Data.Text.Internal.Builder

Warning: this is an internal module, and does not have a stable API or name. Functions in this module may not check or enforce preconditions expected by public modules. Use at your own risk!

Efficient construction of lazy Text values. The principal operations on a Builder are singleton, fromText, and fromLazyText, which construct new builders, and mappend, which concatenates two builders.

To get maximum performance when building lazy Text values using a builder, associate mappend calls to the right. For example, prefer

 singleton 'a' `mappend` (singleton 'b' `mappend` singleton 'c')

to

 singleton 'a' `mappend` singleton 'b' `mappend` singleton 'c'

as the latter associates mappend to the left.

Public API

The Builder type

data Builder

A Builder is an efficient way to build lazy Text values. There are several functions for constructing builders, but only one to inspect them: to extract any data, you have to turn them into lazy Text values using toLazyText.

Internally, a builder constructs a lazy Text by filling arrays piece by piece. As each buffer is filled, it is 'popped' off, to become a new chunk of the resulting lazy Text. All this is hidden from the user of the Builder.

Instances

Eq Builder

Ord Builder

Show Builder

IsString Builder

Monoid Builder

toLazyText :: Builder -> Text

O(n). Extract a lazy Text from a Builder with a default buffer size. The construction work takes place if and when the relevant part of the lazy Text is demanded.

toLazyTextWith :: Int -> Builder -> Text

O(n). Extract a lazy Text from a Builder, using the given size for the initial buffer. The construction work takes place if and when the relevant part of the lazy Text is demanded.

If the initial buffer is too small to hold all data, subsequent buffers will be the default buffer size.

Constructing Builders

singleton :: Char -> Builder

O(1). A Builder taking a single character, satisfying

• toLazyText (singleton c) = singleton c

fromText :: Text -> Builder

O(1). A Builder taking a Text, satisfying

• toLazyText (fromText t) = fromChunks [t]

fromLazyText :: Text -> Builder

O(1). A Builder taking a lazy Text, satisfying

• toLazyText (fromLazyText t) = t

fromString :: String -> Builder

O(1). A Builder taking a String, satisfying

• toLazyText (fromString s) = fromChunks [S.pack s]

Flushing the buffer state

flush :: Builder

O(1). Pop the strict Text we have constructed so far, if any, yielding a new chunk in the result lazy Text.

Internal functions

append' :: Builder -> Builder -> Builder

ensureFree :: Int -> Builder

Ensure that there are at least n many elements available.

writeN :: Int -> (forall s. MArray s -> Int -> ST s ()) -> Builder

Ensure that n many elements are available, and then use f to write some elements into the memory.