[Haskell-cafe] Mutable data design question

Keean Schupke k.schupke at imperial.ac.uk
Fri Dec 3 12:42:11 EST 2004

Marcin 'Qrczak' Kowalczyk wrote:

>2. Use a persistent data structure with logarithmic cost of most
>   operations: a balanced tree of text fragments, called a rope
>   (Hans Boehm has made one for C). "Undo" can be made by simply
>   keeping old versions.
>   Hard to implement the core data structure. If done right, the rest
>   is easy, in particular "undo" handling is very robust. There are
>   some overheads for all operations, but the cost of operations
>   scales to extreme cases.
>The second way is more interesting, but I don't know how to implement
>a rope in details.
What happens with this method when the display needs refreshing, does
the current state have to be recomputed every time ... wouldn't this lead
to very slow cursor operations when using 'backspace'? I would have
thought a mutable screen-buffer for editing would still be required.


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