proper exact match and start to execute the code:

```smalltalk
doSomethingWith: argumentObject
    self size > 4 ifTrue: [^argumentObject sizeRelatingTo: self].
```   

Everything here except the `^` involves sending more messages. Event the `ifTrue:` that you might think is a language control structure is just Smalltalk code.

We start by sending `size` to `self`. `self` is the object currently running the code - so in this case it is the myObject we started with. `size` is a very common message that we might anticipate tells us something about how big an object is; you could look it up with the Smalltalk tools very simply. The result we get is then sent the message `>` with the plain old integer 4 (which is an object too; no strange primitive types to pollute the system here) and nobody should be surprised the `>` is a comparison that answers true or false. That boolean (which is actually a Boolean object in Smalltalk) is sent the message `ifTrue:` with the block of code between the `[]` as its argument; obviously a true boolean might be expected to run that block of code and a false to ignore it. 

If the block is run then we do some more message sending to the argument object and noting the `^` we return the answer back to our starting point and it gets assigned to `result`. If the block is ignored we seem to run out of code and so `self` is returned and assigned to `result`.

## Smalltalk quick reference cheat-sheet
Taken from [Smalltalk Cheatsheet](http://www.angelfire.com/tx4/cus/notes/smalltalk.html)

#### Allowable characters:
- a-z
- A-Z
- 0-9
- .+/\*~<>@%|&?
- blank, tab, cr, ff, lf

#### Variables:
- variable names must be declared before use but are untyped
- shared vars (globals, class vars) conventionally begin with uppercase (except the reserved names shown below)
- local vars (instance vars, temporaries, method & block arguments) conventionally begin with lowercase
- reserved names: `nil`, `true`, `false`, `self`, `super`, and `thisContext`

#### Variable scope:
- Global: defined in a Dictionary named 'Smalltalk' and accessible by all objects in system
- Special: (reserved) `Smalltalk`, `super`, `self`, `true`, `false`, & `nil`
- Method Temporary: local to a method
- Block Temporary: local to a block
- Pool: variables in a Dictionary object, possibly shared with classes not directly related by inheritance
- Method Parameters: automatic method temp vars that name the incoming parameters. Cannot be assigned to 
- Block Parameters: automatic block temp vars that name the incoming parameters. Cannot be assigned to
- Class: shared with all instances of a class & its subclasses
- Class Instance: unique to each instance of a class. Too commonly confused with class variables
- Instance Variables: unique to each instance of a class

`"Comments are enclosed in quotes and may be arbitrary length"`

`"Period (.) is the statement separator. Not required on last line of a method"`

#### Transcript:
```smalltalk
Transcript clear.                        "clear to transcript window"
Transcript show: 'Hello World'.          "output string in transcript window"
Transcript nextPutAll: 'Hello World'.    "output string in transcript window"
Transcript nextPut: $A.                  "output character in transcript window"
Transcript space.                        "output space character in transcript window"
Transcript tab.                          "output tab character in transcript window"
Transcript cr.                           "carriage return / linefeed"
'Hello' printOn: Transcript.             "append print string into the window"
'Hello' storeOn: Transcript.             "append store string into the window"
Transcript endEntry.                     "flush the output buffer"
```

#### Assignment:
```smalltalk
| x y |
x _ 4.                            "assignment (Squeak) <-"
x := 5.                           "assignment"
x := y := z := 6.                 "compound assignment"
x := (y := 6) + 1.
x := Object new.                  "bind to allocated instance of a class"
```

#### Constants:
```smalltalk
| b |
b := true.                "true constant"
b := false.               "false constant"
x := nil.                 "nil object constant"
x := 1.                   "integer constants"
x := 3.14.                "float constants"
x := 2e-2.                "fractional constants"
x := 16r0F.               "hex constant".
x := -1.                  "negative constants"
x := 'Hello'.             "string constant"
x := 'I''m here'.         "single quote escape"
x := $A.                  "character constant"
x := $ .                  "character constant (space)"
x := #aSymbol.            "symbol constants"
x := #(3 2 1).            "array constants"
x := #('abc' 2 $a).       "mixing of types allowed"
```

#### Booleans:
```smalltalk
| b x y |
x := 1. y := 2.
b := (x = y).                         "equals"
b := (x ~= y).                         "not equals"
b := (x == y).                         "identical"
b := (x ~~ y).                         "not identical"
b := (x > y).                          "greater than"
b := (x < y).                          "less than"
b := (x >= y).                         "greater than or equal"
b := (x <= y).                         "less than or equal"
b := b not.                            "boolean not"
b := (x < 5) & (y > 1).                "boolean and"
b := (x < 5) | (y > 1).                "boolean or"
b := (x < 5) and: [y > 1].             "boolean and (short-circuit)"
b := (x < 5) or: [y > 1].              "boolean or (short-circuit)"
b := (x < 5) eqv: (y > 1).             "test if both true or both false"
b := (x < 5) xor: (y > 1).             "test if one true and other false"
b := 5 between: 3 and: 12.             "between (inclusive)"
b := 123 isKindOf: Number.             "test if object is class or subclass of"
b := 123 isMemberOf: SmallInteger.     "test if object is type of class"
b := 123 respondsTo: #sqrt.             "test if object responds to message"
b := x isNil.                          "test if object is nil"
b := x isZero.                         "test if number is zero"
b := x positive.                       "test if number is positive"
b := x strictlyPositive.               "test if number is greater than zero"
b := x negative.                       "test if number is negative"
b := x even.                           "test if number is even"
b := x odd.                            "test if number is odd"
b := x isLiteral.                      "test if literal constant"
b := x isInteger.                      "test if object is integer"
b := x isFloat.                        "test if object is float"
b := x isNumber.                       "test if object is number"
b := $A isUppercase.                   "test if upper case character"
b := $A isLowercase.                   "test if lower case character"
```

