WEBVTT

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This will be an overview
of the syntax.

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We'll show you
the entirety of the syntax...

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Don't get stressed
if you don't understand it completely.

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We'll go over it all again.

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The idea is to show you
all there is in Pharo.

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We're going to look
at the main syntactical elements.

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We'll see that there are
3 kinds of messages.

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And well look at block syntax,

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an essential part of Pharo.

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Don't worry if you don't get it all,
we'll repeat all the points.

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Just to remind you,
you have all the syntax on this slide.

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I can go into the details a bit now.

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Here's a method definition,
exampleWithNumber.

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And it has an argument.

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I have local variable definitions
with vertical bars.

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I have the return,
which lets me give a value.

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I have loops, an affectation...

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The period, for example,
is an instruction separator.

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We'll look at all this.

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We'll start
with the traditional Hello World.

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Here, if you like...

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You can execute all instructions
in Pharo yourself

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to see what the result is.

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So here I have a string,

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which I convert into a morph,
a graphic element,

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and I ask it
to open in a window.

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So I send asMorph
to the string object.

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And I send openInWindow

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to the resulting morph.

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So we have two message sends
and one string object.

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A more complicated example.

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Imagine you want to take
the Pharo logo from the web.

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Well, you do it this way.

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You do ZnEasy getPng:
with a string which represents the URL

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of the resource you want to read.

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And once again you convert it
into a graphic object

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and ask it to open in a window.

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So we see that ZnEasy is a class

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because classes start with a capital.

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The colon of the message getPng:
means I'm expecting an argument,

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which is the string
http://pharo.org.

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This string is the argument
of the method getPng:

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The messages asMorph
and openInWindow

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are read from left to right.

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So you can cut'n'paste this code

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or retype it in Pharo,

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and you'll get the Pharo logo.

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So what syntactical elements
are there in Pharo?

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You have comments, which start
with double quotation marks.

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That's a comment.

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Characters are always preceded
by a dollar sign.

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$A is the character A.

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Strings start and finish
with a single quotation mark.

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You have symbols,
which are unique strings.

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These begin like this,
with the hashtag.

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#a is the symbol a.

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There are literal arrays.

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Here I have one with 12, 23 and 36.
Three elements.

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Integers have various representations,

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but we won't dwell on this.

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We usually use representations
in base 10.

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But if you want one in base 2,
that's OK.

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You have reals.
This is the same.

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You can find the syntax if you need.

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You have booleans,
with true and false.

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You have undefined.

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The null of Java is nil in Pharo.

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It's an instance
of the class UndefinedObject.

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And you have points.

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This is described in Pharo
under the form

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of 10 @ 200, for example.

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So I'm creating the point 10,
which is 10 on the x,

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and 200 on the y.

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So we've seen the essential elements
for the syntax.

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Now we have the constructs
of the language.

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You have
temporary variable declaration.

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It's a vertical bar
followed by another vertical bar.

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Assignment
is a colon and an equal sign.

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In the variable var I put aValue.

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I have messages in my system.

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How do I separate them?

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With a period.

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When I want a sequence of messages.

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There's return,

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where a function or method
gives a value.

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I use the little hat,
which is called caret in English.

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Then you have blocks,

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which, technically speaking,
are lexical closures,

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and which you can take
as anonymous methods.

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I'll show you what a block is.

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It's defined with square brackets.

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And it's executed
with the message value.

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We'll look at this.

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There you have all the constructs.

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So what is the essence
of a Pharo program?

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It's creating objects
by using messages,

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sending messages to these objects,

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and, now and then,
using blocks, or anonymous methods.

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That's all.

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There are three types
of message in Pharo. Why?

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In order to minimize
the number of parentheses used.

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It's fairly simple.

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A unary message
is always a receiver and a selector.

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Here for example I've said
that I want 9 squared.

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I want today's date.

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I send the message today
to the class Date.

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There's no argument.

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Then there's the binary message,

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which also takes the form
of a receiver, selector and argument.

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But the selector will be

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plus, minus, tilde, equals, slash...
That sort of thing.

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All those mathematical signs
are for binary messages.

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Here we see 1+2.
This is a message.

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Sending message + to object 1
with argument object 2.

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@ for the creation of a point
is also a message,

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a binary message.

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Here I create the point 3@4

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by sending the message @.

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Then you have
what we call keyword messages.

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A keyword message takes the form

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of receiver key1: arg1 key2: arg2.

