[Haskell-cafe] Type classes for converting to Text and String

Simon Hengel sol at typeful.net
Thu Mar 8 13:20:22 CET 2012

On Thu, Mar 08, 2012 at 12:54:13PM +0200, Roman Cheplyaka wrote:
> * Simon Hengel <sol at typeful.net> [2012-03-08 11:48:41+0100]
> > On Thu, Mar 08, 2012 at 12:18:56PM +0200, Roman Cheplyaka wrote:
> > > If it's fine to depend on FunDeps, you can use ListLike.
> > > http://hackage.haskell.org/package/ListLike
> > 
> > How would that help with toText?
> toText = fromListLike
> (ListLike instance for Text is provided by the listlike-instances
> package.)

Ah, the listlike-instances package is the missing piece.

Not sure if this is going somewhere.  But I'm still trying to get a
clear picture of the performance implications.

Say I have a newtype-wrapped ByteString that I would decode to
String/Text using UTF-8:

    newtype Value = Value ByteString

Would it be possible to go from Value to Text by essentially ending up
with Data.Text.Encoding.decodeUtf8 at runtime (e.g. by using rewrite


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