WEBVTT

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In this session,
I'll mention two points:

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sequence and cascade,
which are very common in Pharo.

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There are often
several expressions in a row.

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They must be separated.

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You do that with a period
as in the example.

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Here you have: Transcript cr
and a period.

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The transcript is a small tool
for log messages.

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I want a new line.
I want to show the object 1.

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I want to show 2.
I could or couldn't have used a period.

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The expressions
are separated by periods.

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Let's see another example.

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I've defined two local variables.

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I define a workstation,
which is a network simulator.

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I write a period
as it's the end of this expression.

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I continue with the next expression.
I could have used a period here.

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As I explained, a period is a separator,
not a terminator.

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In Java, you must use
a semicolon here and there.

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In Pharo, you don't have to.

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What can be a bit strange for beginners

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is that pipes
are definitions of local variables.

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There'll be a lesson about this.

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You don't use a period here.

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Usually, you define the local variable.
Then you start.

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After the first expression,
you use a period.

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There's something else:

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you'd often like to send several
messages to the same object.

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But since we're lazy,
we don't want to repeat the receiver.

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Look at this:

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I write Transcript cr.
Transcript show: Transcript...

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I already said transcript
three times instead of once.

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I can do it:
I'll use a cascade, the semicolon.

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I write: Transcript cr;

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I send the message cr
to the object transcript.

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The cascade says:

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"From now on, all messages are sent
to the same receiver as the first."

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It means show 1 is sent to Transcript

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and show 2 to Transcript.

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I'll say this again as it's unusual.

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I send the first message normally.

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Instead of using a period,
which is a separator, I use a semicolon.

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It means every other message
must be sent to the same receiver.

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show: 1 is sent to same receiver.

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A semicolon means:
show: 2 is sent to the same receiver.

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Another example:
imagine you want to create a collection.

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I have a collection,
so I define a variable c.

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I write the collection in c.
See the period here?

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I add 1 and 2 to the collection.

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These two expressions
are exactly the same.

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It means I write:
OrderedCollection new

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I create it then add the first message
add: 1 to add an element.

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The semicolon means this message
must be sent to this collection.

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As Pharo beginners, I'd advise you

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not to bother using the cascade.

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I introduced it
because you'll read code.

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People use it in code.

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When you feel comfortable
with this syntax and with periods,

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you can start to think
you can be a bit more flexible

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and use the cascade.
That's how I learned.

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Just go step by step.

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What did we study?

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. is a separator.
It's the same as ; in Java.

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; is a cascade which is useful
to avoid repeating the same receiver.

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The cascade returns the value
of the last message sent.