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So the example is...

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is 2 between 10 and 20

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If you wrote it in Java or C
it would be like this...

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You'd write betweenAnd...

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Then, between brackets,
you'd write (10, 20).

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In Pharo you express it
in the form of key and key.

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We'll look at this again, but it gives
you an idea of the syntax.

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There's a precedence
between messages,

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the system will execute in priority
the parentheses,

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then the unary,
binary and keyword messages.

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Why?

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To avoid writing too many parentheses.

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We could have had a system
with parentheses all over the place,

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but the code would be illegible.

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I'll go back over each type of message
in a simple way.

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This unary message, 10000 factorial.

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Try it, it's a very big number.

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I send the message factorial
to the object 10000.

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There's no argument,
it's a unary message.

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Similarly, a binary message.
1+3 is a message, a binary message.

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The selector,
the name of the method, is +.

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I send the message + to the object 1
with the object 3 as argument.

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A keyword message,
as I explained earlier...

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I'll just tell you again.
Teaching is all about repetition.

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I have a keyword message
with keyword and keyword,

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which is the message,
with the arguments,

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which are floating inside the message.

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The idea is to have a syntax
that children can use

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and to have something
close to English.

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So you can introduce the arguments
inside your messages.

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As an example, imagine
I'm sending an HTTP request.

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ZnClient is a Pharo HTTP server.

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So I create an instance of Zn server.

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So new is a unary message,
there's no argument, no colon.

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url is a keyword message,
there's a colon.

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queryAt: put:
is another message.

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It's another keyword message.

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And get is a unary message.

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What we can also see
in this example are semi-colons.

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We call this a cascade,

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which sends all the messages
to the same object.

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You don't need
a temporary variable.

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And you can write more compact code.

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You have to understand
that messages are everywhere.

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Conditionals, loops, iterators and
concurrency are expressed as messages.

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My explanation
about those three messages

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applies across the board.

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It's the cornerstone of the system.

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There's nothing other
than these messages.

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Let's have a look.

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I've taken
the silly factorial definition here.

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How do I define it?

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I define my method factorial.

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I put a comment for the method.
Double quotation marks.

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And I start with self.

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If the object
getting the message is zero,

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then I'll give 1.

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If self is positive,

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for example, factorial 6,
self equals 6...

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If this is true
than what will I give?

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6 multiplied by 6 minus 1 factorial.

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The recursive definition we all know.
And that's that.

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And the interesting thing to note here

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is that ifTrue:, which is a condition,

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is also a message,
a keyword message with a colon,

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sent to a boolean.

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You also have ifFalse:ifTrue:,
ifTrue:ifFalse:...

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All these conditions are messages

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which satisfy the rules,

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and are keyword messages
like I presented earlier.

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So conditions are messages.

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Loops are messages too.

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Here I'll make a loop from 1 to 4.

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From 1 to 4, what do I do?

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A block.
An anonymous method.

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Here I'm saying I want it
to show the value of i,

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and i will take the value
of 1, 2, 3, 4...

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And there you can see that to: do:

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is a keyword message.

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It's a message
that takes the form of a loop.

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There are other loops in Pharo:
timesRepeat:, to:by:do: and so on.

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We'll look at them all.

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But, again, these are messages...

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So here, to: do: is sent to object 1
with 4 as parameter and a block.

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We'll see what a block is very soon.

00:11:14.760 --> 00:11:16.480 align:middle
You also have iterators.

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Iterators are different.

00:11:18.600 --> 00:11:21.040 align:middle
I send the message do:

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to the collection,

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saying what I want to apply
to each of the elements.

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So the each,
the argument of my function,

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will take as value
1, 2, -4 and -86.

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And what I do here
is that the each...

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I apply the absolute value
and display it.

00:11:40.960 --> 00:11:43.840 align:middle
Once again,
this will be another course.

00:11:44.000 --> 00:11:45.720 align:middle
We'll explain iterators.

00:11:45.880 --> 00:11:48.640 align:middle
Iterators are something
you get in Java 8.

00:11:50.280 --> 00:11:53.240 align:middle
And they're part of the core of Pharo.

00:11:54.280 --> 00:11:55.760 align:middle
So what is a block?

00:11:55.920 --> 00:11:57.680 align:middle
Blocks look like functions.

