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2013-12-12T18:30:22.137
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This is definitely a job worth of a parsing library. My primary goal is normally (i.e., for anything I intend to use more than once or twice) to get the data into a non-textual form ASAP, something like <pre><code>module ReportParser where import Prelude hiding (takeWhile) import Data.Text hiding (takeWhile) import Control.Applicative import Data.Attoparsec.Text data ReportHeaderData = Company Text | Program Text | State Text -- ... | FieldNames [Text] data ReportData = ReportData Int Text Int Int Int Int Date Int Text Text data Date = Date Int Int Int </code></pre> and we can say, for the sake of argument, that a report is <pre><code>data Report = Report [ReportHeaderData] [ReportData] </code></pre> Now, I generally create a parser which is a function of the same name as the data type <pre><code>-- Ending condition for a field doubleSpace :: Parser Char doubleSpace = space >> space -- Clears leading spaces clearSpaces :: Parser Text clearSpaces = takeWhile (== ' ') -- Naively assumes no tabs -- Throws away everything up to and including a newline character (naively assumes unix line endings) clearNewline :: Parser () clearNewline = (anyChar `manyTill` char '\n') *> pure () -- Parse a date date :: Parser Date date = Date <$> decimal <*> (char '/' *> decimal) <*> (char '/' *> decimal) -- Parse a report reportData :: Parser ReportData reportData = let f1 = decimal <* clearSpaces f2 = (pack <$> manyTill anyChar doubleSpace) <* clearSpaces f3 = decimal <* clearSpaces f4 = decimal <* clearSpaces f5 = decimal <* clearSpaces f6 = decimal <* clearSpaces f7 = date <* clearSpaces f8 = decimal <* clearSpaces f9 = (pack <$> manyTill anyChar doubleSpace) <* clearSpaces f10 = (pack <$> manyTill anyChar doubleSpace) <* clearNewline in ReportData <$> f1 <*> f2 <*> f3 <*> f4 <*> f5 <*> f6 <*> f7 <*> f8 <*> f9 <*> f10 </code></pre> By proper running of <a href="http://hackage.haskell.org/package/attoparsec-0.10.4.0/docs/Data-Attoparsec-ByteString.html#g:5" rel="nofollow">one of the parse functions</a> and the use of one of the combinators (such as <a href="http://hackage.haskell.org/package/attoparsec-0.10.4.0/docs/Data-Attoparsec-Combinator.html" rel="nofollow"><code>many</code></a> (and possibly <code>feed</code>, if you end up with a Partial result), you should end up with a list of <code>ReportData</code>s. You can then convert them to CSV with some function you've created. Note that I didn't deal with the header. It should be relatively trivial to write code to parse it, and build a <code>Report</code> with e.g. <pre><code>-- Not tested parseReport = Report <$> (many reportHeader) <*> (many reportData) </code></pre> Note that I prefer the <a href="http://hackage.haskell.org/package/base-4.6.0.1/docs/Control-Applicative.html#g:1" rel="nofollow">Applicative</a> form, but it's also possible to use the monadic form if you prefer (I did in <code>doubleSpace</code>). <a href="http://hackage.haskell.org/package/base-4.6.0.1/docs/Control-Applicative.html#g:2" rel="nofollow"><code>Data.Alternative</code></a> is also useful, for reasons implied by the name. For playing with this, I highly recommend GHCI and the <code>parseTest</code> function. GHCI is just overall handy and a good way to test individual parsers, while parseTest takes a parser and input string and outputs the status of the run, the parsed string, and any remaining string not parsed. Very useful when you're not quite sure what's going on.
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1. POParsing Printable Text File in Haskell
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1. USElliot Robinson
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1. USElliot Robinson
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1. COThank you for the excellent answer. I was, unfortunately, unable to get it work. I kept getting complaints about type conversions from/to Char, ByteString, [Char], and String. But I was able to get the code to compile eventually, starting from the simpler answer I marked as the answer. Thank you again!
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