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POHaskell: writing the result of a computation to file
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copied!<p>I have a function which creates a tuple after computation, but I would like to write it to file. </p> <p>I know how to write to a file using <code>writeFile</code>, but do not know how to combine the computation and monads IO together in the type signature.</p> <p>This is my code.</p> <pre><code>invest :: ([Char]->Int->Int->([Char], Int) ) -> [Char]->Int->Int->([Char], Int) invest myinvest x y = myinvest x y myinvest :: [Char]->Int->Int->([Char], Int) myinvest w x y | y > 0 = (w, x + y) | otherwise = error "Invest amount must greater than zero" where </code></pre> <p>I have a function which computes the maximum value from a list, but I want this function to receive input from a file, and then perform the computation of maximum value.</p> <pre><code>maximuminvest :: (Ord a) => [a] -> a maximuminvest [] = error "Empty Invest Amount List" maximuminvest [x] = x maximuminvest (x:xs) | x > maxTail = x | otherwise = maxTail where maxTail = maximuminvest xs </code></pre> <p>Please help. Thanks. </p> <p>[Edit]</p> <ol start="3"> <li>My new question is at below. </li> </ol> <p>The first and second question can be solve through function composition but when i try it say type mismatch.</p> <p>I have check it but i couldn't find any errors.</p> <pre><code>invest :: ( [Char]->Int->Int->([Char], Int) ) -> [Char]->Int->Int-> ([Char], Int) invest theinvest x y = theinvest x y theinvest :: [Char]->Int->Int-> ([Char], Int) theinvest w x y | y > 0 = (w, x + y) | otherwise = error "Invest amount must greater than zero" savefile :: ([Char], Int) -> IO() savefile (x, y) = do let name = fst (x, y) let temp = snd(x, y) let amount = show temp writeFile "C:\\Invest.txt" (name ++ " " ++ amount) test = savefile . theinvest "asd" 1234 234 </code></pre> <p>The error message is</p> <pre><code> ERROR - Type error in application * Expression : savefile . invest theinvest "234" 234 234 Term : invest theinvest "234" 234 234 Type : ([Char],Int) * Does not match : a -> b </code></pre> <p>Please help. My return type is <code>([Char],Int)</code>. Why it complaint as <code>a -> b</code> ? Thanks</p> <p>I solve this using command like savefile (invest theinvest "asd" 12 12) but why the operator doesn;t works ? </p> <ol start="4"> <li><p>My fourth question is i have something like this ["peter","1000","michell","2000","kelly","3000"] and i would like to convert to [("peter",1000),("michell", 2000),("kelly",3000)]</p></li> <li><p>The reading of file content is ok but i want to filter the string and get the number only. For instance, a file that has "peter 100\nasd 200"</p></li> </ol> <p>I would like to drop the alphabet and remain the integer here. I just want the [100, 200] to be the argument the function.</p> <p>Please help. </p> <p>Thanks. </p>

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