Re: [Haskell-cafe] Mime / Mail library

From: Christopher Done

On 20 March 2011 15:05, Pieter Laeremans wrote:

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Hi all,

The MIME package that can be found on hackage, uses String as input. Would i be considered better if there would be a version based on Text, or ByteString ?

I think the solution to this problem is a generic `string' package which just provides a few classes. The MIME library would export an interface that only deals with instances of these classes, and whether you're using Text, String, ByteString/Lazy/Char8, ropes, whatever, it's not the library writer's concern or assumptions to make.

We already have:

http://hackage.haskell.org/packages/archive/string-combinators/0.6/doc/html/... < http://hackage.haskell.org/packages/archive/string-combinators/0.6/doc/html/...

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Which works on Monoid and IsString, but there needs to be a class like "can be read/outputted via IO" and one for read/show/serialize, both of which are important for speed.

Anyone already done work on this? The Data.ByteString modules could export some instances. It's fair enough that people who need fine-grained speed use the concrete types and all their special-purposes functions, but in the general having to choose arbitrarily (often defaulting to String) is a burden. Can't we standardize on a default set of String classes to use?

I suppose I could try reducing Data.ByteString's function set into a set of essential core methods, seeing as the ByteString modules are a very good spec of what's required for a String type to be completely usable.

Data.ListLike (http://hackage.haskell.org/package/ListLike) provides this via the "StringLike" class (and StringLikeIO). There are built-in instances for Strings and ByteStrings, with orphan Text instances in http://hackage.haskell.org/package/listlike-instances. Probably the StringLike class could be extended to provide more (high-performance) methods, but I don't have a good idea of what's necessary. Suggestions are welcome! John L.