[Haskell-cafe] Re: wanted: HAppS example combining state and io

[Thomas Hartman]

Thanks Martin, that really helped.

After many days reading the source, I'm still trying to grok HAppS.

Meanwhile, here is a patch that adds examples to HAppS/Examples/HTTP1.hs 
for combining state and io, based on your advice.

see especiallly the handler stateioH accepts an arbitrary state action, 
arbitrary io action, and a function for combining the two.

Thomas.


New patches:

[add examples showing state and io
thomas.hartman at db.com**20070906215844] {
hunk ./src/HAppS/Examples/HTTP1.hs 7
+import System.Directory
hunk ./src/HAppS/Examples/HTTP1.hs 68
+
+             ,h ["showbashrc"] GET $ ioshowH readbashrc
+             ,h ["showhttp1"] GET $ ioshowH readhttp1
+
+             ,h ["incrementstate"] GET $ stateH $ incnshow
+             ,h ["decrementstate"] GET $ stateH $ decnshow
+             ,h ["viewstate"] GET $ stateH view
+
+             ,h ["showbashrc_and_inc"] GET $ stateioH incnshow readbashrc 
append_state
+             ,h ["showbashrc_and_dec"] GET $ stateioH decnshow readbashrc 
append_state
+             ,h ["showbashrc_and_view"] GET $ stateioH decnshow 
readbashrc append_state
+
hunk ./src/HAppS/Examples/HTTP1.hs 82
+append_state s io = io ++ "<BR>State: " ++ s
+
+incnshow = modify (+1) >> get >>=^ show
+decnshow = modify (\x -> x-1) >> get >>=^ show 
+view = get >>=^ show
+
+
+readbashrc = do
+  home <- getHomeDirectory
+  readfileSafe $ home ++ "/.bashrc"
+
+readhttp1 = readfileSafe "./HTTP1.hs"
+
+readfileSafe file = catch
+               ( readFile file >>=^ format_html ) 
+               ( \e -> return ( show e ) )
+
+stateioH stateaction ioaction combinestio = \() () -> do
+   stateresult <- stateaction
+   respond $ do 
+      ioresult <- ioaction
+      showresult (combinestio stateresult ioresult) 
+
+
+stateH stateaction = ok $ \() () -> stateaction >>= respond 
+
+ioshowH :: (Monad m, Show a) => IO a -> () -> () -> m (Either Request (IO 
Result))
+ioshowH ioaction = \() () -> respond $ do
+   ioresult <- ioaction
+   showresult ioresult 
+
+showresult showable = sresult 200 (show showable) 
+
+
hunk ./src/HAppS/Examples/HTTP1.hs 151
+
+format_html xs = concat $ map newlinetobr xs
+  where  newlinetobr '\n' = "<br>"
+         newlinetobr x = [x]
+
+f >>=^ g = f >>= return . g
}








Martin Lütke <prionic at gmx.de> 
Sent by: haskell-cafe-bounces at haskell.org
09/01/2007 07:04 PM

To
haskell-cafe at haskell.org
cc

Subject
[Haskell-cafe] Re: wanted: HAppS example combining state and io






Thomas Hartman <thomas.hartman <at> db.com> writes:

> 
> 
> In the latest happs (darcs pulled, updated
> head is 0.9.1 iirc), I am experimenting with the example file in
src/HAppS/Examples/HTTP1.hs.
> I would like to combine state with io.
> Eventually io will mean stuff like reading from a database, but for now
> I'm just reading a file.
> The example file HTTP1.hs has an example
> that demonstrates state with macid.
> I added an example that allows you to
> execute arbitrary io.
> I tried, but was unable to, add a handler
> that combines state and io. 
> 
>    ,  h ["iohandler"]    GET $ ioReadFileHandler
> 
>    ,  h ["statehandler"] GET $ stateHandler
> 
>    --,  h ["ioandstatehandler"] GET $ ioAndStateHandler
> .....
> -- displays contents of HAPPS.hs in
> current directory
> ioReadFileHandler = iohandler $ readFile
> "./HAppS.hs" 
> -- displays incremented state counter
> stateHandler = ok $ \() () -> 
> 
>          modify (+(1::Int)) >> get >>=
> respond . show
> -- should combine effect of iohandler
> with statehandler
> -- specifically, should display contents
> of HAppS.hs, and under that an incremented state handler
> -- is this possible
> ioAndStateHandler = undefined undefined
> Is mixing state and io possible with
> HAppS? If so, an example showing how to do it would be extremely 
helpful.
> best, thomas.
> ---This e-mail may contain confidential and/or privileged information. 
If you
are not the intended recipient (or have received this e-mail in error) 
please
notify the sender immediately and destroy this e-mail. Any unauthorized 
copying,
disclosure or distribution of the material in this e-mail is strictly 
forbidden.
> 
> Attachment (https1-whatsnew): application/octet-stream, 1933 bytes
> Attachment (HTTP1.hs): application/octet-stream, 4794 bytes
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe <at> haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 


I had no trouble getting this handler to work:

    h ["iohandler"] GET $ \() () -> do
            modify (+1)
            x <- get
            respond $ do
                cnts <- readFile "./sometext.txt"
                sresult 200 (cnts ++ show x)

I believe the trick is that you cant mix io INTO the HAppS ServerPart 
monad. 
But from the ServerPart monad you can RETURN an io action.

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe at haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe



---

This e-mail may contain confidential and/or privileged information. If you 
are not the intended recipient (or have received this e-mail in error) 
please notify the sender immediately and destroy this e-mail. Any 
unauthorized copying, disclosure or distribution of the material in this 
e-mail is strictly forbidden.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/haskell-cafe/attachments/20070906/464fbf09/attachment.htm