#### Arithmetic expressions:
```smalltalk
| x |
x := 6 + 3.                             "addition"
x := 6 - 3.                             "subtraction"
x := 6 * 3.                             "multiplication"
x := 1 + 2 * 3.                         "evaluation always left to right (1 + 2) * 3"
x := 5 / 3.                             "division with fractional result"
x := 5.0 / 3.0.                         "division with float result"
x := 5.0 // 3.0.                        "integer divide"
x := 5.0 \\ 3.0.                        "integer remainder"
x := -5.                                "unary minus"
x := 5 sign.                            "numeric sign (1, -1 or 0)"
x := 5 negated.                         "negate receiver"
x := 1.2 integerPart.                   "integer part of number (1.0)"
x := 1.2 fractionPart.                  "fractional part of number (0.2)"
x := 5 reciprocal.                      "reciprocal function"
x := 6 * 3.1.                           "auto convert to float"
x := 5 squared.                         "square function"
x := 25 sqrt.                           "square root"
x := 5 raisedTo: 2.                     "power function"
x := 5 raisedToInteger: 2.              "power function with integer"
x := 5 exp.                             "exponential"
x := -5 abs.                            "absolute value"
x := 3.99 rounded.                      "round"
x := 3.99 truncated.                    "truncate"
x := 3.99 roundTo: 1.                   "round to specified decimal places"
x := 3.99 truncateTo: 1.                "truncate to specified decimal places"
x := 3.99 floor.                        "truncate"
x := 3.99 ceiling.                      "round up"
x := 5 factorial.                       "factorial"
x := -5 quo: 3.                         "integer divide rounded toward zero"
x := -5 rem: 3.                         "integer remainder rounded toward zero"
x := 28 gcd: 12.                        "greatest common denominator"
x := 28 lcm: 12.                        "least common multiple"
x := 100 ln.                            "natural logarithm"
x := 100 log.                           "base 10 logarithm"
x := 100 log: 10.                       "floor of the log"
x := 180 degreesToRadians.              "convert degrees to radians"
x := 3.14 radiansToDegrees.             "convert radians to degrees"
x := 0.7 sin.                           "sine"
x := 0.7 cos.                           "cosine"
x := 0.7 tan.                           "tangent"
x := 0.7 arcSin.                        "arcsine"
x := 0.7 arcCos.                        "arccosine"
x := 0.7 arcTan.                        "arctangent"
x := 10 max: 20.                        "get maximum of two numbers"
x := 10 min: 20.                        "get minimum of two numbers"
x := Float pi.                          "pi"
x := Float e.                           "exp constant"
x := Float infinity.                    "infinity"
x := Float nan.                         "not-a-number"
x := Random new next; yourself. x next. "random number stream (0.0 to 1.0)"
x := 100 atRandom.                      "quick random number"
```

#### Bitwise Manipulation:
```smalltalk
| b x |
x := 16rFF bitAnd: 16r0F.           "and bits"
x := 16rF0 bitOr: 16r0F.            "or bits"
x := 16rFF bitXor: 16r0F.           "xor bits"
x := 16rFF bitInvert.               "invert bits"
x := 16r0F bitShift: 4.             "left shift"
x := 16rF0 bitShift: -4.            "right shift"
"x := 16r80 bitAt: 7."              "bit at position (0|1) [!Squeak]"
x := 16r80 highbit.                 "position of highest bit set"
b := 16rFF allMask: 16r0F.          "test if all bits set in mask set in receiver"
b := 16rFF anyMask: 16r0F.          "test if any bits set in mask set in receiver"
b := 16rFF noMask: 16r0F.           "test if all bits set in mask clear in receiver"
```

#### Conversion:
```smalltalk
| x |
x := 3.99 asInteger.               "convert number to integer (truncates in Squeak)"
x := 3.99 asFraction.              "convert number to fraction"
x := 3 asFloat.                    "convert number to float"
x := 65 asCharacter.               "convert integer to character"
x := $A asciiValue.                "convert character to integer"
x := 3.99 printString.             "convert object to string via printOn:"
x := 3.99 storeString.             "convert object to string via storeOn:"
x := 15 radix: 16.                 "convert to string in given base"
x := 15 printStringBase: 16.
x := 15 storeStringBase: 16.
```

#### Blocks:
- blocks are objects and may be assigned to a variable
- value is last expression evaluated unless explicit return
- blocks may be nested
- specification [ arguments | | localvars | expressions ]
- Squeak does not currently support localvars in blocks
- max of three arguments allowed
- `^`expression terminates block & method (exits all nested blocks)
- blocks intended for long term storage should not contain `^`

```smalltalk
| x y z |
x := [ y := 1. z := 2. ]. x value.                          "simple block usage"
x := [ :argOne :argTwo |   argOne, ' and ' , argTwo.].      "set up block with argument passing"
Transcript show: (x value: 'First' value: 'Second'); cr.    "use block with argument passing"

"x := [ | z | z := 1.]. *** localvars not available in squeak blocks"
```

#### Method calls:
- unary methods are messages with no arguments
- binary methods
- keyword methods are messages with selectors including colons standard categories/protocols:
- initialize-release    (methods called for new instance)
- accessing             (get/set methods)
- testing               (boolean tests - is)
- comparing             (boolean tests with parameter
- displaying            (gui related methods)
- printing              (methods for printing)
- updating              (receive notification of changes)
- private               (methods private to class)
- instance-creation     (class methods for creating instance)

```smalltalk
| x |
x := 2 sqrt.                                  "unary message"
x := 2 raisedTo: 10.                          "keyword message"
x := 194 * 9.                                 "binary message"
Transcript show: (194 * 9) printString; cr.   "combination (chaining)"
x := 2 perform: #sqrt.                        "indirect method invocation"
Transcript                                    "Cascading - send multiple messages to receiver"
   show: 'hello ';
   show: 'world';
   cr.
x := 3 + 2; * 100.                            "result=300. Sends message to same receiver (3)"
```

