Add an option to skip the header in decodeWith

Data/Csv/Encoding.hs

@@ -56,6 +56,8 @@ import Data.Csv.Types
 -- | Efficiently deserialize CSV records from a lazy 'L.ByteString'.
 -- If this fails due to incomplete or invalid input, @'Left' msg@ is
 -- returned. Equivalent to @'decodeWith' 'defaultDecodeOptions'@.
+--
+-- Use the 'decSkipHeader' and 'decodeWith' if the input has a header.
 decode :: FromRecord a => L.ByteString -> Either String (Vector a)
 decode = decodeWith defaultDecodeOptions
 {-# INLINE decode #-}

Data/Csv/Parser.hs

@@ -27,6 +27,7 @@ module Data.Csv.Parser
 import Blaze.ByteString.Builder (fromByteString, toByteString)
 import Blaze.ByteString.Builder.Char.Utf8 (fromChar)
 import Control.Applicative
+import Control.Monad (when)
 import Data.Attoparsec.Char8 hiding (Parser, Result, parse)
 import qualified Data.Attoparsec as A
 import qualified Data.Attoparsec.Lazy as AL
@@ -46,17 +47,25 @@ import Data.Csv.Types
 data DecodeOptions = DecodeOptions
     { -- | Field delimiter.
       decDelimiter  :: {-# UNPACK #-} !Word8
+
+      -- | If 'True', the CSV file must have a header and this header
+      -- will be skipped.
+    , decSkipHeader :: !Bool
     }
 
 -- | Decoding options for parsing CSV files.
 defaultDecodeOptions :: DecodeOptions
 defaultDecodeOptions = DecodeOptions
-    { decDelimiter = 44  -- comma
+    { decDelimiter  = 44  -- comma
+    , decSkipHeader = False
     }
 
 -- | Parse a CSV file that does not include a header.
 csv :: DecodeOptions -> AL.Parser Csv
 csv !opts = do
+    when (decSkipHeader opts) $ do
+        _ <- header (decDelimiter opts)
+        return ()
     vals <- record (decDelimiter opts) `sepBy1` endOfLine
     _ <- optional endOfLine
     endOfInput
@@ -66,7 +75,11 @@ csv !opts = do
 
 -- | Parse a CSV file that includes a header.
 csvWithHeader :: DecodeOptions -> AL.Parser (Header, V.Vector NamedRecord)
-csvWithHeader !opts = do
+csvWithHeader !opts
+    | decSkipHeader opts = moduleError "csvWithHeader" $
+                           "decSkipHeader must not be used together with " ++
+                           "header-based parsing"
+csvWithHeader opts = do
     hdr <- header (decDelimiter opts)
     vals <- map (toNamedRecord hdr) . removeBlankLines <$>
             (record (decDelimiter opts)) `sepBy1` endOfLine
@@ -155,3 +168,7 @@ doubleQuote, newline, cr :: Word8
 doubleQuote = 34
 newline = 10
 cr = 13
+
+moduleError :: String -> String -> a
+moduleError func msg = error $ "Data.Csv.Parser." ++ func ++ ": " ++ msg
+{-# NOINLINE moduleError #-}