embed applicative forms in monad form s.t. the error msg and labeling functionaliy from applicative fields are maintained but you can customize the overall feel of the larger form

join.hs

joinForm :: Html -> MForm Handler (FormResult Join, Widget)
joinForm extra = do
  let
    mustAgreeField :: Text -> Field Handler Bool

    mustAgreeField errorMsg = checkBool id errorMsg checkBoxField
    accept1Def = areq (mustAgreeField
                         "You must specify that you accept Section 1")
                    "Accept Section 1" Nothing
    accept2Def = areq (mustAgreeField
                         "You must specify that you accept Section 2")
                    "Accept Section 2" Nothing
    fullNameDef = areq
                    (checkBool
                      ((>0) . length)
                      ("You must include your full, legal name" :: Text)
                      textField)
                    "Full Name"
                    Nothing

  (accept1, accept1Widget) <- renderDivs accept1Def mempty
  (accept2, accept2Widget) <- renderDivs accept2Def mempty

  (fullName, fullNameWidget) <- renderDivs fullNameDef mempty

  let
    widget =
      [whamlet|
              ^{extra}
              <p.my-4> this is a sentence
              ^{accept1Widget}
              <p.my-4> a sep
              ^{accept2Widget}
              <p.my-4> another sep
              ^{fullNameWidget}
              |]

    joinRes = Join <$> accept1 <*> accept2 <*> fullName

  return (joinRes, widget)

data Join = Join
  { joinSignedSection1 :: Bool
  , joinSignedSection2 :: Bool
  , joinFullName :: Text
  }
  deriving Show