[Forms] Make either of two fields required

[Vincent Ambo]

Hej,

I'm building a form (monadic in case that matters) which, among other things, has a field for a telephone number and a field for a mail address. Only one of the two is required but both are okay as well.

Is there any way to represent this relation in Yesod?

Cheers,
Vincent

[Michael Snoyman]

You'd really need to define a special datatype to represent that, such as:

data Contact = JustTelephone Telephone | JustAddress Address |
Both Telephone Address

Then you could write some kind of a function to combine them:

makeContact :: FormResult (Maybe Telephone) -> FormResult (Maybe
Address) -> FormResult Contact
makeContact fmt fma =
go $ (,) <$> fmt <*> fma
where
go (FormSuccess (mt, ma)) =
case (mt, ma) of
(Nothing, Nothing) -> FormFailure ["You must provide
either a telephone number or mailing address."]
(Just t, Just a) -> FormSuccess $ Both t a
...
go (FormFailure es) = FormFailure es
go FormMissing = FormMissing

Michael

[Max Cantor]

You could also write a custom field (as in www.yesodweb.com/book/forms )

passwordConfirmField :: Field sub master Text passwordConfirmField = Field { fieldParse = \rawVals -> case rawVals of [a, b] | a == b -> return $ Right $ Just a | otherwise -> return $ Left "Passwords don't match" [] -> return $ Right Nothing _ -> return $ Left "You must enter two values" , fieldView = \idAttr nameAttr _ eResult isReq -> [whamlet| <input id=#{idAttr} name=#{nameAttr} type=password> <div>Confirm: <input id=#{idAttr}-confirm name=#{nameAttr} type=password> |] } getRootR :: Handler RepHtml getRootR = do ((res, widget), enctype) <- runFormGet $ renderDivs $ areq passwordConfirmField "Password" Nothing defaultLayout [whamlet| <p>Result: #{show res} <form enctype=#{enctype}> ^{widget} <input type=submit value="Change password"> |] main :: IO () main = warpDebug 3000 Password

[Vincent Ambo]

I actually like the custom field idea a lot, I'll go with that! 

Thanks to both of you :-)