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They come back! Before we can
start with any serious work,

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00:00:10,395 --> 00:00:12,255
let's do some housekeeping.

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As you know, this year is a tad special.
While the broad direction is clear,

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00:00:17,380 --> 00:00:19,730
there are some organizational
details that

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00:00:19,730 --> 00:00:22,370
still need to be worked
out as we go along.

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The main hub for

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00:00:23,930 --> 00:00:27,215
all the information is the
KEATS page of this module.

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Let me say a few words on how

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it is organized. The module is
organized into weekly topics.

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So there are entries for weeks
one up till week ten.

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Let's also proceed in
approximately weekly steps.

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Because if you
already asked me in

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week two something
about week ten,

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then you might confuse me

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and also your fellow students.

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All the communication in

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this module can be done in
the course discussion area.

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You can ask any questions.

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For example, I haven't
understood this point,

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this video isn't clear,

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I cannot run this code,

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I have problems with
accessing the coursework.

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This can be all discussed here.

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If you have any private matter,

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like, I can't understand why

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did I get such a good
mark, for example?

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Or there are some private
reasons why you can't keep up.

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Please feel free to use
my private email address.

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But for any other matter
related to the module,

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try to use the course
discussion area.

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And I will try to stay on top

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of all the discussions
as much as I can.

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Each week is organized into

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a mandatory section and
an optional section.

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The mandatory section
contains videos,

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a handout, and the slides,

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which I used to
produce the videos.

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I recommend that your
first read the handouts,

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then watch the videos and then

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read the handout
again for each week.

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Apologies, some of these
handouts are quite lengthy.

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I think the longest
one is 20 pages.

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On the good side,

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these handouts are
written in such a way

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that you can read them just
before you fall asleep

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and you should still be able

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to understand what is going on.

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Also, they contain lots
of pictures and code.

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So 20 pages is
a bit misleading.

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You can see the second week
is organized similarly.

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You will have some videos.

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You will have a handout,

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you have the slides,

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and some optional resources.

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I have also put up a general
section, with general

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material, where I put
a PDF about my notation.

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This might be very
useful because

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remember this topic
is already many,

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many decades old,
at least 50 years,

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and over the time,

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many authors and many lecturers

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have introduced
their own notation.

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So if you read anything
on the web or in books,

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you might be confused about that

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they call something, which
I call X, they call Y.

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So in this PDF,

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I have collected all the
information on what kind of

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notation I am using and where
I introduce some shortcuts.

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The problem is, you always
want to be precise,

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but we also lazy.

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We don't want to write
everything into the last detail.

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So here I say something
about my notation.

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I have also put up
a document about

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the Scala I'm going to
use in this module.

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This is important
for the coursework.

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In the coursework which
will come in a moment,

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you can use any
programming language you like

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to solve the questions and
implement your code.

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But, I'm sorry,

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all the code I'm going to
show you will be in Scala.

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And the main difference is that

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between PEP course from last year

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is that I'm going to
use the Ammonite

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REPL instead of
the Scala REPL.

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They work very similarly.

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For example,

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I can now evaluate code
and get a feedback of what

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it calculates, just like the original one.

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The difference is that
Ammonite is

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an extension and
provides some features

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which will be very useful for us.

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And I recorded some
of the features

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we are going to use
in this document.

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The last point to note
on the KEATS webpage

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is that in the optional section,

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I will always give
the source code of

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the programs I discussed
in the videos and in the handouts.

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And I really, really
encourage you

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that you play around with this code

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to make sure you understand
what was discussed.

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At the also have sometimes
some additional pointers

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to interesting topics, which

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you can read up in your own time.

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Exams, I'm sorry,
there will be exams.

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There will be a final exam in
January, counting for 30%.

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There will be a
midterm shortly after

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Reading Week, accounting for 10%.

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This will be a normal exams,

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just that they will be online
in some form or shape.

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There will be also a weekly
engagement component.

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So 1% in each week,

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where I make sure that
you are engaged with

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the material and you will
get 1% each week for that.

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How that is going to be
working out in practice,

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unfortunately, I do not know

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yet what tools we use
or what it means,

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but I will let you know about it.

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There's also an optional
weekly homework.

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The homework is
uploaded on KEATS.

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You should send your answers
via email to me.

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I will respond individually
and give some feedback.

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Normally, if everything is okay

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with a question, I will
just respond "OK"?

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If there is
something wrong,

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I will sometimes answer with a longer

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email. All the questions in

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the exam and in the midterm
will be from this homework.

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So I do not give out the
solutions to the homework.

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You have to email me first

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what do you think
the solution is...

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and I will give answers
individually back.

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And I will then ensure
that all the questions in

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the exam and the midterm coming
only from this homework.

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The simple reason for that is

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that I hate if students ask me

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if something is relevant
for the exam or not.

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I really like this material
and whatever I tell you,

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I feel like you
should know about it.

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So, to prevent that question,

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if it's relevant to the exams,

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you can just look at
what's in the homework.

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And if this question
is in the homework,

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then yes, it will be relevant.

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And if not, it will
not. Thank you.

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Can you please make one more
point about the homework?

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Please submit your
answers only as PDF.

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That just makes it easy
for me to look at.

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Remember, I might get

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60 or more emails about

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that and it's just much
easier for me to read PDFs.

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Also, please in your answer
copy the question.

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I have an extremely limited memory

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and have no idea what I actually
asked in this homework until

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I actually look it up.

