[Haskell-cafe] Clever generic ByteString hack?

John Goerzen jgoerzen at complete.org
Wed Jul 5 09:16:13 EDT 2006

On Wed, Jul 05, 2006 at 12:25:53PM +0100, Duncan Coutts wrote:
> > different types of input?  I'd rather avoid having 3 versions, that are
> > exactly the same except for imports.
> People sometimes talk about doing a type class to cover string like
> modules.

Yes, that makes sense to me.  I was sorta hoping to avoid having to say
something like:

instance StringLike B.ByteString where
     vlength = B.length
     vcons = B.cons
     ...  with about 50 of these lines ...

> What functions are you thinking of btw? We may want to include them in
> the ByteString modules anyway (possibly directly rather than in terms of
> other functions, to take advantage of tricks with the representation).

Most everything here:


The appropriate bits from:


And perhaps even:


Also, it would be nice to see direct regexp support in ByteString.  It
seems ugly to have to convert to a String just to pass it back to C.

But even if you did implement all of that, I think there is still
utility in having a generic typeclass that can take any of the three
string-like types that we have in Haskell these days.  Otherwise, you
are going to see library fracturization -- some code works with Strings,
some with ByteStrings, some with lazy ByteStrings, and woe to the
programmer that has to integrate all this mess.

(OCaml has this problem in a big way with its lists vs. Streams and
built-in handicapped IO vs. Posix IO)

-- John

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