text-1.2.1.3: An efficient packed Unicode text type.

Copyright | (c) 2009, 2010 Bryan O'Sullivan
License | BSD-style
Maintainer | bos@serpentine.com
Stability | experimental
Portability | GHC
Safe Haskell | None
Language | Haskell98

Data.Text.Foreign

Contents

- Interoperability with native code
- Safe conversion functions
  - Encoding as UTF-8
- Unsafe conversion code
- Low-level manipulation

Description

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

Synopsis

- data I16
- fromPtr :: Ptr Word16 -> I16 -> IO Text
- useAsPtr :: Text -> (Ptr Word16 -> I16 -> IO a) -> IO a
- asForeignPtr :: Text -> IO (ForeignPtr Word16, I16)
- peekCStringLen :: CStringLen -> IO Text
- withCStringLen :: Text -> (CStringLen -> IO a) -> IO a
- lengthWord16 :: Text -> Int
- unsafeCopyToPtr :: Text -> Ptr Word16 -> IO ()
- dropWord16 :: I16 -> Text -> Text
- takeWord16 :: I16 -> Text -> Text

# 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.