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| − | == Working environment == | + | = Interpreter of Arithmetic Expressions = |
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| − | Using the installation guide from [[Functional programming | Functional programming]] prepare your working environment.
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| − | ===How to verify it is working?===
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| − | *Run <code>ghci</code> from the command line. it will start GHC Interpreter, the output should be something like this:
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| − | <syntaxhighlight lang="Haskell" class="myDark" >
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| − | GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help
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| − | Prelude>
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| − | </syntaxhighlight >
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| − | *If you write expression, for example <code>1+2*3</code>, it should be evaluated. You can close this interpreter by typing <code>:q</code>.
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| − | *Open Visual Studio Code, create a file <code>simple.hs</code> and put there following lines of code:
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| − | <syntaxhighlight lang="Haskell" >
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| − | doubleMe x = x * x
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| − | plus x y = x + y + 'a'
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| − | </syntaxhighlight >
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| − | It should report a problem in function <code>plus</code> (you can not use <code>+</code> with letter, it can be repaired by removing <code>+ 'a'</code>). Report from VS Code is refreshed whenever the source file is saved on disk.
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| − | == First program in Haskell ==
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| − | In your favorite development environment (VS Code by default):
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| − | * Crate a file <code>simple.hs</code>.
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| − | * Create a function <code>pythagoras a b</code> that computes <code>c</code> based on <math>c^2 = a^2 + b^2 \,,</math>. Necessary functions can be found: [https://hoogle.haskell.org/ Hoogle]
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| − | * Open <code>ghci</code> and run the implemented function with <code>3 4</code>. File can be loaded using command <code>:l</code> (<code>:load</code>) and reloaded with <code>:r</code> (<code>:reload</code>).
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| − | <div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
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| − | <syntaxhighlight lang="Haskell">
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| − | pythagoras a b = sqrt (a*a + b*b)
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| − | </syntaxhighlight>
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| − | [[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/DEAQ69276]]
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| − | </div>
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| − | <div style="clear:both"></div>
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| − | == Real first program in Haskell ==
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| − | If you are complaining, that all programming courses should start with printing <code>"Hello world!"</code> on the screen and that is why previous task sucks. Do the following exercise.
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| − | *Crate a file <code>firstProgram.hs</code> with following content:
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| − | <syntaxhighlight lang="Haskell">
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| − | main = do putStr "Hello world!"
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| − | </syntaxhighlight >
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| − | *Compile it with 'GHC compiler' (command <code>ghc</code>).
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| − | *It should produce an executable file <code>firstProgram(.exe)</code>, run this file.
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