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Just to prevent that,

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that I have to look it up myself,

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please send in
always the question

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and then give your answer.

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And finally, there are some

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optional homework. They are just to

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reminders actually that

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you really should
have a look at that.

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But they're optional. The ones

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that you are supposed to
solve, they look like this.

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And as I said,

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please copy the question
and then give your answer.

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And at the end,
package it into a PDF.

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Thank you. A very
important component

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for assessment in this
module is the coursework.

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There will be five of them.

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We will first implement a matcher.

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Then a lexer building
on top of the matcher.

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Then build a parser
and an interpreter.

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And then a
compiler for the JVM

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and a compiler
targetting the LLVM.

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So you can see this
accounts for 45%.

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You will submit your
code and you also have

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to give some explanation
about your code.

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This will be always

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explained in the
coursework description.

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For the coursework, you can use

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any programming
language you like.

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In the past, people have
used Haskell and Rust.

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Obviously many go for Scala.

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You can use any code
I showed you in

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the videos or in handouts
or uploaded on KEATS.

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But nothing else.

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Remember, unlike
in the PEP course,

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here, in the Compiler course,

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I actually will look with

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my own eyes at the submissions
and make judgments.

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And I'll see if people have
copied from each other.

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Please don't do that!

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That's very annoying
for everybody involved.

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To conclude this
housekeeping video,

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let me tell you a
bit more about how

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this module is organized.

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The first five weeks we will
spend on lexing and parsing.

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This is essentially the
frontend to our compiler.

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The first part will
be about lexing.

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Actually, we will emphasize quite a
bit on the lexing part,

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because that's about my research.

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And sorry, I can talk
about this for hours.

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But I also like to show you that

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there's actually something really

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interesting going on and
I want to

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show you a number of techniques.

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Then obviously we have
to do parsing because

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lexing essentially only
finds the words in our programs.

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00:11:01,669 --> 00:11:03,860
We then have to put
them into sentences to

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understand what our
programs actually do.

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00:11:09,820 --> 00:11:12,200
The next five weeks,

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actually that overlaps
with the parsing part,

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we will first start with
writing an interpreter.

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This is essentially to get

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the baseline for our compiler.

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Also, you will see compilers are

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00:11:24,325 --> 00:11:27,370
sometimes fiendishly
difficult to get correct.

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00:11:27,370 --> 00:11:30,880
And to actually know what
the results should be, 

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by having it calculated with

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00:11:32,320 --> 00:11:35,515
an interpreter, is
really important.

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00:11:35,515 --> 00:11:40,030
And then we really
spent time on a compiler.

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We will first write JVM code
for a little While language.

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That is an extremely,

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00:11:46,780 --> 00:11:50,335
extremely simple C-like
language, if you want.

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And also JVM Code for
a functional language.

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Again, something very small.

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00:11:55,615 --> 00:11:57,815
And then for that
functional language

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00:11:57,815 --> 00:12:03,080
also generate LLVM-IR code
that can be

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00:12:03,080 --> 00:12:09,270
then used to generate directly
CPU code for X86 or ARM.

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00:12:09,460 --> 00:12:12,095
Just to whet your appetite,

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here's the first compiler for

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the While-language calculating
the Mandelbrot program.

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00:12:20,240 --> 00:12:22,160
It generates code for

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the JVM, for the Java
virtual machine.

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So what it first does, like in

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the example I showed you earlier,

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00:12:29,855 --> 00:12:33,215
it takes the Mandelbrot
program from the BF language,

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generates a While program

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00:12:35,480 --> 00:12:38,520
in our language we are
going to implement...

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this has produced a program which is

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00:12:40,940 --> 00:12:44,795
approximately 70k of source code.

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00:12:44,795 --> 00:12:47,585
Then our compiler produced

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00:12:47,585 --> 00:12:53,015
a Java Virtual Machine
byte code file.

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00:12:53,015 --> 00:12:54,890
This is the readable version of

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00:12:54,890 --> 00:12:57,500
the Java Virtual Machine bytecode.

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00:12:57,500 --> 00:12:59,480
And we use then an assembler

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00:12:59,480 --> 00:13:01,535
to actually produce
the class file.

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00:13:01,535 --> 00:13:04,460
And then this compiler
just runs this class file.

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00:13:04,460 --> 00:13:06,830
It takes a little while and
unfortunately this compiler

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00:13:06,830 --> 00:13:09,365
doesn't show it incrementally.
Only at the end

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00:13:09,365 --> 00:13:13,205
it shows us it needed
approximately 40 seconds.

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00:13:13,205 --> 00:13:16,745
And you have to
remember the GCC with -O0

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00:13:16,745 --> 00:13:21,485
took a little
bit more than 20 seconds.

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00:13:21,485 --> 00:13:24,440
And so this is quite
remarkable result

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00:13:24,440 --> 00:13:27,575
considering we are
running it on the JVM.

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00:13:27,575 --> 00:13:29,345
Just to assure you,

258
00:13:29,345 --> 00:13:33,245
the Mandelbrot program will not be the
only program we can compile.

259
00:13:33,245 --> 00:13:36,380
But we will focus on integers

260
00:13:36,380 --> 00:13:39,605
and strings in our
programming language.

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Because for more complicated
data structures 

262
00:13:43,280 --> 00:13:46,250
we don't have enough time
to fit into this module.

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00:13:46,250 --> 00:13:49,040
So let's start now
with the serious work.

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I hope I see you in a bit.