Graham Klyne <[EMAIL PROTECTED]> writes: > I raise a topic that has occurred to me repeatedly during my time with > Haskell. I am prompted to do so by a discussion in another place, where a > significant (and, apparently, recurring) concern about the use and abuse of > Java's toString() function is being raised. > > It seems to me that there are (at least) two important uses for a function > like 'show', which may sometimes have very different requirements: > > (1) creation of some human-readable representation of a value, which may or > may not contain sufficient information to reconstruct the value, and > > (2) creation of a textual serialization of a value from which the value can > subsequently be recreated. > > Where this leads is that I think there should be *two* common value-to-string > type classes, one of which is reversible (in the sense that the output of > show is intended to be consumable by read), and another that is not required > to be reversible and provides output for human consumption. E.g., let's call > the new class 'Format':
This is similar Python's str() (string) vs repr() (representation) functions. Python's repr is designed to work like "read . show = id" such that eval(repr(x)) == x and repr also makes a string (only ASCII as far as I know). But maybe this doesn't have to be limited to strings? I've wanted "deriving WebPublish" and at some level that also involves a "show as html/xml" My WebPublish ideas would be easier with "readXML.showXML == id" Dominic Steinitz' ASN.1 code might be easier with readASN1/showASN1 I get the feeling there's a higher-level pattern here, but I don't how to capture it with Haskell's Read/Show classes. Some discussion on #haskell turned up: Björn Bringert mentioned the THDeriveXmlRpcType module in his XmlRpc library. So maybe Show can be parameterized on various 'transports' ? Philippa Cowderoy suggested "Show signal carrier" instead of the present "Show signal [implicit String]" Maybe deriving (Show Transport) like deriving (Show XmlRpc)? Any thoughts along these lines? -- Shae Matijs Erisson - Programmer - http://www.ScannedInAvian.org/ "I will, as we say in rock 'n' roll, run until the wheels come off, because I love what I do." -- David Crosby _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
