DrScheme for My TCS Community

8/8/2019 DrScheme for My TCS Community

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DrScheme TutorialDrScheme Tutorial

PartPart II

dedicated todedicated to

TCS PreTCS Pre--ILP FriendsILP Friends

What to know? And .. What not toWhat to know? And .. What not to

know?know?


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Before Getting into this Download DrScheme, version 372 (not any

other version) from the web. Visithttp://download.plt-

scheme.org/drscheme/all-versions.htmland choose Version 372. Done

If you know any language like C or Java oranything else, dump them into a dark room

as long as you learn Scheme. I mean,dont compare Scheme with any other lang.It will lead to problems in understanding.


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Roll up your sleeves. NOW!!!

Install DrScheme 372, run it.

In the bottom of the window, choose

Textual (includesR5R

S) from thelanguage menu.

This Textual language is what wehave to use for learning in Pre-ILP.

Click on the Run button in the topright corner of screen.

Now, you are done with initial things.


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What is DrScheme? DrScheme is a programming

language like C, C++ or Java.

But, it is very much different fromany other language.

It speaks the language of humanintuition. Youll see this soon.

Nobody needs to teach you schemesyntax for more than, say tenminutes.


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Why Scheme? Scheme is not a serious language currently used in

industry.

It is just a language which is used to learn the basicsof programming.

The concept of Scheme is to learn the art ofProgramming and not to learn any particular language.

So, you are expected to learn about how to program or,how to think logically about solving a given problem.

So, learn programming but, not thelanguage.

If you are able to solve a given problem using Scheme,then, you can solve it using any other language once thesyntax is known to you.


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What do we see there? Once you run DrScheme, you will see a

window with two text areas one aboveanother.

First, we will concentrate about the bottomone and will come to the top one soon.

The bottom one is called Interactionswindow. It is used to get results from the

programs and to give input to theprograms.

We will start our experiments in theinteractions window.


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Into DrScheme In the interactions window, after the

> mark, type any number, say 5

and press Enter. You will get thesame number as the result in(default) blue colour.


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Experimenting DrScheme Type hello (include the double

quotes also) and you will get hello

as output.

Now, if you want to add twonumbers, try (+ 3 5)


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Experimenting DrScheme I know, by now, you would have tried

-, * and / operators. I said, Its thelanguage of intuition

Then, try experimenting + with morethan 2 operators, say (+ 3 5 6 4)

Yes, same as what you guessed. Isntit?


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Variables To declare a variable (used to store something), use

the keyword define, as (define a 10). This means a=10. So, now execute (define a 10) and what do you

expect as output?

Amazed? It returns nothing as output because its jobis to say that a=10 and its job is not to return thevalue of a. So, it wont return 10. Got it?

This is called Data Abstraction, as we hide thevalue (data) and give a name to it.


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Manipulating Variables

Now, look at the following and youwill understand for yourself.

No need of explanation. Right?


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Playing with operations Now, try this (+ 3 (+ 5 6)). I hope

you will all say the result unanimously

as 14. Yes. You did the Math right.. But, how

come you understood this Schemesyntax even before I explained!


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Into Text Data To handle texts, we have Strings,

which are collections of characters

between and .

And, as you say, we can do this also:


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YOU UGLY CHAM

ELEON !!! Now, look at this..

Stop screaming! The variable a is anumber in first line and then itbecomes a string later, showing noopposition!You ugly chameleon!!!


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Scheme and (Y)OUR

mind

If I say a=3 to you, you will assume in your mindthat the variable a must be an integer, or number. Ineed not say to you that it is a number. Your intuitiondoes this work.

Similarly, Scheme does the work of intuition byassuming what you are coming to say.

So, no need for type declaration of variables as insome other languages.

Yipee!! Free from int, char, float, double, pointeretc.

And, actually, the chameleon is you, who screamed atScheme at the end of the last slide and who isdancing with joy at the end of this slide. No offense!Just for fun! LOL


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This or That? To handle, true or false type,there is a data

type called boolean.

#t denotes true and #fdenotes false.

Now, look at this

The my_answer is now a boolean variable.


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Scheme Sabhas Speaker Seat

To display, or shout, or whisper, or singanything, we use a keyword display.

Note the pink colour of the outputs! Evendouble quotes are missing in the stringoutput.


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A

Bigconfusion, indeed !!!

I can hear you saying Why to unnecessarily use(display 10) instead of just typing 10 and pressingEnter?

First of all, note the colour change, from blue to pink.

A good joke!!! Indeed, its not a joke. It gives a clear indication thatsomething seriously different is happening internallybetween these two. Yes!!!

If you can guess the difference, you are a prodigy. But, if you cant then, you are fit for the job of a

software professional because, you have TRIED toguess. Trying is what matters. Only brave peopletry.

Ok. The answer is in the next slide.


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The Serious Difference Look at this first and I will explain later.

The difference is simple. The results ofdisplay function are not reusable whereasthe results of +,-,*,/ are reusable.


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End of Part I More about reusability in the next part..

The next part will be uploaded as soon as itis ready.

Please drop your suggestions, queries atthe forum or to [email protected]

Thank you. And, all the best.

Vivek Ganesan,

SASTRA University,

Thanjavur.

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DrScheme for My TCS Community