Pharo Syntax in a Nutshell

Transcription

1 Pharo Syntax in a Nutshell Damien Cassou, Stéphane Ducasse and Luc Fabresse W1S06, 2015

2 W1S06 2 / 28 Getting a Feel About Syntax In this lecture we want to give you the general feel to get started: Overview of simple syntactical elements Message composition Overview of block syntax No stress if you do not get it right now!

3 The Complete Syntax on a Postcard No need to understand everything! But everything is on this screen :) W1S06 3 / 28 examplewithnumber: x "This method illustrates the complete syntax except primitive invocation." <amethodannotation> y true & false not & (nil isnil) iffalse: [ self halt ]. y := self size + super size. #($a #a a 1 1.0) do: [ :each Transcript show: (each class name); show: (each printstring); show: ]. ^ x < y

4 Hello World W1S06 4 / 28 Hello World asmorph openinwindow We send the message asmorph to a string and get a graphical element that we open in a window

5 W1S06 5 / 28 Getting the Pharo Logo (ZnEasy getpng: ) asmorph openinwindow. ZnEasy designates a class Class names start with an uppercase character Message getpng: is sent to the ZnEasy class getpng: is a keyword message Messages asmorph and openinwindow are sent they are unary messages

6 Sending an unary message W1S06 6 / 28 receiver selector Example factorial We send the message factorial to the object 10000

7 A Simple Method W1S06 7 / 28 factorial "Answer the factorial of the receiver." self = 0 iftrue: [ ^ 1 ]. self > 0 iftrue: [ ^ self * (self 1) factorial ]. self error: Not valid for negative integers

8 Within the Browser part of the Pharo IDE W1S06 8 / 28

9 W1S06 9 / 28 A Simple Method factorial "Answer the factorial of the receiver." self = 0 iftrue: [ ^ 1 ]. self > 0 iftrue: [ ^ self * (self 1) factorial ]. self error: Not valid for negative integers factorial is the method name =, >, * and - are binary messages ^ is for returning a value factorial is an unary message iftrue: is a message sent to a boolean expression

10 Presentation Convention W1S06 10 / 28 factorial "Answer the factorial of the receiver." self = 0 iftrue: [ ^ 1 ]. self > 0 iftrue: [ ^ self * (self 1) factorial ]. self error: Not valid for negative integers is displayed in this lecture as: Integer >> factorial "Answer the factorial of the receiver." self = 0 iftrue: [ ^ 1 ]. self > 0 iftrue: [ ^ self * (self 1) factorial ]. self error: Not valid for negative integers Integer >> is not part of the syntax: it tells you the method s class

11 Sending a keyword message W1S06 11 / 28 receiver keyword1: arg1 keyword2: arg2

12 W1S06 12 / 28 Example: Sending an HTTP Request ZnClient new url: ; queryat: title put: Pharo ; queryat: action put: edit ; get new is a unary message sent to a class queryat:put: is a keyword message get is a unary message ; sends all messages to the same receiver

13 W1S06 13 / 28 Essential Constructs temporary variable declaration: var variable assignment: var := avalue To be explained later: Block [ :x x + 2 ] value: 5 > 7 Cascade: receiver selector ; selector... Separator: message. message Return: ^ expression

14 W1S06 14 / 28 Messages To minimize the use of parentheses, Pharo distinguishes 3 kinds of messages Unary message: receiver selector Node new Binary message: receiver selector argument 1+2 3@4 Keyword message: receiver key1: arg1 key2: arg2 2 between: 10 and: 20

15 W1S06 15 / 28 Messages Messages are everywhere: Conditionals Loops Iterators Concurrency

16 W1S06 16 / 28 Conditionals are also Message Sends factorial "Answer the factorial of the receiver." self = 0 iftrue: [ ^ 1 ]. self > 0 iftrue: [ ^ self * (self 1) factorial ]. self error: Not valid for negative integers iftrue: is sent to an object, a boolean! iffalse:iftrue:, iftrue:iffalse: and iffalse: also exists Read their implementation, this is not magic!

17 W1S06 17 / 28 Loops are also Message Sends 1 to: 4 do: [ :i Transcript << i ] > 1 > 2 > 3 > 4 to:do: is a message sent to an integer Many other messages implement loops: timesrepeat:, to:by:do:, whiletrue:, whilefalse:,...

18 With Iterators W1S06 18 / 28 We ask the collection object to perform the iteration #( ) do: [ :each Transcript show: each abs printstring ; cr ] > 1 > 2 > 4 > 86

19 W1S06 19 / 28 Messages and Their Composition 3 kinds of messages: Unary: Node new Binary: 1+2, 3@4 Keywords: 2 between: 10 and: 20 Message Priority: (Msg) > unary > binary > keyword Same-Level messages: from left to right

20 W1S06 20 / 28 Message Examples (ZnEasy getpng: ) asmorph openinwindow. first getpng: returns a Form object (internal graphics) then asmorph transforms it into a Morph (interactive graphics) then openinwindow

21 W1S06 21 / 28 Blocks A kind of anonymous method Are plain objects: can be passed as method arguments can be stored in variables can be returned Look like maths functions: fct(x) = x*x+3 can be written fct := [ :x x * x + 3 ] fct(2) can be written fct value: 2

22 W1S06 22 / 28 Block Usage #( ) do: [ :each Transcript show: each abs printstring ; cr ] > 1 > 2 > 4 > 86 :each is the block argument It will take the value of each element of the array

23 Class Definition W1S06 23 / 28

24 Class Definition with the IDE W1S06 24 / 28

25 Class Definition with the IDE W1S06 25 / 28 Object subclass: #Point instancevariablenames: x y classvariablenames: category: Graphics We ask the superclass to create the class.

26 W1S06 26 / 28 Method Definition Defined in a browser (or by invoking the compiler) Methods are public Methods are virtual (i.e., looked up at runtime) By default return self factorial "Answer the factorial of the receiver." self = 0 iftrue: [ ^ 1 ]. self > 0 iftrue: [ ^ self * (self 1) factorial ]. self error: Not valid for negative integers

27 Method Definition W1S06 27 / 28

28 W1S06 28 / 28 Conclusion Compact syntax Few constructs but really expressive Mainly messages and closures 3 kinds of messages Support for Domain Specific Languages