#### Conditional Statements:
```smalltalk
| x |
x > 10 ifTrue: [Transcript show: 'ifTrue'; cr].     "if then"
x > 10 ifFalse: [Transcript show: 'ifFalse'; cr].   "if else"

"if then else"
x > 10                                                      
   ifTrue: [Transcript show: 'ifTrue'; cr]
   ifFalse: [Transcript show: 'ifFalse'; cr].

"if else then"
x > 10                                                      
   ifFalse: [Transcript show: 'ifFalse'; cr]
   ifTrue: [Transcript show: 'ifTrue'; cr].
Transcript
   show:
      (x > 10
         ifTrue: ['ifTrue']
         ifFalse: ['ifFalse']);
   cr.

"nested if then else"
Transcript                                                  
   show:
      (x > 10
         ifTrue: [x > 5
            ifTrue: ['A']
            ifFalse: ['B']]
         ifFalse: ['C']);
   cr.

"switch functionality"
switch := Dictionary new.     
switch at: $A put: [Transcript show: 'Case A'; cr].
switch at: $B put: [Transcript show: 'Case B'; cr].
switch at: $C put: [Transcript show: 'Case C'; cr].
result := (switch at: $B) value.
```

#### Iteration statements:
```smalltalk
| x y |
x := 4. y := 1.
[x > 0] whileTrue: [x := x - 1. y := y * 2].     "while true loop"
[x >= 4] whileFalse: [x := x + 1. y := y * 2].   "while false loop"
x timesRepeat: [y := y * 2].                     "times repeat loop (i := 1 to x)"
1 to: x do: [:a | y := y * 2].                   "for loop"
1 to: x by: 2 do: [:a | y := y / 2].             "for loop with specified increment"
#(5 4 3) do: [:a | x := x + a].                  "iterate over array elements"
```

#### Character:
```smalltalk
| x y |
x := $A.                         "character assignment"
y := x isLowercase.              "test if lower case"
y := x isUppercase.              "test if upper case"
y := x isLetter.                 "test if letter"
y := x isDigit.                  "test if digit"
y := x isAlphaNumeric.           "test if alphanumeric"
y := x isSeparator.              "test if separator char"
y := x isVowel.                  "test if vowel"
y := x digitValue.               "convert to numeric digit value"
y := x asLowercase.              "convert to lower case"
y := x asUppercase.              "convert to upper case"
y := x asciiValue.               "convert to numeric ascii value"
y := x asString.                 "convert to string"
b := $A <= $B.                   "comparison"
y := $A max: $B.
```

#### Symbol:
```smalltalk
| b x y |
x := #Hello.                                      "symbol assignment"
y := #Symbol, #Concatenation.                     "symbol concatenation (result is string)"
b := x isEmpty.                                   "test if symbol is empty"
y := x size.                                      "string size"
y := x at: 2.                                     "char at location"
y := x copyFrom: 2 to: 4.                         "substring"
y := x indexOf: $e ifAbsent: [0].                 "first position of character within string"
x do: [:a | Transcript show: a printString; cr].  "iterate over the string"
b := x conform: [:a | (a >= $a) & (a <= $z)].     "test if all elements meet condition"
y := x select: [:a | a > $a].                     "return all elements that meet condition"
y := x asString.                                  "convert symbol to string"
y := x asText.                                    "convert symbol to text"
y := x asArray.                                   "convert symbol to array"
y := x asOrderedCollection.                       "convert symbol to ordered collection"
y := x asSortedCollection.                        "convert symbol to sorted collection"
y := x asBag.                                     "convert symbol to bag collection"
y := x asSet.                                     "convert symbol to set collection"
```

#### String:
```smalltalk
| b x y |
x := 'This is a string'.                           "string assignment"
x := 'String', 'Concatenation'.                    "string concatenation"
b := x isEmpty.                                    "test if string is empty"
y := x size.                                       "string size"
y := x at: 2.                                      "char at location"
y := x copyFrom: 2 to: 4.                          "substring"
y := x indexOf: $a ifAbsent: [0].                  "first position of character within string"
x := String new: 4.                                "allocate string object"
x                                                  "set string elements"
   at: 1 put: $a;
   at: 2 put: $b;
   at: 3 put: $c;
   at: 4 put: $e.
x := String with: $a with: $b with: $c with: $d.  "set up to 4 elements at a time"
x do: [:a | Transcript show: a printString; cr].  "iterate over the string"
b := x conform: [:a | (a >= $a) & (a <= $z)].     "test if all elements meet condition"
y := x select: [:a | a > $a].                     "return all elements that meet condition"
y := x asSymbol.                                  "convert string to symbol"
y := x asArray.                                   "convert string to array"
x := 'ABCD' asByteArray.                          "convert string to byte array"
y := x asOrderedCollection.                       "convert string to ordered collection"
y := x asSortedCollection.                        "convert string to sorted collection"
y := x asBag.                                     "convert string to bag collection"
y := x asSet.                                     "convert string to set collection"
y := x shuffled.                                  "randomly shuffle string"
```