00:11:57.840 --> 00:12:01.320 align:middle
If in maths you wrote f(x) = x²+3,

00:12:01.480 --> 00:12:03.920 align:middle
you'd write it like this, literally.

00:12:04.440 --> 00:12:07.320 align:middle
I define a variable
in which I affect a block.

00:12:07.480 --> 00:12:10.520 align:middle
A block is something
inside square brackets.

00:12:10.680 --> 00:12:13.160 align:middle
Here, the block has an argument
which is x.

00:12:13.520 --> 00:12:16.640 align:middle
And I put a core, which is x+3.

00:12:16.800 --> 00:12:18.600 align:middle
And when I want
to execute this block...

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The application of the function.

00:12:21.040 --> 00:12:24.600 align:middle
That's the definition of the function,
now I have the application.

00:12:24.760 --> 00:12:30.360 align:middle
I send the message value:
to the block. I put value: 2.

00:12:31.520 --> 00:12:35.080 align:middle
x is 2,
so my block will give me 5.

00:12:35.520 --> 00:12:36.680 align:middle
OK?

00:12:36.960 --> 00:12:41.560 align:middle
So what's a block? It's a kind
of anonymous function, it has no name.

00:12:41.960 --> 00:12:46.160 align:middle
In fact, it's a lexical closure.

00:12:46.320 --> 00:12:48.240 align:middle
We'll explain that.

00:12:48.400 --> 00:12:50.360 align:middle
Blocks are real objects.

00:12:50.520 --> 00:12:54.440 align:middle
They can be passed as method
arguments, stored in variables,

00:12:54.600 --> 00:12:55.720 align:middle
returned...

00:12:55.880 --> 00:12:58.600 align:middle
So they can be used
as button triggers,

00:12:58.760 --> 00:13:02.960 align:middle
as callbacks in web applications...
These can be blocks.

00:13:04.480 --> 00:13:06.560 align:middle
We've already seen block usage.

00:13:06.720 --> 00:13:08.800 align:middle
In iterators you have blocks.

00:13:08.960 --> 00:13:11.680 align:middle
We saw blocks were used
in conditions.

00:13:11.840 --> 00:13:13.600 align:middle
There'll be a course about blocks.

00:13:13.840 --> 00:13:16.440 align:middle
It's elegant,
it was introduced in Eiffel,

00:13:16.600 --> 00:13:19.200 align:middle
it was recently introduced in Java 8,

00:13:19.360 --> 00:13:21.800 align:middle
there was a first version in C#...

00:13:21.960 --> 00:13:23.200 align:middle
So it's fundamental.

00:13:23.360 --> 00:13:26.320 align:middle
Blocks are a fundamental element

00:13:26.480 --> 00:13:30.400 align:middle
of Pharo's syntax
and computational model.

00:13:30.720 --> 00:13:33.600 align:middle
How do we define a class in Pharo?

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The browser you see here
shows you packages.

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You have the classes inside.

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And it shows you a template.

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The template is saying that
by default you inherit an object,

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and the name of the class.

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We'll see it for the class Point,
for example.

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So the definition of the class...

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I have the class object.
It's also a message!

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The message subclass:
InstanceVariableNames:

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blah blah blah...

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With...

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I define the class Point,

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and I give the instance variables
x and y.

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That's just to show the syntax always
follows the same model with messages.

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You don't usually write it out
by hand.

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The tool gives you the template
and you just fill it in.

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So how do we define a method?

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As I said, the methods
are public and virtual,

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and by default return self.

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So, when you're in the browser,

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it suggests a template,

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the name of the potential method
and a comment...

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We're nice and polite
so we comment on our code.

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We can also put temporary
variable names and statements.

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What does this gives us?
We've seen the method factorial.

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Here I'm in the class Integer.

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I look at the method factorial,
I have its code,

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with the name of the method,
its comment

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and the core of the method
that I've defined.

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So, to sum up, what have we seen?

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There are 3 kinds of messages:
unary messages, without arguments,

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binary messages,
where the selectors are mathematical,

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and keyword messages,
where there can be several arguments.

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There's a priority:
parentheses first,

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then unary, binary and keyword.

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And if there are same-level messages
it's from left to right.

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What have we seen?
The syntax is very compact.

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There are few constructs
but they're really expressive.

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It's mainly messages
and lexical closures, or blocks.

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There are three kinds of messages.

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You'll do an exercise
to develop a language.

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Like that you can define what we call
Domain Specific Languages.