[Haskell-beginners] When to use ByteString rather than [Char] ...?

[Daniel Fischer]

Am Sonntag 11 April 2010 15:29:38 schrieb Stephen Tetley:
> Hi James
>
> There's a paper describing the implementation of ByteStrings here:
>
> http://www.cse.unsw.edu.au/~dons/papers/CSL06.html
> http://www.cse.unsw.edu.au/~dons/papers/fusion.pdf
>
> For my own work, I generally need short immutable strings and haven't
> found ByteStrings compelling,

ByteStrings shine for long strings.
When you're using long strings, ByteStrings almost certainly are *much* 
faster (utf8-ByteStrings are probably significantly slower, but should 
still beat [Char] comfortably).

I've found ByteStrings better than [Char] when dealing with short strings 
only for a few things (e.g. as keys of Maps, ByteStrings tend to be better 
[at least if using ByteStrings there doesn't introduce too much packing and 
unpacking], things like edit-distance are faster on ByteStrings;
UArray Int Char is slower than ByteString [in my measurements] for these 
tasks, but it can also be used for characters > toEnum 255 and isn't too 
much slower).
Other things [see below] were faster for short [Char] than for short 
ByteStrings.

When dealing with short strings, in my experience there are rarely 
compelling reasons to choose one over the other.

> though the results presented in the
> above suggest [Char] is better at nothing

[Char] is (far) better at sorting short Strings; it often is better for map 
and filter.

> and worse at many things.

[Char]-IO is abysmally slow in comparison, [Char] uses much more memory, 
random access is horrible for lists.

> [Hmm - insert emoticon here]
>
> Best wishes
>
> Stephen