#### Array:
Fixed length collection
- ByteArray:     Array limited to byte elements (0-255)
- WordArray:     Array limited to word elements (0-2^32)

```smalltalk
| b x y z sum max |
x := #(4 3 2 1).                                 "constant array"
z := #(1 2 3 'hi').                              "mixed type array"
x := Array with: 5 with: 4 with: 3 with: 2.      "create array with up to 4 elements"
x := Array new: 4.                               "allocate an array with specified size"
x                                                "set array elements"
   at: 1 put: 5;
   at: 2 put: 4;
   at: 3 put: 3;
   at: 4 put: 2.
b := x isEmpty.                                  "test if array is empty"
y := x size.                                     "array size"
y := x at: 4.                                    "get array element at index"
b := x includes: 3.                              "test if element is in array"
y := x copyFrom: 2 to: 4.                        "subarray"
y := x indexOf: 3 ifAbsent: [0].                 "first position of element within array"
y := x occurrencesOf: 3.                         "number of times object in collection"
x do: [:a | Transcript show: a printString; cr]. "iterate over the array"
b := x conform: [:a | (a >= 1) & (a <= 4)].      "test if all elements meet condition"
y := x select: [:a | a > 2].                     "return collection of elements that pass test"
y := x reject: [:a | a < 2].                     "return collection of elements that fail test"
y := x collect: [:a | a + a].                    "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].          "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.      "sum array elements"
sum := 0. 1 to: (x size) 
            do: [:a | sum := sum + (x at: a)].   "sum array elements"
sum := x inject: 0 into: [:a :c | a + c].        "sum array elements"
max := x inject: 0 into: [:a :c | (a > c)        "find max element in array"
   ifTrue: [a]
   ifFalse: [c]].
y := x shuffled.                                 "randomly shuffle collection"
y := x asArray.                                  "convert to array"
"y := x asByteArray."                            "note: this instruction not available on Squeak"
y := x asWordArray.                              "convert to word array"
y := x asOrderedCollection.                      "convert to ordered collection"
y := x asSortedCollection.                       "convert to sorted collection"
y := x asBag.                                    "convert to bag collection"
y := x asSet.                                    "convert to set collection"
```

#### OrderedCollection:
acts like an expandable array

```smalltalk
| b x y sum max |
x := OrderedCollection 
     with: 4 with: 3 with: 2 with: 1.            "create collection with up to 4 elements"
x := OrderedCollection new.                      "allocate collection"
x add: 3; add: 2; add: 1; add: 4; yourself.      "add element to collection"
y := x addFirst: 5.                              "add element at beginning of collection"
y := x removeFirst.                              "remove first element in collection"
y := x addLast: 6.                               "add element at end of collection"
y := x removeLast.                               "remove last element in collection"
y := x addAll: #(7 8 9).                         "add multiple elements to collection"
y := x removeAll: #(7 8 9).                      "remove multiple elements from collection"
x at: 2 put: 3.                                  "set element at index"
y := x remove: 5 ifAbsent: [].                   "remove element from collection"
b := x isEmpty.                                  "test if empty"
y := x size.                                     "number of elements"
y := x at: 2.                                    "retrieve element at index"
y := x first.                                    "retrieve first element in collection"
y := x last.                                     "retrieve last element in collection"
b := x includes: 5.                              "test if element is in collection"
y := x copyFrom: 2 to: 3.                        "subcollection"
y := x indexOf: 3 ifAbsent: [0].                 "first position of element within collection"
y := x occurrencesOf: 3.                         "number of times object in collection"
x do: [:a | Transcript show: a printString; cr]. "iterate over the collection"
b := x conform: [:a | (a >= 1) & (a <= 4)].      "test if all elements meet condition"
y := x select: [:a | a > 2].                     "return collection of elements that pass test"
y := x reject: [:a | a < 2].                     "return collection of elements that fail test"
y := x collect: [:a | a + a].                    "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].          "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.      "sum elements"
sum := 0. 1 to: (x size) 
            do: [:a | sum := sum + (x at: a)].   "sum elements"
sum := x inject: 0 into: [:a :c | a + c].        "sum elements"
max := x inject: 0 into: [:a :c | (a > c)        "find max element in collection"
   ifTrue: [a]
   ifFalse: [c]].
y := x shuffled.                                 "randomly shuffle collection"
y := x asArray.                                  "convert to array"
y := x asOrderedCollection.                      "convert to ordered collection"
y := x asSortedCollection.                       "convert to sorted collection"
y := x asBag.                                    "convert to bag collection"
y := x asSet.                                    "convert to set collection"
```

#### SortedCollection:
like OrderedCollection except order of elements determined by sorting criteria

```smalltalk
| b x y sum max |
x := SortedCollection 
     with: 4 with: 3 with: 2 with: 1.              "create collection with up to 4 elements"
x := SortedCollection new.                         "allocate collection"
x := SortedCollection sortBlock: [:a :c | a > c].  "set sort criteria"
x add: 3; add: 2; add: 1; add: 4; yourself.        "add element to collection"
y := x addFirst: 5.                                "add element at beginning of collection"
y := x removeFirst.                                "remove first element in collection"
y := x addLast: 6.                                 "add element at end of collection"
y := x removeLast.                                 "remove last element in collection"
y := x addAll: #(7 8 9).                           "add multiple elements to collection"
y := x removeAll: #(7 8 9).                        "remove multiple elements from collection"
y := x remove: 5 ifAbsent: [].                     "remove element from collection"
b := x isEmpty.                                    "test if empty"
y := x size.                                       "number of elements"
y := x at: 2.                                      "retrieve element at index"
y := x first.                                      "retrieve first element in collection"
y := x last.                                       "retrieve last element in collection"
b := x includes: 4.                                "test if element is in collection"
y := x copyFrom: 2 to: 3.                          "subcollection"
y := x indexOf: 3 ifAbsent: [0].                   "first position of element within collection"
y := x occurrencesOf: 3.                           "number of times object in collection"
x do: [:a | Transcript show: a printString; cr].   "iterate over the collection"
b := x conform: [:a | (a >= 1) & (a <= 4)].        "test if all elements meet condition"
y := x select: [:a | a > 2].                       "return collection of elements that pass test"
y := x reject: [:a | a < 2].                       "return collection of elements that fail test"
y := x collect: [:a | a + a].                      "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].            "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.        "sum elements"
sum := 0. 1 to: (x size) 
            do: [:a | sum := sum + (x at: a)].     "sum elements"
sum := x inject: 0 into: [:a :c | a + c].          "sum elements"
max := x inject: 0 into: [:a :c | (a > c)          "find max element in collection"
   ifTrue: [a]
   ifFalse: [c]].
y := x asArray.                                     "convert to array"
y := x asOrderedCollection.                         "convert to ordered collection"
y := x asSortedCollection.                          "convert to sorted collection"
y := x asBag.                                       "convert to bag collection"
y := x asSet.                                       "convert to set collection"
```

