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POThe questions regarding my first haskell program
 

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  1. POThe questions regarding my first haskell program
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    <p>The program return all possible combinations of '0' and '1' length N.</p> <pre><code>addToElement :: String -&gt; String -&gt; String addToElement element symbol = element ++ symbol addOneToElement :: String -&gt; String addOneToElement element = addToElement element "1" addZeroToElement :: String -&gt; String addZeroToElement element = addToElement element "0" processListOnce :: [String] -&gt; [String] processListOnce lst = do let s1 = map addOneToElement lst let s2 = map addZeroToElement lst s1 ++ s2 processList :: [String] -&gt; Integer -&gt; [String] processList lst 1 = processListOnce lst processList lst n = do let tmp = processListOnce(lst) processList tmp (n - 1) {- processList2 :: [String] -&gt; Integer -&gt; [String] processList2 lst n = iterate (map processListOnce) lst !! n -} main = do let s = processList ["0", "1"] 2 let ss = show s putStrLn ss </code></pre> <p>It is my first Haskell program so I will be thankful if you help me:</p> <ul> <li><p>First of all pls refactore my code Haskell-way. I already know one magic refactring:</p> <pre><code> Control.Monad.replicateM n [0,1] </code></pre> <p>but this solution is not good for studying purposes :)</p></li> <li><p>Why I can not use ProcessList2 instead ProcessList and get error:</p> <pre><code>all_possible_combinations.hs:44:51: Couldn't match expected type `[Char]' against inferred type `Char' Expected type: [String]] Inferred type: [String] In the second argument of `iterate', namely `lst' In the first argument of `(!!)', namely `iterate (map processListOnce) lst' </code></pre> <ul> <li><p>Is there any way to skip (not use) the 'tmp' variable in the processList? I have tried, but got the error:</p> <pre><code>processList :: [String] -&gt; Integer -&gt; [String] processList lst 1 = processListOnce lst processList lst n = processList processListOnce(lst) (n - 1) all_possible_combinations.hs:39:32: Couldn't match expected type `[String]' against inferred type `[String] -&gt; [String]' In the first argument of `processList', namely `processListOnce' In the expression: processList processListOnce (lst) (n — 1) In the definition of `processList': processList lst n = processList processListOnce (lst) (n — 1) </code></pre></li> </ul></li> </ul> <p>Thanks in advance.</p>
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