On Sun, Nov 29, 2009 at 11:08 PM, Malcolm Wallace <malcolm.wall...@cs.york.ac.uk> wrote: > Are you sure that there can be no error recovery, to continue with events > after a mal-formed event has been discarded? In many cases, it is possible. > However, if you really want to terminate the stream at the first error, and > to reflect this in the type, then I guess you can define your own list type: > > data ListThenError e a = Cons a (ListThenError e a) > | Error e > > Of course this has the disadvantage that then your consumer must change to > use this type too.
If it is correct, there is no disadvantage. Using a list when it is not the appropriate structure will make both the producer and the consumer code uglier. You might gain a little notational convenience, but you bubble implicit assumptions, such as an error terminates a stream, through the code where they can not be checked. Of course, when you have a stream from which errors can be recovered, do not use a type that terminates with errors. Everything cleans up so nicely when your model perfectly captures your problem. Luke _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