#### Bag:
like OrderedCollection except elements are in no particular order

```smalltalk
| b x y sum max |
x := Bag with: 4 with: 3 with: 2 with: 1.        "create collection with up to 4 elements"
x := Bag new.                                    "allocate collection"
x add: 4; add: 3; add: 1; add: 2; yourself.      "add element to collection"
x add: 3 withOccurrences: 2.                     "add multiple copies to collection"
y := x addAll: #(7 8 9).                         "add multiple elements to collection"
y := x removeAll: #(7 8 9).                      "remove multiple elements from collection"
y := x remove: 4 ifAbsent: [].                   "remove element from collection"
b := x isEmpty.                                  "test if empty"
y := x size.                                     "number of elements"
b := x includes: 3.                              "test if element is in collection"
y := x occurrencesOf: 3.                         "number of times object in collection"
x do: [:a | Transcript show: a printString; cr]. "iterate over the collection"
b := x conform: [:a | (a >= 1) & (a <= 4)].      "test if all elements meet condition"
y := x select: [:a | a > 2].                     "return collection of elements that pass test"
y := x reject: [:a | a < 2].                     "return collection of elements that fail test"
y := x collect: [:a | a + a].                    "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].          "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.      "sum elements"
sum := x inject: 0 into: [:a :c | a + c].        "sum elements"
max := x inject: 0 into: [:a :c | (a > c)        "find max element in collection"
   ifTrue: [a]
   ifFalse: [c]].
y := x asOrderedCollection.                       "convert to ordered collection"
y := x asSortedCollection.                        "convert to sorted collection"
y := x asBag.                                     "convert to bag collection"
y := x asSet.                                     "convert to set collection"
```

#### Set:
like Bag except duplicates not allowed

#### IdentitySet:
uses identity test (== rather than =)

```smalltalk
| b x y sum max |
x := Set with: 4 with: 3 with: 2 with: 1.        "create collection with up to 4 elements"
x := Set new.                                    "allocate collection"
x add: 4; add: 3; add: 1; add: 2; yourself.      "add element to collection"
y := x addAll: #(7 8 9).                         "add multiple elements to collection"
y := x removeAll: #(7 8 9).                      "remove multiple elements from collection"
y := x remove: 4 ifAbsent: [].                   "remove element from collection"
b := x isEmpty.                                  "test if empty"
y := x size.                                     "number of elements"
x includes: 4.                                   "test if element is in collection"
x do: [:a | Transcript show: a printString; cr]. "iterate over the collection"
b := x conform: [:a | (a >= 1) & (a <= 4)].      "test if all elements meet condition"
y := x select: [:a | a > 2].                     "return collection of elements that pass test"
y := x reject: [:a | a < 2].                     "return collection of elements that fail test"
y := x collect: [:a | a + a].                    "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].          "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.      "sum elements"
sum := x inject: 0 into: [:a :c | a + c].        "sum elements"
max := x inject: 0 into: [:a :c | (a > c)        "find max element in collection"
   ifTrue: [a]
   ifFalse: [c]].
y := x asArray.                                  "convert to array"
y := x asOrderedCollection.                      "convert to ordered collection"
y := x asSortedCollection.                       "convert to sorted collection"
y := x asBag.                                    "convert to bag collection"
y := x asSet.                                    "convert to set collection"
```

#### Interval:
```smalltalk
| b x y sum max |
x := Interval from: 5 to: 10.                     "create interval object"
x := 5 to: 10.
x := Interval from: 5 to: 10 by: 2.               "create interval object with specified increment"
x := 5 to: 10 by: 2.
b := x isEmpty.                                   "test if empty"
y := x size.                                      "number of elements"
x includes: 9.                                    "test if element is in collection"
x do: [:k | Transcript show: k printString; cr].  "iterate over interval"
b := x conform: [:a | (a >= 1) & (a <= 4)].       "test if all elements meet condition"
y := x select: [:a | a > 7].                      "return collection of elements that pass test"
y := x reject: [:a | a < 2].                      "return collection of elements that fail test"
y := x collect: [:a | a + a].                     "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].           "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.       "sum elements"
sum := 0. 1 to: (x size) 
            do: [:a | sum := sum + (x at: a)].    "sum elements"
sum := x inject: 0 into: [:a :c | a + c].         "sum elements"
max := x inject: 0 into: [:a :c | (a > c)         "find max element in collection"
   ifTrue: [a]
   ifFalse: [c]].
y := x asArray.                                   "convert to array"
y := x asOrderedCollection.                       "convert to ordered collection"
y := x asSortedCollection.                        "convert to sorted collection"
y := x asBag.                                     "convert to bag collection"
y := x asSet.                                     "convert to set collection"
```

