On 7 September 2010 22:50, Ian Lynagh <igloo@earth.li> wrote:> Are there cases when Data.Text is significantly faster than
> Data.Text.Lazy? Do we need both? (Presumably .Lazy is built on top of
> Data.Text, but do we need the user to have a complete interface for
> both?)

Mm, this is a fair question. In the case of bytestring we need both
because sometimes for dealing with foreign code or IO you need the
representation to be a contigious block of memory. For text the
representation is more abstract so that need does not arrise. One
might argue that if it is simply to control strictness then one could
use the lazy version and provide a deepseq instance.

Here's an alternative argument: suppose we change the representation
of strict text to be a tree of chunks (e.g. finger tree). We could
achieve effecient concatenation. This representation would be
impossible while preserving semantics of a lazy tail. A tree impl that
has any kind of balance needs to know the overall length so cannot
have a lazy tail.