95.3002

1. 95.3002 Smalltalk on a Dime

2. Little Things Java (or C++) Smalltalk separator 1+2; 1+3; statement terminator/separator 1+2. 1+3 terminator 1+2. 1+3. Declaration | a b | No types int a; boolean b; //Hello /*Hello*/ "Hello" comments characters $a 'a' 'I''ll go' strings "I\'ll go" Escape character as in C++ 2 single quotes concatenation "ab" + "cd" 'ab' , 'cd' collection1 , collection2 return statement return 10; ^10. a := b. assignment a = b; a +- b; No “operate and assign” operators

3. Little Things Java (or C++) Smalltalk (new String ("a")).intern () symbol (unique string) #a OR #'a' 'a' asSymbol Java #a asString Objects.equals (a, b) a = b equality (new String ("a")) = (new String ("a")) true 'a' copy = 'a' copy true #a = #a true #a = 'a' false a == b identity a == b 'a' copy = 'a' copy true (new String ("a")) == (new String ("a")) false 'a' copy == 'a' copy false (new String ("a")).intern () == (new String ("a")).intern () #a copy == #a true true Symbols can’t be copied

4. Little Things Smalltalk Java Boolean a = Boolean.True Boxes (objects) Does not exist a.booleanValue () true Integer a = Integer (2016) Does not exist a.intValue () 2016 a := 2016. Integers/booleans int a = 2016; a := true. boolean a = true; Ints and booleans are NOT objects(so you can’t store them in Object collections) Everything is an object

5. Little Things Java (or C++) Smalltalk a block C++ int plus (int a) {return a+1;} functions plus := [:a| a+1]. add := plus. Blocks are unnamed functions x.getA ().getB ().getC () method invocation x getAgetBgetC Dot is superfluous Parentheses too are superfluous Control Structures { } [ ] while (e) {x = 2*x;} [e] whileTrue: [x := 2*x] for (long v = 1; v < 11; v++) {…} 1 to: 10 do: [:v | …]

6. A Bit More About Blocks Smalltalk C++ a block C++ int plus (int a) {return a+1;} int (*add) (int a); add = plus; functions plus := [:a| a+1]. add := plus. Blocks are unnamed functions plus (10) => 11 (*add) (10) => 11 function/block invocation plus value: 10 => 11add value: 10 => 11 usage #(10 20) collect: add Can be passed as parameter (rare to see it) => #(11 21) #(10 20) collect: [:a | a – 1] Can, and usually do, inline => #(9 19) Can implement your own control structures (2 slides further)

7. Expression Syntax (This is everything) Method Name Highest Priority First unary a factorial factorial binary a + 1 + keyword a between: 1 and: 10 between:and: selectors receiver message a factorial between: a - b and: c negated + 1 No operator precedence; A+B*C Smalltalkers will write (A+B)*C instead Highest priority Medium priority Lowest priority (a factorial between: a - b and: c negated + 1) ifTrue: [a := b] Parentheses needed if more than 1 keyword message

8. Little Things Period versus semicolon in Smalltalk Sending Multiple Messages to the SAME Receiver a scan; parse; output. equivalent to a scan. a parse. a output. Motivated by english: “I can; therefore I do.” Java (or C++) Smalltalk Blocks is short for ‘CODE BLOCK’ Blocks instead of Scopes a block C++ while (a > b) { a = a+1;} blocks instead of scopes [a > b] whileTrue: [ a := a+1.] where blocks are objects

9. Little Things File prompters FileDialogpromptTitle: 'Grammar'  Full path name or nil if cancelled Input files e.g., 'C:work\data.txt' File pathNameReadOnly: fileName  Input File Stream Output File Stream File newFile: aString   Input stream of characters ReadStream on: aString Input stream of objects in the collection ReadStream on: aCollection Streams aStream contents  A string or a collection of objects aStream peek  Next character or object (still there after) aStream next  Next character or object removed aStreamatEnd  true (nothing to peek at), false (there is) aStream close  Needed for file streams

10. Little Things Printing Your Own Objects e.g., Banana printOn: aStreamaStream << ‘a Banana type '; << self type printOn: aStream << is defined in WriteStream << anObject anObject isCharacter ifTrue: [^self nextPut: anObject]. anObject isString ifTrue: [^self nextPutAll: anObject]. anObject printOn: self printString  aString Uses your printOn: indirectly storeString  aString Code that will recreate your object Fairly high level looping Iterate through the successive objects one by one #(hi 32 (5 6) 'hello') do: [:object | …]

11. Class Person • Class Person with name, friends • initialize name := #unknown. friends := OrderedCollection new. • friends • ^friends • add: friend • friends add: friend • friendsDo: aBlock • friends do: aBlock • friendsChainDo: aBlock • | all | • all := OrderedCollection new. all addAll: friends. • all do: [:person | aBlock value: person. all addAllIfIdenticalAbsent: person friends]. USAGE aPerson friendsDo: [:friend| Transcript cr; << friend] aPerson friendsChainDo: [:friend | Transcript cr; << friend] New control structures Collections can grow while you loop over them...

