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ever ready welcome back to

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ft 10 on ax functional programming

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an and over granted

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to do today is taking the first

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baby steps in learning haskell now

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one of my favorite movies of all time

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is the Karate Kid and if you haven't
seen this movie

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stop this yeah watching

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this lecture and go watch this movie
first

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every time I need to learn something new
I rewatched the Karate Kid

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and I can tell you I've seen it you know
maybe

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20-30 times and every time i watch it

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I learn something new if you're

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a watch the movie you will see that

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the and the boy here Danielle and wants
to learn karate

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and mister me I got it the gentlemen
here

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I'm on the other side and make him do a
lot of

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what and Danielle things are pointless
exercise any gets kinda frustrated

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but in order to learn something you have
to go

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through a lot of exercises because
there's love muscle memory or and

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case of programming you have to have the
muscle memory in your fingers they're

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certain things should not have to think
about

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that you have to drill that you have to
do over and over and over again

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and that's what we are going to do in
this lecture today

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don't get frustrated don't be like
Daniel

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be a grownup and just do your exercises

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on and on wax on wax off wax on wax off

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until it becomes completely automatic

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and then you can use your brain to solve
the real problem

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you don't have to think about the basics
any okay and every time you learn

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something new

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re watch this great movie alright

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and show some ask has complementation
that we're using

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in this course a is the Glasgow Haskell
Compiler

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sometimes also called the glorious
Haskell Compiler

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&gt is the leading implementation of
Haskell

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and it has both a compiler an
interactive

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Rep a loop that you can use to typing
your

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got and the interactive nature

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of the GATT interpreter makes it really
easy

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to experiment and with has car

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and that's why it's also very useful for
discourse

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am many of the exercises

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that you will get during the course you
can do

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by using ght I don't care I don't

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see that as cheating an because

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as programmers reshoot really use to
compiler

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to help us okay so the computer is there
to help us programmed the computer

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if we don't use that that would be
stupid GT

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is freely available from that website
here there will be also be on the

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an course website sorry you can also

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Google or Bing for the Haskell platform

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and it's available for all major
platforms

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Mac when does and Linux to start GHz

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you just type from the command line Ghei

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and then you get some

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text blur and there you see a bronze

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preludes and that's where you can start
typing an

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expressions for example we can type in
expression to

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plus three times for and result if
that's the

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Ghei will then printed the result for
that in this case were really using

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GA CIS gotta day calculator

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it's a little bit I can now calculate
their own a command line interface

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and set up a girl getting a red buttons
well we also see here's that since

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to last three times for apparently age
14

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that an not obligation bind stronger

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then addition as so there's no surprises
there

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most languages have that and everyone to

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at first duty addition and
multiplication we have two boots

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a.m. brand to see a show we ride to
blustery

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I'm for and then there is all this
trendy and we can do

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more complicated expressions like the
square root of dead three to the power

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of two

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for to the bar of two and we get five am

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as you saw there was is it gonna be a
the prelude

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and and from

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here so and at school prelude it's not
the SDK for Haskell these are all the

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standard functions

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that come for free and what has gone on
the website

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you will we will tell you how to get
other libraries for Haskell

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but an rewards discuss that in too much
detail right here you

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you can read up on that we own will

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will try to stake with just this
standard library functions standard

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values

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and most of them are most influential
order to function in the prelude

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are functions over lists am

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and we're going to get walked through a
couple of them and then later lectures

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we well implemented these functions in
several different

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manners the first function years had
which takes a list

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and the way the right mission has
college with square brackets and the

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elements separated by commas

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showed ahead of wanted 3-for-5 s

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and surprisingly Wong the tail

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that's the opposite of Hatcher it is
everything on the list

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accept that so detail wanted 3-for-5

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is the list to treat for we can also
select

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and the and element of the list which
this year

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double action mission mark operators are
if we want to select the second element

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of the list

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I wanted 3-for-5 we get

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3 so what do we learn from this well

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that the first element of the list

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as index 0 K so

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like it should be haskell starch

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indexing lists by zero now there's

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to exclamation marks here and there's

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a good reason for that biggest in
Haskell

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lists are not to raise show indexing

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into the analyst here at the second
element

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will traverse the Leisure World reversal
estro a long

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throw a to and then returned three so
this is not a constant I'm

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operation to indexing into a list unlike
induction into an array

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and Haskell is then they ran the length
of the list

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are and then there and and this number
but in general linear in the size of the

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list

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and but fortunately

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an reveal hardly see uses

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of a this operator in practice and

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if you find yourself wanting to use less
than texting

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then you know that you have not done
than of wax on wax off wax on wax off

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you're still too much in the mindset of

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impaired if programming using a race and

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and Haskell we typically use higher
order functions like Matt filter fault

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and not indexing to a.m.

