[Haskell-cafe] What's a thread doing / Erlang-style processes
/ Message passing
bulatz at HotPOP.com
Wed Dec 7 02:49:41 EST 2005
Tuesday, December 06, 2005, 8:30:32 PM, you wrote:
JR> Assuming I typed events like that I think I would need a typed sink
JR> for them as well. I only have one sink for the events and that is my
JR> message queue.
i don't understand you. remember that i'm not native English speaker :)
JR> I expect users to want User X, User Y, User Z within
JR> the same module and that's why I used Dynamic.
if you can define all these datatags (X, Y and Z) in one type then you
can use pattern matching:
data UserEvent = X ... | Y ... | Z ...
if not - then can't. of course, you can use this "subtyping trick"
several times, but it is not very interesting:
data Event a = ... | User a
data UserEvent1 a = X ... | User2 a
data UserEvent2 a = Y ... | User3 a
send chan (User $ User2 $ Y) -- type of expression inside brackets is
"Event (UserEvent1 (UserEvent2 a))", where a is unspecified
or you can define
data Event a b c = ... | User1 a | User2 b | User3 c
but this is also bad :(
you can also use classes, but Dynamic actually does the same, and this
gives you no ability to do pattern-matching
Bulat mailto:bulatz at HotPOP.com
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