haskell - Yesod route containing a `Maybe a` argument -

haskell - Yesod route containing a `Maybe a` argument -

i've been trying utilize maybe a in route. far tried

class="lang-hs prettyprint-override">/u/#maybe userid /u/#(maybe userid) /u/#maybe-userid

and

class="lang-hs prettyprint-override">/u/#maybeuserid

where

class="lang-hs prettyprint-override">type maybeuserid = maybe userid

but without much success.

strangely enough, #maybe-userid compiles fine handler using maybe userid but, it's not able find match new pathpiece instance below.

class="lang-hs prettyprint-override">instance (pathpiece a) => pathpiece (maybe a) frompathpiece s = case s of "nothing" -> nil _ -> $ frompathpiece s topathpiece m = case m of s -> topathpiece s _ -> "nothing"

what missing create maybe routes , not having declare type , instance each , every maybe a want use?

edit: instance works fine when using other Ǹothing reason.

edit2: "nothing" -> nothing actualy indicates pathpiece failed parsing, not desired outcome. "nothing" -> nothing right thing.

a route empty parameter (ending slash) reverts route ending previous path piece, "/u/" never match "/u/#maybeuserid"

so there 2 different routes in optional userid proposition:

/u usernoidr /u/#userid userwithidr

update:

you may serve them both mutual handler, if want:

getusernoidr = getusermaybe nil getuserwithidr userid = getusermaybe (just userid)

haskell routes yesod maybe