On Sun, Oct 14, 2007 at 12:55:28 +0200, apfelmus wrote:
Magnus Therning wrote:
I've just created the page http://haskell.org/haskellwiki/Library/Data_encoding (there are no links into it at the moment). Any comments on what I've written there? Are the locations in the hierarchy good?
Nice, but do you really need separate modules for each encoding? I mean, Ashely's proposal
There is no particular need for separate modules, except that in the current version there would be name clashes.
2. Codecs, i.e. encoder/decoder pairs such as charset converters data Codec base derived = MkCodec { encode :: derived -> base, decode :: base -> Maybe derived -- or other Monad } utf8 :: Codec [Word8] String xml :: Codec String XML
from the recent thread
http://article.gmane.org/gmane.comp.lang.haskell.libraries/7663
would fit the bill perfectly, wouldn't it? In other words, encodings are just pairs of functions, nothing complicated
base16 :: Codec String [Word8] -- decode Strings to Word8 base32 :: Codec String [Word8] base64 :: ... base64url :: uuencode ::
For more documentation in the types, a type synonym may come in very handy
type ASCII = String base16 :: Codec ASCII [Word8] ...
Want to encode an example? Here you go
encode base16 [0xde,0xad,0xbe,0xef] :: ASCII
A similar result could be gotten by using phantom types, right? But then there must be some way of liberating the result. I'm not sure yet whether they are worth it. AFAIU the example from above then changes to encode [0xde,0xad,0xbe,0xef] :: Base16 ASCII
Btw, it is essential that decode may fail on bad input!
I will for sure change the result of decode to deal with failures.
Also, I don't have a clue about what chop and unchop are supposed to do.
For some encodings there are standard ways of splitting an encoded string over several lines. Unfortunately it's not always as simple as just splitting a string at a particular length. Uuencode is the most complicated I've come across so far. That's what chop/unchop is for. /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus．therning＠gmail．com http://therning.org/magnus