Copyright | Copyright (c) 2008--2011 Don Stewart |
---|---|
License | BSD2/MIT |
Maintainer | wren@community.haskell.org |
Stability | stable |
Portability | Haskell98 |
Safe Haskell | None |
Language | Haskell98 |
Efficiently parse floating point literals from a ByteString
.
- readDouble :: ByteString -> Maybe (Double, ByteString)
- unsafeReadDouble :: ByteString -> Maybe (Double, ByteString)
Documentation
readDouble :: ByteString -> Maybe (Double, ByteString) Source
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)
unsafeReadDouble :: ByteString -> Maybe (Double, ByteString) Source
Bare bones, unsafe wrapper for C's strtod(3)
. This provides
a non-copying direct parsing of Double values from a ByteString.
It uses strtod
directly on the bytestring buffer. strtod
requires the string to be null terminated, or for a guarantee
that parsing will find a floating point value before the end of
the string.