#### Associations:
```smalltalk
| x y |
x := #myVar->'hello'.
y := x key.
y := x value.
```

#### Dictionary:
#### IdentityDictionary:
uses identity test (== rather than =)

```smalltalk
| b x y |
x := Dictionary new.                   "allocate collection"
x add: #a->4; 
  add: #b->3; 
  add: #c->1; 
  add: #d->2; yourself.                "add element to collection"
x at: #e put: 3.                       "set element at index"
b := x isEmpty.                        "test if empty"
y := x size.                           "number of elements"
y := x at: #a ifAbsent: [].            "retrieve element at index"
y := x keyAtValue: 3 ifAbsent: [].     "retrieve key for given value with error block"
y := x removeKey: #e ifAbsent: [].     "remove element from collection"
b := x includes: 3.                    "test if element is in values collection"
b := x includesKey: #a.                "test if element is in keys collection"
y := x occurrencesOf: 3.               "number of times object in collection"
y := x keys.                           "set of keys"
y := x values.                         "bag of values"
x do: [:a | Transcript show: a printString; cr].            "iterate over the values collection"
x keysDo: [:a | Transcript show: a printString; cr].        "iterate over the keys collection"
x associationsDo: [:a | Transcript show: a printString; cr]."iterate over the associations"
x keysAndValuesDo: [:aKey :aValue | Transcript              "iterate over keys and values"
   show: aKey printString; space;
   show: aValue printString; cr].
b := x conform: [:a | (a >= 1) & (a <= 4)].      "test if all elements meet condition"
y := x select: [:a | a > 2].                     "return collection of elements that pass test"
y := x reject: [:a | a < 2].                     "return collection of elements that fail test"
y := x collect: [:a | a + a].                    "transform each element for new collection"
y := x detect: [:a | a > 3] ifNone: [].          "find position of first element that passes test"
sum := 0. x do: [:a | sum := sum + a]. sum.      "sum elements"
sum := x inject: 0 into: [:a :c | a + c].        "sum elements"
max := x inject: 0 into: [:a :c | (a > c)        "find max element in collection"
   ifTrue: [a]
   ifFalse: [c]].
y := x asArray.                                   "convert to array"
y := x asOrderedCollection.                       "convert to ordered collection"
y := x asSortedCollection.                        "convert to sorted collection"
y := x asBag.                                     "convert to bag collection"
y := x asSet.                                     "convert to set collection"

Smalltalk at: #CMRGlobal put: 'CMR entry'.        "put global in Smalltalk Dictionary"
x := Smalltalk at: #CMRGlobal.                    "read global from Smalltalk Dictionary"
Transcript show: (CMRGlobal printString).         "entries are directly accessible by name"
Smalltalk keys do: [ :k |                         "print out all classes"
   ((Smalltalk at: k) isKindOf: Class)
      ifFalse: [Transcript show: k printString; cr]].
Smalltalk at: #CMRDictionary put: (Dictionary new). "set up user defined dictionary"
CMRDictionary at: #MyVar1 put: 'hello1'.            "put entry in dictionary"
CMRDictionary add: #MyVar2->'hello2'.               "add entry to dictionary use key->value combo"
CMRDictionary size.                                 "dictionary size"
CMRDictionary keys do: [ :k |                       "print out keys in dictionary"
   Transcript show: k printString; cr].
CMRDictionary values do: [ :k |                     "print out values in dictionary"
   Transcript show: k printString; cr].
CMRDictionary keysAndValuesDo: [:aKey :aValue |     "print out keys and values"
   Transcript
      show: aKey printString;
      space;
      show: aValue printString;
      cr].
CMRDictionary associationsDo: [:aKeyValue |           "another iterator for printing key values"
   Transcript show: aKeyValue printString; cr].
Smalltalk removeKey: #CMRGlobal ifAbsent: [].         "remove entry from Smalltalk dictionary"
Smalltalk removeKey: #CMRDictionary ifAbsent: [].     "remove user dictionary from Smalltalk dictionary"
```

#### Internal Stream:
```smalltalk
| b x ios |
ios := ReadStream on: 'Hello read stream'.
ios := ReadStream on: 'Hello read stream' from: 1 to: 5.
[(x := ios nextLine) notNil] whileTrue: [Transcript show: x; cr].
ios position: 3.
ios position.
x := ios next.
x := ios peek.
x := ios contents.
b := ios atEnd.

ios := ReadWriteStream on: 'Hello read stream'.
ios := ReadWriteStream on: 'Hello read stream' from: 1 to: 5.
ios := ReadWriteStream with: 'Hello read stream'.
ios := ReadWriteStream with: 'Hello read stream' from: 1 to: 10.
ios position: 0.
[(x := ios nextLine) notNil] whileTrue: [Transcript show: x; cr].
ios position: 6.
ios position.
ios nextPutAll: 'Chris'.
x := ios next.
x := ios peek.
x := ios contents.
b := ios atEnd.
```

#### FileStream:
```smalltalk
| b x ios |
ios := FileStream newFileNamed: 'ios.txt'.
ios nextPut: $H; cr.
ios nextPutAll: 'Hello File'; cr.
'Hello File' printOn: ios.
'Hello File' storeOn: ios.
ios close.

ios := FileStream oldFileNamed: 'ios.txt'.
[(x := ios nextLine) notNil] whileTrue: [Transcript show: x; cr].
ios position: 3.
x := ios position.
x := ios next.
x := ios peek.
b := ios atEnd.
ios close.
```

