Marc Weber wrote:
Andrew Coppin wrote:
What I ended up writing is this: http://www.hpaste.org/fastcgi/hpaste.fcgi/view?id=25782 lookup :: KeyID -> Key -> Container -> Maybe Value
Does anybody have a less-insane way of doing this?
Sure:
type MyMap = Map (KeyID, Key) Value
Don't use multiple keys. Put the keys into a tuple and use that as key.
Actually, it's a disjoint sum type: data a :+: b = Inl a | Inr b -- also known as Either type DB3 e k1 k2 k2 = D1 e (k1 :+: k2 :+: k3) Hm, that's not quite right either because every e has multiple keys. The following should work, however: type DB3 e k1 k2 k2 = D1 e k1 :*: DB1 e k2 :*: DB2 e k3 lookup :: (k1 :+: k2 :+: k3) -> DB3 e k1 k2 k3 -> Maybe e In any case, I recommend using a special key type for combining keys anyway, as explained here http://article.gmane.org/gmane.comp.lang.haskell.cafe/23648 Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com