parse.hs

import Text.ParserCombinators.Parsec

-- A CSV file contains 0 or more lines, each of which is terminated
--    by the end-of-line character (eol). 
csvFile :: GenParser Char st [[String]]
csvFile = 
    do result <- many line
       eof
       return result

-- Each line contains 1 or more cells, separated by a comma
line :: GenParser Char st [String]
line = 
    do result <- cells
       eol                       -- end of line
       return result
                         
                         -- Build up a list of cells.  Try to parse the first cell, then figure out 
                         -- what ends the cell.
cells :: GenParser Char st [String]
cells = 
    do first <- cellContent
       next <- remainingCells
       return (first : next)

                                           -- The cell either ends with a comma, indicating that 1 or more cells follow,
                                           -- or it doesn't, indicating that we're at the end of the cells for this line
remainingCells :: GenParser Char st [String]
remainingCells =
    (char ',' >> cells)            -- Found comma?  More cells coming
    <|> (return [])                -- No comma?  Return [], no more cells

                                                   -- Each cell contains 0 or more characters, which must not be a comma or
                                                  -- EOL
cellContent :: GenParser Char st String
cellContent = 
    many (noneOf ",\n")
                                                              

                                                              -- The end of line character is \n
eol :: GenParser Char st Char
eol = char '\n'

parseCSV :: String -> Either ParseError [[String]]
parseCSV input = parse csvFile "(unknown)" input