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POWhy isn't Haskell Partial Application Working?
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copied!<p>My work in Haskell comes in the form of re-working .Net F# projects in Haskell for the fun of it.</p> <p>I'm parsing a regular Windows configuration file--one key/value pair per line, key separated from value by <code>=</code>. This file is very simple and straight-forward, which allows my parsing code to be simple and straight-forward, which I like.</p> <p>My question is why partial application is not working on the last line of code below. It's obviously working in prior lines and other functions.</p> <pre><code>module Configuration (Config (..), load) where import Data.Char (isSpace) import Data.List (isPrefixOf) data Config = Config { aliases :: [String] , headers :: [String] } -- This is a naive implementation. I can't decide if I like it better than -- trim = unpack . strip . pack. trim :: String -> String trim = reverse . dropSpaces . reverse . dropSpaces dropSpaces :: String -> String dropSpaces = dropWhile isSpace split _ [] = [] split c cs = [takeWhile (/= c) cs] ++ split c (tail' $ dropWhile (/= c) cs) where tail' [] = [] tail' (x:xs) = xs load :: String -> Config load text = let ss = lines text hs = map getValue $ getLines "Header" ss as = split ',' $ getValue $ getLine "AliasList" ss in Config { aliases=as, headers=hs } where getLines p = filter (p `isPrefixOf`) getValue = trim . drop 1 . dropWhile (/= '=') getLine = head . getLines -- Why isn't partial application working here? </code></pre> <p>The error I'm getting follows:</p> <pre><code>Configuration.hs:30:29: Couldn't match expected type `[c0]' with actual type `[[a0]] -> [[a0]]' Expected type: [a0] -> [c0] Actual type: [a0] -> [[a0]] -> [[a0]] In the second argument of `(.)', namely `getLines' In the expression: head . getLines </code></pre> <p>Thanks!</p>

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