On Thu, 3 Jul 2008, Dougal Stanton wrote:
Here's a snippet from the parser for one option (others omitted for clarity):
options :: [OptDescr (Opts -> Opts)] options = [ Option "b" ["bus"] (ReqArg busNum "NUM") "Bus number" , ... ] where busNum n os = let b = (query os) { queryBusNumber = Just n } in if isBusId n then os { query = b } else os
Variations on that ugliness are repeated four times for other fields. Is there an alternative way to change the value of nested fields?
For access to nested record fields I implemented the record-access package. Unfortunately the field accessors must still be written manually. http://darcs.haskell.org/record-access/src/Data/Accessor/Example.hs E.g.: infix2 :: ((Char, Int), String) infix2 = (('b',7),"hallo")$%first^:second^=10 (second^=10) replaces the second member of pair with a value. (^:) applies that change to the outer record (again a pair). ($%) applies the modifier (first^:second^=10) to a concrete pair.