#### Date:
```smalltalk
| x y |
x := Date today.                                "create date for today"
x := Date dateAndTimeNow.                       "create date from current time/date"
x := Date readFromString: '01/02/1999'.         "create date from formatted string"
x := Date newDay: 12 month: #July year: 1999    "create date from parts"
x := Date fromDays: 36000.                      "create date from elapsed days since 1/1/1901"
y := Date dayOfWeek: #Monday.                   "day of week as int (1-7)"
y := Date indexOfMonth: #January.               "month of year as int (1-12)"
y := Date daysInMonth: 2 forYear: 1996.         "day of month as int (1-31)"
y := Date daysInYear: 1996.                     "days in year (365|366)"
y := Date nameOfDay: 1                          "weekday name (#Monday,...)"
y := Date nameOfMonth: 1.                       "month name (#January,...)"
y := Date leapYear: 1996.                       "1 if leap year; 0 if not leap year"
y := x weekday.                                 "day of week (#Monday,...)"
y := x previous: #Monday.                       "date for previous day of week"
y := x dayOfMonth.                              "day of month (1-31)"
y := x day.                                     "day of year (1-366)"
y := x firstDayOfMonth.                         "day of year for first day of month"
y := x monthName.                               "month of year (#January,...)"
y := x monthIndex.                              "month of year (1-12)"
y := x daysInMonth.                             "days in month (1-31)"
y := x year.                                    "year (19xx)"
y := x daysInYear.                              "days in year (365|366)"
y := x daysLeftInYear.                          "days left in year (364|365)"
y := x asSeconds.                               "seconds elapsed since 1/1/1901"
y := x addDays: 10.                             "add days to date object"
y := x subtractDays: 10.                        "subtract days to date object"
y := x subtractDate: (Date today).              "subtract date (result in days)"
y := x printFormat: #(2 1 3 $/ 1 1).            "print formatted date"
b := (x <= Date today).                         "comparison"
```

#### Time:
```smalltalk
| x y |
x := Time now.                                      "create time from current time"
x := Time dateAndTimeNow.                           "create time from current time/date"
x := Time readFromString: '3:47:26 pm'.             "create time from formatted string"
x := Time fromSeconds: (60 * 60 * 4).               "create time from elapsed time from midnight"
y := Time millisecondClockValue.                    "milliseconds since midnight"
y := Time totalSeconds.                             "total seconds since 1/1/1901"
y := x seconds.                                     "seconds past minute (0-59)"
y := x minutes.                                     "minutes past hour (0-59)"
y := x hours.                                       "hours past midnight (0-23)"
y := x addTime: (Time now).                         "add time to time object"
y := x subtractTime: (Time now).                    "subtract time to time object"
y := x asSeconds.                                   "convert time to seconds"
x := Time millisecondsToRun: [                      "timing facility"
   1 to: 1000 do: [:index | y := 3.14 * index]].
b := (x <= Time now).                               "comparison"
```

#### Point:
```smalltalk
| x y |
x := 200@100.                            "obtain a new point"
y := x x.                                "x coordinate"
y := x y.                                "y coordinate"
x := 200@100 negated.                    "negates x and y"
x := (-200@-100) abs.                    "absolute value of x and y"
x := (200.5@100.5) rounded.              "round x and y"
x := (200.5@100.5) truncated.            "truncate x and y"
x := 200@100 + 100.                      "add scale to both x and y"
x := 200@100 - 100.                      "subtract scale from both x and y"
x := 200@100 * 2.                        "multiply x and y by scale"
x := 200@100 / 2.                        "divide x and y by scale"
x := 200@100 // 2.                       "divide x and y by scale"
x := 200@100 \\ 3.                       "remainder of x and y by scale"
x := 200@100 + 50@25.                    "add points"
x := 200@100 - 50@25.                    "subtract points"
x := 200@100 * 3@4.                      "multiply points"
x := 200@100 // 3@4.                     "divide points"
x := 200@100 max: 50@200.                "max x and y"
x := 200@100 min: 50@200.                "min x and y"
x := 20@5 dotProduct: 10@2.              "sum of product (x1*x2 + y1*y2)"
```

#### Rectangle:
```smalltalk
Rectangle fromUser.
```

#### Pen:
```smalltalk
| myPen |
Display restoreAfter: [
   Display fillWhite.

myPen := Pen new.                            "get graphic pen"
myPen squareNib: 1.
myPen color: (Color blue).                   "set pen color"
myPen home.                                  "position pen at center of display"
myPen up.                                    "makes nib unable to draw"
myPen down.                                  "enable the nib to draw"
myPen north.                                 "points direction towards top"
myPen turn: -180.                            "add specified degrees to direction"
myPen direction.                             "get current angle of pen"
myPen go: 50.                                "move pen specified number of pixels"
myPen location.                              "get the pen position"
myPen goto: 200@200.                         "move to specified point"
myPen place: 250@250.                        "move to specified point without drawing"
myPen print: 'Hello World' 
      withFont: (TextStyle default fontAt: 1).
Display extent.                              "get display width@height"
Display width.                               "get display width"
Display height.                              "get display height"

].
```

#### Dynamic Message Calling/Compiling:
```smalltalk
| receiver message result argument keyword1 keyword2 argument1 argument2 |

"unary message"
receiver := 5.
message := 'factorial' asSymbol.
result := receiver perform: message.
result := Compiler evaluate: ((receiver storeString), ' ', message).
result := (Message new setSelector: message arguments: #()) sentTo: receiver.

"binary message"
receiver := 1.
message := '+' asSymbol.
argument := 2.
result := receiver perform: message withArguments: (Array with: argument).
result := Compiler evaluate: ((receiver storeString), ' ', message, ' ', (argument storeString)).
result := (Message new setSelector: message arguments: (Array with: argument)) sentTo: receiver.

"keyword messages"
receiver := 12.
keyword1 := 'between:' asSymbol.
keyword2 := 'and:' asSymbol.
argument1 := 10.
argument2 := 20.

result := receiver
   perform: (keyword1, keyword2) asSymbol
   withArguments: (Array with: argument1 with: argument2).
   
result := Compiler evaluate:
   ((receiver storeString), ' ', keyword1, (argument1 storeString) , ' ', keyword2, (argument2 storeString)).
   
result := (Message
   new
      setSelector: (keyword1, keyword2) asSymbol
      arguments: (Array with: argument1 with: argument2))
   sentTo: receiver.
```

