Data.Text.Internal

A module containing private Text internals. This exposes the Text representation and low level construction functions. Modules which extend the Text system may need to use this module.

You should not use this module unless you are determined to monkey with the internals, as the functions here do just about nothing to preserve data invariants. You have been warned!

Types

Internally, the Text type is represented as an array of Word16 UTF-16 code units. The offset and length fields in the constructor are in these units, not units of Char.

Invariants that all functions must maintain:

• Since the Text type uses UTF-16 internally, it cannot represent characters in the reserved surrogate code point range U+D800 to U+DFFF. To maintain this invariant, the safe function maps Char values in this range to the replacement character (U+FFFD, '�').
• A leading (or "high") surrogate code unit (0xD800–0xDBFF) must always be followed by a trailing (or "low") surrogate code unit (0xDC00-0xDFFF). A trailing surrogate code unit must always be preceded by a leading surrogate code unit.

data Text

A space efficient, packed, unboxed Unicode text type.

Constructors

Text !Array !Int !Int

Instances

Eq Text

Data Text

This instance preserves data abstraction at the cost of inefficiency. We omit reflection services for the sake of data abstraction.

This instance was created by copying the updated behavior of Data.Set and Data.Map. If you feel a mistake has been made, please feel free to submit improvements.

Original discussion is archived here:

could we get a Data instance for Data.Text.Text?

The followup discussion that changed the behavior of Data.Set and Data.Map is archived here

Proposal: Allow gunfold for Data.Map, ...

Ord Text

Read Text

Show Text

Typeable Text

IsString Text

Monoid Text

NFData Text

Construction

text :: Array -> Int -> Int -> Text

Construct a Text without invisibly pinning its byte array in memory if its length has dwindled to zero.

textP :: Array -> Int -> Int -> Text

Deprecated: Use text instead

Safety

safe :: Char -> Char

Map a Char to a Text-safe value.

UTF-16 surrogate code points are not included in the set of Unicode scalar values, but are unfortunately admitted as valid Char values by Haskell. They cannot be represented in a Text. This function remaps those code points to the Unicode replacement character (U+FFFD, '�'), and leaves other code points unchanged.

Code that must be here for accessibility

empty :: Text

O(1) The empty Text.

Utilities

firstf :: (a -> c) -> Maybe (a, b) -> Maybe (c, b)

Apply a function to the first element of an optional pair.

Debugging

showText :: Text -> String

A useful show-like function for debugging purposes.