text-0.11.3.1: An efficient packed Unicode text type.

PortabilityGHC
Stabilityexperimental
Maintainerbos@serpentine.com, rtomharper@googlemail.com, duncan@haskell.org
Safe HaskellNone

Data.Text.Foreign

Contents

Description

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

Synopsis

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 Source

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

fromPtrSource

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 aSource

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)Source

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

Unsafe conversion code

lengthWord16 :: Text -> IntSource

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 ()Source

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 -> TextSource

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 -> TextSource

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.