[Haskell-cafe] Policy for taking over a package on Hackage

Ivan Lazar Miljenovic ivan.miljenovic at gmail.com
Wed May 25 14:59:44 CEST 2011

On 25 May 2011 22:52, Johan Tibell <johan.tibell at gmail.com> wrote:
> On Wed, May 25, 2011 at 2:01 PM, Ivan Lazar Miljenovic
> <ivan.miljenovic at gmail.com> wrote:
>> With my wl-pprint-text package, Jason Dagit suggested to me on
>> #haskell that it would make sense to make such a pretty-printer be
>> class-based so that the same API could be used for String, ByteString,
>> Text, etc.
> I'm a bit skeptical of using type classes to abstract over Unicode
> string types and byte sequence types. The only API shared by the two
> kind of types is that of a sequence. Things like dot , spaces, etc.
> don't make much sense on binary data. You must assume that the
> ByteString contains text in some encoding to make sense of such
> concepts.

Well, using the Char8 version.  I was thinking of a class looking
something like:

class (IsString s, Monoid (Builder s)) => Prettyable s where
    type Builder s

    toBuilder :: s -> Builder s

    fromBuilder :: Builder s -> s

And then Doc now takes in a type parameter, which needs to be an
instance of Prettyable.  The IsString constraint is so that
combinators like "int" and "double" can be defined via show (rather
than have them being class-level methods), toBuilder is used to
convert an actual s value to (Doc s) and fromBuilder is used for the
final rendering at the end.

The only other thing I can think of that _may_ need to be done on a
class level is the allowable size lengths of values (Int64 for lazy
ByteString and Text, and possibly just Int for convenience with
String).  Though if displayIO is going to be kept some kind of "s ->
IO ()" method will also be needed, though arguably displayIO isn't
that necessary.

Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com

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