Data.ByteString.Lex.Lazy.Double

Efficiently parse floating point literals from a ByteString.

Documentation

readDouble :: ByteString -> Maybe (Double, ByteString)

Parse the initial portion of the ByteString as a Double precision floating point value. The expected form of the numeric literal is given by:

• An optional + or - sign
• Decimal digits, OR
• 0 [oO] and a sequence of octal digits, OR
• 0 [xX] and a sequence of hexadecimal digits, OR
• An optional decimal point, followed by a sequence of decimal digits,
• And an optional exponent

The result is returned as a pair of a double-precision floating point value and the remaining input, or Nothing should no parse be found.

For example, to sum a file of floating point numbers, one per line,

import qualified Data.ByteString.Char8  as S
import qualified Data.ByteString.Unsafe as S
import Data.ByteString.Lex.Double

main = print . go 0 =<< S.getContents
  where
    go n s = case readDouble s of
                    Nothing       -> n
                    Just (k,rest) -> go (n+k) (S.tail rest)