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16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage

16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 1/32 https://www.tutorialspoint.com/haskell/haskell_quick_guide.htm Copyright © tutorialspoint.com HASKELL - QUICK GUIDE HASKELL - OVERVIEW Haskell is a Functional Programming Language that has been specially designed to handle symbolic computation and list processing applications. Functional programming is based on mathematical functions. Besides Haskell, some of the other popular languages that follow Functional Programming paradigm include: Lisp, Python, Erlang, Racket, F#, Clojure, etc. In conventional programing, instructions are taken as a set of declarations in a specific syntax or format, but in the case of functional programing, all the computation is considered as a combination of separate mathematical functions. Going Functional with Haskell Haskell is a widely used purely functional language. Here, we have listed down a few points that make this language so special over other conventional programing languages such as Java, C, C++, PHP, etc. Functional Language − In conventional programing language, we instruct the compiler a series of tasks which is nothing but telling your computer "what to do" and "how to do?" But in Haskell we will tell our computer "what it is?" Laziness − Haskell is a lazy language. By lazy, we mean that Haskell won't evaluate any expression without any reason. When the evaluation engine finds that an expression needs to be evaluated, then it creates a thunk data structure to collect all the required information for that specific evaluation and a pointer to that thunk data structure. The evaluation engine will start working only when it is required to evaluate that specific expression. Modularity − A Haskell application is nothing but a series of functions. We can say that a Haskell application is a collection of numerous small Haskell applications. Statically Typed − In conventional programing language, we need to define a series of variables along with their type. In contrast, Haskell is a strictly typed language. By the term, Strictly Typed language, we mean the Haskell compiler is intelligent enough to figure out the type of the variable declared, hence we need not explicitly mention the type of the variable used. Maintainability − Haskell applications are modular and hence, it is very easy and cost-effective to maintain them. Functional programs are more concurrent and they follow parallelism in execution to provide more accurate and better performance. Haskell is no exception; it has been developed in a way to handle multithreading effectively. Hello World It is a simple example to demonstrate the dynamism of Haskell. Take a look at the following code. All that we need is just one line to print "Hello Word" on the console. main = putStrLn "Hello World" Once the Haskell compiler encounters the above piece of code, it promptly yields the following output − Hello World 16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 2/32 We will provide plenty of examples throughout this tutorial to showcase the power and simplicity of Haskell. HASKELL - ENVIRONMENT SET UP Try it Online You really do not need to set up your own environment to start learning Haskell programming language. Reason is very simple, we already have set up Haskell Programming environment online, so that you can compile and execute all the available examples online at the same time when you are doing your theory work. This gives you confidence in what you are reading and to check the result with different options. Feel free to modify any example and execute it online. This online editor has plenty of options to practice Haskell programing examples. Go to the terminal section of the page and type "ghci". This command automatically loads Haskell compiler and starts Haskell online. You will receive the following output after using the ghci command. sh-4.3$ ghci GHCi,version7.8.4:http://www.haskell.org/ghc/:?forhelp Loading package ghc-prim...linking...done. Loading packageinteger gmp...linking... done. Loading package base...linking...done. Prelude> If you still want to use Haskell offline in your local system, then you need to download the available Haskell setup from its official webpage − https://www.haskell.org/downloads There are three different types of installers available in the market − Minimal Installer − It provides GHC , CABAL , and Stack tools. Stack Installer − In this installer, the GHC can be downloaded in a cross-platform of managed toll chain. It will install your application globally such that it can update its API tools whenever required. It automatically resolves all the Haskell-oriented dependencies. Haskell Platform − This is the best way to install Haskell because it will install the entire platform in your machine and that to from one specific location. This installer is not distributive like the above two installers. We have seen different types of installer available in market now let us see how to use those installers in our machine. In this tutorial we are going to use Haskell platform installer to install Haskell compiler in our system. Environment Set Up in Windows To set up Haskell environment on your Windows computer, go to their official website https://www.haskell.org/platform/windows.html and download the Installer according to your customizable architecture. TheGlasgowHaskellCompiler CommonArchitectureforBuildingApplicationsandLibraries 16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 3/32 Check out your system’s architecture and download the corresponding setup file and run it. It will install like any other Windows application. You may need to update the CABAL configuration of your system. Environment Set Up in MAC To set up Haskell environment on your MAC system, go to their official website https://www.haskell.org/platform/mac.html and download the Mac installer. 16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 4/32 Environment Set Up in Linux Installing Haskell on a Linux-based system requires to run some command which is not that much easy like MAC and Windows. Yes, it is tiresome but it is reliable. You can follow the steps given below to install Haskell on your Linux system − Step 1 − To set up Haskell environment on your Linux system, go to the official website https://www.haskell.org/platform/linux.html and choose your distribution. You will find the following screen on your browser. 16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 5/32 Step 2 − Select your Distribution. In our case, we are using Ubuntu. After selecting this option, you will get the following page on your screen with the command to install the Haskell in our local system. 16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 6/32 Step 3 − Open a terminal by pressing Ctrl + Alt + T. Run the command "$ sudo apt-get install haskell- platform" and press Enter. It will automatically start downloading Haskell on your system after authenticating you with the root password. After installing, you will receive a confirmation message. Step 4 − Go to your terminal again and run the GHCI command. Once you get the Prelude prompt, you are ready to use Haskell on your local system. To exit from the GHCI prolog, you can use the command ":quit exit". HASKELL - BASIC DATA MODELS Haskell is a purely functional programing language, hence it is much more interactive and intelligent than other programming languages. In this chapter, we will learn about basic data models of Haskell which are actually predefined or somehow intelligently decoded into the computer memory. Throughout this tutorial, we will use the Haskell online platform available on our website (https://www.tutorialspoint.com/codingground.htm). Numbers Haskell is intelligent enough to decode some number as a number. Therefore, you need not mention its type externally as we usually do in case of other programing languages. As per example go to your prelude command prompt and just run "2+2" and hit enter. sh-4.3$ ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> 2+2 You will receive the following output as a result. 4 In the above code, we just passed two numbers as arguments to the GHCI compiler without predefining their type, but compiler could easily decode these two entries as numbers. Now, let us try a little more complex mathematical calculation and see whether our intelligent compiler give us the correct output or not. Try with "15+ -40" 5 ∗5 16.12.2017 Haskell Quick Guide https://www.tutorialspoint.com/cgi-bin/printpage.cgi 7/32 Prelude> 15+(5*5)-40 The above expression yields "0" as per the expected output. 0 Characters Like numbers, Haskell can intelligently identify a character given in as an input to it. Go to your Haskell command prompt and type any character with double or single quotation. Let us provide following line as input and check its output. Prelude> :t "a" It will produce the following output − "a" :: [Char] Remember you use (:t) while supplying the input. In the above example, is to include the specific type related to the inputs. We will learn more about this type in the upcoming chapters. Take a look at the following example where we are passing some invalid input as a char which in turn leads to an error. Prelude> :t a <interactive>:1:1: Not in scope: 'a' Prelude> a <interactive>:4:1: Not in scope: 'a' By the error message "<interactive>:4:1: Not in scope: `a'" the Haskell compiler is warning us that it is not able to recognize your input. Haskell is a type of language where everything is represented using a uploads/Ingenierie_Lourd/ haskell-quick-guide.pdf