WEBVTT

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In this session, we will revisit
Pharo syntax.

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We will review it entirely
using a concrete example,

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the example of a simple
HTTP application from the real world.

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We will analyze the code and review
Pharo syntax through it.

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This application
is a simple web application

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which displays information on books.

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I will give you the first example:
I'll use the framework Zinc,

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a HTTP framework
we'll study in another course.

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It comes in two parts:
client and server.

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It can make HTTP requests, etc.

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First, we can see ZnClient is a class.

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So it starts with uppercase Z
as we saw previously.

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Names of classes and global variables
start with uppercase.

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ZnClient is a class.

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You send the message new
to this class;

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it will create
a new instance of ZnClient.

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To this new instance, you send
a first message url: with a parameter,

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which is a string.

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Then we'll use the cascade.

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Let me remind you
that ";" at the end means:

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you send a new message, get,
to the same receiver.

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This bit of code simulates
what your navigator will do

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when you type in the url
and press enter.

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If I type in an url and press enter,

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it contacts the server
of this web application

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and it returns a HTTP response:

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in this case, the information
on a book, the book number 1.

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I will give you another example,

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another request
built with Pharo and ZnClient.

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So it's the same:
you instantiate an object Znclient.

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You send messages using cascades.

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And then, you can see something
we have already studied:

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in Pharo, we have keyword messages,

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meaning that the method name
is formAt: put:.

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This is equivalent
in typical Java syntax

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to formAtput
(the method name is all attached).

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And I put all the arguments
between parentheses.

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On this slide, I'd like to show you

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the complete code
of this web application

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constructed with Zinc.

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I will show you some parts
of this code one element at a time.

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First of all, the first part corresponds
to the server configuration.

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On the first line,

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there are local variable declarations.

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Remember they start with lowercase.

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books and teapot are two local variables
between vertical bars.

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Next, there are assignments:
here is the first one.

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It's := in Pharo.

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You can have symbols.

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Thirdly: there is #port

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which is located here in the code.

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It corresponds to a symbol,
a unique string.

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It's created only once.

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There are messages sent
to the class Teapot.

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For example, the class Teapot is here.

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And I can send
the message configure to it.

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Look at configure:.

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Let me remind you that ":"
marks the presence of an argument

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which you send to this method.

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The argument starts with a brace

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and ends with a brace.

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So what's between the braces
is a dynamic array:

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all this between braces.

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Each expression separated by "."
will be evaluated

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and we'll build an array
with the results of each expression.

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There's only one argument
in the method configure.

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And inside this dynamic array
between braces,

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you will use an arrow
to build association objects.

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So it's one key, one value.

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So to make the server work,

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you won't just define
the server's configuration

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but also routes.

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I will explain using a smaller example:
this is an extract of the complete code.

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If I want my application to process
URLs like this one,

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which ends with books/1,

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if I want the information
on the book 1, for example,

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I define a route
in my Zinc application.

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When I receive a request
of the type GET,

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which starts with /books/
and an integer,

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- can you see this ? -
it executes this block of code.

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Remember that a block
starts and ends with brackets.

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So it's an anonymous method
which can take a parameter:

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in this case,
the parameter is called :request

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and it is separated by a vertical bar.

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Next, the body of the block is all here.

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There's only one expression here,
this one.

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So you send the message at:
to the object books.

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What book do you want
in the book collection?

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You want the book whose id
was passed as parameter in the url.

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I query the request.

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The variable here is the parameter
of the block defined in the beginning.

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I get the element called id
in this request.

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I convert this element.
Remember, it's an integer.

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I convert it into a string.

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This allows me to get the book 1.

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To conclude, we have reviewed
all the Pharo syntax

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in this class.

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The goal was to take an interest
in syntax,

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but we were also able to rediscover
the syntax through a package

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which is quite interesting
and fun to program with, Teapot.

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Go find out by yourself.
You can download it from smalltalk.

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You can build
HTTP applications very easily.

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Also, it's a package
built based on Zinc.

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Zinc is one of the very strong
libraries in Pharo

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to make more complex web applications,

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as we will see
in following courses.