I wanted to represent a reasonably small list of Publishers.
So I created:
> module Publisher where
> data Publisher = Publisher { name::String, func::Registration->Bool}
> data Registration =
> Registration { data::String, pub::Publisher} deriving (Read,Show)
Notice that the Publisher data type includes functions so I can't just
store these publishers as tuples in a database. Instead I store
information on each publisher in a file e.g. Yahoo.lhs CNN.lhs
DoubleClick.lhs
> module Yahoo where
> import Publisher
> Yahoo = Publisher "Yahoo" (\x -> x)
Another file, PublisherDB.lhs, imports each of these
> module PublisherDB where
> import Yahoo
> import DoubleClick
> publishers = [("Yahoo",Yahoo),("DoubleClick",DoubleClick)]
> getPublishers::String -> Publisher
> getPublisher name = lookup publishers name
The trouble I have is that Registration requires me to define
read/show for Publisher and read/show requires access to getPublisher
which leads to a circular import problem:
* getPublisher needs to be defined in PublisherDB because it requires a
complete list of Publishers.
* PublisherDB imports each individual publisher (e.g. Yahoo, DoubleClick)
Individual publishers import Publisher
For literate programming reasons, as well as general program modularity
reasons, I would prefer not to merge all of these into a single large
file.
Is there another way?
-Alex-
___________________________________________________________________
S. Alexander Jacobson i2x Media
1-212-697-0184 voice 1-212-697-1427 fax
