Funnily enough, I'm currently ruminating on the possibility of adding extensible records to GHC. My current thought is: much like TRex, except with 'has' predicates instead of 'lacks' predicates. That would give polymorphic field selection and update but not polymorphic record extension So the main thing you *wouldn't* be able to do, that TRex can handle is: f :: (r\l) => {r} -> {r | l::Int} f x = {x | l = 3} Main reason: I'd like to translate records into tuples in the intermediate language, and polymorphic extension is problematic. On the other hand, you *could* do all the other things TRex supports, such as f :: (r has l::Int) => r -> Int f x = x.l f :: (r has l::Int) => r -> r f x = x { l <- 3 } (Syntax uncertain.) Question: does anyone really care about polymorphic extension. Sorry that this message is a bit brief; I'm just back from a week away. I can elaborate if anyone would be interested. Simon | -----Original Message----- | From: Dominic Steinitz [mailto:dominic.steinitz@blueyonder.co.uk] | Sent: 26 January 2003 10:19 | To: libraries@haskell.org | Cc: daan@cs.uu.nl | Subject: HaskellDB | | Having used HToolkit successfully to extract information from a MySQL | database, I am painfully aware of the limitations of sending embedded SQL | strings and finding out at runtime that something didn't quite work (in an | often subtle and difficult to track down way). | | I'd love to be able to put HaskellDB on top of HToolkit. There are two | approaches: i) add extensible records to ghc or ii) modify HaskellDB so it | uses Haskell records not extensible records (I'd have modify HaskellDB | anyway to use HToolkit rather than talk to ODBC directly). The latter sounds | as though it might be more feasible that the former. Having read the paper | and briefly looked at the code, I assume the extensibility is required if | you have two tables each with the same column name and therefore you want to | use the same label in two different records. Obviously you can't do this | with Haskell records as the labels become top level functions. However, if I | rename labels then I won't have this problem. For example, if I have two | tables, passwd and notify each containing a column called email then I could | have labels notifyEmail and passwdEmail and remember that they really | referred to email. | | Does anyone have any views on this? | | Dominic Steinitz | | _______________________________________________ | Libraries mailing list | Libraries@haskell.org | http://www.haskell.org/mailman/listinfo/libraries