#### Class/Meta-Class:
```smalltalk
| b x |
x := String name.                     "class name"
x := String category.                 "organization category"
x := String comment.                  "class comment"
x := String kindOfSubclass.           "subclass type - subclass: variableSubclass, etc"
x := String definition.               "class definition"
x := String instVarNames.             "immediate instance variable names"
x := String allInstVarNames.          "accumulated instance variable names"
x := String classVarNames.            "immediate class variable names"
x := String allClassVarNames.         "accumulated class variable names"
x := String sharedPools.              "immediate dictionaries used as shared pools"
x := String allSharedPools.           "accumulated dictionaries used as shared pools"
x := String selectors.                "message selectors for class"
x := String sourceCodeAt: #size.      "source code for specified method"
x := String allInstances.             "collection of all instances of class"
x := String superclass.               "immediate superclass"
x := String allSuperclasses.          "accumulated superclasses"
x := String withAllSuperclasses.      "receiver class and accumulated superclasses"
x := String subclasses.               "immediate subclasses"
x := String allSubclasses.            "accumulated subclasses"
x := String withAllSubclasses.        "receiver class and accumulated subclasses"
b := String instSize.                 "number of named instance variables"
b := String isFixed.                  "true if no indexed instance variables"
b := String isVariable.               "true if has indexed instance variables"
b := String isPointers.               "true if index instance vars contain objects"
b := String isBits.                   "true if index instance vars contain bytes/words"
b := String isBytes.                  "true if index instance vars contain bytes"
b := String isWords.                  "true if index instance vars contain words"
Object withAllSubclasses size.        "get total number of class entries"
```

#### Debugging:
```smalltalk
| a b x |
x yourself.                             "returns receiver"
String browse.                          "browse specified class"
x inspect.                              "open object inspector window"
x confirm: 'Is this correct?'.
x halt.                                 "breakpoint to open debugger window"
x halt: 'Halt message'.
x notify: 'Notify text'.
x error: 'Error string'.                "open up error window with title"
x doesNotUnderstand: #cmrMessage.       "flag message is not handled"
x shouldNotImplement.                   "flag message should not be implemented"
x subclassResponsibility.               "flag message as abstract"
x errorImproperStore.                   "flag an improper store into indexable object"
x errorNonIntegerIndex.                 "flag only integers should be used as index"
x errorSubscriptBounds.                 "flag subscript out of bounds"
x primitiveFailed.                      "system primitive failed"

a := 'A1'. b := 'B2'. a become: b.      "switch two objects"
Transcript show: a, b; cr.
```

#### Miscellaneous
```smalltalk
| x |
x := 1.2 hash.                                  "hash value for object"
y := x copy.                                    "copy object"
y := x shallowCopy.                             "copy object (not overridden)"
y := x deepCopy.                                "copy object and instance vars"
y := x veryDeepCopy.                            "complete tree copy using a dictionary"
"Smalltalk condenseChanges."                    "compress the change file"
x := FillInTheBlank request: 'Prompt Me'.       "prompt user for input"
Utilities openCommandKeyHelp
```

## Ready For More?

### Online Smalltalk systems
Most Smalltalks are either free as in OSS or have a free downloadable version with some payment required for commercial usage.
* [Squeak](https://www.squeak.org)
* [Pharo](http://pharo.org)
* [Smalltalk/X](https://www.exept.de/en/smalltalk-x.html)
* [Gemstone](http://gemtalksystems.com/)
* [VA Smalltalk](http://www.instantiations.com/products/vasmalltalk/)
* [VisualWorks Smalltalk](http://www.cincomsmalltalk.com/)

### Online Smalltalk books and articles
* [Smalltalk Programming Resources](http://www.whoishostingthis.com/resources/smalltalk/)
* [Smalltalk Cheatsheet](http://www.angelfire.com/tx4/cus/notes/smalltalk.html)
* [Smalltalk-72 Manual](http://www.bitsavers.org/pdf/xerox/parc/techReports/Smalltalk-72_Instruction_Manual_Mar76.pdf)
* [GNU Smalltalk User's Guide](https://www.gnu.org/software/smalltalk/manual/html_node/Tutorial.html)

#### Historical Documentation(s)
* [BYTE: A Special issue on Smalltalk](https://archive.org/details/byte-magazine-1981-08)
* [Smalltalk-72 Manual](http://www.bitsavers.org/pdf/xerox/parc/techReports/Smalltalk-72_Instruction_Manual_Mar76.pdf)
* [Smalltalk, Objects, and Design](https://books.google.co.in/books?id=W8_Une9cbbgC&printsec=frontcover&dq=smalltalk&hl=en&sa=X&ved=0CCIQ6AEwAWoVChMIw63Vo6CpyAIV0HGOCh3S2Alf#v=onepage&q=smalltalk&f=false)
* [Smalltalk: An Introduction to Application Development Using VisualWorks](https://books.google.co.in/books?id=zalQAAAAMAAJ&q=smalltalk&dq=smalltalk&hl=en&sa=X&ved=0CCgQ6AEwAmoVChMIw63Vo6CpyAIV0HGOCh3S2Alf/)