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. I find it's not always entirely clear which of these 'show' is intended to be: its pairing with 'read', and the way that String values are formatted including quotes suggests that it is intended to be a case of (2). Language in the Haskell report also strongly gives this impression. But in other situations, 'show' is commonly used in the sense of (1). For example, in the Haskell report, section 7.1, (print function) the Show class is used to create output that is specifically intended for user consumption ("the standard output device (this is normally the user's terminal)"). 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': class Format a where format :: a -> String formatList :: [a] -> String instance Format Int where format = show formatList x = showList x [] instance Format Char where format c = [c] formatList = id In many cases, format and show might be the same, built there would be no requirement for an instance for an instance of Format to be an instance of Show, or vice versa. A practical version of format should probably provide for operation via ShowS values, but I don't currently think an equivalent to showsPrec would be necessary. #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact