The type signature for creating hidden fields in Yesod is: hiddenField :: (Monad m, PathPiece p, RenderMessage (HandlerSite m) FormMessage) => Field m p
. This is the only field which requires the PathPiece
constraint, why is that?
hiddenField
is a very free-form field, unlike e.g. textField
which specifically works on Text
. hiddenField
will work on any type which can be marshalled to and from a textual representation, which is where the PathPiece
constraint comes into play.