text- An efficient packed Unicode text type.

Safe HaskellNone




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!



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 Source

A space efficient, packed, unboxed Unicode text type.


Text !Array !Int !Int 


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 


text :: Array -> Int -> Int -> TextSource

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

textP :: Array -> Int -> Int -> TextSource

Deprecated: Use text instead


safe :: Char -> CharSource

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 :: TextSource

O(1) The empty Text.


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

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


showText :: Text -> StringSource

A useful show-like function for debugging purposes.