[Haskell] string type class
haskell at list.mightyreason.com
Fri Mar 6 14:16:33 EST 2009
Matthew Pocock wrote:
> It seems every time I look at hackage there is yet another stringy
> datatype. For lots of apps, the particular stringy datatype you use
> matters for performance but not algorithmic reasons. Perhaps this is a
> good time for someone to propose a stringy class?
I did define my own (private) class for regular expressions, to abstract over
String, the ByteStrings, and Seq Char. But it is used in one place and is a
wart that should be removed.
The simple task of looping over the contents of a String (once, forward) is
quite different from a Strict ByteString (using an index and a lookup).
This means for decent efficiency I need two copies of my code, hand specialized
to each case.
"tail" or "(x:xs)" : very efficient for String (no allocation)
"tail" or "uncons" : not efficient for ByteString (allocation, might as well
convert to [Char]
And indexing by Int is O(n) for String and O(1) for ByteString.
So there are few algorithm that can access both efficiently.
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