12. Big Things Since variables are not typed (but objects are), collections can contain ANYTHING #(2016 $a 'hello' #you and #between:and: #(1 2 3.0e0)) an integer a character a string symbols an array The Library is MODIFIABLE  Add method #+ in String to perform concatenation The Compiler Can Be Invoked By Sending Messages Classes can be created with code

13. Collections: Creating and Initializing array := (Array new: 2) at: 1 put: 'hi'; at: 2 put: 'you'; yourself. orderedCollection := OrderedCollection new add: 'hi'; add: ‘you'; yourself. dictionary := Dictionary new at: 1 put: 'hi'; at: 'two' put: 'you'; yourself. Returns the receiver (the dictionary in this case). Without it, you get back 'you'.

14. Low Level Control Structures Block (because of square brackets) [expression] whileTrue: [body] expression ifTrue: [body] Blocks with no parameters 1 to: 10 do: [:index | body] 10 to: 1 by: -1 do: [:index | body] (1 to: 10) do: [:index | body] Blocks with 1 parameter (the loop variable) This is an interval object, useful for collecting

15. Higher Level Control Structures #(10 20 30) do: [:item | Transcript space; << item] aDictionarydo: [:value | …] aDictionarykeysDo: [:key | …] aDictionarykeysAndValuesDo: [:key :value | …]

16. A Bit More About Collections #(10 20 30) collect: [:x | x+1]  #(11 21 31) #(1 2 3) select: [:x | x odd]  #(1 3) #(1 2 3) collect: [:x | x+10] when:[:x | x odd]  #(11 13) • people asSortedCollection: [:x :y | • "Return true if x and y in order, false if not" • x parents size > y parents size or: [ • x parents size = y parents size and: [ • x children size >= y children size]]] •  Above sorts by decreasing parent size and when equal, by decreasing children size equivalent to C++’s || and &&

17. There’s also groupsDo: which other Smalltalk’s Don’t have Plural version (many groups) groupsDo: aBlock " #((1) (10) (100)) groupsDo: [:a | Transcript cr; << a]. #((1 2) (10 20) (100 200)) groupsDo: [:a :b | Transcript cr; << a; << ' '; << b]. #((1 2 3) (10 20 30) (100 200 300)) groupsDo: [:a :b :c | Transcript cr; << a; << ' '; << b; << ' '; << c]. #((1 2 3 4) (10 20 30 40) (100 200 300 400)) groupsDo: [:a :b :c :d | Transcript cr; << a; << ' '; << b; << ' '; << c; << ' '; << d]. " self do: [:collection | aBlock evaluateWithArguments: collection] This is the complete implementation The alternative is to use “… do: [:element | …” but then you have to say a := element first. b := element second. c := element third

18. And also groupDo: which other Smalltalk’s Don’t have Singular version (one group) groupDo: aBlock " #(1) groupDo: [:a | Transcript cr; << a]. #(1 2) groupDo: [:a :b | Transcript cr; << a; << ' '; << b]. #(1 2 3) groupDo: [:a :b :c | Transcript cr; << a; << ' '; << b; << ' '; << c]. #(1 2 3 4) groupDo: [:a :b :c :d | Transcript cr; << a; << ' '; << b; << ' '; << c; << ' '; << d]. " aBlock evaluateWithArguments: self asArray This is the complete implementation The alternative is to use the “array” directly but then you have to say a := array first. b := array second. c := array third

19. A Bit More About Collections anOrderedCollectionaddIfAbsent: anObject aDictionary at: key  error if key is missing anOrderedCollectionaddIfIdenticalAbsent: anObject anOrderedCollectionincludes: anObject anOrderedCollectionincludesIdentical: anObject anOrderedCollectionincludesAll: aCollection anOrderedCollectionincludesAllIdentical: aCollection aDictionaryat: key ifAbsent: [“any value”]. aDictionaryat: key ifAbsentPut: [“any value”]  value

20. Short Accessors aCollectionfirst aCollectionat: 1 aCollectionsecond aCollectionat: 2 aCollectionthird aCollectionat: 3 aCollectionsecondLast aCollectionat: aCollectionsize - 1 aCollectionlast aCollectionat: aCollectionsize aCollectionrest aCollectioncopyFrom: 2 aCollectionallButLast aCollectioncopyFrom: 1 to: aCollectionsize - 1

21. Useful Knowledge • (Smalltalk at: #OrderedCollection) gives you back the OrderedCollection class. • Execute a method in a variable The symbol could originally have been in a file that you read in (as a string you converted to a symbol) • Comparing ordered collections O1 and O2 for containing the identical objects… (O1includesAllIdentical: O2) and: [(O2includesAllIdentical: O1)] No nice C++ short circuit Booleans such as A && (B || C) aBananaperform: variable aBananaperform: variable with: 25 aBananaperform: variablewithArguments: anArray