Data.Text.Foreign

Support for using Text data with native code via the Haskell foreign function interface.

Interoperability with native code

The Text type is implemented using arrays that are not guaranteed to have a fixed address in the Haskell heap. All communication with native code must thus occur by copying data back and forth.

The Text type's internal representation is UTF-16, using the platform's native endianness. This makes copied data suitable for use with native libraries that use a similar representation, such as ICU. To interoperate with native libraries that use different internal representations, such as UTF-8 or UTF-32, consider using the functions in the Encoding module.

data I16

A type representing a number of UTF-16 code units.

Instances

Bounded I16

Enum I16

Eq I16

Integral I16

Num I16

Ord I16

Read I16

Real I16

Show I16

Safe conversion functions

fromPtr

Arguments

:: Ptr Word16

source array

-> I16

length of source array (in Word16 units)

-> IO Text

O(n) Create a new Text from a Ptr Word16 by copying the contents of the array.

useAsPtr :: Text -> (Ptr Word16 -> I16 -> IO a) -> IO a

O(n) Perform an action on a temporary, mutable copy of a Text. The copy is freed as soon as the action returns.

asForeignPtr :: Text -> IO (ForeignPtr Word16, I16)

O(n) Make a mutable copy of a Text.

Encoding as UTF-8

peekCStringLen :: CStringLen -> IO Text

O(n) Decode a C string with explicit length, which is assumed to have been encoded as UTF-8. If decoding fails, a UnicodeException is thrown.

withCStringLen :: Text -> (CStringLen -> IO a) -> IO a

Marshal a Text into a C string encoded as UTF-8 in temporary storage, with explicit length information. The encoded string may contain NUL bytes, and is not followed by a trailing NUL byte.

The temporary storage is freed when the subcomputation terminates (either normally or via an exception), so the pointer to the temporary storage must not be used after this function returns.

Unsafe conversion code

lengthWord16 :: Text -> Int

O(1) Return the length of a Text in units of Word16. This is useful for sizing a target array appropriately before using unsafeCopyToPtr.

unsafeCopyToPtr :: Text -> Ptr Word16 -> IO ()

O(n) Copy a Text to an array. The array is assumed to be big enough to hold the contents of the entire Text.

Low-level manipulation

Foreign functions that use UTF-16 internally may return indices in units of Word16 instead of characters. These functions may safely be used with such indices, as they will adjust offsets if necessary to preserve the validity of a Unicode string.

dropWord16 :: I16 -> Text -> Text

O(1) Return the suffix of the Text, with n Word16 units dropped from its beginning.

If n would cause the Text to begin inside a surrogate pair, the beginning of the suffix will be advanced by one additional Word16 unit to maintain its validity.

takeWord16 :: I16 -> Text -> Text

O(1) Return the prefix of the Text of n Word16 units in length.

If n would cause the Text to end inside a surrogate pair, the end of the prefix will be advanced by one additional Word16 unit to maintain its validity.