What's the syntax of using multiple handlers in Happstack?

Question

Sorry for my basic question, but I'm new to Haskell.

I'm following this example to receive some values from a request body, but my server also serves static files from a directory using the following code:

fileServing :: ServerPart Response
fileServing = serveDirectory EnableBrowsing ["index.html"] "./Path/"

mainFunc = simpleHTTP nullConf $ msum [ 
                                        fileServing                                     
                                      ]

I added the below code to my library but I'm not sure where to use the handlers function, because I already have an msum in the mainFunc.

handlers :: ServerPart Response
handlers =
    do decodeBody myPolicy
       msum [ 
               myGetData
            ]

myGetData :: ServerPart Response
myGetData =
    do method POST
       username <- look "username"
       password <- look "password"
       ok $ toResponse (username ++ ", " ++ password)

score 1 · Accepted Answer · answered Feb 12 '18 at 05:09

fileServing, myGetData, msum [fileServing], msum [myGetData] and handlers all have ServerPart Response type, which is the type of what you are passing to simpleHTTP nullConf in mainFunc. That being so, you probably want...

mainFunc = simpleHTTP nullConf handlers

-- etc.

handlers :: ServerPart Response
handlers =
    do decodeBody myPolicy
       msum [ fileServing
            , myGetData
            ]

msum here combines a list of handlers into a single handler (note that also means msum on a list with a single handler is redundant).

What's the syntax of using multiple handlers in Happstack?

1 Answers1