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POType error in Haskell program
 

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  1. POType error in Haskell program
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    <p>User can give id, width, height and description rectangle and then I write it to a file. Now I would like to load this content from the file to my program but I have error: </p> <p>Couldn't match expected type [RectangleType] against inferred type IO [Rectangletype]. In the first argument of menuRectangles namely db. In the expression menuRectangles db. In a do expression menuRectangles db. </p> <p>What is going on ? This is content of my file: [Rectangle 2 5 6 "abcabc",Rectangle 1 2 4 "abcabc"]</p> <p>This is code:</p> <pre><code>import IO import Char import System.Exit import Maybe data RectangleType = Rectangle Int Int Int deriving(Show, Read) loadFile :: FilePath -&gt; IO [RectangleType] loadFile fname = catch (do fileContent &lt;- readFile fname return (read fileContent) ) errorHandler where errorHandler e = do putStrLn ("Error file") exitFailure db = loadFile "db.txt" main = do putStrLn "Choose option:" n &lt;- getLine case n of "1" -&gt; do menuRectangles db; main "2" -&gt; putStrLn "bye, bye" otherwise -&gt; do putStrLn "Bad option"; main menuRectangles :: [RectangleType] -&gt; IO [RectangleType] menuRectangles rs = do putStrLn "Please choose option:" putStrLn "1 - Add rectangle" putStrLn "2 - Show rectangle" putStrLn "3 - Quit" putStr "Number: " n &lt;- getLine case n of "1" -&gt; do { {- rs_new &lt;- addRectangle rs; -} menuRectangles rs }; "2" -&gt; do { {- showRectangle rs; -} menuRectangles rs } "3" -&gt; do { putStrLn "Quitting"; return rs } otherwise -&gt; do { putStrLn "The End"; return rs } </code></pre> <p><strong>EDIT: correct code:</strong></p> <pre><code>import IO import Char import System.Exit import Maybe data RectangleType = Rectangle Int Int Int deriving(Show, Read) loadFile :: FilePath -&gt; IO [RectangleType] loadFile fname = catch (do fileContent &lt;- readFile fname return (read fileContent) ) errorHandler where errorHandler e = do putStrLn ("Error file") exitFailure main = do db &lt;- loadFile "db.txt" mainMenu db mainMenu rs = do putStrLn "Choose option:" n &lt;- getLine case n of "1" -&gt; do menuRectangles rs; mainMenu rs "2" -&gt; putStrLn "bye, bye" otherwise -&gt; do putStrLn "Bad option"; mainMenu rs menuRectangles :: [RectangleType] -&gt; IO [RectangleType] menuRectangles rs = do putStrLn "Please choose option:" putStrLn "1 - Add rectangle" putStrLn "2 - Show rectangle" putStrLn "3 - Quit" putStr "Number: " n &lt;- getLine case n of "1" -&gt; do { {- rs_new &lt;- addRectangle rs; -} menuRectangles rs }; "2" -&gt; do { {- showRectangle rs; -} menuRectangles rs } "3" -&gt; do { putStrLn "Quitting"; return rs } otherwise -&gt; do { putStrLn "The End"; return rs } </code></pre>
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    2. COPresumably so that the question and answers still make sense.
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      1. POType error in Haskell program
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