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perform complex operations over list
here's another

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an example take three it takes the first
three element of a list so if we have

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the list went 3-for-5

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guess what readers the first three
elements

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123 drop

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is the opposite side takes a number

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and the list and it drops the first
three elements of the list so in some

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sense drop

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and take are

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the generalizations of head and tail at
entail

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just take the first and the rest of the
last and then which day can drop

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you can you now you can generalized that
too arbitrary numbers

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and calculating the length of the last

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alright we do that by saying Lancs

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the going to function length length
wanted 3-for-5 is five

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and again and lesson at school are not
like a race

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in other languages so taking the length
is not a constant I'm operation

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it is takes let its time linear in the
length of the list

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and some sums up all the elements show
every goal some unwanted 345

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the result is fifty product

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is the same as some acceptance data
adding up the numbers

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multiplies all of them so want to
multiplying long

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to three four and five like taking
effect or l5

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is 120 offending two lists is another
common operation you take to less the

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smashing together into a new list so I

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a band 123 with four and five

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we get the less wanted three for $5 and
the loss function here

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on this and slides is reversing a list

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reverse 1,2,3,4,5 it's you

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5 for 321 in the rest of this

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these lectures we will define these all
the functions ourselves

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in several ways an but right now

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it's good to kind of play with them to
see what they do

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an and then we will be ready to
implement them

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an in our then we will know other
supposed to do

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here's the

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and another very important slight

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and that is about function application
because has girl

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is very different than mathematics on
the one side

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and very different from other
programming languages as well

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in mathematics when you apply function
mathematics that you do in school or

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college when you take analysis

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when you apply a function to an argument

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you always use parentheses so in this
case

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when we apply a function here this is

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applying a function have to arguments a
NB

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and then adding C

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space D now in mathematics

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typically art and that's gone from
physics

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is that space mange multiplication

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right so if you look at the mathematical
textbook

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and you see ya see space D

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usually need see multiplied by D

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and therefore when you apply a function
you're using

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Prentice's like this to to disambiguate
since in Haskell

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function application is used much more
often

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then multiplication virus in physics

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and multiplication is used more often so
that's where

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not obligation is given the Kaneohe the
most whites involved at least gonna

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visible symbolic motion white spaces Mr
and Haskell

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function application is denoted by white
space

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so that it can if it's not so much in
your face

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when haskell and celebrating at of a
call might be

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plus she space D function application
becomes

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denoted by a spatial its after apply to
a

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apply to be plus see times the

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alright and most programming languages

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you would ride at for an

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a go might be goes for so they are in
some sense the world

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worst of two worlds their are your your
have to write everything explicit

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the National we make that decision that
function application

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is done by using a space and
multiplication

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is done by using multiplication

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and also

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function application by stronger

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then any other operator so if you see af

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of a place be that means after applied
to a

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plus be doesn't mean af

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applied to a-plus be game disc and get

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yeah people have to get used to this
this doesn't mean

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00:13:01,080 --> 00:13:04,210
after dimes a-plus be it means

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F apply

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to a blessed be so that's

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got similar to multiplication binding
stronger than addition

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okay here's a table that give you sum up
the

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am problem more expressions

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and on that one side's haskell

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and on the other side mathematics so
this is what you should forget

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I'm going to stand in front of that this
is what you should forget

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and this is what you should learn
alright

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00:13:34,320 --> 00:13:38,590
so forget what's behind me and learn

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00:13:38,590 --> 00:13:42,670
what's on this site okay so

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00:13:42,670 --> 00:13:45,890
instead of after opened brand actually
write

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at SpaceX instead of passing two
parameters to at

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ripon we apply have to action and then
apply that revealed to why

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instead of at opened brand GOP brown
actually can ride

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00:14:00,540 --> 00:14:04,110
at of geoVax and later we'll see

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00:14:04,110 --> 00:14:07,120
that we can write that using function
composition

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00:14:07,120 --> 00:14:11,680
have as as at combos G okay

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and their and the rest up the examples

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should be obvious okay but if you just
look at

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shapes have these two don't try to
interpret them you will see that the

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00:14:22,680 --> 00:14:24,300
Haskell code here

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looks much lighter weight than the code

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on this side and Haskell programmers are
lazy we don't want to dive too much

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so this looks much more beautiful and
this

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00:14:36,470 --> 00:14:39,860
and that's why Azkals index is designed
the way it is

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00:14:39,860 --> 00:14:43,350
thank you this was the end of Part long

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00:14:43,350 --> 00:14:46,680
see you in a bit for the remainder of

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kept their own