It sounds like you need to split up your types a bit more.
data HttpRequest = HttpRequest ...
data HttpResponse = HttpResponse ...
data HttpMessage = MsgRequest HttpRequest | MsgResponse HttpResponse
-- alternatively
-- type HttpMessage = Either HttpRequest HttpResponse
Now you can have functions that take/return just an HttpRequest or
just an HttpResponse, as well as functions that use either one via
HttpMessage. In the latter case, you do need to pattern match to
decide which one you have.
-- ryan
On 6/18/08, Stephen Howard
Thanks Brandon, forgot to send my reply to the list:
Ok, so I am confusing things. Good to know. So my question is how do I fulfill this scenario?
- I have an action that might return either an HttpResponse or an HttpRequest, depending on if the IO in the action determined more work needed doing. It's here, though I doubt it's "correct" yet:
requestHandler :: HttpRequest -> IO HttpResponse requestHandler request = do session <- sessionHandler request ret <- uriHandler request case ret of HttpResponse -> ret HttpRequest -> resourceHandler session ret
uriHandler :: HttpRequest -> IO HttpMessage sessionHandler :: HttpRequest -> IO HttpSession
I've given the uriHandler a signature of IO HttpMessage because the HttpMessage might be either an HttpResponse or an HttpRequest, and I don't know how I should be specifying that. Ideas?
- Stephen
Brandon S. Allbery KF8NH wrote:
On Jun 18, 2008, at 15:31 , Stephen Howard wrote:
HttpMessage.hs:36:20: Not in scope: type constructor or class
`HttpRequest'
The troublesome line is the definition of the cookie function at the end
of the code. I've made
Right. "HttpRequest" is a data constructor associated with the type constructor "HttpMessage". (Data constructors are effectively functions; you used it in the context of a type, not a function name.)
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